Rohit Chakraborty

Multi-technique observations of convective rain events at a tropical location

The effects of the convective rain on various atmospheric parameters have been investigated at Kolkata (22.57°N, 88.37°E), India, during pre-monsoon and monsoon period of 2013. Various parameters like cloud base height and depth, liquid water content, rain rate and rain drop size distribution (DSD) are observed concurrently. The atmospheric electric field measured with an electric field monitor and the attenuation and depolarisation of satellite signals measured by a Ku-band receiving system are also studied during rain events. The instability indices obtained from radiometric measurements and the rain height profiles from micro rain radar are used to classify rain into two types, namely, convective and stratiform. The signatures of rain events on multi-technique observations are studied to indicate the various aspects of convective processes at a tropical location.

Nowcasting of tropical rain using dual frequency atmospheric brightness temperatures at Kolkata

Nowcasting of thunderstorm has important implication on minimizing the loss of properties and life. Conventional approaches for such purpose using radiometer measured brightness temperature of only water vapor line usually tend to overestimate the occurrence probability. In this paper, we demonstrate that use of brightness values of oxygen absorption lines in addition with the water vapor absorption lines can provide unique signature of heavy rain.

Rain attenuation over earth space path from radar and propagation measurements at tropical location

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.

Rain prediction using radiometric observations at a tropical location

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%.

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

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

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.

Prediction of convective rainfall using multi-technique observations

Nowcasting of rain amount is extremely essential in various fields of life. In this paper, we have shown that monitoring of brightness temperature at 31.4 GHz, the frequency having strong absorption due to liquid water, can give an estimate of rain accumulation with a prediction efficiency of ~ 80 % and a lead time of 75 minutes. It has also been observed that atmospheric electric field also shows definite changes before rain the magnitude of which can be related with the rainfall amount.