Institution
Vikram Sarabhai Space Centre
Facility•Thiruvananthapuram, India•
About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the authors present a linear relationship that exists between the daytime integrated equatorial electrojet strength and the maximum elevated height of the F-layer during post-sunset hours (denoted as peak h'F).
Abstract: . Several investigations have been carried out to identify the factors that are responsible for the day-to-day variability in the occurrence of equatorial spread-F (ESF). But the precise forecasting of ESF on a day-to-day basis is still far from reality. The nonlinear development and the sustenance of ESF/plasma bubbles is decided by the background ionospheric conditions, such as the base height of the F-layer (h'F), the electron density gradient (dN/dz), maximum ionization density (Nmax), geomagnetic activity and the neutral dynamics. There is increasing evidence in the literature during the recent past that shows a well developed Equatorial Ionization Anomaly (EIA) during the afternoon hours contributes significantly to the initiation of ESF during the post-sunset hours. Also, there exists a good correlation between the Equatorial Ionization Anomaly (EIA) and the Integrated Equatorial ElectroJet (IEEJ) strength, as the driving force for both is the same, namely, the zonal electric field at the equator. In this paper, we present a linear relationship that exists between the daytime integrated equatorial electrojet (IEEJ) strength and the maximum elevated height of the F-layer during post-sunset hours (denoted as peak h'F). An inverse relationship that exists between the 6-h average Kp-index prior to the local sunset and the peak h'F of the F-layer is also presented. A systematic study on the combined effects of the IEEJ and the average Kp-index on the post-sunset, peak height of the F-layer (peak h'F), which controls the development of ESF/plasma bubbles, is carried out using the ionosonde data from an equatorial station, Trivandrum (8.47° N, 76.91° E, dip.lat. 0.5° N), an off-equatorial station, SHAR (13.6° N, 79.8° E, dip.lat. 10.8° N) and VHF scintillations (244 MHz) observed over a nearby low-latitude station, Waltair (17.7° N, 83.3° E, dip.lat. 20° N). From this study, it has been found that the threshold base height of the F-layer at the equator for the development of plasma bubbles is reduced from 405 km to 317 km as the solar activity decreases from March 2001 (mean Rz=113.5) to March 2005 (mean Rz=24.5). This decrease in threshold height with the decreasing solar activity is explained on the basis of changes in the local linear growth rate of the collisional Rayleigh-Taylor instability, due to the variability of various terms such as inverse density gradient scale length (L−1), ion-neutral collision frequency (νin) and recombination rate (R) with the changes in the solar activity.
22 citations
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TL;DR: In this paper, postbuckling analysis of uniform cantilever columns subjected to three types of loading, namely a concentrated tip load, a uniformly distributed load and a linearly varying load has been presented using the Galerkin Finite Element Method.
22 citations
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TL;DR: In this article, the origin of the Moon's ionosphere has been explored using radio occultation (RO) measurements and a photochemical model and the electron density near the Moon surface, obtained on 31 July 2009 (~300 cm −3 ), is compared with results from a model which includes production and recombination of 16 ions, solar wind proton charge exchange, and electron impact ionization.
Abstract: The origin of the Moon's ionosphere has been explored using Chandrayaan-1 radio occultation (RO) measurements and a photochemical model. The electron density near the Moon's surface, obtained on 31 July 2009 (~300 cm −3 ), is compared with results from a model which includes production and recombination of 16 ions, solar wind proton charge exchange, and the electron impact ionization. The model calculations suggest that in the absence of transport, inert ions, namely Ar + , Ne + , and He + , dominate lunar ionosphere (density ~5 × 10 4 cm −3 ). Interaction with solar wind, however, leads to their complete removal (~2–3 cm −3 ). Assuming the Moon's exosphere to have CO 2 , H 2 O, O, OH, H 2 , CH 4 , and CO molecules in addition to the inert gases, the model calculations suggest that the lunar ionosphere is dominated by molecular ions, namely H 2 O + , CO math formula, and H 3 O + , with near-surface density ~250 cm −3 . We surmise that lunar ionosphere can be molecular in nature.
22 citations
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TL;DR: In this paper, the mesosphere and lower thermosphere (MLT) zonal winds show remarkable interannual variability during northern hemispheric spring equinox and much less during fall equINox, suggesting a modulation by the quasi-biennial oscillation, which is identified with the strength of stratospheric westward winds.
