Bibliography - Yoshio Kurihara

1. Wu, C-C, Morris A Bender, and Yoshio Kurihara, 2000: Typhoon forecast with the GFDL Hurricane Model: Forecast skill and comparison of predictions using AVN and NOGAPS global analyses. Journal of the Meteorological Society of Japan, 78(6), 777-788.
   [ Abstract PDF ]

   A hurricane model developed at GFDL, NOAA, was combined with each of AVN and NOGAPS global analyses to construct typhoon prediction systems GFDS and GFDN, respectively. The GFDS system performed 125 (178) forecast experiments for 16 (24) storms in the western North Pacific basin during 1995 (1996). It exhibited considerable skill in the forecast of tropical cyclone tracks. The average forecast position errors as 12, 24, 36, 48 and 72 h in 1995 (1996) were 95 (108), 146 (178), 193 (227), 249 (280), and 465 (480) km. The improvement with GFDS in the typhoon position forecast over CLIPER was roughly 30%. The reduction of position errors in both average and standard deviations indicates superior forecast accuracy and consistency of GFDS, although there existed systematic northward bias in the forecast motion at low latitudes. On the other hand, intensity forecast was not satisfactory, showing a tendency to overpredict weak storms and underpredict strong storms, similar to the tendency in the Atlantic Two sets of forecasts performed in the 1996 season, the one by GFDS and the other by GFDN, were compared with each other. Forecast skills of the storm position with the two systems were comparable. However, the two forecast positions tended to be systematically biased toward different directions. As a result, when the two forecasts were averaged, the mean error was 10% smaller than that of each forecast. Also, overall improvement in track forecast was obtained in supplemental experiments in which individual forecasts were corrected for systematic biases. Though systematic biases is not steady, there may be ways to utilize it for improvement of tropical cyclone forecasts.

2. Knutson, Thomas R., Robert E Tuleya, and Yoshio Kurihara, 1998: Simulated increase of hurricane intensities in a CO2-warmed climate. Science, 279(5353), 1018-1020.
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   Hurricanes can inflict catastrophic property damage and loss of human life. Thus, it is important to determine how the character of these powerful storms could change in response to greenhouse gas-induced global warming. The impact of climate warming on hurricane intensities was investigated with a regional, high-resolution, hurricane prediction model. In a case study, 51 western Pacific storm cases under present-day climate conditions were compared with 51 storm cases under high-CO2 conditions. More idealized experiments were also performed. The large-scale initial conditions were derived from a global climate model. For a sea surface temperature warming of about 2.2°C, the simulations yielded hurricanes that were more intense by 3 to 7 meters per second (5 to 12 percent) for wind speed and 7 to 20 millibars for central surface pressure.

3. Kurihara, Yoshio, and Robert E Tuleya, 1998: A prospect of improvement in the forecast of hurricane landfall In 16th Conference on Weather Analysis & Forecasting and Symposium on the Research Foci of the U.S. Weather Research Program, Boston, MA, American Meteorological Society, 524-525.
4. Kurihara, Yoshio, Robert E Tuleya, and Morris A Bender, 1998: Application and improvement of the GFDL Hurricane Prediction System In Research Activities in Atmospheric and Oceanic Modelling, WMO/TD No. 865, Geneva, Switzerland, World Meteorological Organization, 5.31.
5. Kurihara, Yoshio, Robert E Tuleya, and Morris A Bender, 1998: The GFDL Hurricane Prediction System and its performance in the 1995 hurricane season. Monthly Weather Review, 126(5), 1306-1322.
   [ Abstract PDF ]

   The Geophysical Fluid Dynamics Laboratory (GFDL) Hurricane Prediction System was adopted by the U.S. National Weather Service as an operational hurricane prediction model in the 1995 hurricane season. The framework of the prediction model is described with emphasis on its unique features. The model uses a multiply nested movable mesh system to depict the interior structure of tropical cyclones. For cumulus parameterization, a soft moist convective adjustment scheme is used. The model initial condition is defined through a method of vortex replacement. It involves generation of a realistic hurricane vortex by a scheme of controlled spinup. Time integration of the model is carried out by a two-step iterative method that has a characteristic of frequency-selective damping. The outline of the prediction system is presented and the system performance in the 1995 hurricane season is briefly summarized. Both in the Atlantic and the eastern Pacific, the average track forecast errors are substantially reduced by the GFDL model, compared with forecasts by other models, particularly for the forecast periods beyond 36 h. Forecasts of Hurricane Luis and Hurricane Marilyn were especially skillful. A forecast bias is noticed in cases of Hurricane Opal and other storms in the Gulf of Mexico. The importance of accurate initial conditions, in both the environmental flow and the storm structure, is argued.

6. Bender, Morris A., C-C Wu, M A Rennick, and Yoshio Kurihara, 1997: Comparison of the GFDL Hurricane Model prediction in the Western Pacific using the NOGAPS and AVN Global Analysis In 22nd Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 615-616.
7. Knutson, Thomas R., Robert E Tuleya, and Yoshio Kurihara, 1997: Exploring the sensitivity of hurricane intensity to CO2-induced global warming using the GFDL Hurricane Prediction System In 22nd Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 587-588.
8. Kurihara, Yoshio, Morris A Bender, and Robert E Tuleya, 1997: For hurricane intensity forecast: Formulation of a new initialization method for the GFDL Hurricane Prediction Model In 22nd Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 543-544.
9. Kurihara, Yoshio, Robert E Tuleya, and Morris A Bender, 1997: Improvement of the GFDL Hurricane Prediction System In CAS/JSC Working Group on Numerical Experimentation - Research Activities in Atmospheric & Oceanic Modelling, Report No. 25, WMO/TD-No. 792, Geneva, Switzerland, World Meteorological Organization, 5.22.
10. Bender, Morris A., Robert E Tuleya, Yoshio Kurihara, and S J Lord, 1996: Results of the operational GFDL hurricane model at NCEP In 11th Conference on Numerical Weather Prediction, Boston, MA, American Meteorological Society, 393-395.
11. Kurihara, Yoshio, Robert E Tuleya, and Morris A Bender, 1996: Simulation studies of tropical cyclones In Research Activities in Atmospheric and Oceanic Modelling, CAS/JSC Working Group on Numerical Experimentation, Report No. 23 WMO/TD No. 734, World Meteorological Organization, 5.17-5.18.
12. Tuleya, Robert E., Morris A Bender, and Yoshio Kurihara, 1996: Prediction of hurricane landfall using the GFDL model In 11th Conference on Numerical Weather Prediction, Boston, MA, American Meteorological Society, 407-408.
13. Wu, C-C, and Yoshio Kurihara, 1996: A numerical study of the feedback mechanisms of hurricane-environment interaction on hurricane movement from the potential vorticity perspective. Journal of the Atmospheric Sciences, 53(15), 2264-2282.
    [ Abstract PDF ]

    The interaction between a hurricane and its environment is studied by analyzing the generation and influence of potential vorticity (PV) from the Geophysical Fluid Dynamics Laboratory hurricane model analysis system. Two sets of numerical experiments are performed: one with and the other without a bogused hurricane vortex in the initial time, for cases of Hurricanes Bob (1991), Gilbert (1988), and Andrew (1992). The PV budget analysis of Bob shows that the condensational heating within the vortex redistributes the PV, causing a PV sink in the upper part of the vortex and a PV source in the lower part. This tendency is compensated for largely, but not entirely, by the upward transport of high-PV air from the lower levels to the upper levels. The net effect contributes to the increase of the negative upper-level PV anomaly during the vortex intensification period. This result indicates that the diabatic heating effect plays a crucial role in the evolution of the PV field in hurricanes. It also suggests the importance of accurate representation of the heating profile in hurricane models. It is shown that the negative upper-level PV anomaly is spread out by the upper-level outflow and the large-scale background flow. The impact of the spread of the negative upper PV anomaly to the storm is quantitatively evaluated by computing the nonlinear balanced flow associated with the PV perturbation. Notable contribution to the steering of the storm from the upper-level PV anomaly is found. The result supports the theory advanced by Wu and Emanuel concerning the effect of the upper negative PV anomaly on hurricane motion. This study also indicates the need of enhanced observation and accurate analysis and prediction in the upper troposphere in order to improve hurricane track forecasting.

