Characteristics of the Z–R Relationships Observed Using Micro Rain Radar (MRR-2) over Darjeeling (27.05° N, 88.26° E): A Complex Terrain Region in the Eastern Himalayas

The relationship ( $$\varvec{Z} = \varvec{AR}^{\varvec{b}}$$ ) between radar reflectivity factor, $$\varvec{ Z }$$ and rainfall rate, $$\varvec{R }$$ is studied using the micro rain radar (MRR) observation located over Darjeeling (27.05° N, 88.26° E, 2194 m above the msl) in the foothills of the eastern Himalayan Mountains during Indian summer monsoon and post monsoon seasons (June–October) 2013. Observations from MRR are classified mainly into two types, stratiform and convective, based on the bright band and non-bright band signatures in the radar reflectivity, respectively. We have observed 12 and 7 cases for the stratiform convective rain events, respectively. In the present study MRR is operated mostly during low intensity rainfall rate (0.02–20 mm/h). During southwest monsoon season $$\varvec{Z} {-} \varvec{R }$$ relation for the stratiform and convective rainfall types are found to be $$\varvec{Z} = 272\varvec{R}^{1.78}$$ and $$\varvec{Z} = 192\varvec{R}^{1.54}$$ respectively. $$\varvec{Z} {-} \varvec{R }$$ relation for both stratiform and convective rain shows high temporal variation during different months of monsoon and post monsoon seasons. The coefficient $$\varvec{A}$$ varies between 225 and 289 for stratiform rain and between 153 and 235 for convective rain. The exponent $$\varvec{b}$$ varies between 1.4 and 2.1 for stratiform rain while between 1.2 and 1.8 for convective rain. Interestingly, we observed a distinct relation with smaller values of $$\varvec{A}$$ and $$\varvec{b}$$ for convective rain than stratiform rain over Darjeeling. The height dependence of $$\varvec{A}$$ and $$\varvec{b}$$ are also studied which is found to be very small up to ~ 1.5 km above the surface for both types of the precipitating systems.