Introducing a new observation instrument has abruptly increased our knowledge about the ocean and atmosphere. One of the examples would be Aerosonde, a new observation tool presented by Dr. Holland. It is an unmanned aircraft to measure wind, temperature, moisture and pressure as a normal sonde observes. It would be very useful observation system for the air-sea interaction study over the western Pacific.
(Prepared by T. Nakazawa)
Fourth Session: Monsoon Dynamics (Chairs: A. Navarra and H. Nakamura)
In this session, 14 talks as a whole provided an integrated view of the latest progress in the study of the variability in the Asian summer/winter monsoon systems from sub-seasonal to decadal timescales. From many of those talks, the western Pacific, including the South China Sea, Philippine Sea (PS) and the maritime continent, has emerged as the key region for the ENSO-monsoon relation. Dr. Wang emphasized the importance of the lower-tropospheric anticyclonic (cyclonic) anomalies that form over the PS in boreal winter after the maturity of an El Nino (La Nina) event and are maintained throughout the cold season probably via their coupling with the underlying ocean. Those anomalies locally force the upper-ocean thermal anomalies, part of which may propagate into the equatorial Pacific to terminate that event. Dr. Lau argued that the PS anomalies strengthen the ENSO-Monsoon relation imposing strong biennial modulation on the ENSO cycle. It is speculated that the dominant biennial rhythm in precipitation, as identified in the Tropical Oscillation by Dr. Navarra, may be related to the PS anomalies. Dr. Kimoto argued the possibility that IOD may also contribute to the maintenance of the PS anomalies during boreal summer.
In this session, the seasonally-alternating thermal contrast between the Indian Ocean and Asian Continent emerged as another important factor in the monsoon system. As pointed out by Dr. Kawamura, coupled anomalies that prevail over the tropical Indian Ocean through the WES (wind-evaporation-SST) feedback until the reversal of the thermal contrast in early summer may act as a relay mechanism in the ENSO influence on the summer monsoon. Dr. Xie argued that the dynamical instability of a tropical easterly jet that forms in association with that reversal may lead to an abrupt monsoon onset. He showed eddies thus generated may contribute to the westward spread of the monsoon activity. those eddies are also important in monsoon breaks, as shown by Dr.Krishnan.
