Showing papers by "Animesh Maitra published in 2017"

East-west coastal asymmetry in the summertime near surface wind speed and its projected change in future climate over the Indian region

Abstract: The behaviors of various meteorological parameters during 1981–2010 are investigated to obtain any asymmetric variability of summertime near surface wind over Indian coastal boundaries. No significant changes were obtained in the trends of surface pressure, surface relative humidity, 2-metre temperature and surface precipitation; although, near surface wind speed is found to have significantly declined on the eastern coast with respect to the western coast during this period. Summertime surface wind speed on the eastern coast have decreased from 3.5 to 2.5 m s − 1 (7 to 5 knots) whereas 4.5 to 4 m s − 1 (9 to 8 knots) during the last three decades (statistical significance level ~ 95%). A decrease in the atmospheric instability may serve as the potential reason for the suppression of severe convective occurrences manifested by a parallel decrease in surface wind speeds over these regions. The local heating up of middle atmosphere (300–500 hPa pressure level) due to increased humidity and the difference in net heat flux over Arabian Sea and Bay of Bengal due to the variance of temperature gradient (1000–925 hPa) along the coastal boundaries might be responsible for this climatic disparity between the coastal regions of India since the last three decades. Summertime near surface wind speed projections for Indian sub-continent based on 7 best climate models, for RCP8.5 scenarios, has been calculated to show a mean increase by ~ 10–15% on the eastern coast (Eastern Ghats), ~ 1–2% on the western coasts (Western Ghats), ~ 1–5% decrease in the Indo-Gangetic Basin and ~ 3% decrease in the Gangetic West Bengal and adjoining Bangladesh.

Prerain Scintillations of Ku-Band Satellite Signal in Relation to Cloud and Convective Parameters at a Tropical Location

Abstract: In this letter, the tropospheric scintillations occurring just before rain commencement have been investigated. This letter indicates the association of the prerain scintillations with both the cloud thickness and the prevailing convection. The convective available potential energy has been considered as a parameter indicating the strength of the associated convection.

Rain drop size variation with cloud base height at a tropical location

Abstract: The inter-relation of rain drop size distribution with cloud base height has been investigated at a tropical location, Kolkata (22°34′N, 88°22′E). The study focuses the association of rain drop size distribution with cloud base height during the summer monsoon and pre-monsoon. It is observed that the mean diameter of the largest drop increases with the lowering of cloud base height. A notable difference between the pre-monsoon and monsoon rain events have been identified in the inter-relation of rain drop size with cloud base height. Results indicate that the large drops are more frequent in the pre-monsoon season than the monsoon.

Radiometric measurements of cloud attenuation over Earth-space path at a tropical location

Abstract: In this study, real time estimates of cloud attenuation have been made using ground based microwave radiometric observations of Liquid Water Content at a tropical location. It is found that the significant amount of cloud attenuation occurs during monsoon season. Individual case study additionally shows that cloud attenuation can contribute significantly to the overall signal degradation at various frequency bands.

Boundary layer anomalies observed from radiometric observations during convective rain

Abstract: In this study, anomalous observations in relative humidity at relative humidity profiles during heavy rain have been presented. Radiometric observations of relative humidity profiles show a significant fall at around 1 to 2 km height region during heavy rain events. An extensive investigation shows that the fall of relative humidity is strongly related to the characteristics of boundary layer temperature lapse rate profiles. However, these observations have only been reported during convective rain and are not very prominent in stratiform precipitation as the boundary layer dynamics does not play a significant role in those types of rain. The analysis also reveals the role of atmospheric pollutants as heating agents in the planetary boundary layer which can be crucial in causing such anomalies in atmospheric profiles.

Rain prediction using radiometric observations at a tropical location

Abstract: Nowcasting of intense rain is important in various fields of life. In this paper, radiometric brightness temperature measurements at Ka and V bands are utilized to predict rain event associated with impending convective processes. The instability parameters are estimated from radiometric data to point the development of atmospheric instability and an estimation of liquid water content is made from brightness temperature at 31.4 GHz, prior to rain events. The nowcasting technique is, therefore, able to predict both rain occurrence and rain accumulation. The model, when validated, gives a reasonable prediction efficiency of around 80%.

Characteristics of high velocity small drops in tropical convective rain

Abstract: The characteristics of high velocity small drops (super-terminal) are observed during different types of rain in a tropical region, Kolkata. Measurements using a Laser Precipitation Monitor (LPM) for several rain events spanning the monsoon season of 2013 at Kolkata, India, shows that the presence of high velocity small drops is significant in tropical convection. Additionally, the fraction of super-terminal drops in natural rain is found to decrease with increasing rain rate. The decrease of superterminal drops in high rain intensities, implies increase in rain drop coalescence over drop break up.