SANTOSH KUMAR
Articles written in Journal of Earth System Science
Volume 117 Issue S1 July 2008 pp 303-313
Characteristics of spectral aerosol optical depths over India during ICARB
S Naseema Beegum K Krishna Moorthy Vijayakumar S Nair S Suresh Babu S K Satheesh V Vinoj R Ramakrishna Reddy K Rama Gopal K V S Badarinath K Niranjan Santosh Kumar Pandey M Behera A Jeyaram P K Bhuyan M M Gogoi Sacchidanand Singh P Pant U C Dumka Yogesh Kant J C Kuniyal Darshan Singh
Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived ˚Angström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The ˚Angström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from the adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the ˚Angström exponent (𝛼) remained significantly lower (∼1) over the Arabian Sea compared to Bay of Bengal (BoB) (∼1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of 𝛼, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in 𝛼 over the BoB.
Volume 121 Issue 2 April 2012 pp 439-451
A P Singh O P Mishra Dinesh Kumar Santosh Kumar R B S Yadav
We analyzed 3365 relocated aftershocks with magnitude of completeness (
Volume 125 Issue 7 October 2016 pp 1329-1352
Brajesh Singh Santosh Kumar Masao Ban Kazuo Nakashima
Felsic magmatism in the southern part of Himachal Higher Himalaya is constituted by Neoproterozoic granite gneiss (GGn), Early Palaeozoic granitoids (EPG) and Tertiary tourmaline-bearing leucogranite (TLg). Magnetic susceptibility values ($\lt$3 ×10$^{−3}$ SI), molar Al$_2$O$^3$/(CaO+Na$_2$O+K$_2$O) ($\geq$1.1), mineral assemblage (bt–ms–pl–kf–qtz ± tur ± ap), and the presence of normative corundum relate these granitoids to peraluminous S-type, ilmenite series (reduced type) granites formed in a syncollisional tectonic setting. Plagioclase from GGn (An$_{10}$–An$_{31}$) and EPG (An$_{15}$–An$_{33}$) represents oligoclase to andesine and TLg (An$_2$–An$_{15}$) represents albite to oligoclase, whereas compositional ranges of K-feldspar are more or less similar (Or$_{88}$ to Or$_{95}$ in GGn, Or$_{86}$ to Or$_{97}$ in EPG and Or$_{87}$ to Or$_{94}$ in TLg). Biotites in GGn (Mg/Mg+Fe$^t$ = 0.34–0.45), EPG (Mg/Mg+Fe$^t$ = 0.27–0.47), and TLg (Mg/Mg+Fe$^t$ = 0.25–0.30) are ferribiotites enriched in siderophyllite, which stabilised between FMQ and HM buffers and are characterised by dominant 3Fe$\rightleftarrows$2Al, 3Mg$\rightleftarrows$2Al substitutions typical of peraluminous (S-type), reducing felsic melts. Muscovite in GGn (Mg/Mg+Fe$^t$ = 0.58–0.66), EPG (Mg/Mg+Fe$^t$ = 0.31−0.59), and TLg (Mg/Mg+Fet = 0.29–0.42) represent celadonite and paragonite solid solutions, and the tourmaline fromEPG and TLg belongs to the schorl-elbaite series, which are characteristics of peraluminous, Li-poor, biotite-tourmaline granites. Geochemical features reveal that the GGn and EPG precursor melts were most likely derived from melting of biotite-rich metapelite and metagraywacke sources, whereas TLg melt appears to have formed from biotite-muscovite rich metapelite and metagraywacke sources. Major and trace elements modelling suggest that the GGn, EPG and TLg parental melts have experienced low degrees (∼13, ∼17 and ∼13%, respectively) of kf–pl–bt fractionation, respectively, subsequent to partial melting. The GGn and EPG melts are the results of a pre-Himalayan, syn-collisional Pan-African felsicmagmatic event, whereas the TLg is a magmatic product of Himalayan collision tectonics.
Volume 129 All articles Published: 25 April 2020 Article ID 0114 Research Article
VISHWA JOSHI SUMER CHOPRA SANTOSH KUMAR
The calibration of local magnitude scale to local tectonics is essential for seismic hazard assessment and quantifying the seismicity in active regions. In the present study, we have developed a local magnitude scale $M_{L}$, for the Saurashtra region, which is a horst, located in the western continental margin of India. The local magnitude scale is developed using 1968 amplitude measurements from horizontal component recordings of 319 earthquakes, obtained from sites in the Saurashtra region, with hypocentral distances ranging from 3 to 298 km. All the 1968 amplitude measurements were inverted simultaneously to determine attenuation curve, magnitudes and station corrections for the studied region. The resultant distance correction term for the Saurashtra is $-log(A_{0}) = 1.31 log(r/100) + 0.0002 (r - 100) + 3$ for 100 km normalization, where $A_{0}$ is the distance correction and $r$ is the hypocentral distance. The distance correction term ($-log A_{0}$) suggests that the attenuation in the Saurashtra region is lower as compared to neighbouring Kachchh region. The station corrections obtained in the present study varies from $-0.31$ to $+0.24$. Overall, standard deviation of the magnitude residuals without station correction is 0.28, while with station correction, it is 0.23, which indicates that applying station correction reduces the variance by 31% and brings the average residual closer to zero.
Volume 129, 2020
All articles
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode
© 2021-2022 Indian Academy of Sciences, Bengaluru.