Annual and shorter-frequency variability in the equatorial Indian Ocean, and their links to the monsoon
J.S. Godfrey
CSIRO Marine Research, Hobart, Australia
and P.J. Webster
PAOS, University of Colorado, Boulder, USA
At its recent meeting, the CLIVAR Panel on the Asian-Australian Monsoon was set the task of considering how a Monsoon Observing System might be established, to enhance our ability to predict monsoon climate variations. The Panel concluded that the most appropriate way to foster the development of a MOS was to undertake a moderate level of field process studies in the monsoonal oceans (i.e. much of the tropical Indian Ocean, and the west Pacific), and to use results from this activity to slowly build a long-term observing system. The network itself should be designed to capture ocean/atmosphere activity in the known empirical modes of monsoon variability. At least one of these modes (The Indian Ocean Dipole, e.g. Saji et al., 1999; Webster et al, 1999) needs observations across the width of the equatorial Indian Ocean. More generally, the Monsoon Panel concluded that a better understanding of the Intraseasonal Oscillation - and a better ability to model it - are prime requirements for improving predictions of monsoon variability. Composites over a number of ISO events show that SST varies by nearly 2 -C in a month, in the course of a typical ISO episode; the composite pattern of SST change is broadly compats, but there are several surprises. We discuss strategies for designing the oceanographic part of an observational campaign (focussing on the Indian Ocean), aimed at improving our ability to model SST change during ISO episodes. The experiment should also be designed to improve our understanding of the mean seasonal cycle of Indian Ocean circulation, and their relations with surface heat and momentum flux, and SST.