14. Kurihara, Yoshio, Morris A Bender, and Robert E Tuleya, 1995: Performance evaluation of the GFDL Hurricane Prediction System in the 1994 hurricane season In 21st Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 41-43.
15. Kurihara, Yoshio, Morris A Bender, Robert E Tuleya, and R Ross, 1995: Improvements in the GFDL Hurricane Prediction System. Monthly Weather Review, 123(9), 2791-2801.
    [ Abstract PDF ]

    The hurricane model initialization scheme developed at GFDL was modified to improve the representation of the environmental fields in the initial condition. The filter domain defining the extent of the tropical cyclone in the global analysis is determined from the distribution of the low-level disturbance winds. The shape of the domain is generally not circular in order to minimize the removal of important nonhurricane features near the storm region. An optimum interpolation technique is used to determine the environmental fields within the filter domain. Outside of the domain, the environmental fields are identical to the original global analysis. The generation process of the realistic and mode-compatible vortex has also undergone some minor modifications so that reasonable vortices are produced for various data conditions. The upgraded hurricane prediction system was tested for a number of cases and compared against the previous version and yielded an overall improvement in the forecasts of storm track. The system was run in an automated semioperational mode during the 1993 hurricane season for 36 cases in the Atlantic and 36 cases in the eastern Pacific basin. It demonstrated satisfactory skill in the storm track forecasts in many cases, including the abrupt recurvature of Hurricane Emily in the Atlantic and the landfall of Hurricane Lidia onto the Pacific coast of Mexico.

16. Ross, R, and Yoshio Kurihara, 1995: A numerical study on influences of Hurricane Gloria (1985) on the environment. Monthly Weather Review, 123(2), 332-346.
    [ Abstract PDF ]

    The influence of Hurricane Gloria (1985) on the environment is investigated by comparing hurricane model integrations either including or excluding the hurricane in the initial condition. Results for three cases of Gloria at different states of development are presented. The hurricane's cumulative influence is identified as the differences between the hurricane and nonhurricane integrations. Throughout the integration period, area with sea level pressure differences exceeding 1 hPa in magnitude expanded in each of the three cases and was centered at the hurricane location. The influence radius of the storm, which was determined from the sea level pressure difference field, eventually reached approximately 1500 km in all cases. Comparisons of the sea level pressure differences among the three cases showed that the expansion rate differed for each case but was only weakly related to the intensity or intensity change of the particular storm. The comparisons of the wind and temperature fields from the hurricane and nonhurricane integrations indicated that the areal extent of the hurricane's influence was much larger at the upper layer than at the lower layer. A stronger anticyclonic circulation and relatively warmer temperatures developed at the upper layer in the hurricane integration compared to the nonhurricane fields. These upper-layer changes extended over an area comparable in size with the sea level pressure differences. These general features were identified in all three cases. At the lower layer, the differences between the hurricane and nonhurricane wind and temperature fields showed the impact of hurricane on the passage of a cold front over the eastern United States. Apparently, the hurricane's cyclonic circulation at the lower layer affected the movement of the front approaching from the west. The frontal passage was delayed north of the storm in the hurricane integration because of the reduction in the eastward component of the wind. To the south of the hurricane, the westerly winds were enhanced to accelerate the front movement. There were related changes in the fields of precipitation and the low-level temperature; for example, southwest of the hurricane, there was a reduction in the accumulated frontal precipitation in the hurricane integration because of the faster frontal movement.

17. Lighthill, J, G Holland, W Gray, C Landsea, G Craig, J Evans, Yoshio Kurihara, and C Guard, 1994: Global climate change and tropical cyclones. Bulletin of the American Meteorological Society, 75(11), 2147-2157.
    [ Abstract ]

    This paper offers an overview of the authors' studies during a specialized international symposium (Mexico, 22 November-1 December 1993) where they aimed at making an objective assessment of whether climate changes, consequent on an expected doubling of atmospheric CO2 in the next six or seven decades, are likely to increase significantly the frequency or intensity of tropical cyclones (TC). Out of three methodologies available for addressing the question they emply two, discarding the third for reasons set out in the appendix. In the first methodology, the authors enumerate reasons why, in tropical oceans, the increase in sea surface temperature (SST) suggested by climate change models might by expected to affect either (i) TC frequency, because a well-established set of six conditions for TC formation include a condition that SST should exceed 26°C, or (ii) TC intensity, because this is indicated by thermodynamic analysis to depend critically on the temperature at which energy transfer to air near the sea surface takes place. But careful study of both suggestions indicates that the expected effects of increased SST would be largely self-limiting (i) because the other five conditions strictly control how far the band of latitudes for TC formation can be further widened, and (ii) because intense winds at the sea surface may receive their energy input at a temperature significantly depressed by evaporation of spray, and possibly through sea surface cooling. In the second methodology, the authors study available historical records that have very large year-to-year variability in TC statistics. They find practically no consistent statistical relationships with temperature anomalies; also, a thorough analysis of how the El Niño-Southern Oscillation cycle influences the frequency distribution of TCs shows any direct effects of local SST changes to be negligible. The authors conclude that, even though the possibility of some minor indirect effects of global warming on TC frequency and intensity cannot be excluded, they must effectively be "swamped" by large natural variability.

18. Bender, Morris A., I Ginis, and Yoshio Kurihara, 1993: Numerical simulations of hurricane-ocean interaction with a high-resolution coupled model In 20th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 563-566.
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19. Bender, Morris A., I Ginis, and Yoshio Kurihara, 1993: Numerical simulations of tropical cyclone-ocean interaction with a high-resolution coupled model. Journal of Geophysical Research, 98(D12), 23,245-23,263.
    [ Abstract PDF ]

    The tropical cyclone-ocean interaction was investigated using a high-resolution tropical cyclone ocean coupled model. The model design consisted of the NOAA Geophysical Fluid Dynamics Laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model. Coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress, heat, and moisture fluxes computed in the hurricane model. The new sea surface temperature (SST) calculated by the ocean model was then used in the tropical cyclone model. A set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2.5, 5, and 7.5 m s^-1 with a fourth experiment run with no basic flow specified initially. The profile of the trangential wind for Hurricane Gloria at 1200 UTC 22, September 1985 was used as the initial condition of the tropical cyclone for each of the experiments. The model ocean was initially horizontally homogenous and quiescent. To clarify the impact of the ocean response to the hurricane's behavior, analogous experiments were also carried out with the SST kept constant (control cases). The experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased SST. The sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower. In the experiments run without an initial basic flow,the maximum SST anomaly was about -5.6°C with a resulting difference in the minimum sea level pressure and maximum surface winds of 16.4 hPa and -7 m s^-1, respectively. In contrast, in the experiments run with the 7.5 ms^-1 basic flow, the maximum SST anomalies ranged from about 2.6° to 3.0°C with a difference in the minimum sea level pressure and maximum surface winds of about 7.3 hPa and -2.7 m s^-1. The tropical cyclone-ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2.5 m s^-1 easterly flow. In these cases the storm with the ocean interaction turned more to the north and east (no basic flow) or the north (2.5 m s^-1 easterly flow) of the experiments with constant SST. In the first case, the storm by 72 hours was located over 70 km to the east-southeast of the control case. A possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift.

20. Bender, Morris A., R Ross, Robert E Tuleya, and Yoshio Kurihara, 1993: Improvements in tropical cyclone track and intensity forecasts using the GFDL initialization system. Monthly Weather Review, 121(7), 2046-2061.
    [ Abstract PDF ]

    The initialization scheme designed at GFDL to specify a more realistic initial storm structure of tropical cyclones was tested on four real data cases using the GFDL high-resolution multiply nested movable mesh hurricane model. Three of the test cases involved Hurricane Gloria (1985) in the Atlantic basin; the fourth involved Hurricane Gilbert (1988) in the Gulf of Mexico. The initialization scheme produced an initial vortex that was well adapted to the forecast model and was much more realiztic in size and intensity than the storm structure obtained from the NMC T80 global analysis. As a result, the erratic storm motion seen in previous intergrations of the GFDL model has been nearly eliminated with dramatic improvements in track forecasts during the first 48 h of the prediction. Using the new scheme, the average 24-h and 48-h forecast error for the four test cases was 58 and 94 km, respectively, compared with 143 and 191 km for the noninitialized forecasts starting from the global analysis. The average National Hurricane Center operational forecast error at 24 and 48 h was 118 and 212 km for the same four cases. After 48 h the difference in the average track error became small between the integrations starting from the global analysis and the forecasts starting from the fields obtained by the initialization scheme With accurate specification of the initial vortex structure, changes in the storm intensity were also well predicted in these cases. The model correctly forecasted the rapid intensification of Hurricane Gloria just after the system was first upgraded to a hurricane. The model storm intensification also ceased at approximately the same time as observed, with gradual weakening as the storm moved north and approached the east coast of the United States. In the forecast of Hurricane Gilbert, the model storm initially weakened as it moved over the Yucatan Peninsula and underwent only moderate reintensification after moving over the Gulf of Mexico, in good agreement with observations Finally, in the case where the track of Hurricane Gloria was well forecast, the distribution of the maximum low-level winds was accurately predicted as the storm moved up the east coast of the United States. During this period the model successfully reproduced many observed features such as large asymmetries in the wind field, with strongest winds occurring well east of the storm center, and a sharp decrease of the wind speed at the coast. Although asymmetry in the wind distribution was reproduced to a first order in the forecast starting with the global analysis, the agreement with observations was much better with the specified vortex, primarily due to a more realistic radius of maximum wind and storm intensity.

