Browsing by Author "Lal, D.M."

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    A laboratory investigation of electrical influence on the freezing of water drops: A cloud physics perspective
    (Springer, 2021) Mudiar, Dipjyoti; Pawar, S.D.; Hazra, Anupam; Gangane, Abhijeet; Gopalakrishnan, V.; Lal, D.M.; Srivastava, Manoj K
    Electro-crystallization, the freezing of water droplet induced by an electric field has been investigated by many investigators previously. But disagreements regarding the cause of freezing still persist in the literature. A cloud chamber of the internal dimension of 1 ft � 1 ft has been designed to study electro-crystallization of �mm� size pure water drops. More than 150 experiments have been performed in the chamber in the absence and presence of an electric field. Preliminary results suggest that in normal conditions, maximum drops freeze in the temperature ranging from ?10� to �15�C, consistent with the previous laboratory studies. When the drops are subjected to an electric field of magnitude 2�5 kV cm?1, the drops are observed to freeze in a much warmer temperature ranging from �6� to �10�C indicating an electric field induced crystallization. No movement of the drops is observed during the freezing, which suggests that the freezing may be initiated by absorption of the latent heat of fusion by the Nylon wire where the drops are kept suspended. The implication of the electrically induced freezing from the perspective of cloud physics also has been discussed. � 2021, Indian Academy of Sciences.
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    Lightning and precipitation: The possible electrical modification of observed raindrop size distributions
    (Elsevier Ltd, 2021) Mudiar, Dipjyoti; Pawar, S.D.; Hazra, Anupam; Gopalkrishnan, V.; Lal, D.M.; Chakravarty, Kaustav; Domkawale, Manoj A.; Srivastava, Manoj K.; Goswami, B.N.; Williams, Earle
    Many studies of cloud electrification have suggested that the presence of precipitation in the mixed phase region of the cloud is essential for charge separation and lightning initiation in clouds. However, observations of the rain gush phenomenon, a transient amplification in near-surface intensity after an overhead lightning also suggest that the lightning discharge can substantially enhance precipitation intensity at the ground. But the microphysical link between lightning and enhanced precipitation intensity after lightning is not well understood. With the observation of a transient amplification in the rain intensity and broadening of the corresponding Raindrop Size distribution (RDSD) after the lightning, it is inferred here that the lightning-induced atmospheric ions and prevailing electrical forces may potentially modulate the RDSD as well as the rain intensity by influencing the collision-coalescence process and the growth rate of raindrops after lightning. The time delay between the lightning and subsequent increase in rain intensity at the Earth's surface was observed to be between 2-4 min. Also, a good correlation was observed between the variations in lightning frequency and the rain intensity during thunderstorms with an average time lag of 4 min. Piepgrass et al. (1982) have reported a good correlation between lightning frequency and rainfall when the precipitation lagged the lightning by times of 4 and 9 min. These observations indicate that the association between lightning frequency and rainfall with 4-min time lag (the shorter one) may be a result of the lightning-induced growth of raindrops below the melting layer rather than the enhancement in precipitation in the mixed phase region of cloud. The new knowledge, coupled with our related work (MUDIAR et al., 2018) on stratiform clouds provides a compelling basis for the parameterization of the electrical processes in weather/climate models. � 2021
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    Lightning Characteristics Over Humid Regions and Arid Regions and Their Association With Aerosols Over Northern India
    (Birkhauser, 2022) Jnanesh, S.P.; Lal, D.M.; Gopalakrishnan, V.; Ghude, Sachin D.; Pawar, Sunil D.; Tiwari, S.; Srivastava, Manoj K.
    The association between aerosol and lightning has been investigated with long-term decadal data (2005�2014) for lightning, aerosol optical depth (AOD), relative humidity, and effective cloud droplet size. To understand the complex relationship between aerosol and lightning, two different regions with different climatic and weather conditions, a humid region R1 (22��29� N, 89��92� E) and an arid region R2 (23��28� N, 70��76� E) of northern India, were chosen for the study domain. The results show that lightning activity was observed to occur more over the humid region R1, i.e., 1141�days (1/3 of total days), than over the arid region R2, i.e., 740�days (1/5 of total days). Also, over the humid region R1, the highest lightning flash density was recorded as nearly 4.6 � 10�4 flashes/km2/day observed for 18�days (1.5%); on the contrary, over the arid region R2, the maximum lightning flash density was observed to be 2.5 � 10�4 flashes/km2/day and occurred for about 22�days (2.9%). The analysis shows that a nonlinear relationship exists between aerosol and lightning with a highly associated influence of relative humidity. A very significant positive and negative co-relation that varies with relative humidity has been observed between AOD and lightning for both humid and arid regions. This shows relative humidity is the key factor in determining the increase or decrease of lightning activity. This study also shows that the larger the cloud droplet size, the higher the relative humidity and vice versa. This study emphasizes that aerosol concentration in the atmosphere influences cloud microphysics by modulating the size of cloud droplets and thereby regulating the lightning frequency. The atmospheric humidity is the driving factor in deciding the positive or negative co-relationship between aerosol and lightning. � 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
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    Role of Lightning NOx in Ozone Formation: A Review
    (Birkhauser, 2021) Verma, Sunita; Yadava, Pramod Kumar; Lal, D.M.; Mall, R.K.; Kumar, Harshbardhan; Payra, Swagata
    This paper provides an overview on the spatiotemporal distribution and evolution mechanism of lightning. The predominant mechanism of ozone formation in the upper troposphere is lightning-induced precursors such as oxides of nitrogen (NOx), carbon monoxide (CO), and hydrocarbons (HC). Lightning-induced NOx (LNOx) is one of the major ordinary sources of NOx in the upper atmosphere, particularly in the tropical region, but it is still highly uncertain as to the exact quantity. Various ground measurements, satellite observations and modelling studies on the lightning and global NOx source rate have been extensively studied and compared to find the variability in estimated global lightning-induced NOx. Lightning can influence the climate via the production of nitrogen oxides (NO + NO2 = NOx) followed by the production of ozone, another efficient greenhouse gas. The global annual lightning NOx of 5 � 3 Tg�year?1 has been estimated by modelling studies with an ozone creation efficiency of 6.5 � 4.7 times that of surface NOx sources. Understanding and quantifying the processes and production of lightning and LNOx is important for assessment of ozone concentrations and its associated impacts on the global climate. � 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.