The Role of Radiative Processes in the Tropical Intraseasonal Oscillation

The tropical 30-60 day oscillation (intraseasonal oscillation - IO) is a topic of contemporary interest and a unified theory as to how it is created, why it behaves so erratically, and what is the mode of propagation does not exist. Theories and observational studies have emphasized the role of tropical convection in the Western Pacific Ocean with less attention paid to the role of radiative cooling in the area of the downward branch of the Walker circulation. This research focuses on that area (the tropical Eastern Pacific Ocean) where it is hypothesized that radiative cooling interacts with IO- circulations. Analysis is made in terms of calculated radiative heating fields and Kelvin winds (used as a proxy for IO-circulations). Radiative heating is calculated for seventeen pressure levels (1000-100 mb) for a 6 1/2 year period (1985 to mid-1991) at a 5-day frequency based on NCEP/NCAR gridded data and ISCCP/Cl clouds. Concurrently, normal mode projections of NCEP/NCAR gridded data are made to isolate the Kelvin mode response in the wind and height field. These calculated radiative heating and Kelvin winds are then spectrally filtered to isolate frequencies associated with the IO. Finally, a diagnostic analysis is made based on composite comparisons, lagged correlations, and a selected case study between filtered-Kelvin-winds and filtered- radiative-cooling. The analysis reveal three primary conclusions. First, there is a significant relationship between IO-circulations and IO-scale radiative heating in the Eastern Pacific Ocean. Second, this relationship exhibits both a remote scale spanning the entire Pacific and a local scale unique to the Eastern Pacific. Third, the radiative heating signal precedes the upstream response in the Kelvin wind by 5 to 10 days.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'The Role of Radiative Processes in the Tropical Intraseasonal Oscillation' with ISBN 9781423584421 and ISBN 1423584422.