Browsing by Author "Manoj K. Srivastava"

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Absorbing aerosols, possible implication to crop yield - a comparison between IGB stations
(AAGR Aerosol and Air Quality Research, 2017) R. Latha; B.S. Murthy; K. Lipi; Manoj K. Srivastava; Manoj Kumar
The current study compares black carbon radiative effects at the densely populated plain station, Varanasi and the lesser populated plateau station Ranchi with large forest cover but with numerous open coal mines. While the measured average black carbon mass density (BC) reduces from February to March at Ranchi following an increase in convective mixing, it is observed to increase by 150% from February to March in Varanasi, as transport from northeast forest fires increases. It is observed that absorption due to black carbon of non-fossil fuel origin is prevalent throughout the day, in Varanasi, while this contribution is most significant during post sunset hours in Ranchi. Radiative forcing, estimated hourly using chemical model (to derive BC-aod) and radiative transfer model, indicates that at least 5% of the incoming radiation is always cutoff during any time of the day in Varanasi while this is about 4% in Ranchi. BC effectively causes an apparent delayed sunrise by reducing the incoming radiation on the plains of Indo Gangetic Basin (IGB) by up to 25% at the daybreak. An estimate of crop loss due to cut off in radiation, using an empirical formula for crop yield as a function of radiation, indicates a possible loss of more than a quintal per hectare considering anthesis (February) and maturity (March) periods for the winter wheat in both the IGB stations with consistently higher losses in Varanasi. © Taiwan Association for Aerosol Research.
Aerosol characteristics during the coolest june month over new delhi, northern india
(Taylor and Francis Ltd., 2011) Atul Kumar; Suresh Tiwari; Deewan Singh Bisht; Panuganti China Sattilingam Devara; Philippe Goloub; Zhengqiang Li; Manoj K. Srivastava
June 2008, which is also the transition month between two major seasons for Indo-Gangetic Basin (IGB), has been identified the coolest June over New Delhi during the past century, showing mean temperature of 31.6 ± 1.7°C, which was found to be ~2°C less than its climatological mean (33.9°C). Aerosol optical properties for this month and thus obtained physical parameters have been studied using data from the CIMEL sun/sky radiometer, installed in New Delhi under the Aerosol Robotic Network (AERONET) programme. Results reveal bimodal aerosol volume size distribution. The monthly mean values for aerosol optical depth (AOD) at 500 nm (0.96 ± 0.31) and Ångström exponent at the wavelength pair of 440-870 nm (0.79 ± 0.42) show significant lower values whereas single scattering albedo at 675 nm shows a significantly larger value (0.94 ± 0.04) compared with previous measurements over the station. Results suggest dominance of scattering- type particles such as water-soluble aerosols from anthropogenic sources and dust aerosols from natural sources with higher relative humidity over the station. Radiative forcing caused due to the aerosols for the month of June 2008, which have been computed using the radiative-transfer model, informs low forcing at the top of atmosphere (TOA, +14 W -m) as well as at surface (-33 W m-2). The resultant atmospheric forcing (+47 W m-2) indicates warming effect that caused heating of lower atmosphere at the rate of 0.89 K day-1. © 2011 Taylor & Francis.
Aerosol chemistry over a high altitude station at northeastern Himalayas, India
(2010) Abhijit Chatterjee; Anandamay Adak; Ajay K. Singh; Manoj K. Srivastava; Sanjay K. Ghosh; Suresh Tiwari; Panuganti C. S. Devara; Sibaji Raha
Background: There is an urgent need for an improved understanding of the sources, distributions and properties of atmospheric aerosol in order to control the atmospheric pollution over northeastern Himalayas where rising anthropogenic interferences from rapid urbanization and development is becoming an increasing concern. Methodology/Principal Findings: An extensive aerosol sampling program was conducted in Darjeeling (altitude~2200 meter above sea level (masl), latitude 27°01'N and longitude 88°15'E), a high altitude station in northeastern Himalayas, during January-December 2005. Samples were collected using a respirable dust sampler and a fine dust sampler simultaneously. Ion chromatograph was used to analyze the water soluble ionic species of aerosol. The average concentrations of fine and coarse mode aerosol were found to be 29.5±20.8 μg m-3 and 19.6±11.1 μg m-3 respectively. Fine mode aerosol dominated during dry seasons and coarse mode aerosol dominated during monsoon. Nitrate existed as NH4NO3 in fine mode aerosol during winter and as NaNO3 in coarse mode aerosol during monsoon. Gas phase photochemical oxidation of SO2 during premonsoon and aqueous phase oxidation during winter and postmonsoon were the major pathways for the formation of SO42- in the atmosphere. Long range transport of dust aerosol from arid regions of western India was observed during premonsoon. The acidity of fine mode aerosol was higher in dry seasons compared to monsoon whereas the coarse mode acidity was higher in monsoon compared to dry seasons. Biomass burning, vehicular emissions and dust particles were the major types of aerosol from local and continental regions whereas sea salt particles were the major types of aerosol from marine source regions. Conclusions/Significance: The year-long data presented in this paper provide substantial improvements to the heretofore poor knowledge regarding aerosol chemistry over northeastern Himalayas, and should be useful to policy makers in making control strategies. © 2010 Chatterjee et al.
