Bibliography - Song-Miao Fan

1. Cassar, N, M Bender, B A Barnett, Song-Miao Fan, Walter Moxim, Hiram Levy II, and B Tilbrook, 2008: Response to comment on. Science, 319(5860), doi:10.1126/science.1150011.
   [ Abstract ]

   Net community production in the Southern Ocean is correlated with simulated local dust deposition, and more so with modeled deposition of soluble iron. Model simulations of the latter two properties are consistent with observations in both hemispheres. These results provide strong evidence that aerosol iron deposition is a first-order control on net community production and export production over large areas of the Southern Ocean.

2. Fan, Song-Miao, February 2008: Photochemical and biochemical controls on reactive oxygen and iron speciation in the pelagic surface ocean. Marine Chemistry, 109(1-2), 152-164.
   [ Abstract PDF ]

   A time-dependent chemistry model is used to predict reactive oxygen species (ROS = H₂O₂ + O₂⁻) and dissolved Fe (DFe) speciation in the surface ocean. A new feature of the model is inclusion of biological sources of superoxide. The model suggests that biochemistry mediated by phytoplankton cells is as important as photochemistry for the formation of ROS. Formation of stable organic Fe(III) complexes (FeL) maintains the concentration of DFe in seawater. Iron speciation in the model is also controlled by biochemical and photochemical processes, and is far from thermodynamic equilibrium. During light periods, photo-reduction of FeL produces dissolved inorganic iron much more than thermal decomposition and cell-surface reduction of FeL, thus facilitating phytoplankton uptake of iron in the ocean. During the nighttime, O₂⁻produced by reductases on cell surfaces both reacts with FeL, producing Fe(II), and retards the oxidation of Fe(II) and subsequent formation of FeL; therefore significant levels of bio-available Fe is maintained through this period. Photo-reduction nearly balances the formation of FeL in the model, and may control bioavailability of dissolved iron. This suggests a possible extracellular mechanism of iron and light colimitation to primary productivity. A phytoplankton growth limitation by FeL photo-reduction depends on its rate coefficient for which we need extensive measurements in natural seawater.

3. Law, R M., W Peters, C Aulagnier, D J Bergmann, Song-Miao Fan, and Shian-Jiann Lin, et al., 2008: TransCom model simulations of hourly atmospheric CO₂: Experimental overview and diurnal cycle results for 2002. Global Biogeochemical Cycles, 22, GB3009, doi:10.1029/2007GB003050.
   [ Abstract ]

   A forward atmospheric transport modeling experiment has been coordinated by the TransCom group to investigate synoptic and diurnal variations in CO₂ . Model simulations were run for biospheric, fossil, and air-sea exchange of CO₂ and for SF₆ and radon for 2000–2003. Twenty-five models or model variants participated in the comparison. Hourly concentration time series were submitted for 280 sites along with vertical profiles, fluxes, and meteorological variables at 100 sites. The submitted results have been analyzed for diurnal variations and are compared with observed CO₂ in 2002. Mean summer diurnal cycles vary widely in amplitude across models. The choice of sampling location and model level account for part of the spread suggesting that representation errors in these types of models are potentially large. Despite the model spread, most models simulate the relative variation in diurnal amplitude between sites reasonably well. The modeled diurnal amplitude only shows a weak relationship with vertical resolution across models; differences in near-surface transport simulation appear to play a major role. Examples are also presented where there is evidence that the models show useful skill in simulating seasonal and synoptic changes in diurnal amplitude.

4. Patra, P K., Song-Miao Fan, and Shian-Jiann Lin, et al., December 2008: TransCom model simulations of hourly atmospheric CO₂ : Analysis of synoptic-scale variations for the period 2002-2003. Global Biogeochemical Cycles, 22, GB4013, doi:10.1029/2007GB003081.
   [ Abstract ]

