3.1. Reflectivity statistics over convective and stratiform
regions
An implementation of the convective-stratiform separation algorithm is
depicted in Figure 5 during the convective event on
13th May, 2018. Figure 5a shows the reflectivity field
averaged between 2.5 and 3.5 km height. Convective-stratiform separation
algorithm is then applied on this horizontal reflectivity field and the
results are shown in Figure 5b. The red and blue pixels are identified
as convective and stratiform precipitation respectively. Not only high
reflectivity regions, but also other regions with strong gradient have
been identified as convective regions. The convective-stratiform
separation has been implemented for all the volume scans available for
all the eleven convective events during Mar-May, 2018 and the
corresponding reflectivity statistics are shown in Figure 6. Figure 6(a,
b) shows the contour frequency by altitude diagram (CFAD) of the
reflectivity over the convective and stratiform regions. The convective
core is visible near 3 km height though such feature is not visible in
case of stratiform. Figure 6c shows the mean vertical profile of
reflectivity over the convective and stratiform regions. For the
convective case (red), mean reflectivity gradually increases with height
from ground level and reaches a maxima near 3 km height and then
gradually decreases with height. Similar features in the reflectivity
profile were found over the tropical region by Zipser and Lutz (1994).
The peak value of the reflectivity is about 32 dBZ. On the other hand,
in stratiform case mean reflectivity remains almost uniform up to 4 km
height and it peaks near 5 km height and then gradually decreases with
height. This peak in the reflectivity signifies the bright band (caused
by enhanced reflectivity from melting ice particles near 0 °C level)
over stratiform regions. Figure 6d shows the frequency distribution of
reflectivity at 3 km height. The peak of the distributions over the
convective (red) and stratiform (blue) regions are well separated though
there is an overlap between the two distributions. The dashed vertical
line represents the reflectivity corresponding to the rain rate of 10 mm
h-1. Here we have used Z=168R1.4relation, which was obtained from another study by Jash et al. (2019)
over this region using micro rain radar data. This result clearly shows
that use of a rain rate threshold (e.g., 10 mm h-1) to
separate convective and stratiform rain is questionable, though such
simple classification method is often useful in many studies (Testud et
al. 2001; Bringi et al. 2003; Sisodiya et al. 2020).