HR: 1340h
AN: OS13A-1011    [Abstracts]
TI: A 10-15year Modulation Cycle of ENSO Intensity and its ENSO Asymmetry-Basic State Interaction Mechanism
AU: * Sun, F
EM: sunf@uci.edu
AF: Department of Earth System Science, University of California, Irvine, 2101 Croul Hall, ESS, UC-Irvine, Irvine, CA 92697-3100, United States
AU: Yu, J
EM: jyyu@uci.edu
AF: Department of Earth System Science, University of California, Irvine, 2101 Croul Hall, ESS, UC-Irvine, Irvine, CA 92697-3100, United States
AB: A 10-15year decadal modulation cycle of ENSO intensity is identified from historical data and paleoclimate proxy based on the "envelope function" of Nino3.4 SST anomalies. Further composite analyses reveal significant spatial asymmetries between El Nino and La Nina within this modulation cycle. During the strong-ENSO-intensity periods of the cycle, SST anomalies center in the eastern Pacific for El Nino but in the central Pacific for La Nina; while during the weak-ENSO-intensity periods, the spatial asymmetry pattern is reversed. It is demonstrated that the El Nino-La Nina asymmetries allow ENSO to interact with the Pacific basic state to give rise to the 10-15year ENSO intensity modulation cycle. The ENSO asymmetry-basic state interaction mechanism is manifested by the east-west shifting of the Pacific Walker circulation. The migration of the mean location of Walker circulation changes the mean patterns of surface wind and thermocline slopes along the equatorial Pacific, and then sets the stages for the ENSO asymmetry to switch, leading to the slow modulation cycle. This study finds that the decadal modulation of ENSO intensity is closely linked with the slowly varying basic state in the tropical Pacific through ENSO asymmetry and can be self-sustained without the need of external forcing. Model experiments performed with NCAR CCSM3 is also used to further demonstrate this decadal modulation mechanism.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1620 Climate dynamics (0429, 3309)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4513 Decadal ocean variability (1616, 1635, 3305, 4215)
DE: 4522 ENSO (4922)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting