Review of monsoons, interannual variability and decadal trends that underpin climate prediction

Understanding and predicting the interannual variations of the whole monsoon climate system has been, and will continue to be, one of the major reasons for studying the oceanography of the Indian Ocean; but there are other reasons. Knowledge about Indian Ocean current systems may have diverse practical applications, from fisheries through search and rescue to management of Exclusive Economic Zones. Our discussion mainly concerns the open ocean and the climate applications, but the results are important for most continental shelves of the Indian Ocean region on all but the shortest timescales. We start by discussing what we know now of the Indian Ocean’s mean annual cycle, painfully gleaned from sparse observations over the last four decades. This data base for understanding the interannual variability of the Indian Ocean climate has not been adequate until very recently; however, this data base is in the process of expanding radically, due to the availability of four new tools. These are: satellite data (altimeter, wind stress); surface flux products, from weather forecast reanalyses; output of fine-scale numerical models, driven with those fluxes; and data from profiling floats. As we will see in various talks, this is revolutionising our understanding of variability in the Indian Ocean. CLIVAR’s Asian-Australian Monsoon Panel is starting to plan a programme of further observations, to coincide with a useful conjunction of observation satellites in 2003. This will be aimed at filling the larger remaining gaps in our understanding of Indian Ocean dynamics, (with emphasis on understanding its role in the monsoon cycle).