21. Kurihara, Yoshio, Morris A Bender, and R Ross, 1993: An initialization scheme of hurricane models by vortex specification. Monthly Weather Review, 121(7), 2030-2045.
    [ Abstract PDF ]

    A scheme is presented to improve the representation of a tropical cyclone in the initial condition of a high-resolution hurricane model. In the proposed method, a crudely resolved tropical cyclone in the large-scale analysis is replaced by a vortex that is properly specified for use in the prediction model. Appropriate filters are used to remove the vortex from the large-scale analysis so that a smooth environmental field remains. The new specified bogus vortex takes the form of a deviation from the environmental field so that it can be easily merged with the latter field at the correct position. The specified vortex consists of both axisymmetric and asymmetric components. The symmetric component is generated by the time integration of an axisymmetric version of the hurricane prediction model. This ensures dynamical and thermodynamical consistency in the vortex structure, including the moisture field, and also compatibility of the vortex with the resolution and physics of the hurricane model. In the course of the integration of the axisymmetric model, the tangential wind component is gradually forced to a target wind profile determined from observational information and empirical knowledge. This makes the symmetric vortex a good approximation to the corresponding real tropical cyclone. The symmetric flow thus produced is used to generate an asymmetric wind field by the time integration of a simplified barotropic vorticity equation, including the beta effect. The asymmetric wind field, which can make a significant contribution to the vortex motion, is then added to the symmetric flow. After merging the specified vortex with the environmental flow, the mass field is diagnosed from the divergence equation with an appropriately controlled time tendency. The wind field remains unchanged at this step of initialization. Since the vortex specified by the proposed method is well adapted to the hurricane prediction model, problems of initial adjustment and false spinup of the model vortex, a long-standing difficulty in the dynamical prediction of tropical cyclones, are alleviated. It is anticipated that the improvement of the initial conditions can reduce the error in hurricane track forecasting and extend the feasibility of tropical cyclone forecasting to intensify change.

22. Kurihara, Yoshio, Robert E Tuleya, Morris A Bender, and R Ross, 1993: Advanced modeling of tropical cyclones In Tropical Cyclone Disasters, Proceedings of ICSU/WMO International Symposium, October 12-16, 1992, Beijing, China, Peking University Press, 190-201.
    [ Abstract ]

    Advanced tropical cyclone models of sufficiently fine resolution are capable of representing important internal structure of the vortex. In the model, a vortex should interact with ocean and land in a realistic manner. Interaction with the ocean can significantly moderate the storm intensity. Inclusion of the heat budget of the soil layer retards the storm intensity over land. How to improve the treatment of deep convection is an issue which is wide open for future study. Specification of a realistic, yet model-adapted vortex in the initial condition of the model is essential for improvement of tropical cyclone track and intensity prediction.

23. Kurihara, Yoshio, Morris A Bender, Robert E Tuleya, and R Ross, 1993: Hurricane forecasting with the GFDL automated prediction system In 20th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 323-326.
24. Kurihara, Yoshio, 1993: Hurricanes and atmospheric processes In Relating Geophysical Structures and Processes: The Jeffreys Volume, Geophysical Monograph 76, IUGG Volume 16, Washington, DC, American Geophysical Union, 19-26.
    [ Abstract ]

    Hurricanes are among cyclonic vortices in which the gradient wind relationship holds during their evolution. The development of hurricanes proceeds with a persistent thermal forcing and the continual adjustment of fields to a new state of gradient wind balance. The forcing is largely due to the release of the latent heat received at the ocean surface. The adjustment is achieved by the development of a transverse circulation and the generation of inertia gravity waves. The behavior of the vortex also strongly depends on how it responds and adjusts itself to the environmental forcing. Thus, the spatial and temporal variability of the tropical cyclone climatology is related to regional and seasonal changes in the conditions of the larger scale environment. As exemplified by the evolution of hurricanes, the dynamics of an atmospheric system which undergoes slow structural change is controlled by the processes of forcing and adjustment. An atmospheric process may play a dual role: it contributes to the adjustment of one system while it provides forcing to another system, thus linking atmospheric systems of distinctly different scales.

25. Ross, R, and Yoshio Kurihara, 1993: Hurricane-environment interaction in hurricanes Gloria and Gilbert In 20th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 27-30.
26. Ross, R, and Yoshio Kurihara, 1992: A simplified scheme to simulate asymmetries due to the beta effect in barotropic vortices. Journal of the Atmospheric Sciences, 49(17), 1620-1628.
    [ Abstract PDF ]

    A simplified scheme to generate vortex asymmetries due to the beta effect from an initially symmetric vortex on a beta plane is described. This approach, based on the time integration of the nondivergent barotropic vorticity equation, was developed to generate asymmetric vortex structure for inclusion in the initial conditions for the GFDL Hurricane Model. The simplification is derived from truncation of an azimuthal wavenumber expansion of the vorticity field variables. In order to determine the optimum lowest-order system, the influence of other wavenumbers (specifically 0, 2, and 3) on the asymmetric dipolar (wavenumber 1) structure and the associated vortex drift was investigated by comparing the results of a hierarchy of models differing in truncation level. The model truncated at wavenumber 2 and, including time-dependent symmetric flow, was chosen as the optimum system. Vortex drift tracks computed with this model compare very well with existing numerical model simulations. The models with a time-dependent symmetric flow produced systematically more westward-(less northward-) directed drift with slower speeds for cyclonic vortices than the models with time-dependent symmetric flow. The results presented here clearly show the importance of including time-dependent symmetric flow in a simplified barotropic system. Discussion is developed regarding the interactions between the dipolar vortex and the wavenumber 0 and 2 flows. It appears acceptable to truncate the wavenumber expansion at wavenumber 2. The differences between the models with different levels of simplification increase when a larger initial vortex is used. The generation of the asymmetric flow for incorporation into the hurricane model initial conditions involves several aspects of uncertainty not present in idealized cases. A particular problem is the development of overly strong far-field vorticity (i.e., lying much beyond the hurricane region) possibly resulting from inaccuracies in the symmetric wind profile. During the generation of asymmetries, this is suppressed by damping at large radii. Further investigation is needed into the sensitivity of the resulting hurricane drift to the symmetric wind profile and to the integration cutoff time.

27. Bender, Morris A., R Ross, Yoshio Kurihara, and Robert E Tuleya, 1991: Improvements in tropical cyclone track and intensity forecasts using a bogus vortex In 19th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 324-325.
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28. Kurihara, Yoshio, R Ross, and Morris A Bender, 1991: Toward improvement of the dynamical prediction of tropical cyclones: A hurricane model initialization scheme In 19th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Geophysical Union, 326-327.
29. Kurihara, Yoshio, Morris A Bender, Robert E Tuleya, and R Ross, 1990: Prediction experiments of Hurricane Gloria (1985) using a multiply nested movable mesh model. Monthly Weather Review, 118(10), 2185-2198.
    [ Abstract PDF ]

    The prediction capability of the GFDL triply nested, movable mesh model, with finest grid resolution of 1/6 degree, was investigated using several case studies of Hurricane Gloria (1985) during the period that the storm approached and moved up the east coast of the United States. The initial conditions for these experiments were interpolated from an NMC T80 global analysis at 0000 UTC 25 September and 1200 UTC 22 September. The integrations starting from 0000 UTC 25 September were run 72 h, while those starting on 1200 UTC 22 September were run 132 h. The lateral boundary conditions were obtained from either an integration of the NMC T80 forecast model or the T80 global analysis, or were fixed to the initial value. The model's predicted track of Gloria for each integration was compared against the best track determined by the National Hurricane Center (NHC). For the case starting from 0000 UTC 25 September using a forecasted boundary condition, the model successfully forecasted significant acceleration of the storm's movement after 48 h. The 72 h forecast error was about 191 km, compared to 480 km for the official track forecast made by the NHC. To examine the model's skill in simulating the storm structure, distributions of the low level maximum wind and total storm rainfall during passage of the model storm are shown and compared with observed values. The model successfully reproduced many observed features such as the occurrence of strong winds well east of the storm center, with an abrupt decrease of the wind field along the coastline. When the storm track was accurately forecasted, the total storm rainfall amounts agreed well with the observed values. In both the model integration and observations, a significant structural change took place as the storm accelerated toward the north with little significant precipitation occurring south of the storm center and heavy precipitation spreading well north of the storm. It appears that the gross features of the structure of the storm's outer region resulted from the interaction of the vortex with its environment. Sensitivity of the model forecast to the lateral boundary condition and the horizontal resolution was also investigated. The storm's track error was greatly affected after the boundary error propagated by advection to the storm region. The impact of the horizontal resolution on the forecast was such that the model with one degree resolution produced a fairly good track forecast up to 48 h, but failed to simulate some of the main structural features. In the experiments starting from the 0000 UTC September 25 initial field, the interior storm structure did not develop, and the storm exhibited too large a radius of maximum wind throughout the integration. However, the integrations starting from 1200 UTC September 22 developed a more intense storm, with a more realistic radius of maximum wind. These differences were due to the spinup time necessary for the storm to develop in the model when starting from a coarse resolution global analysis which did not adequately resolve the fine structure of the storm interior. This indicates the importance of proper specification of the storm in the initial field.

