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 from
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 on a month-by-month basis,
active-break periods and the diurnal cycle. We find a modal maximum in
CTH around 6–8 km for all sites. Cell-averaged 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. For south-eastern India, the phase of the diurnal cycle
depends on whether the surface is land or ocean, with the frequency of
oceanic cells typically exhibiting an earlier morning peak compared to
land, consistent with the diurnal cycle of precipitation. Our findings
confirm that Indian monsoon convective regimes are partly regulated by
the large-scale synoptic environment within which they are embedded.
This demonstrates the excellent potential for weather radars to improve
understanding of convection in tropical regions