Geomorphic and structural evidences of neotectonic activity in the Sub-Himalayan belt of Nahan Salient,NW India     

Tejpal Singh  Umakant Sharma  A. K. Awasthi  N. S. Virdi  Ravindra Kumar 《Journal of the Geological Society of India》2011,77(2):175-182

Neotectonism in the Sub-Himalayan belt is not new. Moreover, the word ‘Sub-Himalaya’ is almost synonymous with ‘neotectonic activity’. In the present paper, we report some of the most convincing geomorphic and structural evidences of neotectonic activity from the Sub-Himalayan belt in the Nahan Salient. The geomorphic evidences mainly include the four geomorphic surfaces identified from the transverse topographic profiles drawn parallel to the Himalayan front. These surfaces are commonly covered with terrace deposits that are tilted as well as faulted at a number of places. A number of faults, directly observable in the field, are normal in nature and they are oriented at high angles to the Himalayan Frontal Thrust (HFT). These faults are similar to the E-W extension in southern Tibet in response to the oblique convergence of India at ∼N20°E in the NW Himalaya. They are attributable to the kinematics of neotectonic compression along the HFT, the frontal ramp-oblique ramp-frontal ramp geometry of the thrust fault and related adjustments.  相似文献   

Triggering an Eruptive Flare by Emerging Flux in a Solar Active-Region Complex     

Rohan E. Louis  Bernhard Kliem  B. Ravindra  Georgios Chintzoglou 《Solar physics》2015,290(12):3641-3662

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Observations of Photospheric Vortical Motions During the Early Stage of Filament Eruption     

Sajal Kumar Dhara  B. Ravindra  Ravinder Kumar Banyal 《Solar physics》2014,289(12):4481-4500

Solar filaments/prominences exhibit rotational motion during different phases of their evolution from their formation to eruption. We have observed the rotational/vortical motion in the photosphere near the ends of ten filaments during their initial phase of eruption, at the onset of the fast rise phase. All the filaments were associated with active regions. The photospheric vortical motions we observed lasted for 4?–?20 minutes. In the vicinity of the conjugate ends of the filament the direction of rotation was opposite, except for two cases, where rotational motion was observed at only one end point. The sudden onset of a large photospheric vortex motion could have played a role in destabilizing the filament by transporting axial flux into the activated filament thereby increasing the outward magnetic pressure in it. The outward magnetic pressure may have pushed the filament/flux rope to the height where the torus instability criterion was satisfied, and hence it could have caused the filament instability and eruption.  相似文献   

The Evolution of the Net Twist Current and the Net Shear Current in Active Region NOAA 10930     

Yogita Suthar  P. Venkatakrishnan  B. Ravindra  S. N. A. Jaaffrey 《Solar physics》2014,289(7):2459-2471

The electric current exists because of the non-potential magnetic field in solar active regions. We present the evolution of net current in the solar active region NOAA 10930 as the sum of shear current and twist current by using 27 high-resolution vector magnetograms obtained with Hinode/SOT-SP during 9?–?15 December 2006. This active region was highly eruptive and produced a large number of flares ranging from B to X class. We derived local distribution of shear and twist current densities in this active region and studied the evolution of net shear current (NSC) and net twist current (NTC) in the N-polarity and S-polarity regions separately. We found the following: i) The twist current density was dominant in the umbrae. ii) The footpoint of the emerging flux rope showed a dominant twist current. iii) The shear current density and twist current density appeared in alternate bands around the umbrae. iv) On the scale of the active region, NTC was always larger than NSC. v) Both NTC and NSC decreased after the onset of an X3.4 class flare that occurred on 13 December 2006.  相似文献   

Transient temperature analysis in a system of thin shells combined with convective and radiative cooling     

Ravindra Prasad  N. K. Samria 《Astrophysics and Space Science》1989,151(1):161-168

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Effect of magnetic field on the free-convection and mass transfer flow through a porous medium     

Basant Kumar Jha  Ravindra Prasad 《Astrophysics and Space Science》1989,161(2):195-200

An analytical study is performed to examine the effects of magnetic field on the free-convection and mass transfer flow through porous medium. The effects of various parameters on the velocity field are discussed by tables.  相似文献   

Chemical characterization and multivariate analysis of atmospheric PM<Subscript>2.5</Subscript> particles     

Khaiwal Ravindra  Marianne Stranger  Rene Van Grieken 《Journal of Atmospheric Chemistry》2008,59(3):199-218

