Global-scale intraseasonal oscillations of outgoing longwave radiation and 250 mb zonal wind during Northern Hemisphere summer.

Abstract

Intraseasonal fluctuations of satellite-based observations are outgoing longwave radiation (OLR) and NMC analyses of 250 mb zonal wind (U250) are described based on global data from 9 Northern Hemisphere summers (May-October). Cross-spectral analysis of the 28-72 day spectral band is used to establish statistically significant relationships for the entire data period. Hovmoller diagrams are used to examine individual events and to estimate the oscillation's time scale and propagation characteristics. The phase relationships between tropical OLR and U250 anomalies seem dynamically consistent, generally showing 250 mb u-component divergence flanking regions of convection. Although the eastward propagation of OLR anomalies along 5oN-5oS is not continuous around the globe, areas of significant coherence scattered throughout the tropics exhibit a zonal wavenumber-one phase structure. In these remote regions, OLR anomalies may be dynamically linked by an eastward-propagating tropical circulation feature.-from Authors