Recorded presentation13.1
Indian Ocean capacitor effect: El Nino's long grip on the Asian-western Pacific summer monsoon
Shang-Ping Xie, Univ. of Hawaii, Honolulu, HI; and Y. Du, Y. Du, J. Hafner, J. Hafner, H. Tokinaga, K. Hu, T. Sampe, G. Huang, H. Tokinaga, and T. Sampe
Significant climate anomalies persist through the summer (June-August) after El Nino dissipates in spring over the equatorial Pacific. They include the tropical Indian Ocean (TIO) sea surface temperature (SST) warming, increased tropical tropospheric temperature, and an anomalous anticyclone over the subtropical Northwest Pacific. The cause of these lingering El Nino effects during summer is investigated using observations and an atmospheric general circulation model. Our results indicate that the TIO warming acts like a capacitor anchoring atmospheric anomalies over the Indo-western Pacific Oceans. It causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection, emanating a baroclinic Kelvin wave into the Pacific. In the Northwest Pacific, this equatorial Kelvin wave induces northeasterly surface wind anomalies, and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone. Model results support this Kelvin wave-induced Ekman divergence mechanism. In response to a prescribed SST increase over the TIO, the model simulates the Kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical Northwest Pacific. An additional experiment further indicates that the North Indian Ocean warming is most important for the Kelvin wave and Northwest Pacific anticyclone, a result corroborated by observations.
Our results have important implications for the predictability of Indo-western Pacific summer climate: the spatial distribution and magnitude of the TIO warming, rather than simply whether there is an El Nino in the preceding winter, affect summer climate anomalies over the Indo-Pacific and East Asia.
Session 13, Coupled ocean-atmosphere interactions and their contribution to climate variability on all time scales: Part 2
Thursday, 15 January 2009, 11:00 AM-12:15 PM, Room 128A
Next paper