MULTISCALE VARIABILITY ASSOCIATED WITH THE INTRASEASONAL OSCILLATION OVER THE WESTERN PACIFIC WARM POOL (PACIFIC OCEAN, TOGA COARE, WIND BURSTS).

摘要

A 4-dimensional gridded dataset is generated based on sounding data collected during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) over the tropical western Pacific. Along with surface and satellite data, we document mean and transient behavior of the atmosphere, and investigate multiscale variability associated with the Intraseasonal Oscillation (ISO) over the Pacific warm pool. In particular, the behavior of the atmosphere and the response of the ocean surface before, during, and after the passages of westerly wind bursts are quantitatively examined.; Three prominent westerly wind bursts occurred over the Intensive Flux Array (IFA) during the four-month Intensive Observing Period in association with the ISOs. Heavy precipitation usually fell 1 to 3 weeks prior to the peak westerly wind bursts. Subsidence dominated when the westerly winds prevailed. The tropospheric vertical wind shear associated with tropical low-frequency oscillations strongly modulated convective heating and moistening. SSTs reached their maximum during the undisturbed phase of the ISOs, gradually decreased as convection intensified, and reached their minimum during the periods of peak westerly winds when deep convection was generally suppressed over the IFA. A descriptive model of the kinematic and thermodynamic characteristics of a westerly wind burst is proposed. Evidence has been found against certain popular ISO theories.; The vertical distributions of heating and moistening at different phases of the ISO are determined for different areas within the warm pool, with specific attention to the periods of westerly wind bursts. They agree very well with observations from surface, Doppler radar and satellites. Large-scale rainfall rates are calculated from the moisture budget and surface observations, and are compared with remote sensing and operational model forecasts. Some deficiencies of remote sensing and model forecasts are pointed out.; There are striking differences between long-term mean profiles along the equator and those in the ITCZ bands, suggesting great care should be exercised in generalizing divergence, vertical motion, heating, and moistening profiles from one region to another over the western Pacific warm pool.; Cloud spectral model results indicate that the western Pacific warm pool boundary layer outside the ITCZ frequently develops tradewind-like characteristics with abundant shallow cumulus during suppressed and undisturbed periods. These episodic trade-like regimes are prominent enough to impact the seasonal distributions of boundary-layer heating and moistening.