THE JASMINE PILOT STUDY zyxwvutsrqponmlkjihgf BY P. J. WEBSTER, E. F. BRADLEY, C . W . FAIRALL, J. S. GODFREY, P. HACKER, R. A. HOUZE JR., R. LUKAS, Y. SERRA, J. M. HUMMON, T. D. M. LAWRENCE, C . A. RUSSELL, M . N . RYAN, K. SAHAMI, AND P. ZUIDEMA 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 zyxwvutsrponmlkihgfedcbaZYXWVU A t 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 po- tential to produce monsoon variability. 1 The first mechanism, the role of external forcing (e.g., Charney 1 Proceedings of the workshop on "The Variability of the Asian- Australian Monsoon" can be viewed online at http:// paos.colorado.edu/~webster. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA A F F I L I A T I O N S : WEBSTER, LAWRENCE, SAHAMI, AND Z U I D E M A — P r o g r a m in Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado; BRADLEY—Division of Land and Water, Commonwealth Scientific and Industrial Research Organisation, Canberra, Australia; FAIRALL, RUSSELL, AND RYAN—NOAA Environ- mental Technology Laboratory, Boulder, Colorado; GODFREY— Division of Marine Science, Commonwealth Scientific and Industrial Research Organisation, Hobart, Australia; HACKER, LUKAS, AND HUMMON—School of Ocean and Earth Sciences and Technology, University of Hawaii at Manoa, Honolulu, Hawaii; HOUZE AND SERRA— Department of Atmospheric Sciences, University of Washington, Seattle, Washington. CORRESPONDING AUTHOR: P. J. Webster, School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 221 Bobby Dodd Way, Atlanta, GA 30332-0340 E-mail: pjw@eas.gatech.edu DOI: I0.II75/BAMS-83-11-1603 yxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA In final form 6 August 2002 © 2002 American Meteorological Society AMERICAN METEOROLOGICAL SOCIETY and Shukla 1980), considered the influence on the monsoon of ENSO variability, local sea surface tem- perature anomalies, and ground moisture content. The second mechanism involved the role higher- frequency (intraseasonal) hydrodynamical instabili- ties of the monsoon circulation might play in produc- ing interannual variability of the system. Figure la shows time-latitude plots of the Microwave Sound- ing Unit (MSU) satellite precipitation product along 90°E for the spring and summer of 1988. Monsoon precipitation often 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 forc- ing 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 analyses of Hendon et al. (1999) for the Australian monsoon and Lawrence and Webster (2001) for the south Asian monsoon. These questions largely define the limiting factor for predicting monsoon variability. The monsoon may be a slave to other climate components, like ENSO, or may have its own modes of variability re- sulting, perhaps, from the coupling of land, atmo- spheric, and oceanic variability. It may be a hybrid that is forced remotely to some extent yet contains its own local modes of variability, which may include chaotic NOVEMBER 2002 BAfft | 1603 Downloaded from http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-83-11-1603 by guest on 10 June 2020