The tropical circulation in the Australian and Asian region - May to October 2010

Abstract

A summary of the broadscale tropical circulation from 70° E to 180°, for the six months May to October 2010, is presented. During this period the EI Nin̄o/La Nin̄a-Southern Oscillation (ENSO) state shifted gradually from neutral conditions to La Niña conditions by July 2010. The Southern Oscillation Index (SOI) remained mostly above +10 during the season and reached a peak value of+25 in September. The mean SOI for the season was +15.8. Above average convection persisted throughout the season south of the equator between 90°E and 140°E and the South Pacific Convergence Zone (SPCZ). Mostly weak mean sealevel pressure (MSLP) anomalies persisted in the Darwin Regional Specialised Meteorological Centre (RSMC) analysis area except over parts of Australia, where it remained higher than normal. Easterlies in the tropical western Pacific remained stronger than normal. Sea Surface Temperatures in the tropical western Pacific gradually shifted from a warm to cooler pattern during the season and in the tropical Indian Ocean were warmer than their long-term mean. Weak active convective phases of the Madden-Julian Oscillation (MJO) were observed in the the beginning of each month during the season with a periodicity of 30 to 35 days. However, it was difficult to analyse the eastward propagation of the MJO signal mainly due to the developing La Nin̄a conditions. A total of sixteen tropical cyclones (including eight typhoons/severe cyclones) were analysed during the period, less than the mean of 30 for the Darwin RSMC analysis area.