The Tropospheric Biennial Oscillation and Indian Moonsoon Rainfall
Gerald A. Meehl and Julie M. Arblaster
National Center for Atmospheric Research
P. O. Box 3000
Boulder, CO 80307
The tropospheric biennial oscillation (TBO) can be thought of as the tendency
for a relatively strong Indian monsoon to be followed by a relatively weak one,
and vice verse. Various mechanisms associated with these transitions can act
singly, in combination, or not at all in any given year, thus confounding
previous efforts at monsoon forecasting. Here three transition mechanisms
associated with the TBO (large scale influences from tropical Pacific sea
surface temperatures, regional effects from tropical Indian Ocean SSTs, as well
as meridional temperature gradients and associated atmospheric circulation
anomalies over south Asia) are related to interannual variations of regional
patterns of Indian monsoon rainfall. Such patterns are more relevant to
understanding regional scale climate impacts than traditional large-scale
area-averaged indices of monsoon strength. Analysis of observed data from
1979-97 shows that these three mechanisms combine to account for a significant
portion of the observed monsoon rainfall patterns in a majority of years
considered. Inclusion of all three transition mechanisms provides a strong
manifestation of the TBO in reconstructed monsoon rainfall time series. The
quantification of the strength of the associations of the TBO mechanisms with
interannual Indian monsoon rainfall patterns improves the prospects for
predictability of monsoon precipitation anomalies.
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Hongjun Zhang:
zhangho@ucar.edu