30. Kurihara, Yoshio, and Morris A Bender, 1989: On the structure of moving tropical cyclones In 18th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 188-189.
31. Kurihara, Yoshio, C Kerr, and Morris A Bender, 1989: An improved numerical scheme to treat the open lateral boundary of a regional model. Monthly Weather Review, 117(12), 2714-2722.
    [ Abstract PDF ]

    A numerical scheme proposed by Kurihara and Bender is modified so as to improve the behavior of open lateral boundaries of a regional model. In the new scheme, both the local values and the gradients of fields from a larger model are used to define the time-dependent reference values toward which the boundary gridpoint values of the regional model prediction are relaxed at each step of the model integration. Use of the gradients in the boundary forcing imposes constraints on the vorticity, divergence and baroclinicity fields for the regional model. The relaxation time of forcing is set to be short for the normal component of wind. For other variables, the relaxation time at a given boundary gridpoint depends on the wind direction at that gridpoint, with a minimum at a point of normal inflow and a maximum at a point of normal outflow. The forcing strength is reduced in the planetary boundary layer so that the boundary layer structure is determined mainly by the surface condition of the regional model. Also, a simple method to control the total mass in the regional model is described. Numerical results from 96-hour integrations with the improved scheme are compared with those from the previous scheme for the cases of the propagations of a wave and a vortex. The behavior of the model at the lateral boundary was noticeably improved with the use of the new scheme, while the solution in the interior domain was little affected by the scheme modification.

32. Bender, Morris A., and Yoshio Kurihara, 1987: A numerical study of the effect of the mountainous terrain of Japan on tropical cyclones In Short- and Medium-Range Numerical Weather Prediction, Collection of Papers Presented At WMO/IUGG NWP Symposium Tokyo, Japan, Aug. 4-8, 1986, Geneva, Switz, World Meteorological Organization, 651-663.
    [ Abstract PDF ]

    A triply-nested, movable mesh model was used to study the effects of mountainous terrain on the landfall of tropical cyclones onto the islands of Japan. The integration domain spanned 43° latitude and 47° longitude with finest resolution of 1/6°. Numerical experiments were separately performed for three cases. In each experiment a storm was embedded onto a stationary Haurwitz type wave at the initial time, and moved in a north-northeast direction at about 10 to 12 m s-1. In the first experiment, the tropical cyclone struck the southwest Izu Peninsula in eastern Japan. The second and third respectively made landfall on the Kii Peninsula in the central part of Japan and on the island of Kyushu in western Japan. In order to isolate some of the effects on the storm system resulting from its interaction with the mountainous terrain, these simulations were compared with supplemental experiments performed with a flat land condition. In all three cases it was found that the presence of the mountainous terrain greatly enhanced the storm decay after landfall. As the storm approached Tokyo Bay rapid weakening occurred as dry air from the mountain region to the west of Tokyo was advected into the eye and eyewall region of the storm. Upon leaving eastern Japan and again moving over open water, the storm never underwent reintensification. In the case of the storm leaving western Japan, reintensification over the Sea of Japan occurred very slowly as compared with the experiment run with a flat land distribution. Apparently, the above behavior was related to the structural change which occurred to the storm system during the passage over the mountainous islands. The precipitation pattern was also greatly affected by the presence of the mountainous terrain. As the storm made landfall over central Japan, the area of heaviest rainfall shifted to the right of the storm track, where strong upslope winds developed. This storm eventually travelled over the high mountains of east-central Japan and rapidly decayed by the end of the experiment. Although performed for an idealized experimental design, these experiments reveal some of the important effects the mountainous terrain may have on the behavior of tropical cyclones making landfall on Japan. Understanding these effects should prove useful in forecasting more accurately the behavior of the storms.

33. Bender, Morris A., Robert E Tuleya, and Yoshio Kurihara, 1987: A numerical study of the effect of island terrain on tropical cyclones. Monthly Weather Review, 115(1), 130-155.
    [ Abstract PDF ]

    A triply-nested. movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. The storms used for this study were embedded in easterly flows of ~ 5 and ~ 10 m s^-1 initially. Realistic distributions of island topography at 1/6° resolution were inserted into the model domain for the region of the Caribbean, including the islands of Cuba, Hispaniola, and Puerto Rico; the island of Taiwan; and the region of Luzon in the northern Philippines. It was found that the islands affected the basic flow as well as the wind field directly associated with the storm system. The combination of these effects caused changes in the track and translational speed of the storm. In particular, in the case of the 5 m s^-1 easterly flow, the storm accelerated and veered to the north well before reaching Taiwan. For the other island distributions, the northward deflection of the track and the increase of translational speed occurred near and over the islands. After landfall, the surface pressure underwent rapid filling. As the tropical cyclone passed over Hispaniola, the surface low continued to move along with the upper level vortex as it transversed the mountain range, while over Luzon it became obscure before reforming on the lee side slope of the mountain. In case of Taiwan and the 10 m s^-1 easterly zonal flow, secondary surface lows developed behind the mountain range. The upper level vortex in this case became detached from the original surface low and eventually coupled with a secondary one. The intensity changes of the storm near and over the islands were strongly related to the latent energy supply and the vertical coherence of the storm system. Advection of dry air from near or above the mountain tops into the storm area caused significant weakening of all the storm moving with the weaker easterly flow. Storms leaving Hispaniola and moving over open sea quickly reintensified as their vertical structure remained coherent. On the other hand, storms leaving Luzon were disorganized and did not reintensify until several hours later when the vertical coherence of the systems was reestablished Although these experiments were performed for an idealized experimental design and basic flow, many observed storms have exhibited similar behavior in track deviation and decay. This implies that the effect of detailed topography should be considered if an accurate forecast of the storm direction and behavior is to be made.

34. Kurihara, Yoshio, and M Kawase, 1986: Reply. Journal of the Atmospheric Sciences, 43(24), 3284-3286.
    [ PDF ]
35. Bender, Morris A., Robert E Tuleya, and Yoshio Kurihara, 1985: A numerical study of the effect of a mountain range on a landfalling tropical cyclone In 16th Conference on Hurricanes & Tropical Meteorology, Boston. MA, American Meteorological Society, 146-147.
36. Bender, Morris A., Robert E Tuleya, and Yoshio Kurihara, 1985: A numerical study of the effect of a mountain range on a landfalling tropical cyclone. Monthly Weather Review, 113(4), 567-582.
    [ Abstract PDF ]

    A triply-nested, movable mesh model was used to study the effects of a mountain range on a landfalling tropical cyclone embedded in an easterly flow of ~ 10 m s^-1. The integration domain consisted of a 37 degree wide and 45 degree long channel, with an innermost mesh resolution of 1/6 degrees. An idealized mountain range with maximum height of ~ 958 meters was placed parallel to the shoreline. The mountain range, which spanned 19 degrees in the north-south direction and 5 degrees in the east-west direction, was centered in the middle of the channel. Results obtained were compared with a previous landfall simulation, performed without the effect of the mountain range included. In particular, comparison was made of the total storm rainfall, maximum wind distribution and storm decay rate. It was found that the storm filled much more rapidly in the simulation run with the mountain included. The mountain range affected the decay rate through reduction in the supply of latent and kinetic energy into the storm circulation during, as well as after, passage of the storm over the mountain. It was found that a low-level, warm and dry region was produced where the storm winds descended the mountain slope. In order to better isolate the effect of the mountain on the basic easterly flow, a supplemental integration was performed for the flow without the storm. It revealed that the mountain range caused a significant change in the basic flow over the mountain as well as up to several hundred kilometers downstream and extending considerably above the mountain top. A low-level southerly jet was observed to the west of the mountain base.

