• Pandithurai G

      Articles written in Journal of Earth System Science

    • Analysing the characteristic features of a pre-monsoon thunderstorm event over Pune, India, using ground-based observations and WRF model

      Leena P P Pandithurai G Gayatri K Murugavel P Ruchith R D Sakharam S Dani K K Chetana Patil Dharmaraj T Patil M N Thara Prabhakaran

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      In the present work, the characteristic features and factors contributed to the formation of a typical pre-monsoon thunderstorm that occurred over Pune has been studied using various ground-based observations, such as microwave radiometer profiler, wind lidar and surface eddy covariance flux measurements along with weather research and forecast (WRF) model. Initially, the thermodynamic state of atmosphere, variation in fluxes, as well as convective updrafts and downdrafts associated with the thunderstorm event, has been studied using ground-based observations. Thermodynamic indices derived from ground-based microwave radiometer observations showed significant variation before, during and after the development of thunderstorm such as smaller humidity index and higher values of total total index and K-index during the storm. Convective available potential energy (CAPE) and equivalent potential temperature have also shown an increase prior to the event. It is noted that sensible heat flux is higher than latent heat flux before the initiation of storm, however, the latent heat flux increased significantly during the storm. Wind lidar-derived vertical velocities showed strong variation i.e., exceeding 3 m s$^{-1}$ during the event. Signatures of veering effect indicated the transport of moisture to higher levels was noticed from the altitude variability of wind vector. Ground observations suggested strong crosswind wind shear, convergence of moisture that originated at elevated levels in the boundary layer and enhancement of moist static energy in the elevated layer above the surface was pre-storm characteristics that conducive for the storm enhancement. Secondly, the capabilities of a WRF model in simulating the storm development, structure and evolution have been verified. The WRF model was able to recreate major features of the environment in which the storm was developed. The model output was compared with ground observations, which showed that the model has well captured the sensible heat and friction velocity as that of observation compared to mixing ratio and latent heat. It is observed that the water vapour variation in the model is having a lag, about an hour, with that of observations. The detailed analysis of model output did not show triggering of a thunderstorm as noted in the observation at the same location, which may be probably due to model bias in the moisture transport or moisture convergence was weaker in the model.

    • A case study on bright band transition from very light to heavy rain using simultaneous observations of collocated X- and Ka-band radars

      Hari Krishna Devisetty Ambuj K Jha Subrata K Das Sachin M Deshpande Murali Krishna U V Prasad M Kalekar Pandithurai G

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      The observations of bright band carried out simultaneously with X- and Ka-band radars for the first time over the Indian region have been examined to reveal various contrasting characteristics of bright band at the two wavelengths. The study reports the bright band observations on September 12–13, 2015 at millimeter and centimeter wavelengths and brings out a comparative analysis of the bright band features (e.g., intensity, thickness, height, etc.) under three different rain conditions ranging from very light (<0.1 mm/hr) to light (0.1–3 mm/hr) to heavy (3–5 mm/hr). It is seen that the bright band region at Ka-band is always narrower and situated at a higher altitude than at X-band frequency. Our analysis shows that at Ka-band frequency, the polarimetric fields like LDR can be utilized to detect and determine the bright band features using an appropriate selection of a threshold value of LDR, which is found to be −22 dB in this study and could be associated reasonably with the top and bottom heights of the bright band. This study explores the potential of both radars, particularly the Ka-band radar for probing the bright band effect and estimating its features which would be helpful to improve the quantitative estimates of precipitation.

    • Impact of electrified and non-electrified clouds on the inter-seasonal characteristics of surface-based precipitation

      KAUSTAV CHAKRAVARTY MURUGAVEL P ANGEL A CHRISTY SINGH V PANDITHURAI G

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      A multi-sensor analysis of the characteristics of electrified and non-electrified clouds along with their impact on the surface-based raindrop size distribution (DSD) during the inter-seasonal phases of Indian summer monsoon over a heavy precipitation region of Western Ghat (WG) has been highlighted in the present paper. The analysis reveals that during the pre-monsoon (monsoon) months, raindrops of larger diameter dominate the rainfall evolving from the non-electrified (electrified) clouds compared to the rainfall evolving from the electrified (non-electrified) ones. The complex relationship of the convective rainfall with highly charged electrified clouds forces the smaller drops aloft and thereby allowing the larger drops to precipitate locally during the pre-monsoon season. While for the monsoon months, as most of the rainfall originates from the deep clouds, the chances of drops to break-up/evaporate is comparatively less for the precipitation evolving from electrified clouds with charged droplets with respect to the non-electrified ones. Hence, drops of larger diameter dominate the monsoon rainfall associated with lightning. Correspondingly, the paper also highlighted a case study of the changing morphology of the vertical structure of clouds and surface precipitation with the evolution of lightning during various stages of a typical rainfall event over the orographic region of WG.

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