The profiles of rain microstructures have been investigated for different types of precipitation using microrain radar observations at a tropical location Kolkata (22.57° N, 88.37° E). A prominent dip in radar reflectivity ( Z ) profile has been observed near the boundary layer at high rain rates. This phenomenon is due to the break-up of raindrops into smaller sizes at around 2 km height during intense convective events. The boundary layer dynamics decides the dominance of one of the two processes, namely, coalescence and break-up of rain drops, and determines the drop size distribution profile near the boundary layer. A sharp gradient of vertical velocity at 1-2 km heights is responsible for enhanced drop break-up resulting in an increase in the small drop number density. © 2004-2012 IEEE.

A MAITRA

G RAKSHIT

S JANA

R CHAKRABORTY

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Effect of Boundary Layer Dynamics on the Profiles of Rain Drop Size Distribution During Convective Rain

IEEE Geoscience and Remote Sensing Letters

The spectral reflectivity in terms of Doppler velocity obtained by micro rain radar (MRR) at a tropical location can reveal the splitting of Doppler spectrum of falling rain drops caused by strong downdraft. The phenomenon, known as aliasing, occurs in Doppler spectrum of MRR during intense convective events. In this case, the rain drop velocity exceeds the unambiguous Doppler velocity range that can be sensed by MRR. The downdraft affecting the raindrop velocity significantly causes an ambiguity in the Doppler spectrum of the radar signal scattered from raindrops. The aliasing effect is most prominent near the boundary layer height (0.8–2 km) for convective rain. Also at this altitude range, the resultant height gradient obtained from ECMWF vertical velocity of air mass data and drop terminal velocity, is maximum. The importance of the present study lies in the fact that the split in Doppler spectrum can be utilized to estimate downdraft velocity during rain. The de-aliasing technique has been applied to the raw Doppler spectrum of MRR to retrieve the rain drop size distribution conforming to ground based measurements. © 2018 COSPAR

Advances in Space Research

Aliasing effect due to convective rain in Doppler spectrum observed by micro rain radar at a tropical location

Owing to the wide rain variability of the tropical region, the Simple Attenuation Model (SAM) estimated rain attenuation values are often found to exhibit substantial deviation from the actual measurements over the location, Kolkata (22°34′N, 88°22′E). This is due to the variability in rain cell sizes resulting from the diverse rain characteristics of the region. Thus, an attempt has been made to model the rain decay parameter in SAM on the basis of the tropical rain characteristics. A model of rain decay parameter in terms of rain rate is proposed which accounts for different types of rain at the present location. The incorporation of the model of decay parameter provides a better estimation of rain attenuation than the existing SAM and ITU-R model. © 2017 COSPAR

Modelling of rain decay parameter for attenuation estimation at a tropical location

Radiometric observations of relative humidity profile at Kolkata show a significant fall at around 1 to 2 km height during convective rain events. An extensive investigation shows that the fall of relative humidity is not seen during calm conditions but is strongly related to the characteristics of temperature lapse rate profiles. Moreover, the phenomenon may have strong association with boundary layer structure. The reason for such anomalies in the planetary boundary layer humidity profile might be due to the release of latent heat at the mentioned altitude. The abundance of pollutant aerosols in urban regions has also been found to contribute to this relative humidity anomaly. It has also been reported that this boundary layer relative humidity is accompanied by high latent heat release and condensation of vapour to liquid which is not much prominent in other rain types as observed in stratiform rain. Hence, convective rain produces some unique boundary layer characteristics which have also been partially supported with allied satellite and multi-station observations. © 2017 Elsevier B.V.

Atmospheric Research

Anomalies in relative humidity profile in the boundary layer during convective rain

Simultaneous radar measurements of rain from the space and the ground are presented to study the vertical profile of the precipitation structure under varying propagation and raining conditions. The measurements used for this study are the Precipitation Radar (PR) aboard Tropical Rainfall Measuring Mission (TRMM) satellite and a ground based Micro Rain Radar (MRR) operating at the University of Calcutta. The dual frequency radar observations of precipitating atmosphere have been utilized to study the vertical profiles of radar reflectivity and rain rate, indicating the limitations of combining space based and ground based measurements. © 2015 IEEE.

2015 6th International Conference on Computers and Devices for Communication, CODEC 2015

Observations of vertical rain structure using space borne and ground based radars at a Tropical location

Collocated measurements of aerosol optical depth (AOD) and black carbon at different wavelengths over Kolkata, an urban region in eastern India, have been used to calculate aerosol singlescattering albedo (SSA). The wavelength dependence of SSA and AOD has been presented to discriminate the aerosol types over this highly populated metropolitan area. The spectral pattern shows that SSA decreases with wavelength for most of the time in a year and corresponding Ångström coefficient is greater than unity. These optical properties indicate the dominance of fine-mode pollutant particles over the city. The temperature lapse rate profile within the surface boundary layer has been found to be significantly influenced by the heating effect of fine-mode pollutants, and consequently, the growth of the convective processes in the lower troposphere is notably affected. In addition, a back trajectory analysis has also been presented to indicate that transported air masses can have significant impact on spectral pattern of SSA. © 2016 American Geophysical Union. All Rights Reserved.

Journal	Data powered by TypesetIEEE Geoscience and Remote Sensing Letters
Publisher	Data powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
ISSN	1545-598X