HR: 08:15h
AN: A51E-02 INVITED     [Abstracts]
TI: The role of land-atmospheric interactions in the initiation of deep convection for convection- resolving regional-scale models
AU: * Chen, F
EM: feichen@ucar.edu
AF: National Center for Atmospheric Sciences, P.O. Box 3000, Boulder, CO 80307, United States
AB: Understanding and correctly modeling the feedback between land-surface variability and precipitation is important because of its potential benefit in improving weather and climate predictability. In summer, mesoscale boundaries play a critical role in the initiation of heavy precipitation. The zones of enhanced convergence along these boundaries have been recognized as areas of deep-convection initiation. The origin of these mesoscale boundaries includes synoptic-scale fronts, outflows from previous storms, orographic features, and differential surface heating. The differential heating can be enhanced by heterogeneities in land-surface conditions. The land surface may have differing impacts, depending on atmospheric conditions. Small-scale ground features, such as vegetation, hillslopes, and urban or industrial areas can also have subtle impacts that can determine the exact boundary and intensity of storms. We will review recent studies in employing advanced land surface models and high-resolution land data- assimilation system (HRLDAS) in convection-resolving models to investigate land-atmospheric interactions and their impacts on the initiation of deep convection. These studies include a flash flood case, a dryline convection case, and an 11-day heavy-precipitation episode. We found that fine-scale (L~10 km) boundary-layer circulations that directly trigger deep convection are confined within a mesoscale region containing a deeper and more unstable PBL, and that this region is a result of a surface sensible heat-flux maximum over dry soils. Results from these and other recent research studies provide some hope that the careful treatment of land-surface physics and soil moisture in convection-resolving models can lead to increased rainfall predictability. In particular, this should be achievable by improving 1) the representation of land surface processes, 2) the initialization of soil properties, and 3) the specification of various vegetation characteristics by combining modeling, new remote sensing capabilities, and data-assimilation techniques. It is, however, a more daunting challenge to incorporate the complex mesoscale interactions among the land surface, the boundary layer, and clouds, in large-scale climate models. These interactions play a critical role in determining the timing and location of convection initiation, and the intensity of precipitation, but operate on subgrid scales.
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly