- Institute of Radio Physics and Electronics
University of Calcutta
92, Acahrya Prafulla Chandra Road
Kolkata 700009, India - +91-33-2350-9116 (Extn. 28)
Animesh Maitra
University of Calcutta, Institute of RadioPhysics and Electronics, Department Member
- Atmospheric Science, Physics, Earth and Space Sciences, Remote Sensing, Ionosphere and Radio Wave Propagation, Electronics and communication, Mobile Communication, and 21 moreSatellite Communications, Atmosphere, Millimeter Waves, Tropical Climate Variability, Atmospheric Water Vapor, Radiowave Propagation, Solar Eclipse, Pulse Propagation, Rain Attenuation, Signal Attenuation Due to Rainfall, Rain drop size distribution, Wideband, Multiwavelength, Minor Constituents, Ka Band Sugnal, Infrared Wavelength, Optical Wavelenghts, Millimeter Wave Propagation, Ecology, Ethics, and Environmental Sustainabilityedit
- Animesh Maitra obtained his Ph.D. Degree in Radio Physics and Electronics from University of Calcutta. He joined the... moreAnimesh Maitra obtained his Ph.D. Degree in Radio Physics and Electronics from University of Calcutta. He joined the Institute of Radio Physics and Electronics as a Lecturer in 1983. Presently, he is a Professor and a Former Head of the same institute. Prof. Maitra is the Co-ordinator of ISRO sponsored Space Science Promotion Scheme and PIedit
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The Sundarban is the world’s biggest mangrove forest, located on Bangladesh’s and India’s southern coasts. The forest protects biodiversity and the local population from various natural disasters. This paper has primarily focused on the... more
The Sundarban is the world’s biggest mangrove forest, located on Bangladesh’s and India’s southern coasts. The forest protects biodiversity and the local population from various natural disasters. This paper has primarily focused on the change in land use land cover (LULC) of a location in Sundarban delta (21°56’ N, 89°10’ E) using two LANDSAT satellite images for the year 2015 and the lockdown period of 2020, with the help of Geographical Information System (GIS) and supervised machine learning technique. With the reduction of upstream water and sediment supplies, the water body in the Bay of Bengal has increased. The extent of vegetation and agricultural land has decreased due to urbanization and erosion by the Bay of Bengal. The difference between the LULC before and after the Amphan cyclone indicates that land area has been reduced over this area.
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Measurements of rain attenuation at millimeter wavelengths are usually carried out with time constants in the range 1-10 sec. Using a spectrum analyzer at the output of a LOS link receiver, the microstructure of the time variation of rain... more
Measurements of rain attenuation at millimeter wavelengths are usually carried out with time constants in the range 1-10 sec. Using a spectrum analyzer at the output of a LOS link receiver, the microstructure of the time variation of rain attenuation at 94 GHz has been studied in Calcutta. It has been found that fine structures often exceed a few decibels and usually have a dominant time scale of a few milliseconds depending on the rain rate. Analyses of these microstructures, which may have bearings on the performance of high rate digital communications, will be presented in this paper.
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Summary Information of vertical rain structure is important for accurate quantitative precipitation estimation from weather radars and space-borne radars. In this paper, some characteristics of the vertical rain structure observed using a... more
Summary Information of vertical rain structure is important for accurate quantitative precipitation estimation from weather radars and space-borne radars. In this paper, some characteristics of the vertical rain structure observed using a Ka band Micro Rain Radar at three tropical locations in India are presented. The average vertical structure is studied in terms of drop size distribution (DSD), fall velocity, rain rate, liquid water content and radar reflectivity profile. The changes in vertical rain structure with rain rate is observed to be significant only above 20 mm/h in Ahmedabad and Trivandrum, although, in Shillong, significant variation is observed starting from 2 mm/h. Results show a significant negative slope of the fall velocity of rain drops and Ka band radar reflectivity up to melting layer height for rain rate above 20 mm/h indicating a shift in the drop size distribution (DSD) toward lower size at all sites. The near ground measurements show strong variation of rain structure for all rain rates. The mean DSD near ground (
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The effective path length (LE) for the rain attenuation estimation over the Earth‐space path depends on rain cell size, rain rate, and rain height which in turn are determined by the types of rain. The present study examines the variation... more
The effective path length (LE) for the rain attenuation estimation over the Earth‐space path depends on rain cell size, rain rate, and rain height which in turn are determined by the types of rain. The present study examines the variation of LE based on the experimental measurements of Ku‐band attenuation and rain rate at a tropical location Kolkata (22°34′N, 88°22′E) in comparison with the ITU‐R. The study also utilizes measurements from a 24‐GHz micro rain Doppler radar to differentiate the precipitation types as stratiform and convective rain on the basis of the presence and absence of a melting layer. Power‐law models of LE in terms of rain rate are proposed for convective and stratiform types of rain. The investigation reveals the physical phenomena behind the variability of LE at low and high rain rates which are associated with stratiform and convective rain respectively. The proposed models provide a significantly better agreement with the experimental data compared to the I...
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Abstract A comparative study of precipitation microphysics along with the possible causative mechanisms for the inter-seasonal variation of raindrop size distribution over Thiruvananthapuram and Kolkata – the two tropical stations of... more
Abstract A comparative study of precipitation microphysics along with the possible causative mechanisms for the inter-seasonal variation of raindrop size distribution over Thiruvananthapuram and Kolkata – the two tropical stations of Indian sub-continent has been highlighted in this paper. In addition to the contrasting geographical and climatic variations, the importance of the two locations lies in the fact that the rainfall over Thiruvananthapuram represents the Arabian Sea branch of south-west monsoon while that over Kolkata represents the Bay of Bengal branch. The study reveals a distinct domination of raindrops of diameter 2 mm and above for the pre-monsoon months (March–May) over Kolkata with respect to Thiruvananthapuram, while for the monsoon months (June–September), no such appreciable differences are noticed. Correspondingly, the continental and maritime clouds also show their contrasting impacts in the rainfall microphysics during these inter-seasonal phases for the two locations. It has been observed that rainfall evolving from the continental clouds during the pre-monsoon period over Kolkata produces distinct diurnal variation of rainfall occurrences, which are also associated with the presence of raindrop of diameter 3 mm and above. Correspondingly, such variations are absent for the maritime clouds which dominate the monsoon rainfall for both the locations. Thus it can be said that the nature of clouds along with the surface temperature plays an important role in the varying microphysics of precipitation during the inter-seasonal phases of monsoon over these two cities of India.
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Rain attenuation is an important aspect of signal propagation mainly above 10 GHz frequency. It has also been found that the rain rate and attenuation profiles along the vertical and slant propagation path, especially at a higher rain... more
Rain attenuation is an important aspect of signal propagation mainly above 10 GHz frequency. It has also been found that the rain rate and attenuation profiles along the vertical and slant propagation path, especially at a higher rain rates and at tropical location. In this study, a simple approach is taken to study rain attenuation at various frequencies from propagation data and ground based radar measurements at Kolkata, INDIA. The ITU-R Model and the SAM Model has been utilized to provide an estimate of the slant rain rate and total attenuation from the vertical rain rate profiles.
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Atmospheric gravity waves are generated by the interplay of earth's gravity and buoyancy effect on an air parcel. The zonal and meridional wind and temperature perturbations observed in the troposphere and stratosphere exhibit... more
Atmospheric gravity waves are generated by the interplay of earth's gravity and buoyancy effect on an air parcel. The zonal and meridional wind and temperature perturbations observed in the troposphere and stratosphere exhibit signature of gravity waves. These gravity waves can originate from different excitation mechanisms such as deep convection in the tropics, orographic effects and various meteorological disturbances. We have studied the gravity wave generated due to an intense tropical cyclone named, Phailin, using radio occultation data from COSMIC over the Indian region. The radio occultation data are used to obtain the vertical profiles of atmospheric refractivity that bear the manifestation of gravity waves at different heights. The dry temperature and water vapor pressure from the refractivity profile yield the potential energy and the water vapor intrusion due to gravity waves in the lower stratosphere (18–25 km) during the tropical cyclone.
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This letter reveals the prevailing scenario of raindrop size distribution (DSD) in terms of mass-weighted mean drop diameter (<inline-formula> <tex-math notation="LaTeX">$D_{m}$... more
This letter reveals the prevailing scenario of raindrop size distribution (DSD) in terms of mass-weighted mean drop diameter (<inline-formula> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula>) over a tropical metropolis, Kolkata (22.57°N, 88.37°E), India, in a contrasting aerosol environment that occurred during the COVID-19 pandemic in the absence of usual human activities. In the premonsoon months (March–May), the probability of <inline-formula> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula> values exceeding 2 mm has increased in 2020, indicating the dominance of large raindrops, compared to the years 2017–2019. Increased number densities of larger drops have influenced the drop fall velocity spectrum as measured by a laser precipitation monitor in terms of the percentage occurrence of high-velocity small drops (superterminal) and low-velocity large drops (subterminal) for both convective and stratiform precipitations. As measured from a Ka-band microrain Doppler radar, the mean melting layer altitude during stratiform rain has decreased by ~800 m during the premonsoon of 2020 compared to 2017–2019. According to the ERA-5 reanalysis data, changing rain microphysical characteristics are related to decreasing zero-degree isotherm height and reduced wind shear.
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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... more
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.
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... 9, pp 910-913, 2010. [2] Kamaljeet Singh, K. Nagachenchaiah and D.Bhatnagar “Electromagnetic Modeling of Conductor backed-CPW based RF MEMS capacitive shunt switch.” International Journal of Electronics, Vol. 96, No. 8, pp 887 – 893,... more
... 9, pp 910-913, 2010. [2] Kamaljeet Singh, K. Nagachenchaiah and D.Bhatnagar “Electromagnetic Modeling of Conductor backed-CPW based RF MEMS capacitive shunt switch.” International Journal of Electronics, Vol. 96, No. 8, pp 887 – 893, Aug. ... [7] Geetanjali, CL Dube, SC ...
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In this paper parameters of precipitation profiles obtained from precipitation radar aboard tropical rainfall measuring mission satellite and from ground based micro rain radar observations have been compared for different rain events.... more
In this paper parameters of precipitation profiles obtained from precipitation radar aboard tropical rainfall measuring mission satellite and from ground based micro rain radar observations have been compared for different rain events. The dual frequency radar observations of precipitating atmosphere have been utilized to study the vertical profiles of radar reflectivity and rain rate. It is shown that the inclination of the ray path of the satellite borne radar significantly influences the rain rate measurements. The study demonstrates the efficacy of combining space borne and ground-based measurement in obtaining a complete profile of vertical rain structure.
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Distortion of pulses with pulse widths ranging from 0.1 to 1 ns propagating with carrier frequencies in the range 10–100 GHz through rain filled medium has been estimated considering the absorptive and dispersive effects produced by rain... more
Distortion of pulses with pulse widths ranging from 0.1 to 1 ns propagating with carrier frequencies in the range 10–100 GHz through rain filled medium has been estimated considering the absorptive and dispersive effects produced by rain drops on the propagation of millimeter waves. It is found that the rain induced broadening or compression can be quite appreciable for very
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The present study deals with the interplay of multiple atmospheric processes in changing the microphysical properties of precipitation during the pre-monsoon season (March–May) using the long-term experimental data of raindrop size... more
The present study deals with the interplay of multiple atmospheric processes in changing the microphysical properties of precipitation during the pre-monsoon season (March–May) using the long-term experimental data of raindrop size distributions (DSDs) spanning over 15 years (2005–2019) obtained at an urban tropical location, Kolkata (22.57°N, 88.37°E), near the land–sea boundary. The changing pattern of air mass flows from the maritime and continental region, which contribute to the formation of precipitation processes, has been responsible for the varying characteristics of rain. Changes in raindrop sizes are related to aerosol properties, cloud features, temperature, and relative humidity that change mass-weighted mean drop diameter (<inline-formula> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula>) differently in low and high rain rate regimes. <inline-formula> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula> has shown an increasing trend over time for low rain rates (< 15 mm/h), but a decreasing trend for high rain rate regimes (≥15 mm/h). An increase (decrease) in mean temperature (relative humidity) below the atmospheric boundary layer (< 1.6 km) has enhanced the evaporation of small raindrops and altered rain microphysical features. Based on satellite observations, it has been found that the increasing aerosol optical depth (AOD) has been accompanied by an increase in cloud effective radius (CER), resulting in the anti-Twomey effect, which is due to the dominance of maritime influence over continental activities. Because of the predominant maritime activities, sea salt aerosols have a greater presence, causing an increase in CER, which consequently prevents raindrops from becoming large enough before they fall, thereby reducing <inline-formula> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula> at high rainfall rates.
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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... more
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 ...
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This paper presents some important results of propagation channel modeling at a tropical location, Kolkata. Propagation impairments, namely, rain attenuation, cloud attenuation and water vapor attenuation has been investigated using... more
This paper presents some important results of propagation channel modeling at a tropical location, Kolkata. Propagation impairments, namely, rain attenuation, cloud attenuation and water vapor attenuation has been investigated using ground based measurements. Though rain attenuation shows high values at high frequencies and low elevation angles, however the effect of cloud attenuation at earth-space path is also significant. It has been observed that rain has significant impact on bit error probability. Site diversity is a useful fade mitigation technique which is based on the concept of horizontal extent of rain cells. Performance of Different rain cell models have been compared in connection to calculate diversity gain over this location. The ITU-R model shows the best performance.
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Nowcasting of lightning occurrences is essential in tropical locations as lightening causes severe damage to life and property. This study attempts to nowcast lightning events during convective phenomena using an electric field monitor... more
Nowcasting of lightning occurrences is essential in tropical locations as lightening causes severe damage to life and property. This study attempts to nowcast lightning events during convective phenomena using an electric field monitor (EFM) at a tropical urban location, Kolkata (22.65°N, 88.45°E). Before the onset of heavy lightning occurrences, definite changes in the atmospheric electric field (EF) are observed, which in turn are associated with high cloud liquid water content (LWC) and low cloud base height (CBH). A model has been proposed to nowcast lightning strikes within about 17.5 km radius of the present location based on the EF standard deviation (EFSD) values. The proposed technique is tested with the lightning data provided by a collocated lightning detector, which yields a prediction efficiency of ~ 0.91 (~ 0.86), a false alarm rate of ~ 0.23 (~ 0.18), and a critical success index of ~ 0.71 (~ 0.72) with an optimal range of other performance parameters during the monsoon (pre-monsoon) periods, thereby generating an alarm 45 min before lightning events.
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The present investigation outlines the crucial factors that influence the black carbon (BC) concentrations over a polluted metropolis, Kolkata (22.57° N, 88.37° E), India. Located in the eastern part of the Indo Gangetic Plain (IGP)... more
The present investigation outlines the crucial factors that influence the black carbon (BC) concentrations over a polluted metropolis, Kolkata (22.57° N, 88.37° E), India. Located in the eastern part of the Indo Gangetic Plain (IGP) outflow region and close to the land-ocean boundary, Kolkata is subject to contrasting seasonal maritime airflow from the Bay of Bengal and continental air mass from the IGP and Tibetan plateau region, which modulates the local concentration of BC. The origin of aerosol transport and associated atmospheric dynamics with high and low BC activities over Kolkata are examined during 2012-2015 using data from multi-technique sources which include measurements of ground-based instruments of aethalometer and multi-frequency microwave radiometer, reanalysis data from ERA-5 and MEERA-2, and model outputs from HYPSLIT back trajectory model simulations. The study highlights the control of IGP wind inflow on the occurrence of anomalous enhancements in BC concentration during weekends and holidays when local emissions are low. High BC events are associated with enhanced atmospheric heating below the boundary layer (2000 m) and significant negative surface radiative forcing. The response of the boundary layer to high and low BC episodes , shown in the diurnal variation in comparison with the seasonal mean, is investigated. Dominant suppression of morning and night-time boundary layer height is observed on high BC days. During the daytime in pre-monsoon, post-monsoon, and winter seasons, boundary layer height peaks are found to be strongly controlled by high BC episode occurrences as obtained from the hourly data of ERA-5.