Browsing by Author "M.K. Srivastava"

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Aerosol characteristics at a rural station in southern peninsular India during CAIPEEX-IGOC: physical and chemical properties
(Springer Verlag, 2015) D.S. Bisht; A.K. Srivastava; A.S. Pipal; M.K. Srivastava; A.K. Pandey; S. Tiwari; G. Pandithurai
To understand the boundary layer characteristics and pathways of aerosol–cloud interaction, an Integrated Ground Observational Campaign, concurrent with Cloud Aerosol Interaction and Precipitation Enhancement Experiment, was conducted by the Indian Institute of Tropical Meteorology, Pune, under Ministry of Earth Sciences at Mahabubnagar (a rural environment, which is ~100 km away from an urban city Hyderabad in Andhra Pradesh), during the period of July–November 2011. Collected samples of PM2.5 and PM10 were analyzed for water-soluble ionic species along with organic carbon (OC) and elemental carbon (EC). During study period, the average mass concentrations of PM2.5 and PM10 were about 50(±10) and 69(±14) μg m−3, respectively, which are significantly higher than the prescribed Indian National Ambient Air Quality Standards values. The chemical species such as sum of anions and cations from measured chemical constituents were contributed to be 31.27 and 38.49 % in PM2.5 and 6.35 and 5.65 % to the PM10, whereas carbonaceous species contributed ~17.3 and 20.47 % for OC and ~3.0 and 3.10 % for EC, respectively. The average ratio of PM2.5/PM10 during study period was ~0.73(±0.2), indicating that the dominance of fine size particles. Carbonaceous analysis results showed that the average concentration of OC was 14 and 8.7 μg m−3, while EC was 2.1 and 1.5 μg m−3 for PM10 and PM2.5, respectively. The ratios between OC and EC were estimated, which were 6.6 and 5.7 for PM10 and PM2.5, suggesting the presence of secondary organic aerosol. Total carbonaceous aerosol accounts 23 % of PM10 in which the contribution of OC is 20 % and EC is 3 %, while 20 % of PM2.5 mass in which the contribution of OC is 17 % and EC is 3 %. Out of the total aerosols mass, water-soluble constituents contributed an average of 45 % in PM10 and 38 % in PM2.5 including about 39 % anions and 6 % cations in PM10, while 31 % anions and 7 % cations in PM2.5 aerosol mass collectively at study site. © 2014, Springer-Verlag Berlin Heidelberg.
Aerosol chemical characterization and role of carbonaceous aerosol on radiative effect over Varanasi in central Indo-Gangetic Plain
(Elsevier Ltd, 2016) S. Tiwari; U.C. Dumka; D.G. Kaskaoutis; Kirpa Ram; A.S. Panicker; M.K. Srivastava; Shani Tiwari; S.D. Attri; V.K. Soni; A.K. Pandey
This study investigates the chemical composition of PM10 aerosols at Varanasi, in the central Indo-Gangetic Plain (IGP) during April to July 2011, with emphasis on examining the contribution of elemental carbon (EC) to the estimates of direct aerosol radiative effect (DARE). PM10 samples are analysed for carbonaceous aerosols (Organic Carbon, OC and EC) and water-soluble ionic species (WSIS: Cl-, SO42-, NO3-, PO42- NH4+, Na+, K+, Mg2+ and Ca2+) and several diagnostic ratios (OC/EC, K+/EC, etc) have been also used for studying the aerosol sources at Varanasi. PM10 mass concentration varies between 53 and 310 μgm-3 (mean of 168 ± 73 μgm-3), which is much higher than the National and International air quality standards. The OC mass concentration varies from 6 μg m-3 to 24 μg m-3 (mean of 12 ± 5 μg m-3; 7% of PM10 mass), whereas EC ranges between 1.0 and 14.3 μg m-3 (4.4 ± 3.9 μg m-3; ~3% of PM10 mass). The relative low OC/EC of 3.9 ± 2.0 and strong correlation (R2 = 0.82) between them suggest the dominance of primary carbonaceous aerosols. The contribution of WSIS to PM10 is found to be ~12%, out of which ~57% and 43% are anions and cations, respectively. The composite DARE estimates via SBDART model reveal significant radiative effect and atmospheric heating rates (0.9-2.3 Kday-1). Although the EC contributes only ~3% to the PM10 mass, its contribution to the surface and atmospheric forcing is significantly high (37-63% and 54-77%, respectively), thus playing a major role in climate implications over Varanasi. © 2015 Elsevier Ltd.
Aerosol optical properties over delhi and manora peak during a rare dust event in early april 2005
(Taylor and Francis Ltd., 2011) S.K. Srivastava; M.K. Srivastava; A. Saha; S. Tiwari; S. Singh; U.C. Dumka; B.P. Singh; N.P. Singh
Dust storm events are annual phenomena observed over the Indo-Gangetic plain (IGP) during the pre-monsoon period (May-June). These dust storms affect the air quality, weather conditions and radiation budget of the region. In this paper we characterize the aerosol optical parameters associated with a rare dust storm event that hit the IGP during early April 2005. This event was considered rare as it occurred much earlier than the general occurrence of dust storms in India (May-June), and in the year 2005, the warmest year in the span of the previous hundred years. In this study we considered the optical aerosol parameters for two places in the IGP: Delhi (28.5° N, 77.2° E, 325 m asl) and the high altitude station, Manora Peak (29.4° N, 79.5° E, 1958 m asl). Of the two selected stations, Delhi represents a highly populated and polluted location whereas Manora Peak represents a cleaner location in the central Himalayan region. During this dust storm event, the aerosol optical depth (AOD) was observed to increase considerably. The increment was 2.6-4.6 times over Delhi and 1.6-3.2 times over Manora Peak at wavelengths 380 and 1020 nm, respectively, with respect to the background values, whereas the Ångström exponent (α) for both the stations remained close to zero during the event. The effect shows a considerable increase in direct dust radiative forcing in terms of a reduction in the broadband global irradiance for Delhi as well as for Manora Peak stations. The direct aerosol radiative forcing thus obtained was about 34% in the 400-1100 nm wavelength band at Manora Peak. © 2011 Taylor & Francis.
AFM and electronic transport studies of swift heavy ion irradiated Mn/p-Si bilayer structure
(Elsevier, 2008) P.C. Srivastava; M.K. Srivastava; P.S. Pandey
Mn/p-Si structures have been realised by electron beam evaporation of manganese on etched and cleaned p-Si wafers. Bilayer structures have been irradiated by swift heavy ions (of 100 MeV Fe7+ having a fluence of 1 × 1013 ions/cm2). The electronic transport features across the bilayer of the structure (i.e. I-V characteristics across the Mn/p-Si interface) show a significant increase of current (by two orders of magnitude) for the irradiated ones as compared to un-irradiated ones. I-V characteristics across the interface has also been recorded in presence of in-plane (i.e., along the plane of the interface) magnetic field which show a significant magnetic field sensitivity for the irradiated ones. The surface morphological studies from AFM show a granular structure with open face having micro-particles in it, prior to the irradiation and round shaped embedded granular structure after the irradiation. XRD data show the formation of manganese silicide (Mn5Si2). The results are understood in the realm of interfacial intermixing which is tailored by the swift heavy ion irradiation. © 2008 Elsevier B.V. All rights reserved.
Chemical characterization of rainwater at a high-altitude site “Nainital” in the central Himalayas, India
(Springer Verlag, 2017) Deewan Singh Bisht; A.K. Srivastava; H. Joshi; K. Ram; N. Singh; M. Naja; M.K. Srivastava; S. Tiwari
The present study investigates the chemical composition of rainwater (RW) from a high-altitude site “Nainital” (1958 m above msl) in the central Himalaya region, to understand the influence of local, regional, and long-range transport of pollutants. A total of 55 (2 in pre-monsoon and 53 in monsoon) RW samples were collected during the study period (June–September 2012) and were analyzed for major anions and cations using an ion chromatograph. The pH of precipitation events ranged from 4.95 to 6.50 (average 5.6 ± 0.3) was observed during the monsoon period (near to the acidic), whereas during the pre-monsoon, the pH was 6.25 ± 0.49 (alkaline) over the study region; it is due the mixture of anthropogenic as well as the natural chemical constituents. The average ionic concentration (sum of measured chemical constituents) was ∼3 times higher during the pre-monsoon (986 ± 101 μeq/1) compared to that in the monsoon season (373 ± 37 μeq/1). This is mainly due to the presence of more natural aerosols in the pre-monsoon season which is also reflected in the pH of rainwater (average 6.25 ± 0.50) as well as ionic concentration. The chemical composition suggests that Ca2+ was the major contributor (34%) among cations, followed by Na+ (10%), K+ (8%), and Mg2+ (9%), whereas Cl−, NO3 −, and SO4 2− contributed ∼13, 11, and 9%, respectively, among anions. The average ratio of acidic species (SO4 2−/NO3 −) is 1.56, suggesting 61 and 39% contribution of SO4 2− and NO3 −, respectively, which is very close to the estimated contribution of H2SO4 (60–70%) and HNO3 (30–40%) in the precipitation samples. Neutralization factors for Ca2+, Mg2+, and NH4 + in RW at Nainital are 4.94, 1.21, and 0.37, respectively, indicating their crucial role in neutralization of acidic species. The non-sea-salt (NSS) contribution to total Ca2+, K+, and Mg2+ is estimated to be ∼98, 97, and 74%, respectively, suggesting the dominance of crustal sources for cations. In contrast, the NSS contribution to the total Cl− and SO4 2− is 16 and 69% indicating their anthropogenic origin, respectively. Principle component analysis also suggests that the first factor (i.e., natural sources, mainly dust, and sea-salts) accounts for ∼33% variance, whereas the second factor (i.e., fossil fuel and biomass burning) accounts for ∼18% variance of the measured ionic composition. The remaining contributions are attributed to the mixed emission sources and transport of pollutants from Indo-Gangetic Plain (IGP) and western parts of India. The results of the present study reveal a significant contribution of crustal and anthropogenic sources in the RW and neutralization processes in the central Himalaya. © 2016, Springer-Verlag Berlin Heidelberg.
Comparison of neural networks techniques to predict subsurface parameters based on seismic inversion: a machine learning approach
(Springer Science and Business Media Deutschland GmbH, 2024) Nitin Verma; S.P. Maurya; Ravi kant; K.H. Singh; Raghav Singh; A.P. Singh; G. Hema; M.K. Srivastava; Alok K. Tiwari; P.K. Kushwaha; Richa Singh
Seismic inversion, complemented by machine learning algorithms, significantly improves the accuracy and efficiency of subsurface parameter estimation from seismic data. In this comprehensive study, a comparative analysis of machine learning techniques is conducted to predict subsurface parameters within the inter-well region. The objective involves employing three separate machine learning algorithms namely Probabilistic Neural Network (PNN), multilayer feedforward neural network (MLFNN), and Radial Basis Function Neural Network (RBFNN). The study commences by generating synthetic data, which is then subjected to machine learning techniques for inversion into subsurface parameters. The results unveil exceptionally detailed subsurface information across various methods. Subsequently, these algorithms are applied to real data from the Blackfoot field in Canada to predict porosity, density, and P-wave velocity within the inter-well region. The inverted results exhibit a remarkable alignment with well-log parameters, achieving an average correlation of 0.75, 0.77, and 0.86 for MLFNN, RBFNN, and PNN algorithms, respectively. The inverted volumes portray a consistent pattern of impedance variations spanning 7000–18000 m/s*g/cc, porosity ranging from 5 to 20%, and density within the range of 1.9–2.9 g/cc across the region. Importantly, all these methods yield mutually corroborative results, with PNN displaying a slight edge in estimation precision. Additionally, the interpretation of the inverted findings highlights anomalous zones characterized by low impedance, low density, and high porosity, seamlessly aligning with well-log data and being identified as sand channel. This study underscores the potential for seismic inversion, driven by machine learning techniques, to swiftly and cost-effectively determine critical subsurface parameters like acoustic impedance and porosity. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
High concentration of acidic species in rainwater at Varanasi in the Indo-Gangetic Plains, India
(Kluwer Academic Publishers, 2015) D.S. Bisht; S. Tiwari; A.K. Srivastava; J.V. Singh; B.P. Singh; M.K. Srivastava
The Indo-Gangetic Plains (IGP), straddling the northeastern parts of India near the foothills of the Himalayas, are one of the most densely populated and polluted regions on the globe, with consequent large anthropogenic emissions. In particular, the use of traditional biofuels in the rural areas along the plains leads to strong emissions of various pollutants. Due to this importance, a comprehensive study on the chemical characteristics of rainwater was carried out during southwest summer monsoon season of 2009 at two different locations over Varanasi, India, located in the middle of IGP region in the eastern part of Uttar Pradesh. The rainwater samples were analyzed for major chemical constituents along with pH and its electric conductivity. The pH values ranged from 5.18 to 7.08 with a mean of 5.82 ± 0.45 suggest the alkaline nature of rainwater over Varanasi. During the study period, ~14 % rainwater samples were found to be acidic when the winds blew from south–southeast direction. The weighted mean pH and electric conductivity were found higher (5.92 ± 0.45) and (24.59 µS/cm) at Maldahiya site than Banaras Hindu University (5.89 ± 0.46) and (17.16 µS/cm) due to dominance of soil-derived particles. The equivalent concentration of ionic species is of the order: Ca2+ > SO4 2− > NO3 − > Cl− > Mg2+ > Na+ > HCO3 − > NH4 + > K+ > F− > H+. The weighted mean concentration of dominant ions in rainwater over Varanasi was Ca2+ (67.1 ± 56 µeq/l), SO4 2− (37 ± 23 µeq/l) and NO3 − (27.1 ± 28 µeq/l). Significant correlation (r = 0.81; P < 0.001) between the sum of major cations (NH4 + + Ca2+ + Mg2+) and the sum of acidic species (SO4 2− + NO3 −) corroborates that these alkaline species may act as a neutralizing agent for the acidity of rainwater. The source contribution of SO4 2− in rainwater was estimated and was ~95 % by man-made activities, which is mainly derived from burning of fossil/biofuels over this region. The source of nitrate (11 %) emissions was mainly from automobiles and biomass burning. Statistical analysis such as principle component analysis was performed to find out possible sources of measured ions. First factor accounted for ~54 % variance suggested that most of the ions were from natural sources especially soil dust and sea; however, factor 2 accounted only for ~12 % variance suggests their sources from burning of fossil fuel and biomass. The third factor also indicates the mixed sources into the atmosphere. © 2014, Springer Science+Business Media Dordrecht.
Impacts of the high loadings of primary and secondary aerosols on light extinction at Delhi during wintertime
(Elsevier Ltd, 2014) S. Tiwari; A.K. Srivastava; D.M. Chate; P.D. Safai; D.S. Bisht; M.K. Srivastava; G. Beig
High emissions of anthropogenic aerosols over Indo-Gangetic Plain (IGP) inspired continuous measurements of fine particles (PM2.5), carbonaceous aerosols (BC, OC and EC), oxides of nitrogen (NOx) and estimation of light extinction (bext) and absorption (babs) coefficients over Delhi during high pollution season in winter from December 2011 to March 2012. During study period, the mass concentrations of PM2.5, BC and NOx were 186.5±149.7μgm-3, 9.6±8.5μgm-3 and 23.8±16.1ppb, respectively. The mass concentrations of OC and EC were studied by two different techniques (i) off-line (gravimetric method) and (ii) semi-continuous (optical method) and their mean mass concentrations were 51.1±15.2, 10.4±5.5μgm-3 and 33.8±27.7, 8.2±6.2μgm-3, respectively during the study period. The ratios of mass concentration of OC to EC in both cases were in between 4 and 5. The source contribution of carbonaceous aerosols in PM2.5 estimated over 24hrs, during day- and night-time where motor vehicles accounted for ~69%, 90% and 61% whereas coal combustion accounted for ~31%, 10% and 39%, respectively. The estimated mean values of bext and babs over the station were 700.0±268.6 and 71.7±54.6Mm-1, respectively. In day and night analysis, bext is ~37% higher during night-time (863.4Mm-1) than in day-time (544.5Mm-1). Regression analysis between bext and visibility showed significant negative correlation (r=-0.85). The largest contribution in the light extinction coefficients was found to be due to organic carbon (~46%), followed by elemental carbon (~24%), coarse mode particles (~18%), ammonium sulfate (~8%) and ammonium nitrate (~4%). The individual analysis of light extinction due to chemical species and coarse mode particles indicates that scattering type aerosols dominated by ~76% over the absorbing type. The aforementioned results suggest that the policy-induced control measures at local administration level are needed to mitigate the excess emissions of carbonaceous aerosols over IGP region which ranks highest in India and elsewhere in worldwide. © 2014.
Integrated thin layer classification and reservoir characterization using sparse layer reflectivity inversion and radial basis function neural network: a case study
(Springer Science and Business Media B.V., 2024) Raghav Singh; Aditya Srivastava; Ravi Kant; S.P. Maurya; P. Mahadasu; Nitin Verma; G. Hema; P.K. Kushwaha; Richa; K.H. Singh; Ajay P. Singh; M.K. Srivastava; Piyush Sarkar
Understanding subterranean reservoirs, geological characteristics, fluid composition, and hydrocarbon potential strongly relies on precise reservoir characterization. Seismic inversion is a key method in reservoir characterization to approximate the acoustic impedance and porosity of underlying rock formations using seismic and well-log data. A sparse layer reflectivity (SLR) post-stack inversion method approach is used in this study to make thin layers more visible. To generate an impedance volume, it uses a predetermined wavelet library, an objective function, and a regularization parameter, the regularization parameter is a tunable parameter used to control the balance between fitting the data closely (minimizing the misfit) and ensuring a smooth and stable model for and sparseness computed coefficients. This study uses Blackfoot data to estimate the density, velocity, impedance, and porosity of a particular region using the SLR and Radial Basis Function Neural Network (RBFNN). According to the interpretation of the impedance section, a low impedance anomaly zone with an impedance range of (8500–9000) m/s*g/cc is present at a time of (1040–1065) ms. The low impedance zone is classified as a clastic glauconitic sand channel (reservoir zone) based on the correlation between seismic and borehole data. Further, a Radial Basis Function Neural Network (RBFNN) has been applied to the data to estimate porosity volume and to conduct a more thorough examination of the reservoir zone and cross-validate inverted results. The research demonstrates that the high porosity zone, low velocity, and density zone are discovered by the RBFNN technique, and the low impedance zone interpreted in inversion findings are correlating, which confirms the existence of the glauconitic sand channel. This research is crucial for understanding how well SLR, RBFNN, and multi-attribute analysis work to define sand channels. © 2024, The Author(s), under exclusive licence to Springer Nature B.V.
Irradiation induced modifications in magnetic property of Mn/n-Si structure
(Institute of Physics Publishing, 2011) M.K. Srivastava; P.S. Pandey; P.C. Srivastava
Mn films of ∼50 nm were deposited on n-Si (100) substrates by electron beam evaporation technique. The Mn/n-Si structures were irradiated from swift heavy ions with a fluence of 1×1013 ions/cm2. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry and vibrating sample magnetometer facilities. It has been found that surfacial/interfacial granular magnetic silicide phases (of MnxSiy) are formed before and after the irradiation with irradiation induced modifications of surface morphology and magnetic property. The surface roughness has been found to decrease on the irradiation from the atomic force microscopy data. From the X-ray diffraction data, it has been found that after the irradiation MnSi is formed in addition to Mn 5Si2 as compared to unirradiated ones. The magnetization characteristics show that the magnetic parameters such as coercivity, saturation magnetization, remanance and squareness have decreased on the irradiation for in-plane orientation whereas coercivity and remanance is increased after the irradiation for out of plane orientation. The increase of remanance shows the presence of strong exchange coupling in the structure after the irradiation. © Published under licence by IOP Publishing Ltd.
Irradiation induced modifications in microstructural and magnetic property of Fe 50Ni 50 (permalloy)/Si interfacial structure
(2014) P.C. Srivastava; P.S. Pandey; Neelabh Srivastava; M.K. Srivastava
The interfacial structures of Fe50Ni50/Si have been prepared by electron beam evaporation of the alloy on silicon substrates. X-ray diffraction data confirm the formation of the alloy phase of Fe50Ni50 and intermixed silicide phases of Fe5Si3, Ni3Si2, Ni2Si and NiSi. The structures have also been irradiated from swift heavy ions to study the effect of irradiation induced interfacial intermixing. Magnetic force microscopy (MFM) and magnetisation characteristics have been used to characterise the magnetic behaviour of as-prepared and irradiated structures. It is observed from the MFM that the magnetic domains are of sub-micron scale and there is a significant magnetic signal from the surface of the structure which becomes stronger for the irradiated structures. The observed magnetisation (M-H) characteristics show the presence of in-plane and out-of-plane magnetic anisotropy in the structure which has been observed to be removed on the irradiation. The magnetisation characteristics has been understood as the magnetic behaviour of nano-magnetic grains of silicides (and of the alloy, Fe50Ni50) which are formed as a result of interfacial chemistry and modified by irradiation induced interfacial intermixing. The observed magnetic behaviour seems interesting and significant for many applications related to magnetics. © 2013 © 2013 Taylor & Francis.
Irradiation induced modifications in morphology and magnetic property of Mn/Si structure
(2010) M.K. Srivastava; V. Ganesan; P.C. Srivastava
Mn films of ∼50 nm has been deposited by electron beam evaporation technique on cleaned and etched Si [(1 0 0), 8-10 Ω cm] substrates to realize a Mn/Si interfacial structures. The structures have been irradiated from energetic (∼100 MeV) ion beam from Mn side. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry, magnetic force microscopy, and vibrating sample magnetometer facilities. It has been found that surface/interfacial granular silicide phases (of MnxSiy) are formed before and after the irradiation with a irradiation induced modifications of surface morphology and magnetic property. The surface/interface roughness has been found to increase on the irradiation from the atomic force microscopy data. The magnetic property on the irradiation shows an interesting and significant feature of an increased coercivity and a ferromagnetic like behavior in the Mn-Si structure. The observed increased coercivity has been related to the increased roughness on the irradiation. The ferromagnetism after the irradiation is a curious phenomenon which seems due to the formation of Mn-C-Si compound from the carbon dissolved in silicon. © 2010 Elsevier B.V. All rights reserved.
Photoelectron spectroscopy study of Mn/n-Si interfacial structure
(2013) M.K. Srivastava; T. Shripathi; P.C. Srivastava
The Mn/n-Si interfacial structure is susceptible to intermixing even at room temperature. To investigate the chemistry as a result of the intermixing, valence band and core level photoelectron spectroscopy of Mn/Si has been carried out using synchrotron radiation of 134 eV energy and Al Kα X-ray (λ = 1,486.6 Å) source. The fabricated structures have also been irradiated from swift heavy ions (Fe7+ of ∼100 MeV) to investigate the ion beam mixing in such structures. Valence band photoelectron spectroscopy with 134 eV photons shows the evolution of Mn3d, Mn3p and Si2p levels with a shifting towards lower binding energy side compared to their elemental values of the binding energy. This binding energy shift shows the formation of chemical compound of Si and Mn. Evolution of Si2p core level prior to and after the swift heavy ion irradiation shows strong chemical reactivity of manganese thin film with silicon. Deconvolution of Mn3d valence band has shown the formation of silicide phase due to the hybridization of Mn3d and Si3sp states. Mn2p core level study shows that the oxide and silicide formation takes place during the growth and for successive etching, oxide part is decreasing whereas silicide part is increasing. © 2013 Springer Science+Business Media New York.
Quantification of Observed Electrical Effect on the Raindrop Size Distribution in Tropical Clouds
(Blackwell Publishing Ltd, 2018) Dipjyoti Mudiar; S.D. Pawar; Anupam Hazra; Mahen Konwar; V. Gopalakrishnan; M.K. Srivastava; B.N. Goswami
In the backdrop of extensive laboratory and theoretical evidence of broadening of the drop size distribution (DSD) of raindrops in the presence of electric field, quantification of the same in observed tropical clouds is lacking. Here this is quantified using the DSD measured by a microrain radar at 2,400-, 1,200-, and 600-m heights from the surface in six strongly electrified and six weakly electrified stratiform rain events together with the DSD of raindrops at the surface measured by a disdrometer for the same cases. The presence/absence of lightning is used to distinguish between strongly and weakly electrified events. The vertical profile of Median Volume Diameter below the melting layer and DSDs at all three heights for strongly electrified events and weakly electrified events are significantly different from each other, consistent with previous laboratory and numerical studies (Rayleigh, 1879; Davis, 1964; Moore et al., 1964, https://doi.org/10.1175/1520-0469(1964)021<0646:GORAMA>2.0.CO;2). Our results indicate that the electric field and surface charge of raindrops can affect the collision-coalescence process and breakup characteristics of raindrops. Our study suggests that the parameterization of electrical processes in weather/climate models can possibly improve the simulation of tropical rainfall in numerical models as well as a proper representation of DSD will improve the estimation of tropical rainfall in airborne measurements. ©2018. American Geophysical Union. All Rights Reserved.
Rainwater chemistry in the North Western Himalayan Region, India
(Elsevier Ltd, 2012) S. Tiwari; D.M. Chate; D.S. Bisht; M.K. Srivastava; B. Padmanabhamurty
Precipitation chemistry studies were conducted at Kothi (32.31°N, 77.20°E), a rural Indian location, in the North Western Himalayas during June to October of 2006 and 2007. The volume weighted mean pH values ranged from 5.16 to 6.36 with a mean of 5.68±0.26 indicating mostly alkaline precipitation events. However, 18% samples were found acidic due to dominance of acidic components. The alkaline to acidic ions ratio (1.05) confirms that acidic components are neutralized by alkali radicals in rainwater. Of the total ionic composition 159μeq/l, in rainwater samples, dominant were Ca2+ (19%) followed by Na+ (14%). Among the anions, Cl- (17%) was slightly higher than SO42- (16%) and NO3- (11%). The ratio (NO3-+Cl-)/SO42-) 1.05 indicates acidity in rainwater by the cumulative effects of HNO3, H2SO4 and HCl. The ratios NH4+/NO3- as 0.76 and NH4+/SO42- as 0.50 show the pre-dominance of atmospheric NH4NO3 and (NH4)2SO4. Significant correlation between Na+ and Cl- (r=0.97; p<0.0001) and between SO42- and NO3- (r=0.60; p<0.0001) indicates their origin from similar sources. Neutralization factor calculations show that Ca2+ plays a major role in the neutralizing processes. Enrichment factors indicate that Ca2+, SO42- K+ and Mg2+ were originated from non-marine sources. The principle component analysis indicates the influence of transportation of air-born primary and secondary particles on the chemical composition of rainwater. © 2011 Elsevier B.V.
Reservoir characterisation using hybrid optimisation of genetic algorithm and pattern search to estimate porosity and impedance volume from post-stack seismic data: A case study
(Springer, 2024) Nitin Verma; S.P. Maurya; Ravi Kant; K.H. Singh; Raghav Singh; A.P. Singh; G. Hema; M.K. Srivastava; Alok K Tiwari; P.K. Kushwaha; Richa
In the current study, a seismic inversion based on a hybrid optimisation of genetic algorithm (GA) and pattern search (PS) is carried out. The GA is an approach to global optimisation technique that always converges to the global optimum solution but takes much time to converge. On the other hand, the PS is a local optimisation technique and can converge at local or global optimum solution depending on the starting model. If these two techniques are used together (here termed hybrid optimisation), they can enhance one's benefit and reduce the drawbacks of others. The present study developed a methodology to combine GA and PS in a single flowchart and utilise seismic reflection data exclusively to predict porosity and impedance volume in inter-well regions. The algorithms are initially tested on synthetically created data based on the wedge model, the coal coking model, and the 1D convolution model. The performance of the algorithm is remarkably acceptable, according to the error analysis and statistical analysis between the inverted and the anticipated results. After that, the field post-stack seismic data from the Blackfoot field, Canada, is transformed into impedance and porosity using a developed hybrid optimisation technique. The inverted/predicted sections show very high-resolution subsurface information with impedance varying from 6000 to 14000 m/s×g/cc and porosity varying from 5 to 40% in the region. The error decreases from 1.0 to 0.5 for impedance inversion, whereas it varies from 1.4 to 0.5 for porosity inversion within 3000 iterations, which cannot be achieved by a single optimisation technique. The findings also demonstrated a sand channel (reservoir) anomaly with low impedance (6000–9000 m/s×g/cc) and high porosity (12–20%) in between 1040 and 1060 ms time intervals. This study provides evidence that subsurface parameters like acoustic impedance or porosity may be promptly and affordably determined using seismic inversion based on hybrid optimisation. The developed methodology is very helpful in finding subsurface parameters in a limited time and cost, which cannot be achieved only by global or local optimisation. © Indian Academy of Sciences 2024.
Scattering and absorption properties of near-surface aerosol over Gangetic-Himalayan region: The role of boundary-layer dynamics and long-range transport
(Copernicus GmbH, 2015) U.C. Dumka; D.G. Kaskaoutis; M.K. Srivastava; P.C.S. Devara
Light scattering and absorption properties of atmospheric aerosols are of vital importance for evaluating their types, sources and radiative forcing. This is of particular interest over the Gangetic-Himalayan (GH) region due to uplift of aerosol from the plains to the Himalayan range, causing serious effects on atmospheric heating, glaciology and monsoon circulation. In this respect, the Ganges Valley Aerosol Experiment (GVAX) was initiated in Nainital from June 2011 to March 2012 with the aim of examining the aerosol properties, source regions, uplift mechanisms and aerosol-radiation-cloud interactions. The present study examines the temporal (diurnal, monthly, seasonal) evolution of scattering (σsp) and absorption (σap) coefficients, their wavelength dependence, and the role of the Indo-Gangetic plains (IGP), boundary-layer dynamics (BLD) and long-range transport (LRT) in aerosol evolution via the Atmospheric Radiation Measurement Mobile Facility. The analysis is separated for particles 10μm and <1 μm in diameter in order to examine the influence of particle size on optical properties. The σsp and σap exhibit a pronounced seasonal variation between the monsoon low and post-monsoon (November) high, while the scattering wavelength exponent exhibits higher values during the monsoon, in contrast to the absorption Ångström exponent which maximizes in December-March. The elevated-background measuring site provides the advantage of examining the LRT of natural and anthropogenic aerosols from the IGP and southwest Asia and the role of BLD in the aerosol lifting processes. The results reveal higher aerosol concentrations at noontime along with an increase in mixing height, suggesting influence from IGP. The locally emitted aerosols present higher wavelength dependence of the absorption in October-March compared to the rather well-mixed and aged transported aerosols. Monsoon rainfall and seasonally changing air masses contribute to the alteration of the extensive and intensive aerosol properties.
Sources and characteristics of carbonaceous aerosols at Agra "World heritage site" and Delhi "capital city of India"
(Springer Verlag, 2014) A.S. Pipal; S. Tiwari; P.G. Satsangi; Ajay Taneja; D.S. Bisht; A.K. Srivastava; M.K. Srivastava
Agra, one of the oldest cities "World Heritage site", and Delhi, the capital city of India are both located in the border of Indo-Gangetic Plains (IGP) and heavily loaded with atmospheric aerosols due to tourist place, anthropogenic activities, and its topography, respectively. Therefore, there is need for monitoring of atmospheric aerosols to perceive the scenario and effects of particles over northern part of India. The present study was carried out at Agra (AGR) as well as Delhi (DEL) during winter period from November 2011 to February 2012 of fine particulate (PM2.5: d < 2.5 μm) as well as associated carbonaceous aerosols. PM2.5 was collected at both places using medium volume air sampler (offline measurement) and analyzed for organic carbon (OC) and elemental carbon (EC). Also, simultaneously, black carbon (BC) was measured (online) at DEL. The average mass concentration of PM2.5 was 165.42 ± 119.46 μg m-3 at AGR while at DEL it was 211.67 ± 41.94 μg m-3 which is ~27 % higher at DEL than AGR whereas the BC mass concentration was 10.60 μg m-3. The PM2.5 was substantially higher than the annual standard stipulated by central pollution control board and United States Environmental Protection Agency standards. The average concentrations of OC and EC were 69.96 ± 34.42 and 9.53 ± 7.27 μm m-3, respectively. Total carbon (TC) was 79.01 ± 38.98 μg m-3 at AGR, while it was 50.11 ± 11.93 (OC), 10.67 ± 3.56 μg m-3 (EC), and 60.78 ± 14.56 μg m-3 (TC) at DEL. The OC/EC ratio was 13.75 at (AGR) and 5.45 at (DEL). The higher OC/EC ratio at Agra indicates that the formation of secondary organic aerosol which emitted from variable primary sources. Significant correlation between PM2.5 and its carbonaceous species were observed indicating similarity in sources at both sites. The average concentrations of secondary organic carbon (SOC) and primary organic carbon (POC) at AGR were 48.16 and 26.52 μg m-3 while at DEL it was 38.78 and 27.55 μg m-3, respectively. In the case of POC, similar concentrations were observed at both places but in the case of SOC higher over AGR by 24 in comparison to DEL, it is due to the high concentration of OC over AGR. Secondary organic aerosol (SOA) was 42 % higher at AGR than DEL which confirms the formation of secondary aerosol at AGR due to rural environment with higher concentrations of coarse mode particles. The SOA contribution in PM2.5 was also estimated and was ~32 and 12 % at AGR and DEL respectively. Being high loading of fine particles along with carbonaceous aerosol, it is suggested to take necessary and immediate action in mitigation of the emission of carbonaceous aerosol in the northern part of India. © 2014 Springer-Verlag Berlin Heidelberg.
Spatio-temporal variation in chemical characteristics of PM10 over Indo Gangetic Plain of India
(Springer Verlag, 2016) S.K. Sharma; T.K. Mandal; M.K. Srivastava; A. Chatterjee; Srishti Jain; M. Saxena; B.P. Singh; Saraswati; A. Sharma; A. Adak; S. K.Ghosh
The paper presents the spatio-temporal variation of chemical compositions (organic carbon (OC), elemental carbon (EC), and water-soluble inorganic ionic components (WSIC)) of particulate matter (PM10) over three locations (Delhi, Varanasi, and Kolkata) of Indo Gangetic Plain (IGP) of India for the year 2011. The observational sites are chosen to represent the characteristics of upper (Delhi), middle (Varanasi), and lower (Kolkata) IGP regions as converse to earlier single-station observation. Average mass concentration of PM10 was observed higher in the middle IGP (Varanasi 206.2 ± 77.4 μg m−3) as compared to upper IGP (Delhi 202.3 ± 74.3 μg m−3) and lower IGP (Kolkata 171.5 ± 38.5 μg m−3). Large variation in OC values from 23.57 μg m−3 (Delhi) to 12.74 μg m−3 (Kolkata) indicating role of formation of secondary aerosols, whereas EC have not shown much variation with maximum concentration over Delhi (10.07 μg m−3) and minimum over Varanasi (7.72 μg m−3). As expected, a strong seasonal variation was observed in the mass concentration of PM10 as well as in its chemical composition over the three locations. Principal component analysis (PCA) identifies the contribution of secondary aerosol, biomass burning, fossil fuel combustion, vehicular emission, and sea salt to PM10 mass concentration at the observational sites of IGP, India. Backward trajectory analysis indicated the influence of continental type aerosols being transported from the Bay of Bengal, Pakistan, Afghanistan, Rajasthan, Gujarat, and surrounding areas to IGP region. © 2016, Springer-Verlag Berlin Heidelberg.
Statistical evaluation of PM10 and distribution of PM1, PM2.5, and PM10 in ambient air due to extreme fireworks episodes (Deepawali festivals) in megacity Delhi
(Kluwer Academic Publishers, 2012) S. Tiwari; D.M. Chate; M.K. Srivastava; P.D. Safai; A.K. Srivastava; D.S. Bisht; B. Padmanabhamurty
Temporal variation of PM10 using 2-year data (January, 2007-December, 2008) of Delhi is presented. PM10 varied from 42 to 200 μg m-3 over January to December, with an average 114. 1 ± 81. 1 μg m-3. They are comparable with the data collected by Central Pollution Control Board (National Agency which monitors data over the entire country in India) and are lower than National Ambient Air Quality (NAAQ) standard during monsoon, close to NAAQ during summer but higher in winter. Among CO, NO2, SO2, rainfall, temperature, and wind speed, PM10 shows good correlation with CO. Also, PM10, PM2. 5, and PM1 levels on Deepawali days when fireworks were displayed are presented. In these festive days, PM10, PM2. 5, and PM1 levels were 723, 588, and 536 μg m-3 in 2007 and 501, 389, and 346 μg m-3 in 2008. PM10, PM2. 5, and PM1 levels in 2008 were 1. 5 times lower than those in 2007 probably due to higher mixing height (446 m), temperature (23. 8°C), and winds (0. 36 ms-1). © 2011 Springer Science+Business Media B.V.