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Abstract:
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The Tropospheric Biennial Oscillation (TBO), a major interannual
variation phenomenon in the Indo-Pacific region,
is the result of strong ocean-atmosphere coupling over the
Asian-Australian monsoon area. Along with other meteorological
and oceanographic parameters, the tropical circulation
also exhibits interannual oscillations. Even though the
TBO is the result of strong air–sea interaction, the circulation
cells during TBO years are, as yet, not well understood. In
the present study, an attempt has been made to understand
the interannual variability of the mean meridional circulation
and local monsoon circulation over south Asia in connection
with the TBO. The stream function computed from the zonal
mean meridional wind component of NCEP=NCAR reanalysis
data for the years 1950–2003 is used to represent the
meanmeridional circulation. Mean meridional mass transport
in the topics reverses from a weak monsoon to a strong monsoon
in the presence of ENSO, but in normal TBO yearsmean
transport remains weak across the Northern Hemisphere.
The meridional temperature gradient, which drives the mean
meridional circulation, also shows no reversal during the
normal TBO cycle. The local Hadley circulation over the
monsoon area follows the TBO cycle with anomalous ascent
(descent) in strong (weak) monsoon years. During normal
TBO years, the Equatorial region and Indian monsoon areas
exhibit opposite local Hadley circulation anomalies |