   The ability to reliably estimate CO₂ fluxes from current in situ atmospheric CO₂ measurements and future satellite CO₂ measurements is dependent on transport model performance at synoptic and shorter timescales. The TransCom continuous experiment was designed to evaluate the performance of forward transport model simulations at hourly, daily, and synoptic timescales, and we focus on the latter two in this paper. Twenty-five transport models or model variants submitted hourly time series of nine predetermined tracers (seven for CO₂ ) at 280 locations. We extracted synoptic-scale variability from daily averaged CO₂ time series using a digital filter and analyzed the results by comparing them to atmospheric measurements at 35 locations. The correlations between modeled and observed synoptic CO₂ variabilities were almost always largest with zero time lag and statistically significant for most models and most locations. Generally, the model results using diurnally varying land fluxes were closer to the observations compared to those obtained using monthly mean or daily average fluxes, and winter was often better simulated than summer. Model results at higher spatial resolution compared better with observations, mostly because these models were able to sample closer to the measurement site location. The amplitude and correlation of model-data variability is strongly model and season dependent. Overall similarity in modeled synoptic CO₂ variability suggests that the first-order transport mechanisms are fairly well parameterized in the models, and no clear distinction was found between the meteorological analyses in capturing the synoptic-scale dynamics.

5. Cassar, N, M Bender, B A Barnett, Song-Miao Fan, Walter Moxim, Hiram Levy II, and B Tilbrook, 2007: The Southern Ocean biological response to aeolian iron deposition. Science, 317(5841), doi:10.1126/science.1144602.
   [ Abstract ]

   Biogeochemical rate processes in the Southern Ocean have an important impact on the global environment. Here, we summarize an extensive set of published and new data that establishes the pattern of gross primary production and net community production over large areas of the Southern Ocean. We compare these rates with model estimates of dissolved iron that is added to surface waters by aerosols. This comparison shows that net community production, which is comparable to export production, is proportional to modeled input of soluble iron in aerosols. Our results strengthen the evidence that the addition of aerosol iron fertilizes export production in the Southern Ocean. The data also show that aerosol iron input particularly enhances gross primary production over the large area of the Southern Ocean downwind of dry continental areas.

6. Fan, Song-Miao, Walter Moxim, and Hiram Levy II, 2006: Aeolian input of bioavailable iron to the ocean. Geophysical Research Letters, 33, L07602, doi:10.1029/2005GL024852.
   [ Abstract ]

   Atmospheric deposition of mineral dust supplies much of the essential nutrient iron to the ocean. Presumably only the readily soluble fraction is available for biological uptake. Previous ocean models assumed this fraction was constant. Here the variable solubility of Fe in aerosols and precipitation is parameterized with a two-step mechanism, the development of a sulfate coating followed by the dissolution of iron (hydr)oxide on the dust aerosols. The predicted soluble Fe fraction increases with transport time from the source region and with the corresponding decrease in dust concentration. The soluble fraction is ~1 percent near sources, but often 10–40 percent farther away producing a significant increase in soluble Fe deposition in remote ocean regions. Our results may require more rapid biological and physicochemical scavenging of Fe than used in current ocean models. We further suggest that increasing SO2 emission alone could have caused significant Fe fertilization in the modern northern hemisphere oceans.

7. Patra, P K., K R Gurney, Jorge L Sarmiento, and Song-Miao Fan, et al., 2006: Sensitivity of inverse estimation of annual mean CO2 sources and sinks to ocean-only sites versus all-sites observational networks. Geophysical Research Letters, 33(5), doi:10.1029/2005GL025403.
   [ Abstract ]

   Inverse estimation of carbon dioxide (CO2) sources and sinks uses atmospheric CO2 observations, mostly made near the Earth's surface. However, transport models used in such studies lack perfect representation of atmospheric dynamics and thus often fail to produce unbiased forward simulations. The error is generally larger for observations over the land than those over the remote/marine locations. The range of this error is estimated by using multiple transport models (16 are used here). We have estimated the remaining differences in CO2 fluxes due to the use of ocean-only versus all-sites (i.e., over ocean and land) observations of CO2 in a time-independent inverse modeling framework. The fluxes estimated using the ocean-only networks are more robust compared to those obtained using all-sites networks. This makes the global, hemispheric, and regional flux determination less dependent on the selection of transport model and observation network.

