Dependence of Rain Drop Size Distribution Parameters on Atmospheric Instability Over a Tropical Location Near the Land‐Sea Boundary

Abstract

The role of atmospheric instability, expressed by Convective Available Potential Energy (CAPE), in determining raindrop size distribution (DSD) parameters have been investigated over an urban tropical location, Kolkata (22.57°N and 88.37°E), India, near the land‐sea boundary. DSD measurements obtained from a ground‐based disdrometer during both pre‐monsoon (March‐May) and monsoon periods (June‐September) have been used in conjunction with CAPE from ERA‐5 data from 2014 to 2018. Based on collocated observations from a K‐band Doppler micro rain radar, rain events are classified as convective or stratiform. The study has shown that enhanced CAPE values significantly influence DSD parameters by increasing mass‐weighted mean diameter (Dm) during convective rain, but it does not impact directly during stratiform rain. For stratiform rain events, the melting layer becomes a significant factor in determining Dm, which decreases with increasing melting layer height. Convective rain exhibits a bimodal DSD pattern for higher CAPE values, while stratiform rain shows a unimodal DSD feature. The present study location provides a unique opportunity to study the combined influences of air mass flows from the hot land region in Chotanagpur plateau and from the sea region of the Bay of Bengal on precipitation features. The investigation reveals the dominance of continental activities during convective precipitation and of maritime airflows on stratiform rain events, which is more visible during the pre‐monsoon season compared to the monsoon period. For the first time, the dual control of CAPE and melting layer on drop size distributions has been demonstrated for convective and stratiform rain events.

Effective Path Length for Estimating Rain Attenuation Over an Earth‐Space Path Using Features of Stratiform and Convective Precipitation at a Tropical Location

“…The distinguishing nature of path length variations depending on the rain rate urged us to derive different effective path length models for two rain types namely, stratiform and convective. Since we have an MRR for rain measurements which can detect the bright band signature, we have considered the presence or absence of bright bands for classification of rain types (Gatlin et al., 2018; Saha et al., 2022). Rain events during 2009–2010 are classified on this basis of collocated MRR measurements (Maitra et al., 2019).…”

“…One major issue in predicting rain attenuation over satellite signal paths from rain rate measurements is to determine the effective path length ( L E ) which may have significant variability with the type of rain, seasons, and locations (Kang et al., 2018). The situation is more critical in tropical regions where a highly variable raining environment prevails in the pre‐monsoon and monsoon months with distinguishable features (Halder & Maitra, 2020; Rakshit & Maitra, 2016; Rakshit et al., 2017; Saha et al., 2022). Hence the ITU‐R model which provides a global scenario on average is seen to have significantly deviated from the actual rain attenuation measurements limiting its applicability for varied climatic locations, particularly in the tropical regions (Chakravarty & Maitra, 2010; Ramachandran & Kumar, 2007; Yeo et al., 2014).…”

“…In this context, previous investigations identified propagation modeling issues that originate due to the dissimilar impacts of light rain with comparatively larger horizontal coverage and intense rain events with relatively lesser horizontal extent, defined respectively as stratiform and convective rain (Capsoni et al, 2006(Capsoni et al, , 2009Leitao & Watson, 1986). This concern is more significant in the tropical region, where convective and stratiform rain prevails with strong distinguishing features in the form of rain height, cell size, specific attenuation depending on rain drop size distribution (DSD), vertical downdraft, and the presence of a melting layer (Jana et al, 2018;Maitra et al, 2019;Rakshit et al, 2021;Saha et al, 2022). Hence, a single model formulation may not be adequate to specify the path reduction factors for different types of rains such as stratiform and convective rains over the tropics.…”

Characterization of rain microphysics on the leeside of the Western Ghats

“…Saha et al . (2022) examined the DSD difference between premonsoon and monsoon rainfall observed over Kolkata and their dependency on convective available potential energy. Recently, Konwar et al .…”

“…They showed that the underlying dynamical mechanisms can modify the DSD variability over WG. Saha et al (2022) examined the DSD difference between premonsoon and monsoon rainfall observed over Kolkata and their dependency on convective available potential energy. Recently, Konwar et al (2022) and Raut et al (2021) discussed the DSD variability and the possible microphysical mechanisms in the rain shadow region by segregating it into different categories like convective, transition and stratiform types of rain.…”