The spatial and seasonal variability of the vertical structure of precipitation has been studied using 15 years of Tropical Rainfall Measuring Mission's Precipitation Radar (TRMM PR) version 7 data over India and adjoining oceans. Special emphasis has been put on six different climatic rain regimes and on different types of precipitation including the virga rain. The distribution of reflectivity factor (Z) above the freezing level height is broader in northwest India (NWI) and narrower over the Arabian Sea and west coast of India (ASWC) than in other selected regions, due to dominance of deep and shallow convective rain, respectively, in those regions. The height variation of contours in normalized distributions for Z indicates that evaporation of raindrops (low-level hydrometeor growth) could be significant in NWI (ASWC and Bay of Bengal). All the above features show clear seasonal variation and are observed predominantly during the southwest monsoon. The occurrence of virga rain clearly shows land-ocean contrast (less over the oceans) and seasonal variation (preponderant during premonsoon). Among different rain categories, the stratiform (convective) rain had highest (lowest) fraction of virga rain of >15-30% (<10%) over land regions. 1. The storm height (SH) vertical distributions show a peak in the vicinity of bright band (BB) in all regions, except for those regions and seasons, where convective precipitation is dominant. The well-defined BB feature and SH exhibit significant seasonal and regional variations, which are linked to variations in the occurrence of stratiform rain and height of BB. The spatial and seasonal variations of mean SH and the occurrence of deep and overshooting convective rain show good correspondence with the spatial variation of convective available potential energy.

This study presents a comprehensive evaluation of five widely used multisatellite precipitation estimates (MPEs) against 1° × 1° gridded rain gauge data set as ground truth over India. One decade observations are used to assess the performance of various MPEs (Climate Prediction Center (CPC)‐South Asia data set, CPC Morphing Technique (CMORPH), Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Networks, Tropical Rainfall Measuring Mission's Multisatellite Precipitation Analysis (TMPA‐3B42), and Global Precipitation Climatology Project). All MPEs have high detection skills of rain with larger probability of detection (POD) and smaller “missing” values. However, the detection sensitivity differs from one product (and also one region) to the other. While the CMORPH has the lowest sensitivity of detecting rain, CPC shows highest sensitivity and often overdetects rain, as evidenced by large POD and false alarm ratio and small missing values. All MPEs show higher rain sensitivity over eastern India than western India. These differential sensitivities are found to alter the biases in rain amount differently. All MPEs show similar spatial patterns of seasonal rain bias and root‐mean‐square error, but their spatial variability across India is complex and pronounced. The MPEs overestimate the rainfall over the dry regions (northwest and southeast India) and severely underestimate over mountainous regions (west coast and northeast India), whereas the bias is relatively small over the core monsoon zone. Higher occurrence of virga rain due to subcloud evaporation and possible missing of small‐scale convective events by gauges over the dry regions are the main reasons for the observed overestimation of rain by MPEs. The decomposed components of total bias show that the major part of overestimation is due to false precipitation. The severe underestimation of rain along the west coast is attributed to the predominant occurrence of shallow rain and underestimation of moderate to heavy rain by MPEs. The decomposed components suggest that the missed precipitation and hit bias are the leading error sources for the total bias along the west coast. All evaluation metrics are found to be nearly equal in two contrasting monsoon seasons (southwest and northeast), indicating that the performance of MPEs does not change with the season, at least over southeast India. Among various MPEs, the performance of TMPA is found to be better than others, as it reproduced most of the spatial variability exhibited by the reference.

Climatological characteristics of precipitation during the active and break spells of the monsoon are studied using 15 years of TRMM measurements. The spatial variation of rain fraction suggests that most of the seasonal rainfall occurs in spells of active monsoon over India, except for the zones along the east coast. The broader reflectivity distribution at higher altitudes and larger average storm height during active spells indicate the high prevalence of deep systems during this spell. The spatial distribution of the occurrence and fraction of different types of rain exhibits large variability from land to ocean and between the spells. The higher occurrence and fraction of stratiform rain during the active spell, particularly over the core monsoon zone, is due to the prevalence of organized mesoscale systems with large stratiform portions. The break spells are characterized by higher occurrence of shallow rain and larger fraction of convective rain. While an evening peak is observed over land during the break spell, the phase of the diurnal cycle exhibits large spatial variability during the active spell. The rainfall peaks from late night to midnight in southeastern India and in the morning near the foothills of the Himalayas during the active spell. The diurnal and semidiurnal components together explain more than 90% of total variance over many of the zones during both spells. The observed differences in precipitation between the spells are discussed in light of the differences in synoptic- and mesoscale mechanisms responsible for the production of precipitation.

Characteristics of raindrop size distribution (DSD) obtained by Global Precipitation Measurement (GPM) mission dual‐frequency precipitation radar (DPR) are assessed over Gadanki region during southwest (SW) and northeast (NE) monsoon seasons utilizing 2 years (2014–2015) of DSD measurements by an impact‐type disdrometer. The mass weighted mean diameter (Dm in mm) and normalized DSD scaling parameter for concentration (Nw in mm−1 m−3) show pronounced seasonal differences at low to medium rain rates in the disdrometer data, in accordance with the previous studies, but not in the GPM‐DPR data. Similar features are observed every year in disdrometer measurements and over different spatial domains in GPM‐DPR measurements, indicating that sampling mismatch errors are insignificant. The reasons for the absence of seasonal differences in DSDs derived from GPM‐DPR are examined by simulating the reflectivities at Ku‐ and Ka‐bands, utilizing the disdrometer measurements and T‐matrix scattering indices. Results suggest that the Dm and Nw retrieved from single‐frequency and dual‐frequency algorithms utilizing the disdrometer data also show seasonal differences in accordance with the observations with under and overestimation of Dm and Nw, respectively. When compared with the disdrometer, the Dm values retrieved from the GPM‐DPR (official products) are severely underestimated at high rain rates (R > 8 mm h−1) during the SW monsoon season. On the other hand, during low rain rates (R < 8 mm h−1), a slight underestimation (overestimation) of Dm is seen during the SW (NE) monsoon. The mean Nw values retrieved from GPM‐DPR agree poorly with disdrometer data during both the monsoon seasons.

Daily rainfall data obtained from 1025 rain gauges spread across the country over 51 years (1951–2001) are subjected to correlation analysis to identify homogeneous rainfall zones over India. In contrast to earlier studies, which were based on seasonal/annual rainfall, the present study identifies homogeneous rainfall regions with the help of seasonal [southwest monsoon (SWM) and northeast monsoon (NEM)] and annual rainfall. India is divided into 26 (20) homogeneous rainfall zones using annual and SWM (NEM) rainfall. The delineated homogeneous regions are compared and contrasted with those defined by earlier studies, employing a variety of schemes. The interseries correlations of rainfall within each zone are found to be better when the zones are identified by the present study than by other studies. The tests that are performed to evaluate coherency of zones reveal that the zones are homogeneous not only at different temporal scales (interannual and intraseasonal) but also in terms of rain amount, rain frequency, and rain type. Although the delineation of coherent zones is done using interannual/seasonal rainfall data, these zones exhibit coherency in rainfall variations at intraseasonal scale. Nevertheless, the degree of homogeneity is different for rainfall variations occurring at different temporal scales. Further, the zones show better coherency in excess rainfall years than in deficit rainfall years. Longer-term utility of the delineated zones is studied by examining delineated zones and their coherency in the first and second half of the total data period. Although the regions remain the same in both the periods, the coherency is reduced in the second half, suggesting that the homogeneity of regions may vary in the future.