8. Fan, Song-Miao, Walter Moxim, and Hiram Levy II, 2005: Implications of droplet nucleation to mineral dust aerosol deposition and transport. Geophysical Research Letters, 32, L10805, doi:10.1029/2005GL022833.
   [ Abstract ]

   Calculations from a microphysics model are shown which indicate the factors that control droplet nucleation scavenging of hydrophilic mineral dust particles over a large range of conditions including the size, chemical composition, and number density of particles in both cumulus and stratus clouds. We focus specifically on the activation threshold radius (ATR) for droplet nucleation which determines the particles that are activated and those available for further transport and subsequent iron deposition to the remote ocean. Results suggest: the ATR is typically found in the range of clay-sized particles (radius = .1 to 1. µm), a spectrum over which the amount of dust removed declines ~60% both in surface area and particle number; nucleation of silt-sized particles (1.–10. µm) occurs under most conditions; larger fractions of mineral aerosols are removed in cumulus clouds than in stratus; and while acid coating of dust particles in polluted environments acts to decrease the ATR, the effect is reduced by competition with soluble aerosols. Regional mineral dust environments exhibit potentially diverse aerosol wet removal impacts. The ATR representative of the tropical Atlantic ocean basin (<.2 µm) indicates ~80% removal of the total dust surface area, while in the pristine southern hemisphere mid latitudes an ATR ~.5 µm implies ~60%. In contrast, varying conditions in the polluted region of East Asia suggest a large ATR spectrum (.2 to 3. µm) with dust surface area removal ranging from >80% to <10%.

9. Kaufman, Y J., I Koren, L Remer, D Tanré, Paul Ginoux, and Song-Miao Fan, 2005: Dust transport and deposition observed from the Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) spacecraft over the Atlantic Ocean. Journal of Geophysical Research, 110, D10S12, doi:10.1029/2003JD004436.
   [ Abstract ]

   Meteorological observations, in situ data, and satellite images of dust episodes were used already in the 1970s to estimate that 100 Tg of dust are transported from Africa over the Atlantic Ocean every year between June and August and are deposited in the Atlantic Ocean and the Americas. Desert dust is a main source of nutrients to oceanic biota and the Amazon forest, but it deteriorates air quality, as shown for Florida. Dust affects the Earth radiation budget, thus participating in climate change and feedback mechanisms. There is an urgent need for new tools for quantitative evaluation of the dust distribution, transport, and deposition. The Terra spacecraft, launched at the dawn of the last millennium, provides the first systematic well-calibrated multispectral measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument for daily global analysis of aerosol. MODIS data are used here to distinguish dust from smoke and maritime aerosols and to evaluate the African dust column concentration, transport, and deposition. We found that 240 ± 80 Tg of dust are transported annually from Africa to the Atlantic Ocean, 140 ± 40 Tg are deposited in the Atlantic Ocean, 50 Tg fertilize the Amazon Basin (four times as previous estimates, thus explaining a paradox regarding the source of nutrition to the Amazon forest), 50 Tg reach the Caribbean, and 20 Tg return to Africa and Europe. The results are compared favorably with dust transport models for maximum particle diameter between 6 and 12 ìm. This study is a first example of quantitative use of MODIS aerosol for a geophysical research.

10. Fan, Song-Miao, Larry Horowitz, Hiram Levy II, and Walter Moxim, 2004: Impact of air pollution on wet deposition of mineral dust aerosols. Geophysical Research Letters, 31, L02104, doi:10.1029/2003GL018501.
    [ Abstract PDF ]

    Mineral dust aerosols originating from arid regions are simulated in an atmospheric global chemical transport model. Based on model results and observations of dust concentration, we hypothesize that air pollution increases the scavenging of dust by producing high levels of readily soluble materials on the dust surface, which makes dust aerosols effective cloud condensation nuclei (CCN). This implies that air pollution could have caused an increase of dust deposition to the coastal oceans of East Asia and a decrease by as much as 50% in the eastern North Pacific.

11. Battle, M, M Bender, M B Hendricks, D T Ho, R Mika, Galen McKinley, Song-Miao Fan, T Blaine, and R F Keeling, 2003: Measurements and models of the atmospheric Ar/N₂ ratio. Geophysical Research Letters, 30(15), 1786, doi:10.1029/2003GL017411.
    [ Abstract ]

    The Ar/N₂ ratio of air measured at 6 globally distributed sites shows annual cycles with amplitudes of 12 to 37 parts in 106. Summertime maxima reflect the atmospheric Ar enrichment driven by seasonal warming and degassing of the oceans. Paired models of air-sea heat fluxes and atmospheric tracer transport predict seasonal cycles in the Ar/N₂ratio that agree with observations, within uncertainties.

12. Gao, Y, Song-Miao Fan, and Jorge L Sarmiento, 2003: Aeolian iron input to the ocean through precipitation scavenging: A modeling perspective and its implication for natural iron fertilization in the ocean. Journal of Geophysical Research, 108(D7), 4221, doi:10.1029/2002JD002420.
    [ Abstract ]

    Aeolian dust input may be a critical source of dissolved iron for phytoplankton growth in some oceanic regions. We used an atmospheric general circulation model (GCM) to simulate dust transport and removal by dry and wet deposition. Model results show extremely low dust concentrations over the equatorial Pacific and Southern Ocean. We find that wet deposition through precipitation scavenging accounts for ~40% of the total deposition over the coastal oceans and ~60% over the open ocean. Our estimates suggest that the annual input of dissolved Fe by precipitation scavenging ranges from 0.5 to 4 × 10¹² g yr^-1, which is 4-30% of the total aeolian Fe fluxes. Dissolved Fe input through dry deposition is significantly lower than that by wet deposition, accounting for only 0.6-2.4 % of the total Fe deposition. Our upper limit estimate on the fraction of dissolved Fe in the total atmospheric deposition is thus more than three times higher than the value of 10% currently considered as an upper limit for dissolved Fe in Aeolian fluxes. As iron input through precipitation may promote episodic phytoplankton growth in the ocean, measurements of dissolved iron in rainwater over the oceans are needed for the study of oceanic biogeochemical cycles.

13. Gurney, K R., A Lauer, A S Denning, P Rayner, D F Baker, P Bousquet, L Bruhwiler, Y-H Chen, P Ciais, Song-Miao Fan, I Y Fung, M Gloor, M Heimann, K Higuchi, Jasmin John, E Kowalczyk, T Maki, S Maksyutov, P Peylin, M J Prather, B Pak, Jorge L Sarmiento, S Taguchi, T Takahashi, and C-W Yuen, 2003: TransCom 3 CO2 inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information. Tellus B, 55B(2), 555-579.
    [ Abstract PDF ]

    Spatial and temporal variations of atmospheric CO₂ concentration contain information about surface sources and sinks, which can be quantitatively interpreted through tracer transport inversion. Previous CO₂ inversion calculations obtained differing results due to different data, methods and transport models used. To isolate the sources of uncertainty, we have conducted a set of annual mean inversion experiments in which 17 different transport models or model variants were used to calculate regional carbon sources and sinks from the same data with a standardized method. Simulated transport is a significant source of uncertainty in these calculations, particularly in the response to prescribed "background" fluxes due to fossil fuel combustion, a balanced terrestrial biosphere, and air-sea gas exchange. Individual model-estimated fluxes are often a direct reflection of their response to these background fluxes. Models that generate strong surface maxima near background exchange locations tend to require larger uptake near those locations. Models with weak surface maxima tend to have less uptake in those same regions but may infer small sources downwind. In some cases, individual model flux estimates cannot be analyzed through simple relationships to background flux responses but are likely due to local transport differences or particular responses at individual CO₂ observing locations. The response to the background biosphere exchange generates the greatest variation in the estimated fluxes, particularly over land in the Northern Hemisphere. More observational data in the tropical regions may help in both lowering the uncertain tropical land flux uncertainties and constraining the northern land estimates because of compensation between these two broad regions in the inversion. More optimistically, examination of the model-mean retrieved fluxes indicates a general insensitivity to the prior fluxes and the prior flux uncertainties. Less uptake in the Southern Ocean than implied by oceanographic observations, and an evenly distributed northern land sink, remain in spite of changes in this aspect of the inversion setup.

14. McKinley, Galen, M Follows, J Marshall, and Song-Miao Fan, 2003: Interannual variability of air-sea O₂ fluxes and the determination of CO₂sinks using atmospheric O₂/N₂. Geophysical Research Letters, 30(3), 1101, doi:10.1029/2002GL016044.
    [ Abstract ]

    Motivated by the use of atmospheric O₂/N₂ to determine CO₂ sinks under the assumption of negligible interannual variability in air-sea O₂ fluxes, we examine interannual fluctuations of the global air-sea flux of O₂ during the period of 1980-1998 using a global ocean circulation and biogeochemistry model along with an atmospheric transport model. It is found that both the El Niño/ Southern Oscillation (ENSO) cycle and wintertime convection in the North Atlantic are primary drivers of global air-sea oxygen flux interannual variability. Model estimated extremes of O₂ flux variability are -70/+100 x 10¹² mol/yr (Tmol/yr), where positive fluxes are to the atmosphere. O2/N2 variability could cause an up to ±1.0 PgC/yr error in estimates of interannual variability in land and ocean CO₂ sinks derived from atmospheric O₂/N₂ observations

