Strong Ocean-Atmosphere Interactions during a Short-Term Hot Event over the Western Pacific Warm Pool in Response to El Nino

摘要

A short-term hot event with a very high sea surface temperature (SST >= 30 degrees C) occurred in the western Pacific warm pool during November 2006. The interactions between this ocean hot event, atmospheric convection, and large-scale dynamics are studied using satellite observations, buoy measurements, air-sea fluxes analysis, and global reanalysis. It is shown that SST variation and deep convection over the western Pacific behave like a remote response to the El Nino warm SST anomaly in the central Pacific that induces westward-moving atmospheric convection and equatorial waves. The large-scale subsidence associated with propagating convection not only promotes high SSTs in the western Pacific through establishing cloud-free conditions and increasing heat content in a thin ocean mixed layer, but also produces convective instability through capping substantial water vapor in the lower troposphere. Under the precondition of convective instability and the steering of tropical easterlies, some convective systems propagate coherently from the central to western Pacific and intensify. In particular, new cloud clusters are dynamically attracted to the warmest oceans with maximum atmospheric instability. The enhanced convective activity then transfers oceanic energy into the atmosphere, strengthens upper-ocean mixing, and returns the positive SST anomalies to more typical values. In such a coupled system, synoptic-scale convective activities at an interval of 5-8 days are selectively amplified and thus are filtered to an intraseasonal (20-30-day) oscillation, depending on the phase of the hot event over the western Pacific. The observed evidence has implications for the predictability of short-term climate, and it offers critical information for validating the coupled ocean-atmosphere dynamics in climate models.