Short-Term Climate Variability and Atmospheric Teleconnections from Satellite-Observed Outgoing Longwave Radiation. Part I: Simultaneous Relationships

Abstract

Satellite-inferred short-term climate variability and atmospheric teleconnections are studied using seven years (1974–81) of Outgoing Longwave Radiation (OLR) data from NOAA polar orbiters. This study utilizes composite, partition-of-variance and multiple correlation techniques to investigate the simultaneous relationship in OLR fluctuation between remotely separated regions of the globe. Results show that two dominant modes of variation are present in the monthly anomalous OLR time series fluctuation in the tropics. They are 1) variations of 2–3 month time scale associated with quasi-stationary fluctuation in the Walker Circulation and 2) an abrupt shift in the mean level of fluctuation related to the Southern Oscillation. The distribution of diabatic heat sources and sinks appears to exhibit a dipole-like oscillation that alternates between dry and wet periods over the equatorial central Pacific region and the maritime continent of Indonesia. The wet period is characterized by strong convection over the equatorial central Pacific, an eastward migration of the South Pacific convergence zone, and an equatorial migration of the ITCZ over the central and eastern Pacific, resulting in considerable shrinkage of the eastern Pacific dry zone. The dry period corresponds to intense convection over the maritime continent and an extensive eastern Pacific dry zone. While one major transition from dry to wet conditions is believed to occur from March 1976 to December 1977 associated with the 1975–76 El Niño, minor transitions between the two periods also occur frequently in the time scale of 2–3 months. The major significant teleconnections using the equatorial central Pacific OLR fluctuation as reference are (identified by key geographical areas, with the sense of the correlation denoted by the signs in parentheses): It is suggested that the dry period over the equatorial central Pacific corresponds dynamically to stronger zonal teleconnections by equatorially trapped Kelvin and low-order Rossby-type response, and the wet periods, to stronger downstream meridional teleconnections characteristic of external higher-order Rossby-wave response to tropical diabatic forcing.