Structure and Evolution of Baroclinic Waves as Inferred from Regression Analysis

Abstract

The structure of transient disturbances with periods shorter than a week is documented an the basis of one-point regression maps and longitude–height sections derived from the National Meteorological Center (NMC) operational analyses for nine winter seasons. The reference time series for the regression coefficients is highpass filtered, normalized 500-mb height at a grid point in the Pacific stormtrack. The field variables that were regreesed on the reference time series were not filtered. The regression statistics yield quantitative estimates of the amplitudes of the high-frequency fluctuations in the geopotential height, temperature, wind, ageostrophic wind, vorticity, divergence, vertical velocity, and outgoing longwave radiation fields. The observed high-frequency fluctuations exhibit a vertical and meridional structure suggestive of baroclinic waves evolving through the mature phase of their life cycle. Most of the results are in qualitative agreement with previous studies, but the ageostrophic wind field in the lower troposphere exhibits systematic fluctuations in the meridional component that had not been anticipated. An analysis of the temperature and vorticity tendencies in the waves yielded dynamically plausible results, despite the deficiencies in the NMC divergence and vertical velocity fields. The vertical velocity field at the 500-mb level was found to be consistent with the forcing in the quasi-geostrophic omega equation, which exhibits a simple wavelike pattern in the Q-vector field.