NCEP/Climate Prediction Center ATLAS No. 3

The Tropospheric Seasonally Varying Mean Climate over the Western Hemisphere (1979-1995)

1. Introduction

This atlas documents the mean (1979-1995) annual cycle over the Western Hemisphere for selected tropospheric variables. The atmospheric circulation data are taken from the NCEP/NCAR reanalysis archive, which provides state-of-the-art spatially and temporally consistent global analyses 4-times daily. (For more details concerning the NCEP/NCAR Reanalysis archive the reader is referred to Kalnay et al. 1996 and Higgins et al. 1996). Mean monthly and seasonal analyses for the lower and upper troposphere are presented in a series of 4-panel figures. Analyses of precipitation, derived from satellite estimates and rain gauge observations (Xie and Arkin 1996), and outgoing longwave radiation data from NOAA polar-orbiting satellites are included for comparison with circulation features and precipitation rates from the reanalysis archive.

In sections 2-4 we describe monthly and seasonal variations for selected prominent circulation features in the Western Hemisphere, such as the subtropical highs, intertropical convergence zones (ITCZs), the Aleutian and Icelandic lows, the upper-tropospheric Bolivian high, the South Atlantic convergence zone (SACZ), and the Northern and Southern Hemisphere jet streams. Whenever possible, these features are related to the annual cycle of precipitation as derived from satellite estimates and rain gauge observations or inferred from satellite observations of outgoing longwave radiation (OLR).

A brief evaluation of the Reanalysis vertical motion and precipitation rates is presented in section 5, based on comparisons with OLR and with merged satellite estimates and rain gauge observations of precipitation.

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