The jasmine pilot study

摘要

A recent field experiment aimed at supplying critical data from the Indian Ocean region may eventually help climate models reproduce and forecast the intraseasonal and interannual variability of the monsoon. At a workshop on the variability of the Asian-Australasian Monsoon in July 1998 in St. Michaels, Maryland, two major mechanisms were discussed at length, each thought to have the potential to produce monsoon variability. The first mechanism, the role of external forcing (e.g., Charney and Shukla 1980), considered the influence on the monsoon of ENSO variability, local sea surface temperature anomalies, and ground moisture content. The second mechanism involved the role higher-frequency (intraseasonal) hydrodynamical instabilities of the monsoon circulation might play in producing interannual variability of the system. Figure 1a shows time-latitude plots of the Microwave Sounding Unit (MSU) satellite precipitation product along 90 deg E for the spring and summer of 1988. Monsoon precipitationoften appears first at the equator before propagating northward as originally discovered by Sikka and Gadgil (1980). Within the context of the second question discussed at the workshop, it was asked whether these intraseasonal oscillations were controlled and modified by large-scale planetary forcing or were the intraseasonal instabilities themselves determining interannual monsoon variability? The latter question arises from the numerical studies of Ferranti et al. (1997) and the observational analysesof Hendon et al. (1999) for the Australian monsoon and Lawrence and Webster (2001) for the south Asian monsoon.