Monday, 10 January 2005: 4:45 PM
A local perspective on climate
We analyze the climatology of a 6 kilometer resolution, eight-year simulation of the atmosphere over the southern third of California. We find that all climatologically-significant quantities exhibit large variations on spatial scales of tens of kilometers. These include the amplitudes of the diurnal and seasonal cycles as well as mean precipitation and its interannual variability. These small-scale variations are comparable in magnitude to those seen on spatial scales of thousands of kilometers in the current generation of climate models and reanalysis products. We also elucidate the local processes maintaining these small-scale variations. Finally, we identify the primary modes of circulation variability in the region. We find three distinct modes, one corresponding to intense offshore flow (so-called "Santa Ana" events), and two corresponding to vacillations of the climatological alongshore flow. Surprisingly, none of these modes exhibits any correlation with any of the well-known large-scale modes of variability thought to influence the climate of the western United States, such as the Pacific/North American teleconnection pattern. Taken together, our results indicate that local processes play at least as large a role as large-scale processes in determining the climate of the region, including its mean state and interannual variability. This, in turn, suggests local processes must be understood and taken into account in assessing not only the impacts of anthropogenic climate change, but also the signatures of climate variability seen in paleo-records.