2016 Monsoon Convection and its place in the Large-Scale Circulation
using Doppler Radars
Abstract
Convective cloud development during the Indian monsoon helps moisten the
atmospheric environment and drive the monsoon trough northwards each
year, bringing a large amount of India’s annual rainfall. Therefore, an
increased understanding of how monsoon convection develops in
observations will help inform model development. In this study, 139 days
of India Meteorological Department Doppler weather radar data is
analysed for 7 sites across India during the 2016 monsoon season.
Convective cell-top heights (CTH) are objectively identified through the
season, and compared with near-surface (at 2 km height) reflectivity.
These variables are analysed over three time scales of variability
during the monsoon: monsoon progression, active-break periods and the
diurnal cycle. We find a modal maximum in CTH around 6–8 km for all
sites. Reflectivity increases with CTH, at first sharply, then less
sharply above the freezing level. Bhopal and Mumbai exhibit lower CTH
for monsoon break periods compared to active periods. A clear diurnal
cycle in CTH is seen at all sites except Mumbai. The phase of the
diurnal cycle depends on the surface type being land or ocean for
south-eastern India, with the frequency of oceanic cells typically
exhibiting an early morning peak compared to those over land, consistent
with the observed diurnal cycle of precipitation. The cell
characteristics discovered are discussed in light of the differences in
large-scale synoptic and mesoscale mechanisms responsible for different
cell regimes. Our findings confirm that Indian monsoon convective
regimes are partly regulated by the large-scale synoptic environment
within which they are embedded.