Casey Dale Burleyson — Pacific Northwest National Laboratory
Samson M Hagos — Pacific Northwest National Laboratory
Robert Houze — University of Washington
Angela K Rowe — University of Wisconsin
Zhe Feng — Pacific Northwest National Laboratory
Category
Convective clouds, including aerosol interactions
Description
Fig. 1. The observed (top panel) amplitude of the precipitation frequency diurnal cycle over land during March-April-May and the predicted amplitude (bottom panel) from a simple linear model that uses only the slope of the local topography and the distance to a large body of water as input variables.
Thermally driven localized circulations can trigger deep convection by creating areas of convergence associated with permanent topographic features. Potentially important thermal circulations (i.e., sea breezes, river breezes, and mountain-valley breezes) occur on spatial scales that are sub-grid in current GCMs, but may be at least partially resolved in the next generation (Δx ~10’s of km). Deep convection parameterizations often include assumptions that clouds are uniformly distributed over a grid box and lack mechanisms that trigger deep convection in response to the convergence of localized circulations. In this work, we attempt to quantify the influence of local circulations over land using TRMM 3B42 satellite precipitation data and statistical regressions. Early results show that we can statistically explain ~50% of the spatial and temporal variance in precipitation over land using a regression relationship in which the only information provided to the statistical model was the slope of the terrain (a crude proxy for the presence/absence of mountain-valley breezes) and the distance to a large body of water (a crude proxy for the presence/absence of sea and river breezes). Figure 1 shows preliminary results using this simple linear model. We explore the relative importance of localized circulations and stochasticity by season and whether robust relationships are present everywhere over land in the tropics or only in certain regions.