15. Donner, Leo J., Charles J Seman, Richard S Hemler, and Song-Miao Fan, 2001: A cumulus parameterization including mass fluxes, convective vertical velocities, and mesoscale effects: thermodynamic and hydrological aspects in a general circulation model. Journal of Climate, 14(16), 3444-3463.
    [ Abstract PDF ]

    A cumulus parameterization based on mass fluxes, convective-scale vertical velocities, and mesoscale effects has been incorporated in an atmospheric general circulation model (GCM). Most contemporary cumulus parameterizations are based on convective mass fluxes. This parameterization augments mass fluxes with convective-scale vertical velocities as a means of providing a method for incorporating cumulus microphysics using vertical velocities at physically appropriate (subgrid) scales. Convective-scale microphysics provides a key source of material for mesoscale circulations associated with deep convection, along with mesoscale in situ microphysical processes. The latter depend on simple, parameterized mesoscale dynamics. Consistent treatment of convection, microphysics, and radiation is crucial for modeling global-scale interactions involving clouds and radiation. Thermodynamic and hydrological aspects of this parameterization in integrations of the Geophysical Fluid Dynamics Laboratory SKYHI GCM are analyzed. Mass fluxes, phase changes, and heat and moisture transport by the mesoscale components of convective systems are found to be large relative to those of convective (deep tower) components, in agreement with field studies. Partitioning between the convective and mesoscale components varies regionally with large-scale flow characteristics and agrees well with observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. The effects of the mesoscale components of convective systems include stronger Hadley and Walker circulations, warmer upper-tropospheric Tropics, and moister Tropics. The mass fluxes for convective systems including mesoscale components differ appreciably in both magnitude and structure from those for convective systems consisting of cells only. When mesoscale components exist, detrainment is concentrated in the midtroposphere instead of the upper troposphere, and the magnitudes of mass fluxes are smaller. The parameterization including mesoscale components is consistent with satellite observations of the size distribution of convective systems, while the parameterization with convective cells only is not. The parameterization of convective vertical velocities is an important control on the intensity of the mesoscale stratiform circulations associated with deep convection. The mesoscale components are less intense than in TRMM observations if spatially and temporally invariant convective vertical velocities are used instead of parameterized, variable velocities.

16. Gruber, N, M Gloor, Song-Miao Fan, and Jorge L Sarmiento, 2001: Air-sea flux of oxygen estimated from bulk data: Implications for the marine and atmospheric oxygen cycles. Global Biogeochemical Cycles, 15(4), 783-803.
    [ Abstract PDF ]

    We estimate the annual net air-sea fluxes of oxygen for 13 regions on the basis of a steady state inverse modeling technique that is independent of air-sea gas exchange parameterizations. The inverted data consist of the observed oceanic oxygen concentration after a correction has been applied to account for biological cycling. We find that the tropical oceans (13°S-13°N) emit ~212 Tmol O₂ yr ^-1 , which is compensated by uptake of 148 Tmol yr^-1 in the Northern Hemisphere (>13°N) and by uptake of 65 Tmol yr^-1 in the Southern Hemisphere (<13°S). These results imply that the dominant feature of oxygen transport in the combined ocean-atmosphere system is the existence of a closed circulation cell in each hemisphere. These two cells consist of O₂ uptake by the ocean in the middle and high latitudes of both hemispheres and transport in the ocean toward the tropics, where O₂ is lost to the atmosphere and transported in the atmosphere back toward the poles. We find an asymmetry in the two cells involving O₂ uptake in the temperate regions of the Northern Hemisphere versus loss of O₂ in the temperate regions of the Southern Hemisphere. There is an additional asymmetry between the Atlantic basin, which has a net southward transport at all latitudes north of 36°S, in agreement with independent transport estimates, versus the Indian and Pacific Oceans, which have a strong equatorward transport everywhere. We find that these inverse estimates are relatively insensitive to details in the inversion scheme but are sensitive to biases in the ocean general circulation model that provides the linkage between surface fluxes and ocean interior concentrations. Forward simulations of O₂ in an atmospheric tracer transport model using our inversely estimated oxygen fluxes as a boundary condition agree reasonably well with observations of atmospheric potential oxygen (APO O₂ + CO₂ ). Our results indicate that the north-south asymmetry in the strength of the two hemispheric cells coupled with a strong asymmetry in fossil fuel emissions can explain much of the observed interhemispheric gradient in APO. Therefore it might not be necessary to invoke the existence of a large southward interhemispheric transport of O₂ in the ocean, such as proposed by Stephens et al. [1998]. However, we find that uncertainties in the modeled APO distribution stemming from seasonal atmospheric rectification effects and the limited APO data coverage prevent the currently available APO data from providing strong constraints on the magnitude of interhemispheric transport.

