The role which tropical-extratropical interaction plays in the irregular oscillations of the large scale circulation remains controversial. There is synoptic evidence that a characteristic sequence of tropical and extratropical events accompanies both quasi-regular intraseasonal oscillations of the circulation and the development of persistent circulation regimes. This research will investigate the nature of some known composite relationships between tropical convection and the mid- latitude jets through 1) analyzing the annual cycle of these features in detail with high temporal resolution and 2) using a case study approach to the intraseasonal and interannual variability of these connections. Multi-level, twice daily National Meteorological Center (NMC) data from July 1976 to July 1987 will be used to define the circulation and its fluctuations. Outgoing longwave radiation data will be used to infer tropical convection fluctuations. The quality of the divergence field in the NMC data will be evaluated through correlations with the OLR data at different time and space scales. Primary emphasis will be placed on the relationship between 1) the jet stream and its associated ageostrophic flow and 2) tropical convection and its associated divergent flow. This research is important because in order to make useful predictions of weather and climate feature over the US weeks to seasons in advance the processes studied here, that is the interactions between tropical and extra-tropical circulations, must be better understood.