37. Kurihara, Yoshio, 1985: Numerical modeling of tropical cyclones. Advances in Geophysics, 28B, 255-281.
38. Kurihara, Yoshio, and M Kawase, 1985: On the transformation of a tropical easterly wave into a tropical depression: a simple numerical study. Journal of the Atmospheric Sciences, 42(1), 68-77.
    [ Abstract PDF ]

    Through the time integration of a simple numerical model, the transformation of a tropical easterly wave into a tropical depression was investigated. The initial condition selected for the model is a slowly decaying, adiabatic linear normal mode resembling an easterly wave. It was found that the addition of a CISK (conditional instability of the second kind) heating effect to the model results in the growth of the wave. Addition of the nonlinearity effect alone, which includes the nonlinear zonal advection and vertical stretching of relative vorticity, has little impact on the wave evolution. However, if the above nonlinearity effect is combined with the heating effect, it can cause the contraction of the disturbance and enhance the development. The initial free wave undergoes significant structural changes during its transformation into a developing system. Experiments were also performed for three different waves under various basic flow conditions. The obtained results agree with a conclusion of the three-dimensional simulation experiments by Tuleya and Kurihara; the coupling between the upper-level wind and the propagating disturbance at low levels may be an important mechanism in the formation of a tropical depression in the trough region of an easterly wave.

39. Tuleya, Robert E., Morris A Bender, and Yoshio Kurihara, 1984: A simulation study of the landfall of tropical cyclones using a movable nested-mesh model. Monthly Weather Review, 112(1), 124-136.
    [ Abstract PDF ]

    By use of a triply nested, movable mesh model, several ideal simulations of tropical cyclone landfall were performed for a strong zonal flow of ~10 m s-1. The integration domain was a 37 X 45 degree channel with the innermost mesh having a 22 X 22 point resolution of 1/6 degree. General characteristics similar to observed landfalling tropical cyclones are obtained in the primary simulation experiment including an abrupt change in the low level (~68 m) winds at the coastline and a decay of the tropical cyclone as it moves inland. Additional interesting features subject to model and experimental limitations include: little noticeable track change of the model storm when compared to a control experiment with an ocean surface only; a possible temporary displacement of the center of the surface wind circulation from the surface pressure center at landfall; and a distinct decrease in kinetic energy generation and precipitation a few hours after landfall. The sensitivity to the specified land surface conditions was analyzed by performing additional experiments in which the land surface conditions including surface temperature, moisture, and distribution of surface roughness were changed. It was found that a reasonable change in some of these land conditions can make a considerable difference in behavior for a landfalling tropical cyclone. It was also shown that a small, less intense model storm fills less rapidly. This corresponds well with observations that many landfalling hurricanes decay to approximately the same asymptotic value one day after landfall.

40. Tuleya, Robert E., and Yoshio Kurihara, 1984: The formation of comma vortices in a tropical numerical simulation model In 15th Conference on Hurricanes and Tropical Meteorology, Boston, MA, American Meteorological Society, 320-324.
41. Tuleya, Robert E., and Yoshio Kurihara, 1984: The formation of comma vortices in a tropical numerical simulation model. Monthly Weather Review, 112(3), 491-502.
    [ Abstract PDF ]

    A detailed analysis of a numerically simulated tropical disturbance displays a comma-shaped pattern at the mature stage in the low-level vorticity, surface convergence, mid-level upward motion and precipitation fields. This study reveals that the high wind side of the disturbance is the favorable region for the formation of the tail of the comma pattern. The beta effect retards the development of the comma shape in the case of easterly environmental winds and enhances it in the case of westerlies. Analysis of the vorticity field suggests that the initial shape and intensity of the perturbation can influence the wind pattern of an evolving disturbance. Although some indications of band-like features exist in the wind field for dry experiments with no lower-boundary fluxes, surface fluxes of heat, moisture and momentum are found to be vital ingredients for the formative process of the distinct comma shape of the disturbance.

42. Bender, Morris A., and Yoshio Kurihara, 1983: The energy budgets for the eye and eye wall of a numerically simulated tropical cyclone. Journal of the Meteorological Society of Japan, 61(2), 239-244.
    [ Abstract PDF ]

    Energy budgets are analyzed for a tropical cyclone simulated previously in a quadruply nested mesh model (Kurihara and Bender, 1982). It will be shown that the eddy kinetic energy within the eye is comparable in magnitude to that of the mean kinetic energy. It is supplied by import from the eye wall regions as well as by the conversion from total potential energy. At the same time it is converted to the kinetic energy of the mean flow and also lost by the dissipation. The influx of mean kinetic energy from the outer radii to the eye wall region and the export of potential energy both to the outer radii and to the eye region play important roles in the energetics of the eye wall region. Many obtained features agree well with those of a coarser resolution model (Tuleya and Kurihara, 1975) in which the eye of the vortex could not be resolved. This suggests that the eye structure has little impact on the energetics to the eye wall and outer regions of a tropical cyclone.

43. Kurihara, Yoshio, and Morris A Bender, 1983: A numerical scheme to treat the open lateral boundary of a limited area model. Monthly Weather Review, 111(3), 445-454.
    [ Abstract PDF ]

    A numerical scheme to treat the open lateral boundary of a limited-area primitive equation model was formulated. Although overspecification of the boundary condition is inevitable in the pointwise boundary setting, the scheme was designed to keep the overspecification to a minimum degree. To impose the boundary conditions, a damping technique was used. Special care was taken to deal with the boundary layer winds at the lateral boundary. The above scheme is most suitable when gravity waves do not prevail in the vicinity of the open boundary. The scheme was tested in the numerical integrations of prognostic equations for a Haurwitz-type wave. Experimental results are presented which indicate the utility of the proposed method.

44. Tuleya, Robert E., Morris A Bender, and Yoshio Kurihara, 1983: A numerical study of simulated hurricane landfall In Sixth Conference on Numerical Weather Prediction, Boston, MA, American Meteorological Society, 323-324.
45. Kurihara, Yoshio, and Morris A Bender, 1982: Structure and analysis of the eye of a numerically simulated tropical cyclone. Journal of the Meteorological Society of Japan, 60(1), 381-395.
    [ Abstract PDF ]

    A tropical cyclone has been simulated in a quadruply nested mesh model with finest grid resolution of about 5 km. At the center of the vortex, a compact eye was maintained. Azimuthal means as well as asymmetry of the eye and the eye wall structure are described. The asymmetric features within the eye wall moved cyclonically at a much smaller rotation rate than the cyclonic wind within the eye wall. Roles of the mean radial-vertical circulation, the eddy motions and the diffusion effect in the maintenance of the mean structure are analyzed. In the analysis, attention is given to the balance between the wind and pressure fields and also to the budgets of relative angular momentum, heat and water vapor. The eddy motions caused a cooling and moistening effect in the eye which counterbalanced a warming and drying effect due to the mean sinking motion.

46. Kurihara, Yoshio, and Robert E Tuleya, 1982: Influence of environmental conditions on the genesis of a tropical storm In Topics in Atmospheric and Oceanographic Sciences Intense Atmospheric Vortices, Berlin, Germany, Springer-Verlag, 71-79.
    [ Abstract ]

    Numerical experiments have been performed in search of the favorable conditions of environmental wind for the genesis of a tropical storm. The low level basic flow has an impact on the latent energy supply which is essential for genesis. The upper level basic flow has to be coupled with the phase speed of the low level incipient disturbance. The low level cyclonic shear of the basic flow is conducive to storm genesis.

47. Kurihara, Yoshio, and Robert E Tuleya, 1982: On a mechanism of the genesis of tropical storms In MSJ/JMA/WMO/AMS Regional Scientific Conference on Tropical Meteorology, Tsukuba, Japan, 18-22 October 1982, WMO Programme on Research in Tropical Meteorology, World Meteorological Organization, 17-18.
48. Tuleya, Robert E., and Yoshio Kurihara, 1982: A note on the sea surface temperature sensitivity of a numerical model of tropical storm genesis. Monthly Weather Review, 110(12), 2063-2069.
    [ Abstract PDF ]

    In a three-dimensional numerical model of a tropical disturbance, a spectrum of development stages, from a weakening wave to a mature tropical storm, was obtained with a 5 K range (298 to 303 K) sea surface temperature (SST). However, the apparently large SST sensitivity of the model was found to be modulated by other factors including the large-scale environmental temperature and humidity. Through the use of this model, problems concerning a critical value of SST necessary for storm development were discussed.