17. Gloor, M, Song-Miao Fan, S W Pacala, and Jorge L Sarmiento, 2000: Optimal sampling of the atmosphere for purpose of inverse modeling: A model study. Global Biogeochemical Cycles, 14(1), 407-428.
    [ Abstract PDF ]

    The 66 stations of the GLOBALVIEW-CO2 sampling network (GLOBALVIEW-CO2: Cooperative Atmospheric Data Integration Project - Carbon Dioxide, (1997)) are located primarily remotely from continents where signals of fossil fuel consumption and biospheric exchange are diluted. It is thus not surprising that inversion studies are able to estimate terrestrial sources and sinks only to a very limited extent. The poor constraint on terrestrial fluxes propagates to the oceans and strongly limits estimates of oceanic fluxes as well, at least if no use is made of other information such as isotopic ratios. We analyze here the resolving power of the GLOBALVIEW-CO2 network, compare the efficiency of different measurement strategies, and determine optimal extensions to the present network. We find the following: (1) GLOBALVIEW-CO2 is well suited to characterize the meridional distribution of sources and sinks but is poorly suited to separate terrestrial from oceanic sinks at the same latitude. The most poorly constrained regions are South America, Africa, and southern hemispheric oceans. (2) To improve the network, observing stations need to be positioned on the continents near to the largest biospheric signals despite the large diurnal and seasonal fluctuations associated with biological activity and the dynamics of the PBL. The mixing in the atmosphere is too strong to allow positioning of stations remote from large fluxes. Our optimization results prove to be fairly insensitive to the details of model transport and the inversion model with the addition of ~ 10 optimally positioned stations. (3) The best measurement strategy among surface observations, N-S airplane transects, and vertical profiles proves to be vertical profiles. (4) Approximately 12 optimally positioned vertical profiles or 30 surface stations in addition to GLOBALVIEW-CO2 would reduce estimate uncertainties caused by insufficient data coverage from ~ 1 Pg C yr -1 per region to ~ 0.2 Pg C yr -1 per region.

18. Hamilton, K P., and Song-Miao Fan, 2000: Effects of the stratospheric quasi-biennial oscillation on long-lived greenhouse gases in the troposphere. Journal of Geophysical Research, 105(D16), 20,581-20,587.
    [ Abstract PDF ]

    An analysis is presented of results of an extended integration with a global general circulation model that includes treatment of a long-lived tropospheric trace constituent as well as a momentum source that forces a realistic stratospheric quasi-biennial oscillation (QBO). It is shown that the dynamical QBO may modulate stratosphere-troposphere exchange in such a manner as to produce a QBO in global-mean tropospheric tracer mixing ratio. For the growth rate of tropospheric methane this transport-induced QBO is expected to have a peak-to-peak amplitude of 1-2 ppbv yr-1, which, while modest compared with the full range of observed variability in growth rate, is still significant. The observed methane growth rate time series during 1983-1999 is shown to be consistent with the predicted QBO effect, although the record is definitely dominated by other interannual variations.

