Browsing by Author "Sharma, Som"

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A comprehensive statistical study of cloud base height using ceilometer over western India
(2019-03-01)
Vaishnav, Rajesh
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Sharma, Som
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Shukla, K. K.
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Kumar, Prashant
;
Lal, S.
A comprehensive statistical analysis of the cloud base height (CBH) measured by ground-based Vaisala ceilometer (CL31) has been performed to study different layers of the cloud in the lower troposphere up to 7.5 km height over Ahmedabad, western India during 2014 and 2015. The total observations (similar to 69%) of cloud by using ceilometer show annual cloud occurrence frequency of around 64%. Seasonal variation of CBH and cloud occurrence frequency reveal that the maximum/minimum cloud cover is found during southwest (SW) Indian summer monsoon/pre-monsoon season. Three CBHs (CBH1, CBH2, and CBH3) are presented in monsoon period due to high cloud occurrence, and two CBHs (CBH1 and CBH2) are observed in other seasons due to low cloud occurrence by ceilometer over the observational site. The CBH1 (similar to 100-2000 m) and CBH2 (500-3000 m) are observed during SW monsoon and summer season, respectively. The CBH3 is occurred usually in SW monsoon season. Moreover, the cloud cover during the day and night time shows that the occurrence of cloud is more frequent in daytime than nighttime during pre-monsoon and post-monsoon season. The statistical analysis of cloud with ground-based observations is also performed in this study that may be useful for the development/improvement of regional weather and climate models to reduce the uncertainty in the prediction. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved.
Investigations of vertical wind variations at a mountain top in the Himalaya using Doppler Lidar observations and model simulations
(2019-02-01)
Shukla, K. K.
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Phanikumar, D., V
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Newsom, Rob K.
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Ojha, N.
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NiranjanKumar, K.
Hight-resolved observations of vertical winds remain nearly non-existing over the Himalayas, despite of anticipated crucial role of vertical motions in transporting pollution across the Himalayan hills. The present study analyze the vertical wind observations from surface to 1 km above ground level over Manora Peak (29.4 degrees N; 79.5 degrees E; 1958 m amsl) in the Himalaya performed using a Doppler Lidar during the Ganges Valley Aerosol Experiment (GVAX). Vertical wind exhibited a pronounced diurnal variability at Manora Peak comprising of upward motions during the daytime (05-10 UT) and downward motions during nighttime typical of a mountain valley system. Mean vertical wind speeds are observed to be varying from -0.8 to + 0.8 ms(-1) during the study period with a variance of 0.1-1.5 m(2)s(-2), which is attributed to the thermally driven turbulence. Mean vertical winds are observed to be stronger in the Doppler Lidar profiles above Manora Peak (-0.8 to 0.8 ms(-1)) as compared to near surface measurements at this station using an ultrasonic anemometer (-0.4 to 0.4 ms(-1)), and low altitude stations in India. Daytime vertical wind speeds are observed to be higher during pre-monsoon (0.81 ms(-1)), as compared to post-monsoon (0.24 ms(-1)) and winter (0.33 ms(-1)). Average Black Carbon (BC) concentrations are significantly higher during strong upward vertical winds, which indicates efficient transport of polluted air mass from low-altitude regions to the Himalaya. Weather Research and Forecasting (WRF) model reproduces the observed diurnal pattern in the vertical wind at the observation site however the model underestimates the variability.