Aerosol optical properties and their relationship with meteorological parameters during wintertime in Delhi, India
(Elsevier Ltd, 2015) S. Tiwari; G. Pandithurai; S.D. Attri; A.K. Srivastava; V.K. Soni; D.S. Bisht; V. Anil Kumar; Manoj K. Srivastava
In situ and columnar measurements of aerosol optical properties (AOPs) [Aerosol optical depth (AOD), Angstrom Exponent (AE), Aerosol scattering (σscat) and absorption (σabs) coefficients and single scattering albedo (SSA)] along with soot particles (Black carbon: BC) and fine particles (PM2.5: d ≤2.5) were continuously measured at an urban site in Delhi, India during winter period (December 2011 to March 2012). Average values of AOD, σscat, σabs, and SSA at 500nm; and AE for the observation period were found to be 0.95±0.32, 1027.36±797.1Mm-1, 85.95±73.2Mm-1 and 0.93±0.03; and 0.94±0.19, respectively. Higher values of σscat and σabs were occurred in the month of December (1857 and 148Mm-1) while relatively lower values of σscat (585Mm-1) and σabs (44Mm-1) were occurred in March and February respectively. SSA, however, was higher during January (0.94) and lower in March (0.89). The mass concentration of PM2.5 and BC were 195.34±157.99 and 10.11±8.83μgm-3 respectively during study period. Bimodal distributions were observed in σscat and σabs coefficients during 0800 and 0900h LT (traffic rush hours) and at 2200 and 2300h LT (low boundary layer conditions) with lower values during daytime between 1500 and 1700h LT, respectively. The σscat peak in morning may be attributed to large emissions of aerosol in the traffic rush hours and production of secondary aerosols with increasing solar radiation and temperature. During study period, the σscat (mean) coefficient was 13% lower during daytime as compared to nighttime. An interesting feature was seen in monthly analysis of σscat in between day and nighttime which was 18% and 22% higher in December and January in nighttime however ~4% lower during February and March; it is due to effect of local meteorology. The impact of meteorological parameters such as wind speed (WS), wind direction (WD), visibility (VIS) and mixed layer depths (MLDs) on AOPs along with fine and soot particles were studied. A clear negative significant correlation between atmospheric visibility with σscat (-0.64); σabs (-0.57) and PM2.5 (-0.56) were observed. During foggy days (VIS ≤1000m), the AOPs, fine and soot particles were substantially (~1.8 times) higher as compared to clean days, however, it was ~2.3 times higher during dense foggy days (VIS ≤500m). Similarly higher (~2 times) AOPs and aerosol concentrations were also seen below 200m MLDs. In addition to this, ~4 times higher AOPs and aerosol mass concentrations were observed when WS was below 1m/s. In view of the above results and regression analysis, we can say that the meteorological parameters play a crucial role in enhancement of aerosols at ground level during winter period over Delhi. © 2014 Elsevier B.V.
Assessment of air quality during 19th Common Wealth Games at Delhi, India
(Kluwer Academic Publishers, 2013) D.S. Bisht; S. Tiwari; A.K. Srivastava; Manoj K. Srivastava
The 19th Common Wealth Games was organized at Delhi, India, during October 3 to 14, 2010, where more than 8,000 athletes from 71 Commonwealth Nations have participated. In order to give them better environment information for proper preparedness, mass concentrations of particulate matters below 10 microns (PM10) and 2. 5 microns (PM2. 5), black carbon (BC) particles and gaseous pollutants such as carbon monoxide (CO) and nitrogen oxide (NO) were monitored and displayed online for ten different locations around Delhi, including inside and outside the stadiums. This extensive information system for air quality has been set up for the period from September 24 to October 21, 2010, and data have been archived at 5-min interval for further research. During the study period, average concentration of PM10 and PM2. 5 was observed to be 229. 7 ± 85. 5 and 112. 1 ± 56. 0 μg m-3, respectively, which is far in excess of the corresponding annual averages, stipulated by the national ambient air quality standards. Significant large and positive correlation (r = 0. 93) between PM10 and PM2. 5 implies that variations in PM10 mass are governed by the variations in PM2. 5 mass. The mass concentrations of PM2. 5 inside the stadium were found to be ~18 % lower than those outside; however, no large variations were observed in PM10. Mean concentrations of BC, CO and NO for the observation period were 10. 9 μg m-3 (Min, 02 μg m-3; Max, 31 μg m-3), 1. 83 ± 0. 89 ppm (Min, 0. 48 ppm; Max, 4. 55 ppm) and 37. 82 ppb (Min, 2. 4 ppb; Max, 206. 05 ppb), respectively. BC showed positive correlation (r = 0. 73) with CO suggests unified source for both of them, mainly from combustion emissions. All the measured parameters, however, show a significant diurnal variation with enhanced peaks in the morning and late night hours and lower values during daytime. © 2012 Springer Science+Business Media B.V.
Black carbon and chemical characteristics of PM10 and PM 2.5 at an urban site of North India
(2009) Suresh Tiwari; Atul K. Srivastava; Deewan S. Bisht; Tarannum Bano; Sachchidanand Singh; Sudhamayee Behura; Manoj K. Srivastava; D.M. Chate; B. Padmanabhamurty
The concentrations of PM10, PM2.5 and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM10 and PM2.5 concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) μgm -3 respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM 2.5/PM10 varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM10 and PM2.5, is deemed as the contribution of the coarse fraction (PM10-2.5). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 μgm-3, 13.07%), mineral matter (12.32 μgm-3, 10.06%) and salt particles (4.92 μgm-3, 4.02%). PM2.5 are mainly made up of undetermined fractions (39.46 μgm-3, 40.9%), secondary inorganic aerosols (26.15 μgm-3, 27.1%), salt aerosols (22.48 μgm-3, 23.3%) and mineral matter (8.41 μgm-3, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) μgm-3, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM10 and PM2.5. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl-, SO 4 2-, K+, Na+, Ca2+, NO 3 - and Mg 2+ with PM2.5 on one hand and Mg2+ with PM 10 on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi. © 2010 Springer Science+Business Media B.V.
Characterization of carbonaceous aerosols over Delhi in Ganga basin: Seasonal variability and possible sources
(Springer Verlag, 2014) A.K. Srivastava; D.S. Bisht; K. Ram; S. Tiwari; Manoj K. Srivastava
The mass concentration of carbonaceous species, organic carbon (OC), and elemental carbon (EC) using a semicontinuous thermo-optical EC-OC analyzer, and black carbon (BC) using an Aethalometer were measured simultaneously at an urban mega city Delhi in Ganga basin from January 2011 to May 2012. The concentrations of OC, EC, and BC exhibit seasonal variability, and their concentrations were ~2 times higher during winter (OC 38.1 ± 17.9 μg m-3, EC 15.8 ± 7.3 μg m-3, and BC 10.1 ± 5.3 μg m-3) compared to those in summer (OC 14.1 ± 4.3 μg m-3, EC 7.5 ± 1.5 μg m-3, and BC 4.9 ± 1.5 μg m-3). A significant correlation between OC and EC (R = 0.95, n = 232) indicate their common emission sources with relatively lower OC/EC ratio (range 1.0-3.6, mean 2.2 ± 0.5) suggests fossil fuel emission as a major source of carbonaceous aerosols over the station. On average, mass concentration of EC was found to be ~38 % higher than BC during the study period. The measured absorption coefficient (babs) was significantly correlated with EC, suggesting EC as a major absorbing species in ambient aerosols at Delhi. Furthermore, the estimated mass absorption efficiency (σabs) values are similar during winter (5.0 ± 1.5 m2 g-1) and summer (4.8 ± 2.8 m2 g-1). Significantly high aerosol loading of carbonaceous species emphasize an urgent need to focus on air quality management and proper impact assessment on health perspective in these regions. © 2014 Springer-Verlag Berlin Heidelberg.
Chemical characterization, source apportionment and transport pathways of PM2.5 and PM10 over Indo Gangetic Plain of India
(Elsevier B.V., 2021) Srishti Jain; Sudhir Kumar Sharma; Manoj K. Srivastava; Abhijit Chatterjee; Narayanswami Vijayan; S. Swarupa Tripathy; K. Maharaj Kumari; Tuhin Kumar Mandal; Chhemendra Sharma
The present work depicts the spatial and temporal variations in chemical characteristics and sources of PM2.5 and PM10 over Indo Gangetic Plain (IGP) of India from January 2015 to December 2016. PM2.5 and PM10 samples were collected at three typical urban sites of Delhi, Varanasi, and Kolkata of IGP, India and characterized to evaluate their chemical components. The average concentrations of PM2.5 at Delhi, Varanasi, and Kolkata were 135 ± 64, 99 ± 33, and 116 ± 38 μg m−3, respectively. Whereas the average concentrations of PM10 over Delhi, Varanasi, and Kolkata were 242 ± 95, 257 ± 90, and 179 ± 77 μg m−3, respectively. Source apportionment was carried out using the three receptor models i.e. Principal Component Analysis-Absolute Principal Component Score (PCA-APCS), UNMIX, and Positive Matrix Factorization (PMF), implemented on the same data sets to obtain the conjointly validated results. All the models identified that vehicular emissions, secondary aerosols, biomass burning, and soil dust were the dominant sources of PM2.5 and PM10 over IGP, India. Hybrid receptor models revealed the presence of strong local emission sources as well as traversing of pollutants from the parts of Pakistan, Punjab, Haryana, Rajasthan, Uttar Pradesh, Bihar, and Bangladesh. © 2021 Elsevier B.V.
Diurnal and seasonal variations of black carbon and PM2.5 over New Delhi, India: Influence of meteorology
(2013) S. Tiwari; A.K. Srivastava; D.S. Bisht; P. Parmita; Manoj K. Srivastava; S.D. Attri
Black carbon (BC), which is one of the highly absorbing capacities of solar radiation, reduces albedo of atmospheric aerosol. BC along with fine particulate matters (PM2.5), which play crucial role in climate and health, was monitored online for an entire year of 2011 at an urban megacity of Delhi, situated in the northern part of India. Daily mass concentration of BC varies from 0.9 to 25.5μgm-3, with an annual mean of 6.7±5.7μgm-3 displayed clear monsoon minima and winter maxima; however, PM2.5 concentration was ranging from 54.3 to 338.7μgm-3, with an annual mean of 122.3±90.7μgm-3. BC typically peaked between 0800 and 1000 LST and again between 2100 and 2300 LST, corresponding to the morning and evening traffic combined with the ambient meteorological effect. During summer and monsoon, the BC concentrations were found less than 5μgm-3; however, the highest concentrations occurred during winter in segments from <5 to >10μgm-3. In over all study, the BC mass concentration was accounted for ~6% of the total PM2.5 mass, with a range from 1.0% to 14.3%. The relationship between meteorological parameters and BC mass concentrations was studied and a clear inverse relationship (r=-0.53) between BC and wind speed was observed. Relation between visibility and BC mass concentrations was also significantly negative (-0.81), having relatively higher correlation during post-monsoon (-0.85) and winter (-0.78) periods and lower during summer (-0.45) and monsoon (-0.54) periods. The mixed layer depths (MLDs) were found to be shallower during post monsoon (379m) and winter (335m) as compared during summer (1023m) and monsoon (603m). The study indicated that during post-monsoon season, the impact of biomass burning is higher as compared to combustion of fossil fuels. Results are well associated with the rapid growth of anthropogenic emissions and ambient meteorological conditions over the station. © 2013 Elsevier B.V.
Diurnal Variation of Rain Drop Size Distribution over the Western Ghats of India
(National Institute of Science Communication and Policy Research, 2024) Amit Kumar; A.K. Srivastava; K. Chakravarty; Manoj K. Srivastava
Joss-Waldvogel Disdrometer (JWD) measurements at the High-Altitude Cloud Physics Laboratory (HACPL: 17.56°N, 73.4°E, above 1373 m MSL), Mahabaleshwar were investigated for determining the diurnality of the drop size distribution (DSD) associated with the precipitation characteristics over the Western Ghats of India. The JWD data for the period from 2015 to 2019 were collected and examined during the Indian Summer Monsoon (ISM) season. The number concentration of rain droplets of various diameters is considerably varying with the rain rate (R) and type of precipitating cloud. With increasing the value of R, rain droplets having larger diameter concentration significantly increases, and the distribution tail moves towards the biggest droplets. The average value of reflectivity (Z), R, liquid water content (LWC), mass-weighted mean diameter (Dm), and normalized intercept parameter (log10Nw) was found to be higher for the heavy rainfall (Rhigh ≥10 mm h-1) as compared to the low rainfall (Rlow < 10 mm h-1) during the entire study period. The gamma distribution of DSD shows significant differences during the low and heavy precipitation on different time periods (e.g., 00-06, 06-12, 12-18, 18-23 LST). The number of rain events contributing to the total accumulated rain varies with time. The maximum number of rain events occurred during 12-18 LST, with 23.6 % rain events of low rainfall and 4.9% of heavy rainfall. The bimodality is observed in the diurnal variation of Dm, R, and Z, with the largest peak recorded in the late afternoon hour (13-16 LST) and the second crest in the early morning hour (05 LST). At the same time, the log10Nw value drops down, indicating the lowest concentration of rain droplets. © 2024 National Institute of Science Communication and Policy Research. All rights reserved.
Floods and hazardous heavy rainfall in India: Comparison between local versus oceanic impact
(Association of Agrometeorologists, 2010) S.N. Pandey; R. Bhatla; R.K. Mall; Manoj K. Srivastava
Generally, during the south-west monsoon season, several severe/ extreme weather systems form over India, leading to heavy rainfall. Such heavy rainfall result in floods for wider region of northern India, and, which, finally, causes loss of agriculture, human and animal's life, outbreak of diseases/ epidemics, and thus affecting national economy. An attempt has therefore, been made to analyze the disastrous events that occurred in the summer monsoon months over different states in India for the period 1981-2000. The analyses included the raining event which were active, but, caused due to- or without the monsoonal-systems that were formed in north Indian Ocean. Results showed that West Bengal was the mostly affected state during monsoon season, where both, local as well as monsoonal systems were equally responsible for heavy rainfall/flood events. The local atmospheric phenomenon affected highly to Uttar Pradesh, West Bengal, Gujarat, and Maharashtra, whereas for systems that were associated with the north Indian Ocean and Bay of Bengal, the states of West Bengal and Orissa were the mostly affected states. From the study, it may be concluded that all the heavy rainfall related disastrous weather events formed over different states in India was not only due to systems developed over Oceans, rather, local atmospheric phenomena had equally important contributor of similar affects, particularly for northern and western India.
Implications of different aerosol species to direct radiative forcing and atmospheric heating rate
(Elsevier Ltd, 2020) A.K. Srivastava; Bharat Ji Mehrotra; Abhishek Singh; V. Singh; D.S. Bisht; S. Tiwari; Manoj K. Srivastava
The optical and radiative characteristics of water-soluble and carbonaceous aerosol species in the PM2.5 samples were examined for a representative megacity over the Indo-Gangetic Basin (IGB). Aerosol optical and radiative transfer models were used to extract sulphate (SO4), nitrate (NO3), organic carbon (OC) and elemental carbon (EC) from the observations done in 2012. Initial results suggest that the mass concentration of OC dominated over other species, but impacts on optical characteristics were mostly due to the SO4 aerosols. Further, EC shows relatively large impact on radiative forcing. The aerosol optical depth (AOD) at 500 nm for SO4, NO3, EC and OC was found to be contributing ~36%, 20%, 27% and 9%, respectively in the total AOD value (0.61 ± 0.18) during the entire study period. The single scattering albedo (SSA) for SO4 and NO3 was high and suggested their scattering nature; however, being the highly absorbing species, EC was found to show the lowest values of SSA during the study period. SSA for OC was, however, ~0.70, which was found to show the second highest warming species in the atmosphere with contribution of ~10%, after EC, which caused the highest warming (~70%), to the total atmospheric forcing. © 2020 Elsevier Ltd
Influence of aerosol on clouds over the Indo-Gangetic Plain, India
(2013) D.M. Lal; S.D. Patil; H.N. Singh; Sachin D. Ghude; S. Tiwari; Manoj K. Srivastava
Using Total Ozone Mapping Spectrometer Aerosol Index (AI) and NCEP/NCAR reanalysis clouds data for the period 1979-1992, the influence of aerosol on the clouds (low and high cloud cover) over the Indo-Gangetic Plain (IGP) in India has been brought out for the first time in the present study. AI shows increasing tendency over the IGP suggesting that aerosol loading over this region increased significantly during the study period. In our analysis, High Cloud Cover (HCC) shows increasing trend and Low Cloud Cover (LCC) shows decreasing trend over the IGP during the same period. During pre-monsoon season when aerosol loading is more, HCC increases in positive correlation with AI. On the other hand, LCC show decreasing trend and is anti-correlated with AI. During summer monsoon, aerosol shows increasing trend but their effect on HCC and LCC is not seen to be significant. Similarly, the role of humidity on aerosol induced changes in HCC and LCC over the IGP region was also analyzed. In the low to moderate humid areas of IGP region (western and middle IGP), increasing AI leads to increase in HCC and decrease in LCC. On the other hand, in high humid areas (eastern IGP), increase in AI does not show any significant effect on HCC, but LCC shows positive trend. Therefore, we strongly argue that increasing aerosol loading enhances Cloud Condensation Nuclei over the region which in turn, alters the microphysical properties of clouds by reducing the size of cloud droplets, and atmospheric humidity controls the aerosol effect on clouds. During the recent period (2005-2010), similar features have also been observed over the IGP region. © 2013 Springer-Verlag Berlin Heidelberg.
Land surface layer characteristics during monsoon at a tropical station
(Birkhauser Verlag AG, 1997) D.V. Viswanadham; A.N.V. Satyanarayana; Manoj K. Srivastava
The atmospheric surface layer over land may behave differently in the tropics, particularly during the monsoon. A preliminary attempt is made to observe the behavior of surface layer characteristics such as fluxes of momentum, sensible heat and latent heat, friction velocity, friction temperature, M-O length scale, Richardson number and Bowen's ratio over Kharagpur (22°20′N. 87°18′E). a typical moist tropical station. The diurnal and day-to-day variations have been studied It is observed that during the active phase of the monsoon the sensible heat flux and Bowen's ratio are low. The diurnal variation is apparent for most parameters. Mostly near neutral conditions are observed.
Lightning and precipitation: The possible electrical modification of observed raindrop size distributions
(Elsevier Ltd, 2021) Dipjyoti Mudiar; S.D. Pawar; Anupam Hazra; V. Gopalkrishnan; D.M. Lal; Kaustav Chakravarty; Manoj A. Domkawale; Manoj K. Srivastava; B.N. Goswami; Earle Williams
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
Lightning Characteristics Over Humid Regions and Arid Regions and Their Association With Aerosols Over Northern India
(Birkhauser, 2022) S.P. Jnanesh; D.M. Lal; V. Gopalakrishnan; Sachin D. Ghude; Sunil D. Pawar; S. Tiwari; Manoj K. Srivastava
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.
Linkage of water vapor distribution in the lower stratosphere to organized Asian summer monsoon convection
(Springer Science and Business Media Deutschland GmbH, 2021) Bhupendra Bahadur Singh; Raghavan Krishnan; D.C. Ayantika; Ramesh K. Vellore; T.P. Sabin; K. Ravi Kumar; Simone Brunamonti; Sreeharsha Hanumanthu; Teresa Jorge; Peter Oelsner; Sunil Sonbawne; Manish Naja; Suvarna Fadnavis; Thomas Peter; Manoj K. Srivastava
Accumulation of water vapor in the upper troposphere/lower stratosphere (UT/LS) over the Asian continent is a recognized feature during the boreal summer monsoon. While there has been a debate on the role of monsoon convective intensities on the UT/LS water vapor accumulations, there are ambiguities with regard to the effects of organized monsoon convection on the spatial distribution of water vapor. We provide insights into this aspect using high precision balloon measurements of water vapor from a high-elevation site Nainital (29.4° N, 79.5° E), India, located in the Himalayan foothills and satellite retrievals of water vapor from the Microwave Limb Sounder (MLS). We also use precipitation estimates from the Tropical Rainfall Measuring Mission (TRMM) satellite (i.e., merged product 3B42 and precipitation radar 3A25 estimates of rain rate and rain type viz convective/stratiform), reanalysis circulation data, as well as numerical model simulations. We first evaluate the MLS estimates of water vapor mixing ratios with in situ high precision hygrometer balloon observations over Nainital. It is seen from our analyses of the MLS data that the LS water vapor distribution is closely linked to the organization of the South Asian monsoon convection and its influence on the UT/LS circulation. This link between LS water vapor distribution and organized monsoon convection is also captured in the in situ observations on 3 August 2016. It is evidenced that periods of organized summer monsoon convective activity over the Indian subcontinent and Bay of Bengal promote divergence of water vapor flux in the UT/LS; additionally the Tibetan anticyclonic circulation causes widespread distribution of the UT/LS water vapor. In addition to the effects of Asian monsoon convection, we also note that global climate drivers such as El Niño-Southern Oscillation (ENSO), Brewer–Dobson circulation (BDC), and Quasi-Biennial Oscillation (QBO) can contribute to nearly 38% of the UT/LS water vapor variability over the Asian monsoon region. The main result of our study indicates that widespread spatial distribution and accumulation of water vapor in the LS (about 80% of total accumulation between May and August months) tend to co-occur with organized monsoon convection, intensified divergence of water vapor flux in the UT/LS and intensified Tibetan anticyclone. On the other hand, the circulation response and LS water vapor distribution to pre-monsoon localized deep convection tend to have a limited spatial scale confined to Southeast Asia. Results from model experiments suggest that the UT/LS circulation pattern to organized monsoon convection has resemblance to stationary Rossby waves forced by organized latent heating, with the westward extending response larger by about 15° longitudes as compared to that of the pre-monsoon localized deep convection. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Long-term Seasonal Characteristics of Raindrop Microphysics During Different Rain Events Over the Western Ghats of India
(Birkhauser, 2022) Amit Kumar; A.K. Srivastava; K. Chakravarty; Manoj K. Srivastava
The microphysics behind the formation of rain droplets is an important feature influencing orographic precipitation at any location. The raindrop microphysics were determined for the precipitation in Mahabaleshwar, the orographic region of the Western Ghats in the Indian subcontinent, using Joss–Waldvogel Disdrometer (JWD) observational data for the period from 2013 to 2019. Smaller (< 1 mm) rain droplets were found to be dominant in monsoon seasons, while in the pre-monsoon and post-monsoon, a higher concentration of medium-sized (1–3 mm) and larger (> 3 mm) rain droplets were observed. In each season, the peak rain droplet concentration moved toward giant rain droplets with increasing rain rate. The probability density function of mass-weighted mean diameter (Dm), normalized-intercept parameter (log10Nw), rain rate (log10R), liquid water content (log10W), shape parameter (µ), and slope parameter (Λ) indicate a clear distinction in all three seasons. High Dm and lower log10Nw mean values were observed during the convective precipitation, while the opposite was observed during the stratiform rainfall of each season, except for the post-monsoon convective precipitation. Monsoon rainfall of both convective and stratiform nature had the lowest Dm and highest log10Nw compared to the respective cloud structure of pre-monsoon and post-monsoon. The Dm and log10Nw values in post-monsoon stratiform rain lay between the values observed in the monsoon and post-monsoon seasons. At the same time, the convective precipitation in the post-monsoon had the highest Dm value, with a larger log10Nw than the pre-monsoon convective precipitation. A unique µ-Λ quadratic equation was also determined for the pre-monsoon, monsoon, and post-monsoon season rain events. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
Long-Term Trend in Black Carbon Mass Concentration Over Central Indo-Gangetic Plain Location: Understanding the Implied Change in Radiative Forcing
(John Wiley and Sons Inc, 2024) Bharat Ji Mehrotra; Atul K. Srivastava; Amarendra Singh; Dirgha Parashar; Nabankur Majumder; R.S. Singh; Arti Choudhary; Manoj K. Srivastava
For the first-time, analysis of a decade long measurement of Black Carbon mass concentration (BC) was carried out at a representative central Indo-Gangetic Plain (IGP) location, Varanasi (25.30°N, 83.03°E, 79 m asl), from 2009 to 2021 to understand its physical, optical, and radiative impacts. During the 13-year study period, the daily BC mass concentration was found to vary between 0.07 and 46.23 μg m−3 (mean 9.18 ± 6.53 μg m−3) and showed a strong inter-annual and intra-annual variations. The inter-annual variability of BC showed a significant decreasing trend (−0.47 μg m−3 yr−1), with a maximum during the post-monsoon (−1.86 μg m−3 yr−1) and minimum during the pre-monsoon season (−0.31 μg m−3 yr−1). The Black Carbon Aerosol Radiative Forcing (BC-ARF) at the top of the atmosphere (BC-ARFT), surface (BC-ARFS), and within the atmosphere (BC-ARFA) was found to be 10.3 ± 6.4, −30.1 ± 18.9, and 40.5 ± 25.2 W m−2, respectively. BC-ARF also showed a strong inter-annual variability with a decreasing trend for BC-ARFT (−0.47 W m−2 yr−1) and BC-ARFA (−1.94 W m−2 yr−1), while it showed an increasing trend for BC-ARFS (1.33 W m−2 yr−1). Concentrated weighted trajectories (CWT) and potential source contribution function (PSCF) analyses were performed at the station to determine the potential source sectors and transport routes of BC aerosols. These analyses revealed that the long-range source of BC at Varanasi originates from the upper and lower IGP, central highlands, southern peninsular region, Pakistan, and even from the Central East Asia region. © 2024. American Geophysical Union. All Rights Reserved.
Meteorological, atmospheric and climatic perturbations during major dust storms over Indo-Gangetic Basin
(Elsevier, 2015) Sarvan Kumar; Sanjay Kumar; D.G. Kaskaoutis; Ramesh P. Singh; Rajeev K. Singh; Amit K. Mishra; Manoj K. Srivastava; Abhay K. Singh
During the pre-monsoon season (April-June), the Indo-Gangetic Basin (IGB) suffers from frequent and intense dust storms originated from the arid and desert regions of southwest Asia (Iran, Afghanistan), Arabia and Thar desert blanketing IGB and Himalayan foothills. The present study examines the columnar and vertical aerosol characteristics and estimates the shortwave (0.25-4.0μm) aerosol radiative forcing (ARF) and atmospheric heating rates over Kanpur, central IGB, during three intense dust-storm events in the pre-monsoon season of 2010. MODIS images, meteorological and AERONET observations clearly show that all the dust storms either originated from the Thar desert or transported over, under favorable meteorological conditions (low pressure and strong surface winds) affecting nearly the whole IGB and modifying the aerosol loading and characteristics (Ångström exponent, single scattering albedo, size distribution and refractive index). CALIPSO observations reveal the presence of high-altitude (up to 3-5km) dust plumes that strongly modify the vertical aerosol profile and are transported over Himalayan foothills with serious climate implications (atmospheric warming, enhanced melting of glaciers). Shortwave ARF calculations over Kanpur using SBDART model show large negative forcing values at the surface (-93.27, -101.60 and -66.71Wm-2) during the intense dusty days, associated with planetary (top of atmosphere) cooling (-18.16, -40.95, -29.58Wm-2) and significant atmospheric heating (75.11, 60.65, 37.13Wm-2), which is translated to average heating rates of 1.57, 1.41 and 0.78Kday-1, respectively in the lower atmosphere (below ~3.5km). The ARF estimates are in satisfactory agreement with the AERONET ARF retrievals over Kanpur. © 2015 Elsevier B.V.