19. Denning, A S., and Song-Miao Fan, et al., 1999: Three-dimensional transport and concentration of SF₆: A model intercomparison study (TransCom 2). Tellus B, 51B(2), 266-297.
    [ Abstract PDF ]

    Sulfur hexafluoride (SF₆) is an excellent tracer of large-scale atmospheric transport, because it has slowly increasing sources mostly confined to northern midlatitudes, and has a lifetime of thousands of years. We have simulated the emissions, transport, and concentration of SF₆ for a 5-year period, and compared the results with atmospheric observations. In addition, we have performed an intercomparison of interhemispheric transport among 11 models to investigate the reasons for the differences among the simulations. Most of the models are reasonably successful at simulating the observed meridional gradient of SF₆ in the remote marine boundary layer, though there is less agreement at continental sites. Models that compare well to observations in the remote marine boundary layer tend to systematically overestimate SF₆ at continental locations in source regions, suggesting that vertical trapping rather than meridional transport may be a dominant control on the simulated meridional gradient. The vertical structure of simulated SF₆ in the models supports this interpretation. Some of the models perform quite well in terms of the simulated seasonal cycle at remote locations, while others do not. Interhemispheric exchange time varies by a factor of 2 when estimated from 1-dimensional meridional profiles at the surface, as has been done for observations. The agreement among models is better when the global surface mean mole fraction is used, and better still when the full 3-dimensional mean mixing ratio is used. The ranking of the interhemispheric exchange time among the models is not sensitive to the change from station values to surface means, but is very sensitive to the change from surface means to the full 3-dimensional tracer fields. This strengthens the argument that vertical redistribution dominates over interhemispheric transport in determining the meridional gradient at the surface. Vertically integrated meridional transport in the models is divided roughly equally into transport by the mean motion, the standing eddies and the transient eddies. The vertically integrated mass flux is a good index of the degree to which resolved advection vs. parameterized diffusion accomplishes the meridional transport of SF₆. Observational programs could provide a much better constraint on simulated chemical tracer transport if they included regular sampling of vertical profiles in the middle to upper troposphere. Further analysis of the SF₆ simulations will focus on the subgrid-scale parameterized transports.

20. Fan, Song-Miao, T Blaine, and Jorge L Sarmiento, 1999: Terrestrial carbon sink in the Northern Hemisphere estimated from the atmospheric CO₂ difference between Mauna Loa and the South Pole since 1959. Tellus B, 51B(5), 863-870.
    [ Abstract PDF ]

    The difference between Mauna Loa and South Pole atmospheric CO₂ concentrations from 1959 to the present scales linearly with CO₂ emissions from fossil fuel burning and cement production (together called fossil CO₂). An extrapolation to zero fossil CO₂ emission has been used to suggest that the atmospheric CO₂ concentration at Mauna Loa was 0.8 ppm less than that at the South Pole before the industrial revolution, associated with a northward atmospheric transport of about 1 Gt C yr^-1 (Keeling et al., 1989a). Mass conservation requires an equal southward transport in the ocean. However, our ocean general circulation and biogeochemistry model predicts a much smaller pre-industrial carbon transport. Here, we present a new analysis of the Mauna Loa and South Pole CO₂ data, using a general circulation model and a 2-box model of the atmosphere. It is suggested that the present CO₂ difference between Mauna Loa and the South Pole is caused by, in addition to fossil CO2 sources and sinks, a pre-industrial interhemispheric flux of 0.5-0.7 Gt C yr^-1 , and a terrestrial sink of 0.8-1.2 Gt C yr^-1 in the mid-latitude Northern Hemisphere, balanced by a tropical deforestation source that has been operating continuously in the period from 1959 to the present.

21. Fan, Song-Miao, Jorge L Sarmiento, M Gloor, and S W Pacala, 1999: On the use of regularization techniques in the inverse modeling of atmospheric carbon dioxide.. Journal of Geophysical Research, 104(D17), 21,503-21,512.
    [ Abstract PDF ]

    The global distribution of carbon sources and sinks is estimated from atmospheric CO₂ measurements using an inverse method based on the Geophysical Fluid Dynamics Laboratory SKYHI atmospheric general circulation model. Applying the inverse model without any regularization yields unrealistically large CO₂ fluxes in the tropical regions. We examine the use of three regularization techniques that are commonly used to stabilize inversions: truncated singular value decomposition, imposition of a priori flux estimates, and use of a quadratic inequality constraint. The regularization techniques can all be made to minimize the unrealistic fluxes in the tropical regions. This brings inversion estimated CO₂ fluxes for oceanic regions in the tropics and in the Southern Hemisphere into better agreement with independent estimates of the air-sea exchange. However, one cannot assume that stabilized inversions give accurate estimates, as regularization merely holds the fluxes to a priori estimates or simply reduces them in magnitude in regions that are not resolvable by observations. By contrast, estimates of flux and uncertainty for the temperate North Atlantic, temperate North Pacific, and boreal and temperate North American regions are far less sensitive to the regularization parameters, consistent with the fact that these regions are better constrained by the present observations.

