2.4. Hydrometeor identification
A hydrometeor identification (HID) algorithm by Dolan et al. (2013) is
used to identify types of hydrometeors present at different heights
within a convective system. This is a fuzzy logic-based algorithm in
which a fuzzy logic score (μ) is calculated (Equation 2) for each
hydrometeor type and the hydrometeor with the highest fuzzy logic score
is the most probable hydrometeor type at that grid point within the
radar scan volume.
\begin{equation}
\mu_{i}=\left[\frac{W_{Z_{\text{dr}}}\beta_{Z_{\text{dr}},i}+\ W_{K_{\text{dp}}}\beta_{K_{\text{dp}},i}+\ W_{\rho_{\text{hv}}}\beta_{\rho_{\text{hv}},i}}{W_{Z_{\text{dr}}}+\ W_{K_{\text{dp}}}+\text{\ W}_{\rho_{\text{hv}}}}\right]\beta_{T,i}\text{\ β}_{Z_{h},i}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (2)\nonumber \\
\end{equation}\begin{equation}
\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \beta=\ \frac{1}{1+\left[\left(\frac{x-m}{a}\right)^{2}\right]^{b}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (3)\nonumber \\
\end{equation}Where, μi is the fuzzy logic score for the
ith hydrometeor type. βj,i is the
membership function for ith hydrometeor types and
jth variable (Equation 3). Wj is the
weight factor for the jth variable. The values of
these membership function parameters and the weights are taken as in
Dolan et al. (2013), which are obtained from simulation at C-band. Five
variables viz. Zh, Zdr,
Kdp, ρhv and temperature (T) are used to
calculate the fuzzy logic score. Seven types of hydrometeors have been
considered viz. drizzle (DZ), rain (RN), ice crystals (CR), aggregates
(AG), low-density graupel (LDG), high-density graupel (HDG), and
vertically oriented ice (VI). Graupels are ice particles with diameter
of 2-5 mm, which grow mainly due to riming process i.e., collection of
supercooled water droplets onto the surface of ice crystals and
subsequent freezing. Temperature for the HID scheme has been obtained
from radiosonde measurements by IMD Thiruvananthapuram at 5:30 IST
(Indian Standard Time). Radar data interpolated on a 0.5x0.5x0.5 km grid
have been used for the HID analysis.