The paper presents the nature of the variation of refractive index of atmospheric medium with time and altitude before, during and after the onset of thunderstorms over Gangetic West Bengal during the pre-monsoon period. A critical analysis shows that sharp depletion of the refractive index takes place before the onset of Nor'westers and possible explanations are also offered for the said occurrence. © 2011 Springer-Verlag.

SUBRATA MIDYA

Atmospheric Science

H SARKAR

U SAHA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Meteorology and Atmospheric Physics

The present paper reports a comparative study among two neurocomputing models in the form of Multilayer Perceptron (MLP) models and non-linear regression for the prediction of surface ozone (O 3 ) during pre-monsoon season over Gangetic West Bengal (GWB), India considering NO x , SO 2 , PM10 and temperature as predictors. Learning the MLPs through gradient descent (GD) with tanhyperbolic and sigmoid nonlinearities, we found that all the models under consideration have almost the same degrees of prediction efficiency for O 3 over GWB during pre-monsoon season with the said predictors. However, the MLP model with tanhyperbolic activation function is found to produce a significantly higher correlation and Willmott's index of agreement between actual and predicted O 3 than the other models. Finally, MLP with GD learning characterized by tanhyperbolic nonlinearity is identified to have significant efficiency in surface ozone prediction over the region as mentioned above. © 2019 Elsevier Ltd

Journal of Atmospheric and Solar-Terrestrial Physics

MLP based predictive model for surface ozone concentration over an urban area in the Gangetic West Bengal during pre-monsoon season

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%. © 1980-2012 IEEE.

IEEE Transactions on Geoscience and Remote Sensing

Prediction of Rain Occurrence and Accumulation Using Multifrequency Radiometric Observations

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. © 2017 Elsevier B.V.

Global and Planetary Change

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

Radiometric observations of relative humidity profile at Kolkata show a significant fall at around 1 to 2 km height during convective rain events. An extensive investigation shows that the fall of relative humidity is not seen during calm conditions but is strongly related to the characteristics of temperature lapse rate profiles. Moreover, the phenomenon may have strong association with boundary layer structure. The reason for such anomalies in the planetary boundary layer humidity profile might be due to the release of latent heat at the mentioned altitude. The abundance of pollutant aerosols in urban regions has also been found to contribute to this relative humidity anomaly. It has also been reported that this boundary layer relative humidity is accompanied by high latent heat release and condensation of vapour to liquid which is not much prominent in other rain types as observed in stratiform rain. Hence, convective rain produces some unique boundary layer characteristics which have also been partially supported with allied satellite and multi-station observations. © 2017 Elsevier B.V.

Atmospheric Research

Anomalies in relative humidity profile in the boundary layer during convective rain

In this present investigation, a threefold analysis has been portrayed to comprehend the atmospheric dynamics at the Tropopause height on both short and long term basis over the Indian sub-continent. The Tropopause height as determined from the gridded temperature profiles from ERA Interim reanalysis is using a concept of “threshold lapse-rate”. It has also been noticed that an exchange between water vapour and ozone occurs along the Tropopause (100 hPa) region during occurrences of deep moist convection. The eastern Indian coastal region experiences enormous convective strength during summer (March–May), hence an increase in specific humidity (as proxy of water vapour) with subsequent decrease in ozone levels in the east-coastal stations are found comparable with the inland stations. Again, the vertical convective transport during deep convection has been found to be supported by stronger vertical wind in the coastal regions compared to inland locations. Finally, it has been comprehended that vertical transport of water vapour gradually decreases in the eastern Indian coastal regions while not much change has been noticed in inland regions. © 2017 Elsevier B.V.

Tropopause height characteristics associated with ozone and stratospheric moistening during intense convective activity over Indian sub-continent

The sharp depletion of attenuation of 22.235 GHz signal before the onset of Nor'wester over Kolkata, India is observed and possible explanation of such type of variation is presented. It is concluded that this may be taken as one possible method of forecasting severe thunderstorm associated with Nor'wester. Physical explanations based on the formation and dissipation mechanisms of thunderstorm are also presented. © 2010 IACS.

Indian Journal of Physics

Sharp depletion of attenuation of 22.235 GHz associated with Nor'wester over Kolkata, India and possible method of forecasting Nor'wester

A genetic algorithm (GA) is introduced to fix ranges of parameters, in a quantitative manner, pertaining to forecasting the genesis of severe thunderstorms in the pre-monsoon season over Calcutta (22°32′, 88°20′) in the northeastern part of India (20°-24°N latitude, 85°-93°E longitude). The results depict that definite quantitative ranges of parameters can be made available before as well as after the occurrence of severe thunderstorms using a GA. Thus, a suitable combination of these ranges of parameters before the onset can represent a possible predictor of thunderstorm genesis. © World Scientific Publishing Company.

Advances in Complex Systems

Prediction of severe thunderstorms with minimal a priori information

Meteorological Applications

Numerical simulation of a tornado over Ludhiana (India) using WRF-NMM model

Journal of Earth System Science

The interaction of large scale and mesoscale environment leading to formation of intense thunderstorms over Kolkata Part I: Doppler radar and satellite observations

Journal	Data powered by TypesetMeteorology and Atmospheric Physics
Publisher	Data powered by TypesetSPRINGER WIEN
ISSN	0177-7971
Open Access	No