22. Gloor, M, Song-Miao Fan, S W Pacala, Jorge L Sarmiento, and M Ramonet, 1999: A model-based evaluation of inversions of atmospheric transport, using annual mean mixing ratios, as a tool to monitor fluxes of nonreactive trace substances like CO₂ on a continental scale. Journal of Geophysical Research, 104(D12), 14,245-14,260.
    [ Abstract PDF ]

    The inversion of atmospheric transport of CO₂ may potentially be a means for monitoring compliance with emission treaties in the future. There are two types of errors though, which may cause errors in inversions: (1) amplification of high-frequency data variability given the information loss in the atmosphere by mixing and (2) systematic errors in the CO₂flux estimates caused by various approximations used to formulate the inversions. In this study we use simulations with atmospheric transport models and a time independent inverse scheme to estimate these errors as a function of network size and the number of flux regions solved for. Our main results are as follows: (1) When solving for 10-20 source regions, the average uncertainty of flux estimates caused by amplification of high-frequency data variability alone decreases strongly with increasing number of stations for up to ~150 randomly positions stations and then levels off (for 150 stations of the order of ±0.2 Pg C yr^-1). As a rule of thumb, about 10 observing stations are needed per region to be estimated. (2) Of all the sources of systematic errors, modeling error is the largest. Our estimates of SF₆ emissions from five continental regions simulated with 12 different AGCMs differ by up to a factor of 2. The number of observations needed to overcome the information loss due to atmospheric mixing is hence small enough to permit monitoring of fluxes with inversions on a continental scale in principle. Nevertheless errors in transport modeling are still too large for inversions to be a quantitatively reliable option for flux monitoring.

23. Fan, Song-Miao, M Gloor, Jerry D Mahlman, S W Pacala, Jorge L Sarmiento, T Takahashi, and P P Tans, 1998: A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science, 282(5388), 442-446.
    [ Abstract PDF ]

    Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 1015 grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2.2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly incresed atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 ± 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 ± 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 ± 0.9 Pg C year-1.

24. Munger, J W., Song-Miao Fan, P Bakwin, M L Goulden, A H Goldstein, A S Colman, and S C Wofsy, 1998: Regional budgets for nitrogen oxides from continental sources:Variations of rates for oxidation and deposition with season and distance from source regions. Journal of Geophysical Research, 103(D7), 8355-8368.
    [ Abstract PDF ]

    Measurements of nitrogen deposition and concentrations of NO, NO2, NOy (total oxidized N), and O3 have been made at Harvard Forest in central Massachusetts since 1990 to define the atmospheric budget for reactive N near a major source region. Total (wet plus dry) reactive N deposition for the period 1990-1996 averaged 47 mmol m-2 yr-1 (126 umol m-2 d-1, 6.4 kg N ha-1 yr-1), with 34% contributed by dry deposition. Atmospheric input adds about 12% to the N made available annually by mineralization in the forest soil. The corrresponding deposition rate at a distant site, Schefferville, Quebec, was 20 mmol m-2 d-1 during summer 1990. Both heterogeneous and homogeneous reactions efficiently convert NOx to HNO3 in the boundary layer. HNO3 is subsequently removed rapidly by either dry deposition or precipitation. The characteristic (e-folding) time for NOx oxidation ranges from 0.30 days in summer, when OH radical is abundant, to ~1.5 days in the winter, when heterogeneous reactions are dominant and O3 concentrations are lowest. The characteristic time for removal of NOx oxidation products (defined as NOy minus NOx) from the boundary layer by wet and dry deposition is ~1 day, except in winter when it decreases to 0.6 day. Biogenic hydrocarbons contribute to N deposition through formation of organic nitrates but are also precursors of reservoir species, such as peroxyacetylnitrate, that may be exported from the region. A simple model assuming pseudo first-order rates for oxidation of NOx, followed by deposition, predicts that 45% of NOx in the northeastern U.S. boundary layer is removed in 1 day during summer and 27% is removed in winter. It takes 3.5 and 5 days for 95% removal in summer and winter, respectively.

Direct link to page: http://www.gfdl.noaa.gov/bibliography/resultstest.php?author=1038