49. Kurihara, Yoshio, and Robert E Tuleya, 1981: A numerical simulation study on the genesis of a tropical storm. Monthly Weather Review, 109(8), 1629-1653.
    [ Abstract PDF ]

    The genesis of a tropical storm is studied using a numerical simulation model. The model used is an 11-level primitive equation model covering a channel domain of 25 degree span with open lateral boundaries at latitudes 5.5. and 30.5 degrees N. The initial basic flow field is based on the mean condition at 80 degrees W during Phase III of GATE. The superposed wave disturbance is initially confined in the lower troposphere. The time integration of the model is carried out to 96 h, during which a tropical storm develops accompanied by an upper level anticyclone. The genetic sequence of the disturbance system, from a shallow easterly wave into a tropical depression and further into a tropical storm, is described. The minimum surface pressure of the system deepens from 1008.4 to 1002.6 mb at 96 h. The maximum surface wind at 96 h is above 17 m s-1. The relative vorticity at 950 mb intensifies from 43 x 10^-6 s^-1 at the initial time to 237 x 10^-6 s^-1 at 96 h. The surface convergence increases from 24 x 10^-6 s^-1 to 71 x 10^-6 s^-1 . The processes involved in the above transformation are extensively discussed. Attention is given to the change in the area of rainfall and cloud from a zonal pattern to a cluster-type, the deepening of the cloud within the system, the appearance of horizontal tilt of the trough axis and the time variation of its vertical tilt, the evolution of the vertical motion field, the thickening of the convergence layer around the depression center, the formation of a warm core at 335 mb and its downward extension, the appearance of a cold core at a higher level, etc. The intensification of the vortex and the growth of a warm core are analyzed by examining budgets of vorticity and heat at the tropical depression stage. The vorticity increase at low levels is due to stretching of the vortex. Relative horizontal advection causes a decrease of vorticity in some outer areas. At upper levels, the upward protrusion of positive vorticity from below and relative horizontal advection cause a positive tendency. Both the effect due to horizontal divergence and the twisting up of a horizontal vortex make negative contributions. The net effect at upper levels is to produce a compact positive vorticity area within a large region of negative vorticity. Upper level warming is largely due to the excess of the condensation-convection heating over the cooling effect associated with the upward motion. The appearance of an upper level disturbance in the present model is caused entirely by the forcing from below. Supplemental experiments confirm that, although the diabatic heating effect of radiation plays an important role, the heating due to the condensation of water vapor is essential for the formation of a tropical storm in the present case.

50. Tuleya, Robert E., and Yoshio Kurihara, 1981: A numerical study on the effects of environmental flow on tropical storm genesis. Monthly Weather Review, 109(12), 2487-2506.
    [ Abstract PDF ]

    The role of the environmental wind in tropical storm genesis is studied using a numerical simulation model. The model used is an 11-level, primitive equation model covering a channel domain of 25 degrees span with open lateral boundaries at 5.5 and 30.5 degrees N. A number of experiments were integrated for 96 h in which the initial zonal mean flow was specified differently. The superposed initial wave disturbances were identical in all experiments. The role of the environmental wind in tropical storm genesis is studied using a numerical simulation model. The model used is an 11-level, primitive equation model covering a channel domain of 25 degrees span with open lateral boundaries at 5.5 and 30.5 degrees N. The dynamic coupling between the upper-level winds and the low-level movement of the disturbance was found to be an important factor in explaining the role of the environmental wind in storm genesis. Another important factor is the impact of the low-level winds on the latent energy supply. This supply is affected by the relative inflow into a disturbance and by the transfer of momentum from aloft into the boundary layer in a large area surrounding the disturbance. According to the model results, the storm genesis potential is definitely biased toward easterly vertical shear (easterlies increasing with height) of the environmental flow rather than westerly shear when the mean surface flow is easterly, i.e., -5 ms-1. The initial perturbation developed into a vigorous tropical storm when an easterly vertical shear of 15 ms-1 was specified between 150 and 850 mb. In an experiment with a specified westerly vertical wind shear of 15 ms-1, the perturbation failed to develop beyond a weak tropical depression. In a third experiment with no vertical wind shear but with anticyclonic shear aloft, a tropical storm also developed. In analyzing the structure of the disturbances at the early wave stage it was found that the vertical shear modulated the vertical velocity and rainfall patterns relative to the trough axis. In studies involving the horizontal wind shear of the basic flow, it was found that cyclonic shear at low levels and, to a lesser extent, anticyclonic shear at upper levels are conducive for storm genesis. The experimental results also indicate a significant change of structure of the disturbance between uniform westerly and easterly flows. Under uniform westerly environmental flow, the initial perturbation developed more and its low-level structure became more characteristic of mid-latitude cyclones.

51. Kurihara, Yoshio, and Morris A Bender, 1980: Use of a movable nested-mesh model for tracking a small vortex. Monthly Weather Review, 108(11), 1792-1809.
    [ Abstract PDF ]

    The mesh nesting strategy proposed by Kurihara et al. (1979) was used to construct a movable, nested-mesh, 11-level primitive equation model. The framework of the model is described in detail. With the use of a triply nested mesh system with 1 degree, 1/3 degree and 1/6 degree longitude-latitude resolution, a small intense dry vortex in a zonal flow of 10 m s^-1 was successfully advected for 48 h. The shape of the vortex was well preserved during the time integration which involved over 50 movements of the innermost mesh. The noise, which was excited when a mesh moved, was suppressed in ~4 minutes after the movement. For comparison, the results from similar experiments performed with reduced inner mesh resolutions are also presented.

52. Kurihara, Yoshio, and Morris A Bender, 1979: Supplementary note on "A scheme of dynamic initialization of the boundary layer in a primitive equation model". Monthly Weather Review, 107(9), 1219-1221.
    [ Abstract PDF ]

    A scheme is presented for improving the previously proposed method of dynamic initialization of the boundary layer in a primitive equation model (Kurihara and Tuleya, 1978). Performance of the revised scheme is shown for the case of a strong vortex superposed on a zonal flow.

53. Kurihara, Yoshio, 1979: In An Introduction to Dynamics of the Atmosphere, Iwanami Concise Textbook Series, Tokyo, Japan, Iwanami Shoten Publishers, 244 pp.
54. Kurihara, Yoshio, G J Tripoli, and Morris A Bender, 1979: Design of a movable nested-mesh primitive equation model. Monthly Weather Review, 107(3), 239-249.
    [ Abstract PDF ]

    A numerical scheme to construct a two-way, movable, nested-mesh primitive equation model is proposed. Dynamical coupling in a two-way nesting system is performed at a dynamical interface which is separated from a mesh interface by two coarse-grid intervals. Dynamical interaction is achieved by a method which conserves mass, momentum and internal energy of the system. During the course of integration, the nested mesh moves so that the central position of the disturbance contained in the fine-mesh area never deviates from the center of the nest by more than one coarse-mesh interval. New grid data near the leading and trailing edges of the moving nest are obtained by an interpolation method which has a conservation property. The proposed methods of dynamical coupling and mesh movement were extensively tested by a one-dimensional shallow water equation model. Numerical results of these experiments are presented.

55. Kurihara, Yoshio, and Robert E Tuleya, 1978: A scheme of dynamic initialization of the boundary layer in a primitive equation model. Monthly Weather Review, 106(1), 114-123.
    [ Abstract PDF ]

    A scheme of dynamic initialization of a primitive equation model is proposed with an emphasis on the dynamic adjustment in the boundary layer. The pre-initialization analysis is important since the restorative method is used in the subsequent dynamic initialization. The first phase of dynamic initialization is designed to establish a reasonable boundary layer structure. For this purpose, a time integration of the primitive equations is performed under a strong constraint such that all meteorological fields except momentum in the boundary layer are frozen. Use of an implicit form for the vertical diffusion term is recommended. The second phase is formulated to reduce the high-frequency noise in the final initialized field. Cyclic integration with a selective damping scheme is carried out under a restorative constraint. The proposed scheme is applied to a case of simple zonal flow and the evolution of the boundary layer flow is shown. The scheme is also tested for a case of mature tropical cyclone. Starting from the wind data in the free atmosphere only, the initial condition of the model is derived. Subsequent time integration of the model compares favorably with the integration in a control experiment.

