Precipitation and Circulation Covariability in the Extratropics

Abstract

Extratropical precipitation is primarily produced by cold and warm fronts associated with surface cyclones and upper-level troughs. The growth of these midlatitude storms is partially controlled by the dry baroclinicity of the troposphere, which in turn can be roughly quantified by the intensity of the upper-level zonal flow. Orographic rainfall, an important component of the precipitation in several midlatitude regions, is also partially determined by the intensity of the cross-mountain midlevel winds. Thus, at monthly and longer time scales, variations of precipitation and zonal flow aloft (as well as wind shear) at a given location should exhibit some degree of coherence. In this work the local covariability of these variables is documented over intermonthly and interannual time scales, using global precipitation products and atmospheric reanalysis from 1979 to 2004. The spatial correspondence between the precipitation and two indices of synoptic activity in the extratropics is also documented... Abstract Extratropical precipitation is primarily produced by cold and warm fronts associated with surface cyclones and upper-level troughs. The growth of these midlatitude storms is partially controlled by the dry baroclinicity of the troposphere, which in turn can be roughly quantified by the intensity of the upper-level zonal flow. Orographic rainfall, an important component of the precipitation in several midlatitude regions, is also partially determined by the intensity of the cross-mountain midlevel winds. Thus, at monthly and longer time scales, variations of precipitation and zonal flow aloft (as well as wind shear) at a given location should exhibit some degree of coherence. In this work the local covariability of these variables is documented over intermonthly and interannual time scales, using global precipitation products and atmospheric reanalysis from 1979 to 2004. The spatial correspondence between the precipitation and two indices of synoptic activity in the extratropics is also documented...