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K. R. Biswas and A. S. Dennis

Abstract

Salt seeding took place below one end of a line of stratocumulus clouds with 350 lb of NaCl released. Cloud base was 9000 ft and cloud tops were at 15 to 18,000 ft above sea level. Cloud top temperature was near −2C and updraft speeds below the hue were near 3 m sec−1. The resulting shower was monitored by radar with the total rainfall being estimated at 280 acre feet. No rain fell from the unseeded portion of the cloud line or from any other clouds within 50 mi.

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K. R. Biswas and A. S. Dennis

Abstract

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Bh V. Ramana Murty, A. K. Roy, and K. R. Biswas

Abstract

The study of echo intensity profile below bright band, when this appears on radar in certain rain situations, has shown that raindrops, after leaving melting level and falling through clouds in warmer layers below do not, as a rule, undergo any noticeable increase in their sizes, suggesting that lower level clouds at this stage have little or no significant liquid water content. The implications of this on the life cycle of rain situations associated with development of bright band are discussed, with reference to a few instances of study, using radar, of such rain at Delhi.

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A. R. Sen, A. K. Biswas, and D. K. Sanyal

Abstract

An attempt has been made in this paper to study the effect of climatic factors on the growth of annually pruned tea and its components, the early crop, during April to June, the main crop during July to September and the late crop during October to December in northeast India.

Data from two sources have been considered in this study, (i) long-term crop and weather data from the Tocklai experimental station and (ii) short-term data from tea-estates where the rainfall distribution is similar to that at Tocklai.

A multiple regression of the yield of tea during a season on a number of independent climatic variables and age was fitted by the method of least squares and the independent variables were reduced step by step by the method of backward elimination until a set of critical variables associated with yield were obtained.

Of all the climatic factors at Tocklai, rainfall up to 18 cm and the rise in mean temperature during the cold weather, i.e., January–March, proved most beneficial to the early crop which in turn led to an increase in the main crop. There was also some direct beneficial effect of January to March rainfall on the main crop.

Increase in rainfall during January to March proved more beneficial to the crop when the mean temperature was high than when it was low.

Analysis of the crop-weather data from the estates generally supported the above findings.

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K. R. Biswas, R. K. Kapoor, K. K. Kanuga, and Bh V. Ramana Murty

Abstract

An experiment on artificial stimulation of rain using a warm cloud seeding technique was undertaken in three nearby climatologically similar regions, Delhi, Agra and Jaipur in northwest India. Analysis of the data from 18 experiment-seasons has suggested a positive trend of the result, which is found significant by statistical tests.

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Prakash Pithani, Sachin D. Ghude, R. K. Jenamani, Mrinal Biswas, C. V. Naidu, Sreyashi Debnath, Rachana Kulkarni, Narendra G. Dhangar, Chinmay Jena, Anupam Hazra, R. Phani, P. Mukhopadhyay, Thara Prabhakaran, Ravi S. Nanjundiah, and M. Rajeevan

Abstract

A Winter Fog Experiment (WiFEX) was conducted to study the genesis of fog formation between winters 2016–17 and 2017–18 at Indira Gandhi International Airport (IGIA), Delhi, India. To support the WiFEX field campaign, the Weather Research and Forecasting (WRF) Model was used to produce real-time forecasts at 2-km horizontal grid spacing. This paper summarizes the performance of the model forecasts for 43 very dense fog episodes (visibility < 200 m) and preliminary evaluation of the model against the observations. Similarly, near-surface liquid water content (LWC) from models and continuous visibility observations are used as a metric for model evaluation. Results show that the skill score is relatively promising for the hit rate with a value of 0.78, whereas the false alarm rate (0.19) and missing rate (0.32) are quite low. This indicates that the model has reasonable predictive accuracy, and the performance of the real-time forecast is better for both dense fog events and no-fog events. For success cases, the model accurately captured the near-surface meteorological conditions, particularly the low-level moisture, wind fields, and temperature inversion. In contrast, for failed cases, the WRF Model shows large error in near-surface relative humidity and temperature compared to the observations, although it captures temperature inversions reasonably well. Our results also suggest that the model is able to capture the variability in fog onset for consecutive fog events. Errors in near-surface variables during failed cases are found to be affected by the errors in the initial conditions taken from the Indian Institute of Tropical Meteorology Global Forecasting System (IITM-GFS) spectral model forecast. Further evaluation of the operational forecasts for dense fog cases indicates that the error in predicting fog onset stage is relatively large (mean error of 4 h) compared to the dissipation stage.

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