Structure of pre-monsoon
convective systems over a tropical coastal region in southwest India
using C-band polarimetric doppler weather radar observations
Dharmadas Jash1,2, Resmi E.A1,
Unnikrishnan C.K1, Sumesh R.K1, Nita
Sukumar1, Sumit Kumar1,2
1National Centre for Earth Science Studies (NCESS),
P.B. No. 7250 Akkulam,
Thiruvananthapuram, Kerala, India - 695011.
2Department of Atmospheric Sciences, Cochin University
of Science and Technology (CUSAT), Ernakulam, Kerala, India - 682022
Key points:
- Structure of pre-monsoon
convective systems has been revealed using polarimetric radar and
other supporting instruments.
- Reflectivity values greater than 30 dBZ reaching up to 10 km height
has been observed in the rapid development stage of thunderstorms.
- Graupels along the high reflectivity columns inside the storms suggest
presence of strong updraft.
- Existence of vertical ice particles indicate strong electric field
inside thunderstorms.
*Corresponding author address : E. A. Resmi,
National Centre for Earth Science Studies (NCESS), Thiruvananthapuram,
India; E-mail:
resmi.ea@ncess.gov.in
Abstract: The structure of pre-monsoon convective systems over
southern peninsular India using polarimetric doppler weather radar (DWR)
observations has been analyzed. Convective-stratiform separation has
been done for eleven convective events during Mar-May, 2018. The mean
vertical profile of reflectivity shows peak reflectivity of 32 dBZ near
3 km height for convective regions and the bright band signature over
stratiform regions was observed. The frequency distributions of
reflectivity at 3 km height over convective and stratiform regions are
of bell-shaped nature with peaks at 32 dBZ and 18 dBZ respectively. A
comprehensive analysis has been done on two prominent convective cases
on 13th and 25th May 2018. Strong
convective regions represented by high reflectivity (> 45
dBZ) were noticed in the PPI diagrams. Specific differential phase
(Kdp) has been calculated from the slope of the filtered
Φdp. Heavy precipitation near surface is reflected in
the high value of Kdp (> 5°
km-1). High values of
Zdr (> 3 dB) were measured at lower levels
due to the oblate bigger raindrops. A fuzzy logic-based hydrometeor
identification algorithm has been applied with five variables
(Zh, Zdr, ρhv,
Kdp, and T) to understand the bulk microphysical
processes at different heights within convective regions. The presence
of bigger graupel particles near the melting layer indicates strong
updrafts within the convective core regions. The vertical ice
hydrometeor might signify the existence of a strong electric field
causing them to align vertically and this could be linked to lightning
occurrence associated with such systems.