56. Tuleya, Robert E., and Yoshio Kurihara, 1978: A numerical simulation of the landfall of tropical cyclones. Journal of the Atmospheric Sciences, 35(2), 242-257.
    [ Abstract PDF ]

    A GFDL tropical cyclone model was applied to simulate storm landfall. The numerical model is a three-dimensional, primitive equation model and has 11 vertical levels with four in the planetary boundary layer. The horizontal grid spacing is variable with finest resolution being 20 km near the center. This model was used successfully in the past to investigate the development of tropical cyclones over the ocean. In the present experiments, a simple situation is assumed where a mature tropical cyclone drifts onto flat land. In such a case, the landfall can be simulated by changing the position of the coastline in the computational domain rather than by moving the storm. As the coastline moves with a specified speed, the surface boundary conditions are altered at the shore from those for the ocean to those for the land by increasing the surface roughness length and also by suppressing the evaporation. Despite the simplicity and idealization of the experiments, the cyclone's filling rates are quite reasonable and a decay sequence is obtained. Notable asymmetries in the wind, moisture and precipitation fields exist relative to the coastline at the time of landfall. Roughness-induced, quasi-steady convergence and divergence zones are observed where onshore and offshore winds encounter the coastline. Spiral bands propagate and exist over the land area. A comparison of the energy and angular momentum budgets between ocean and land surface boundary conditions indicates a simultaneous broadening and weakening of the storm system in the decay process. The latent energy release through condensational processes is initially augmented over land by greater moisture convergence in the planetary boundary layer which counteracts the lack of evaporation from the land surface. Supplementary experiments indicate that the suppression of evaporation is the most important factor in the decay of a storm upon landfall. When the evaporation is suppressed, the storm eventually weakens whether the surface roughness is increased or not. An increased surface roughness, which causes increased inflow in the boundary layer, has little immediate negative impact on the storm intensity. Indeed, if the supply of latent energy is sufficient, a storm can deepen when encountering an increase in surface roughness. The decay rate in a later period well after landfall is influenced by the rate with which the water vapor of the storm system is depleted in the earlier period immediately after landfall.

57. Kurihara, Yoshio, 1976: On the development of spiral bands in a tropical cyclone. Journal of the Atmospheric Sciences, 33(6), 940-958.
    [ Abstract PDF ]

    Development of the band structure in a tropical cyclone is investigated by solving an eigenvalue problem for perturbations of spiral shape. The perturbations are superposed on a baroclinic circular vortex accompanied with a radial and vertical basic flow. It is shown that the spiral bands in three different modes may be intensified in an inner area of a tropical cyclone. The baroclinicity of a basic field is not required for the development of bands in any mode. A spiral band which propagates outward can grow in the presence of the horizontal shear of the basic azimuthal flow. Without the basic circular vortex, this band is reduced to a neutral gravity-inertia wave with a particular vertical structure. The unstable spiral in this mode takes a pattern which extends clockwise from the center of a storm in the Northern Hemisphere. An azimuthal wavenumber 2 and a radial scale (twice the band width) of 200 km are preferred by this band. Another band with the characteristics of an inward propagating gravity wave may be excited in an inner area of a storm by its strong response to the effect of diabatic heating. The third kind of band has the features of a geostrophic mode and moves inward. Its development in an inner area is associated with the horizontal shear of the basic circular flow. The bands of the second and the third mode have not been observed in real storms. Dynamical behavior as well as the energetics of a band are discussed for each mode. There exists practically no instability in the outer region of the storm for any kind of spiral band. It is speculated that a band which grows in an inner area and propagates outward, i.e., the band of the first mode mentioned above, may become a neutral spiral while moving toward the outer region. Some of the outer spiral bands observed in real tropical cyclones may be interpreted as this kind of internal gravity-inertia waves.

58. Kurihara, Yoshio, and G J Tripoli, 1976: An iterative time integration scheme designed to preserve a low-frequency wave. Monthly Weather Review, 104(6), 761-764.
    [ Abstract PDF ]

    A two-step iterative time integration scheme is formulated, by which the amplitude of a low-frequency wave in a primitive equations model is preserved fairly well for a period of short-range weather prediction while the high-frequency noises are damped. The desired computational characteristics are obtained by separating the terms of the equations at the corrector step. Numerical examples are represented which show the damping property of the proposed scheme. The new scheme does not require more data space in a computer than the amount used in the Euler-backward method.

59. Kurihara, Yoshio, 1975: Budget analysis of a tropical cyclone simulated in an axisymmetric numerical model. Journal of the Atmospheric Sciences, 32(1), 25-59.
    [ Abstract PDF ]

    A tropical cyclone simulated in an axisymmetric numerical model is analyzed in detail from various aspects in order to deepen the understanding of the basic mechanisms of its evolution. Namely, the budget equations of temperature, moisture, relative angular momentum, vorticity, radial-vertical circulation, and kinetic energy are investigated for the different stages of the development of a tropical cyclone. The spatial distributions of each term in the budget equations are shown and their role in the following processes are discussed. In the pre-deepening stage of a large weak vortex in a conditionally unstable atmosphere, a solenoidal field is formed as a result of a delicate heat budget which depends on the static stability and the moisture content. The baroclinicity field thus established drives the system into a deepening stage. A postive feedback process builds up a warm moist core, accelerates the radial-vertical circulation, and intensifies the moist convection. A net outflow of mass from the central region and a resultant drop of central surface pressure take place during this period. The relative angular momentum of the inner column as a whole increases through convergence of relative angular momentum. In terms of relative vorticity, intensification and shrinking of the vortex is due to the combined effects of advection, horizontal convergence and twisting. At the end of the deepening stage, conditional instability in the central region is neutralized. The moment due to Coriolis force acting on the intensified azimuthal flow counterbalances the baroclinicity vector, so that the acceleration of radial-vertical flow ceases. Concentration of relative angular momentum and vorticity in the central region also levels off. In the budget of these quantities, the role of both vertical and lateral stress becomes important. In the troposphere, except the upper part and the boundary layer, the gradient wind relationship is established between the pressure field and the azimuthal flow. In the mature stage, the status in the inner region is quasi-stationary while that of the outer area keeps changing slowly. The importance of evaporation at the central area for the maintenance of an intense tropical cyclone is demonstrated in an additional experiment.

60. Tuleya, Robert E., and Yoshio Kurihara, 1975: The energy and angular momentum budgets of a three-dimensional tropical cyclone model. Journal of the Atmospheric Sciences, 32(2), 287-301.
    [ Abstract PDF ]

    Energy and angular momentum budgets are analyzed for a three-dimensional model hurricane described by Kurihara and Tuleya. Eddies which developed in the model are maintained in the mature stage by energy supply from both mean kinetic and total potential energy. In the evolution of eddies during the early development stage of the storm, the supply from potential energy is more important. Eddies export latent, internal, kinetic energy and relative angular momentum from the storm core region. They also contribute to the outward transfer of energy through pressure work. However, the mean flow dominates the transport by importing those quantities into the inner area and exporting potential energy. The energy and angular momentum budgets are primarily controlled by the mean flow, though the role of eddies is not negligible for the budgets of angular momentum, kinetic and latent energy in the inner region. For the maintenance of mean kinetic energy in the inner area, both generation and advection make positive contributions. The computed transports and budgets are compared with those available for other three-dimensional models as well as with real data analyses made by other investigators.

61. Kurihara, Yoshio, and Robert E Tuleya, 1974: Comments "On the importance of precision for short-range forecasting and climate simulation". Journal of Applied Meteorology, 13(5), 601-602.
    [ PDF ]
62. Kurihara, Yoshio, and Robert E Tuleya, 1974: Structure of a tropical cyclone developed in a three-dimensional numerical simulation model. Journal of the Atmospheric Sciences, 31(4), 893-919.
    [ Abstract PDF ]

    A three-dimensional, 11-level, primitive equation model has been constructed for a simulation study of tropical cyclones. The model has four levels in the boundary layer and its 70 x 70 variable grid mesh encloses a 4000-km square domain with a 20-km resolution near the center. Details of the model, including the parameterization scheme for the subgrid-scale diffusion and convection processes, are described. A weak vortex in the conditionally unstable tropical atmosphere is given as the initial state for a numerical integration from which a tropical cyclone develops in the model. During the integration period of one week, the sea surface temperature is fixed at 302K. The central surface pressure drops to about 940 mb, while a warm moist core is established. The azimuthal component of mean horizontal wind is maximum at about 60 km from the center at all levels. A strong inflow is observed in the boundary layer. At upper levels, a secondary radial-vertical circulation develops in and around the region of negative mean absolute vorticity. In the same region, the azimuthal perturbation of horizontal wind is pronounced. At the mature stage, the domain within 500 km radius is supplied with kinetic energy for asymmetric flow by both barotropic and baroclinic processes. At 60 km radius, the temperature perturbation field is maintained by condensation-convection heating at upper levels and by adiabatic temperature change due to vertical motion at lower levels. An area having an eye-like feature is found off the pressure center. Structure of spiral bands in the outer region is extensively analyzed. The phase relationship among the pressure, horizontal motion, vertical motion, temperature and moisture fields is discussed. The spiral band behaves like an internal gravity wave. Once the band is formed in an area surrounding the center, it propagates outward apparently without appreciable further supply of energy, as far as the present case is concerned.

