Investigating the Atlantic Warm Pool Impact on Precipitation Variability Over the Continental United States (Invited)

Downscaling global climate projections to regional scales is a complex task due to interactions between regional climate systems, partially determined by local conditions, and global teleconnections governed by large scale, low-frequency processes. These interactions are characterized by non-linear relationships and feedbacks that are not sufficiently understood. Within the North American Regional Climate Change Assessment Program (NARCCAP), the Experimental Climate Prediction Center (ECPC)-Regional Spectral Model (RSM) has downscaled the observational forcing (NCEP-DOE AMIP II Reanalysis), and the GFDL CM2.1 present and future climates. The GFDL CM2.1 21st century climate projection used in NARCCAP was forced with the SRES A2. Analysis of the boreal spring-summer extreme climate events, produced by downscaling observational forcing with ECPC-RSM, has shown linkage between upper-level westerly jet positioning and vertically integrated meridional moisture fluxes, and central US precipitation variability. These meridional moisture fluxes are in their turn associated with the moisture carried from Intra-Americas Sea (IAS) by the Great Plains low-level jet (GPLLJ), therefore the regional precipitation over the central US is influenced in part by the larger scale global low-frequency variability modes. Previous studies have discussed the Atlantic Warm Pool (AWP) association with a summertime maximum of easterly winds seen in the lower troposphere over IAS, and known as Caribbean low-level jet (CLLJ). The CLLJ splits into two branches, and one of them can be seen as the southern component of the GPLLJ. One expects that changes in AWP affect the needed moisture transport for precipitation into the continental US, and consequently set conditions for floods or persisted droughts over that region. In this work, some of the patterns and mechanisms of regional-scale climate change are discussed as influenced by global low frequency modes of variability. How the related global variability translates into the regional climate changes is investigated in terms of low-frequency variability indices, and through comparisons with present and future climates, with focus on the correlation between lower- and upper-tropospheric circulations over North America.