TWP-ICE/ACTIVE MONSOON CASE STUDY

Fractional domain areas based on radar measurements (white lines) and simulations (colored lines):



Comments:

• C-Pol data at Darwin are supplied by the Australian Bureau of Meteorology. Reflectivities are instantaneous values > 0 dBZ reported at 3-km elevation at 10-min frequency and 2.5-km horizontal resolution over the TWP-ICE domain area of about 31,000 km².
• Model results are instantaneous reflectivities > 0 dBZ at 3-km elevation at 3-hr frequency and 2.5-km resolution over a square domain of about 31,000 km². Model dBZ are calculated from predicted mass concentrations and assumed size distribution parameters of rain and ice following 'A parameterization of cloud microphysics for long-term cloud-resolving modeling of tropical convection' by W. W. Grabowski, Atmospheric Research, 52, 17-41, 1999.
• Convective and stratiform areas in data and model results are defined according to the algorithm described in `Climatological characterization of three-dimensional storm structure from operational radar and rain gauge data' by M. Steiner, R. A. Houze, Jr., and S. E. Yuter, Journal of Applied Meteorology, 34, 1978-2007, 1995.
• All measurement data have been downloaded from the DOE ARM data archive (www.arm.gov) and use in publications is subject to the policies described there. Any errors in plotting or representation shown here should be blamed on Ann Fridlind.
• Identifying convective areas depends upon realistic reflectivity calculated from modeled rain fields. Using disdrometer data to represent rain properties, commonly used exponential size distributions based on rain water mass concentration assuming a fixed intercept or slope or an intercept diagnosed from rain water content tend to result in overestimates of reflectivity. If slope or intercept values are changed to bring reflectivity into line with observations, rain rate is then underestimated, which is undesirable. For the purposes of this convective area comparison with data, a Z-R relationship based on a fit to disdrometer data can be substituted to diagnose rain reflectivity from modeled rain rate: Z = 271*R^1.32, where Z is reflectivity in mm6/m3 and R is rain rate in mm/h (see details).

Preliminary summary:

• The model sensitivity test (free troposphere nudged to measurements with a 6-hour time-scale) generally reproduces stratiform area better than the baseline simulation, which tends to precipitate too widely. However, both simulations overestimate convective area according to the Steiner et al. algorithm by about a factor of three.