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1 MAY 2002 923M E E H L A N D A R B L A S T E R 2002 American Meteorological Society

Summary: 1 MAY 2002 923M E E H L A N D A R B L A S T E R
2002 American Meteorological Society
Indian Monsoon GCM Sensitivity Experiments Testing Tropospheric Biennial
Oscillation Transition Conditions
National Center for Atmospheric Research,* Boulder, Colorado
(Manuscript received 15 March 2001, in final form 31 October 2001)
Observational studies have shown that the tropospheric biennial oscillation (TBO) involves transitions that
occur from northern spring [March­April­May (MAM)] to the Indian monsoon season [June­July­August­
September (JJAS)] such that a relatively strong monsoon the previous year is often followed by a relatively
weak one, and vice versa. Several conditions involving anomalous land and ocean surface temperature anomalies
in the Indo-Pacific region in MAM have been identified to be associated with TBO monsoon transitions. Though
it is possible to quantify the relative contribution of each transition condition year by year in observations, they
are interrelated and the question remains whether each condition by itself could cause a monsoon transition.
Here, a series of GCM sensitivity experiments is performed to isolate the effects of each of the transition
conditions to document their respective influences on the anomalous patterns of monsoon rainfall associated
with TBO transitions. Three conditions postulated to contribute to these TBO transitions associated with Indian
monsoon rainfall are 1) atmospheric circulation­related anomalous south Asian land temperatures and resulting
meridional temperature gradients, 2) anomalous SSTs in the Indian Ocean, and 3) anomalous tropical Pacific


Source: Arblaster, Julie - Bureau of Meteorology, Australia
Meehl, Gerald A. - Climate and Global Dynamics Division, National Center for Atmospheric Research


Collections: Geosciences