63. Kurihara, Yoshio, 1973: Experiments on the seasonal variation of the general circulation in a statistical-dynamical model. Journal of the Atmospheric Sciences, 30(1), 25-49.
    [ Abstract PDF ]

    A study of the seasonal change of a climatic state of the atmosphere is made through the investigation of a response of a statistical-dynamical model to insolation having seasonal variation. Numerical experiments are performed for the two hypothetical cases: the land-covered earth (LCE) and the ocean-covered earth (OCE). The two cases differ in the thermal and aerodynamical conditions at the surface, and a hydrologic cycle is incorporated only in the model for OCE. Numerical integrations are carried out until the same climatic state as one year before reappears. Then, annual marches of the zonal mean field, the eddy statistics, and the energetics are analyzed. Baroclinicity at the middle latitudes is noticeable, in summertime, only for the OCE. Strong upper level easterly flow evolved at low latitudes for the LCE. The mean meridional circulation at low latitudes for both LCE and OCE is characterized by one big Hadley cell extending from the summer into the winter hemisphere. In the OCE, the water vapor is exported from the subtropics equatorward by the mean meridional circulation and poleward by large-scale eddies. The effect of ocean is to moderate the seasonal change of eddy activity so that the eddy transport of heat for the OCE is smaller in winter and larger in summer than that for the LCE. The additional experiments show the dependency of the eddy statistics of the model on the internal viscosity. It is also shown that the after-effect of a sudden shock lasts about five months in the atmosphere for the OCE.

64. Kurihara, Yoshio, 1973: A scheme of moist convective adjustment. Monthly Weather Review, 101(7), 547-553.
    [ Abstract PDF ]

    A new method of moist convective adjustment is presented. A large-scale state of the atmosphere is assumed to be in a thermodynamically critical condition when a hypothetical cloud element can develop. As a result of the convective adjustment, the atmosphere is altered to a new state that is marginal or unfavorable to the occurrence of a free moist convection. The numerical scheme of the adjustment is described in detail.

65. Kurihara, Yoshio, 1971: Seasonal variation of temperature in an atmosphere at rest. Journal of the Meteorological Society of Japan, 49, 537-544.
    [ Abstract ]

    The variation of temperature of an atmosphere at rest with latitude and time is investigated. The heating of an air column which is due to short-wave and long-wave radiation is estimated by simple parameterization. A condition of heat balance is assumed at the earth's surface to evaluate sensible heat flux there. An analysis of the equation shows that the heat capacity and the properties of the long-wave radiation of the atmosphere determine the time lag between variations in temperature and insolation. In the numerical integration, extreme temperatures at middle latitude occurred about one month after the solstices. In the equatorial region, two maxima and two minima appeared in the temperature variation. The lowest temperature in the polar region took place in spring because of the winter polar night. A comparison of the results of the integration with the observed variation demonstrates the importance of the meridional transport of energy in the atmosphere and ocean. This comparison also suggests the importance of the storage of energy in the ocean and land.

66. Kurihara, Yoshio, 1970: A statistical-dynamical model of the general circulation of the atmosphere. Journal of the Atmospheric Sciences, 27(6), 847-870.
    [ Abstract PDF ]

    A statistical-dynamical, two-layer model of the atmosphere is constructed for the simulation of the climatic state of the global circulation. The meteorological variables, velocity, temperature and pressure, are decomposed into their zonal mean parts and eddy parts or deviations. The state of circulation is expressed by the zonal mean parts as well as eddy statistics which are the zonal averages of the product of the deviations. Eddy statistics such as the amount of eddy kinetic energy, and eddy transfer of heat and angular momentum are longitudinally integrated measures of the intensity and structure of individual synoptic-scale disturbances. The equations for the zonal means of wind, temperature and pressure and that of eddy kinetic energy are obtained from the equations of motion, the thermodynamical equation, and the continuity equation, and include the terms depending on the eddy statistics. The prediction equation for the horizontal eddy transfer of heat, as well as an estimate of the vertical eddy transfer of heat and angular momentum, are derived under the quasi-geostrophic assumption. The horizontal eddy tranfer momentum is estimated by a diagnostic formula similar to the one used by Smagorinsky. The results of theoretical studies of long waves are utilized to determine the pressure interaction term, the characteristic size of eddies, and the phase speed which are involved in certain of the equations. The model atmosphere expressed by the closed system of equations thus established is controlled by insolation, parameters for radiative heat transfer, static stability, lower boundary conditions for the exchange of momentum and heat, and parameters for horizontal stress and for the lateral diffusion of heat in the free atmosphere due to small-scale eddies. The present model does not include the effect of lateral transfer of latent energy. A numerical experiment is performed for a fixed annual mean insolation and a given specification of other control factors. The model consists of two layers, each having 48 zonal rings between the north and south poles. Starting from rest and a constant temperature at the middle level, the integration is done for the first 50 days without eddies. A small amount of eddy kinetic energy is superimposed on the axially symmetric flow at 50 days. Then, the primary features of the actual circulation, such as the jet stream, the Ferrel cell in mean meridional circulation, and the poleward eddy transport of heat, evolve, and a quasi-equilibrium state with a mode of fluctuation is attained.

67. Kurihara, Yoshio, 1968: Note on finite difference expressions for the hydrostatic relation and pressure gradient force. Monthly Weather Review, 96(9), 654-656.
    [ PDF ]
68. Kurihara, Yoshio, and J L Holloway, Jr, 1967: Numerical integration of a nine-level global primitive equations model formulated by the box method. Monthly Weather Review, 95(8), 509-530.
    [ Abstract PDF ]

    Based on the box method, finite-difference versions of a system of primitive equations in spherical coordinates are formulated for a spherical grid. Non-linear computational instability cannot occur in time integrations of these equations. Conservation of total mass is guaranteed by the finite-difference form of the continuity equation. The proposed scheme yields no fictitious sources of energy in the derivation of the difference formula for the budget of the total energy over the entire domain. The finite-difference equations for the budget of the relative and absolute angular momentum are not exact analogs of the continuous forms but nevertheless are very accurate. This system of primitive equations for a nine-level general circulation model of the atmosphere has been numerically integrated for 50 forecast days. The network of grid points covers the entire globe with nearly uniform spacing and has no artificial horizontal boundaries. The initial data were latitude-height-dependent zonal mean winds and pressures and zonal mean temperatures perturbed slightly by random numbers. The time integration was carried out without any finite-difference computational problems and baroclinic waves developed and propagated.

69. Kurihara, Yoshio, 1965: Numerical integration of the primitive equations on a spherical grid. Monthly Weather Review, 93(7), 399-416.
    [ Abstract PDF ]

    A new spherical grid system whose grid density on the globe is almost homogenous is proposed. The elementary rules of finite differencing on the grid system are defined so that a desirable condition for numerical area integration is satisfied. The integrations of primitive equations for a barotropic atmosphere with free surface are made. The patterns of initial fields are the same as Phillips used in 1959 for a test of his map projection system and computation schemes. Ten test runs are performed for a period of 16 days. Three of these are without viscosity and integrated with different time integration schemes. Four runs include the effect of non-linear viscosity with different coefficients, and the remaining three are computed with different amounts of linear viscosity. A noticeable distortion of the flow pattern does not occur in an early period in any run. Analyses of the results suggest that the damping of high frequency oscillation of both long and short wavelengths can be achieved by an iterative time integration scheme, e.g., the modified Euler-backward iteration method, with little effect on the prediction of a trend of the meteorological wave. Either the non-linear or the linear viscosity can be used to suppress a growth of short waves of both low and high frequency modes, if the optimum amount of viscosity for that purpose does not exceed the amount representing the actual diffusion process in the atmosphere. Analyses are also made concerning the effects caused by different specifications of the parameter in the viscosity term in the equations.

70. Kurihara, Yoshio, 1965: On the use of implicit and iterative methods for the time integration of the wave equation. Monthly Weather Review, 93(1), 33-46.
    [ Abstract PDF ]

    The numerical properties of the trapezoidal implicit, the backward implicit, and partly implicit methods are investigated. The computational stability of these methods, the selective damping of waves, and the accuracy of the predicted wave are discussed primarily for wave equations in the simple form. Then, their applicability to the integration of the primitive equations is considered for a system of linearized equations. The characteristic features of four iterative methods, each of which consists of a predictor and a corrector to be used only once, are also described.

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