THE TROPICAL CIRCULATION IN THE AUSTRALIAN ASIAN REGION - MAY TO OCTOBER 1997/

A summary of the broadscale tropical circulation from 70 degrees E to 180 degrees, for the six months May to October 1997, is presented. Coo l-ENSO conditions prevailed during the previous southern hemisphere su mmer period. By the start of this summary period there were indicators (e.g., winds and sea-surface temperatures of the near-equatorial Paci fic and the southern oscillation index) of a dramatic swing to warm-EN SO conditions. These intensified in the first two months and persisted throughout the period. The northern hemisphere southwest monsoon syst em became established over much of Indo-China and the Bay of Bengal du ring an active phase of the 30 to 60-day intraseasonal oscillation (LS O) in May and advanced over India during June. It had retreated from m ost mainland areas early in October. Outgoing long wave radiation and low-level wind anomalies indicate a near-average monsoon season over I ndia and Indo-China, but areas around Indonesia and Papua New Guinea w ere much drier than normal, indicative of the strong warm-ENSO event. Two coherent active phases of the ISO were evident early in the period , near the middle of May and the end of June. After this time the ISO signal became difficult to interpret, possibly due to the warm-ENSO ev ent suppressing convection in the central longitudes of the region. Th ere may have been up to six cycles of the LSO during the summary perio d. A near-average number of tropical cyclones developed during the per iod. More than 65 per cent of those that affected the northwest Pacifi c formed east of 145 degrees E, with several also forming in the south west Pacific, again indicative of the warm-ENSO event.