The tropospheric biennial oscillation and Indian monsoon rainfall

An analysis of observed data shows that the tropospheric biennial oscillati on (TBO, with roughly a 2-3 year period encompasses most ENSO years (with t heir well-known biennial tendency) as well as additional years that contrib ute to biennial transitions in the Indian monsoon. Three conditions (relate d to anomalous surface temperatures) postulated to contribute to TBO transi tions are examined for the northern spring season before the Indian monsoon : 1) anomalous tropical Pacific SSTs, 2) atmospheric circulation-related an omalous south Asian land temperatures and resulting meridional temperature gradients? and 3) anomalous SSTs in the Indian Ocean. We quantify these thr ee interannual transition conditions on a year by year basis, thus taking i nto account intermittent influences and secular variations in the strength of any particular linkage in any given year. The more transition conditions that are included in the analysis, the greater the TBO amplitude in terms of spectral power in the TBO periods of 2-3 years.