Evaluate the Diurnal Cycle in the Multiscale Modeling Framework Using Satellite and ARM Data
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Zhang, Y., Lawrence Livermore National Laboratory
General Circulation and Single Column Models/Parameterizations
Cloud Modeling
Zhang, Y, SA Klein, C Liu, B Tian, RT Marchand, JM Haynes, RB McCoy, Y Zhang, and TP Ackerman. 2008. "On the diurnal cycle of deep convection, high-level cloud, and upper troposphere water vapor in the Multiscale Modeling Fr
Figure 1: Diurnal anomalies for tropical (left) ocean and (right) land: (top) the precipitation index (PI), high-level cloud (CLD) and upper troposphere relative humidity (UTH) based on Geostationary satellite data; (middle) PI, CLD, and UTH from the IR simulator applied to the MMF; (bottom) the MMF actual surface precipitation rate, CLD, and UTH calculated without a simulator. TRMM surface precipitation rates are also shown (blue dashed lines in bottom).
Figure 2: The occurrence fraction of precipitation radar (PR) reflectivity >= 20 dBZ in July in tropics. Blue (red) lines are for tropical ocean (land). Solid lines are from the PR simulator applied to the MMF. Dashed lines are from the TRMM PR data in July averaged over the years 1998 to 2006. The MMF 40-dBZ or greater occurrence fractions are shown in thin lines. Note that the X-axis is in logarithmic scale.
Processes of convection and clouds are usually parameterized in traditional general circulation models (GCMs), which contribute to uncertainties in predicting climate. Recently the Multiscale Modeling Fr
While the actual surface precipitation rate in the MMF has a reasonable diurnal phase and amplitude when compared with TRMM observations, the IR simulator results indicate an inconsistency in the diurnal anomalies of high-level clouds between the model and the Geostationary satellite data.
Primarily due to its excessive high-level clouds, the MMF overestimates the simulated precipitation index (PI, an indicator for deep convection) and fails to reproduce the observed diurnal cycle phase relationships among PI, high-level clouds, and upper troposphere relative humidity (Figure 1). The PR simulator results show that over the tropical oceans, the occurrence fraction of reflectivity in excess of 20 dBZ is almost one order of magnitude larger than the TRMM data at altitudes above 6 km (Figure 2). Both results suggest that the MMF oceanic convection is overactive. Furthermore, the joint distribution of simulated IR brightness temperature and PR reflectivity indicates that the most intense deep convection is found more often over tropical land than ocean, in agreement with previous observational studies.
We will further evaluate MMF using long-term observations at the ARM Climate Research Facility (ACRF) Southern Great Plains (SGP) site. Available ARM data are categorized into different cases ba