Showing papers by "Animesh Maitra published in 2018"

Characterization of tropical precipitation using drop size distribution and rain rate-radar reflectivity relation

Abstract: Characterization of precipitation is important for proper interpretation of rain information from remotely sensed data. Rain attenuation and radar reflectivity (Z) depend directly on the drop size distribution (DSD). The relation between radar reflectivity/rain attenuation and rain rate (R) varies widely depending upon the origin, topography, and drop evolution mechanism and needs further understanding of the precipitation characteristics. The present work utilizes 2 years of concurrent measurements of DSD using a ground-based disdrometer at five diverse climatic conditions in Indian subcontinent and explores the possibility of rain classification based on microphysical characteristics of precipitation. It is observed that both gamma and lognormal distributions are performing almost similar for Indian region with a marginally better performance by one model than other depending upon the locations. It has also been found that shape-slope relationship of gamma distribution can be a good indicator of rain type. The Z-R relation, Z = ARb, is found to vary widely for different precipitation systems, with convective rain that has higher values of A than the stratiform rain for two locations, whereas the reverse is observed for the rest of the three locations. Further, the results indicate that the majority of rainfall (>50%) in Indian region is due to the convective rain although the occurrence time of convective rain is low (<10%).

Study of rain attenuation effects for 5G Mm-wave cellular communication in tropical location

Abstract: Millimetre (mm)-wave communication is a viable solution to the future 5G cellular services. For different temperate locations, rain attenuation does not contribute significantly to the overall path loss at the mm-wave band for a small cell size of 200 m. However, in various tropical locations, the rain attenuation effect cannot be ignored even for this small cell size of the system. If the authors increase either frequency or path length, the attenuation increases significantly under tropical raining conditions. In this study, time series of predicted rain rate values are used for real-time prediction of rain attenuation over terrestrial paths.

Prediction of Rain Occurrence and Accumulation Using Multifrequency Radiometric Observations

Abstract: A nowcasting technique has been proposed to estimate the impending rain accumulation using ground-based radiometric measurements at Kolkata (22.65°N, 88.45°E), a tropical location. It has been observed that the normalized variation of brightness temperature (BT) at 31 GHz along with the standard deviation of BT at 22 GHz and instability indices, namely, lifting index, have shown definite changes before rain events. A combination of these three parameters can be effective in predicting rain events both qualitatively and quantitatively. Accordingly, a prediction model is developed and tested on several intense rain events during the period 2014–2015. The model is found to perform reasonably well in predicting intense rain about 70–75 min in advance with an efficiency of 80%.

Rain Radar Studies of Boundary Layer Dynamics at a Tropical Location

Abstract: Boundary layer dynamics play an important role in determining precipitation structure during convective processes. The radar reflectivity profiles which depend on the sixth moment of rain drop size distribution (DSD) can be employed to sense the precipitation processes. The height profiles of DSD significantly depend on the vertical wind velocity. The observations with a micro rain radar (MRR), an FMCW radar, over Kolkata, have been utilized to study the drop size distribution and its relationship with radar reflectivity at Ka-band. A sharp decrease of radar reflectivity in the height range 1–2 km corresponds to an increase of downdraft velocity observed around the same height range. This indicates that the increased downdraft causes breakup of rain drops into smaller sizes. The split in the Doppler spectrum, known as aliasing effect, is most prominent near the boundary layer height and has been employed to estimate downward wind velocity.

Atmospheric Gravity Wave Features Related to Stratospheric Moistening During Tropical Cyclones

Abstract: 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.