P3.3
Establishment of the low-level wind anomalies over the western North Pacific during ENSO development
PAPER WITHDRAWN
Chia Chou, Academia Sinica, Nankang, Taipei, Taiwan
The low-level anticyclonic circulation anomaly over the western North Pacific is an essential link between the mature and decaying El Niņo and the western North Pacific-East Asian climate. During a La Niņa event, however, the low-level wind anomalies over the western North Pacific reverses the sign. The low-level wind anomalies move eastward from South Asia and are established over the western North Pacific in the fall of the El Niņo (La Niņa) developing year. The low-level anticyclonic circulation anomaly associated with El Niņo is a response to suppressed convection. This suppressed convection is induced by a cooling tendency associated with the anomalous vertical average of the horizontal transport of moist static energy that is defined as ventilation. The El Niņo SST anomalies over the eastern Pacific warm up the tropical troposphere. When the winter monsoon starts to dominate the Asian region, the southward component of the winter monsoon transports cold air that suppresses convection and induces the low-level anticyclonic circulation anomaly. Associated with the mean state of temperature and moisture, the meridional components of the low-level anticyclonic circulation anomaly transports cold and dry air to the southward branch and warm and moist air to the northward branch of the low-level anticyclonic circulation anomaly. Both the anomalous horizontal transports of the moist static energy tend to move the low-level anticyclonic circulation anomaly eastward. The ventilation mechanism implies a phase-locking behavior of the low-level anticyclonic circulation anomaly with the seasonal cycle of the mean state over the western North Pacific-East Asian region.
Poster Session 3, ENSO and Monsoons (Hall 4AB)
Thursday, 15 January 2004, 9:45 AM-11:00 AM, Hall 4AB
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