Abstract: Long-term observations from medium-frequency and meteor radars (1993–2012) and rocket
soundings (1979–1990 and 2002–2007) are used to study mesosphere and lower thermosphere (MLT)
zonal wind variations in relation to the stratospheric winds over northern low latitudes. The combined data
set provides a complete height profile of amplitude of semiannual oscillation (SAO) up to 100 km, with an
exception around 75–80 km. The SAO signal has maxima around 50 km and 82 km and a minimum around
65 km. The MLT zonal winds show remarkable interannual variability during northern hemispheric spring
equinox and much less during fall equinox. Zonal wind mesospheric spring equinox enhancements (MSEE)
appear with a periodicity of 2–3 years, suggesting a modulation by the quasi-biennial oscillation, which we
identified with the strength of stratospheric westward winds. Out of 20 years of observations, the stratospheric
westward winds are strong during 11 years (non-MSEE) and weak during 9 years. Six of these 9 years show large
MLT winds (MSEE), and 3 years (1999, 2004, and 2006) show small MLT winds (missing MSEE). These unexpected
small winds occur in years with global circulation anomalies associated with strong sudden stratospheric
warmings and an early spring transition of zonal winds. With the proposed three MSEE classes, we take into
account local and global forcing factors.
22 citations
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TL;DR: In this paper, the authors examined the spatial variability of the aerosol characteristics across the Brahmaputra valley, a land campaign was conducted during late winter (February 3-March 2, 2011) and measurements of particulate matter (PM, PM10, PM2.5) and black carbon (BC) concentrations were made onboard an interior redesigned vehicle.
Abstract: In order to examine the spatial variability of the aerosol characteristics across the Brahmaputra valley, a land campaign was conducted during late winter (February 3–March 2) 2011. Measurements of particulate matter (PM, PM10, PM2.5) and black carbon (BC) concentrations were made onboard an interior redesigned vehicle. The length of the campaign trail stretched about 700 km, covering the longitude belt of 89.97°–95.55°E and latitude belt of 26.1°–27.6°N, comprising 13 measurement locations. The valley is divided into three sectors longitudinally: western sector (R1: 89.97°–91.75°E), middle sector (R2: 92.5°–94.01°E) and eastern sector (R3: 94.63°–95.55°E). Spatial heterogeneity in aerosol distribution has been observed with higher PM10 and PM2.5 concentrations at the western and middle sectors compared to the eastern sector. The locations in the western sector are found to be rich in BC compared to the other two sectors and there is a gradual decrease in BC concentrations from west to east of the Brahmaputra valley. Two hotspots within the western and middle sectors with high PM and BC concentrations have been identified. The associated physico-optical parameters of PM reveal abundance of PM2.5 aerosols along the entire valley. High population density in the western and middle sectors, together with the contribution of remote aerosols, leads to higher anthropogenic aerosols over those regions. Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) slightly underestimates the measured PM10 and PM2.5 at the eastern sector while the model overestimates the measurements at a number of locations in the western sector. In general, BC is underestimated by the model. The variation of BC within the campaign trail has not been adequately captured by the model leading to higher variance in the western locations as compared to the middle and eastern locations.
22 citations
Authors
Showing all 2111 results
Name | H-index | Papers | Citations |
---|---|---|---|
M. Santosh | 103 | 1344 | 49846 |
Sabu Thomas | 102 | 1554 | 51366 |
S. Suresh Babu | 70 | 498 | 17113 |
K. Krishna Moorthy | 54 | 263 | 9749 |
Sathianeson Satheesh | 53 | 172 | 11099 |
M. Y. Hussaini | 49 | 207 | 16794 |
J.R. Banerjee | 44 | 146 | 5620 |
C. P. Reghunadhan Nair | 37 | 181 | 4825 |
K. N. Ninan | 36 | 159 | 4156 |
Anil Bhardwaj | 35 | 230 | 4527 |
Ivatury S. Raju | 33 | 121 | 6626 |
Venkata Sai Kiran Chakravadhanula | 32 | 102 | 3011 |
P.K. Sinha | 32 | 118 | 2918 |
J.-P. St.-Maurice | 31 | 113 | 3446 |
Subramaniam Gopalakrishnan | 28 | 123 | 2951 |