The new European Council Directive (PE-CONS 3696/07) frames the inhalable (PM₁₀) and fine particles (PM_2.5) on priority to chemically characterize these fractions in order to understand their possible relation with health effects. Considering this, PM_2.5 was collected during four different seasons to evaluate the relative abundance of bulk elements (Cl, S, Si, Al, Br, Cu, Fe, Ti, Ca, K, Pb, Zn, Ni, Mn, Cr and V) and water soluble ions (F⁻, Cl⁻, NO₂ ⁻, NO₃ ⁻, SO₄ ²⁻, Na⁺, NH₄ ⁺, Ca²⁺ and Mg²⁺) over Menen, a Belgian city near the French border. The air quality over Menen is influenced by industrialized regions on both sides of the border. The most abundant ionic species were NO₃ ⁻, SO₄ ²⁻ and NH₄ ⁺, and they showed distinct seasonal variation. The elevated levels of NO₃ ⁻ during spring and summer were found to be related to the larger availability of the NO_x precursor. The various elemental species analyzed were distinguished into crustal and anthropogenic source categories. The dominating elements were S and Cl in the PM_2.5 particles. The anthropogenic fraction (e.g. Zn, Pb, and Cu) shows a more scattered abundance. Furthermore, the ions and elemental data were also processed using principal component analysis and cluster analysis to identify their sources and chemistry. These approach identifies anthropogenic (traffic and industrial) emissions as a major source for fine particles. The variations in the natural/anthropogenic fractions of PM_2.5 were also found to be a function of meteorological conditions as well as of long-range transport of air masses from the industrialized regions of the continent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

International Polar Year: Past,Present and Future     

Manish Tiwari  Rasik Ravindra 《Journal of the Geological Society of India》2009,74(1):144-145

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Precipitation controlled spatial variations in groundwater quality indices-suitability for drinking and irrigation purposes in the basalts of South India     

Soumya Siva B  Ravindra B. Kamble 《Arabian Journal of Geosciences》2017,10(7):171

Regional study on the impact of variations in input rainfall over groundwater quality and its suitability for utilitarian purposes is essential for its extraction and management. Water chemistry from 456 observations wells for 2007–2011 period in hard rock Basaltic terrain of Upper Godavari basin is supported with 8 field samples (in 2014) in this analysis. Based on mean annual rainfall (MAR), four narrow climatic zones are identified in the basin, defined as “humid” (MAR > 1600 mm), “sub-humid” (1600–1000 mm), “semi-arid” (1000–600 mm), and “arid” (MAR < 600 mm). NICB ratio (<±10%), and anionic percentages demarcated the polluted areas from rest “good data”, composing of 1818 samples. Hydrochemical facies are studied using Piper diagram, secondary alkalinity exceeded 50% and not one cation–anion pair exceeded 50%, and silicate–carbonate plot, arid zone nearer to silicate pole indicated the dominance of SiO₂ in Ca/Na vs Mg/Na plot. These geochemical variations emphasize a detailed study on role of climatic gradient on groundwater suitability for different purposes, for groundwater extraction, and its management. Suitability of groundwater for drinking based on water quality indices (WQI) indicated 98% of the samples as suitable (WQI < 50%). TDS in humid zone is 150–500 and 500–1000 mg/L in rest of the zones with ～68% in permissible range, 15% as hard water (TDS > 600 mg/L) and not acceptable for drinking. Suitability of groundwater for irrigation is studied using sodium percentage (Na %), Wilcox diagram, sodium absorption ratio (SAR), US salinity diagram, residual sodium carbonate (RSC), permeability index (PI), Kelly’s ratio (KR), ancd magnesium absorption ratio (MgAR). Na % in four zones is < 60% and permissible for irrigation. Very few water samples fall in “doubtful to unsuitable” and “unsuitable” category of Wilcox diagram. Region is observed to have SAR < 6, indicating that water would not cause any problem to the soil and crop. Humid and sub-humid zones belonged to C1S1 and C2S1 categories (low and medium sodium), while semi-arid extended to C3S1 category (salinity hazard zone) in US salinity plot. RSC for all the three zones ranged from 1 to 1.5 meq/L, with 90–95% of the area safe for irrigation. Out of 1818 samples, 1129 belonged to class 2 of PI classification (PI ranging from 25 to 75%) while rest 689 samples had PI >75% (class 1). KR varied from 0.05 to 12.81, with 70–80% of the area having KR < 1. MgAR ratio ranged from 67% to 96%, with sub-humid, humid zones having higher Mg concentrations (increased salinity). Thus, 90% of the samples indicated non-alkaline water with 1% of normal alkalinity. Hence, the current study systematically analyzed the effect of precipitation and geology on groundwater quality and on its usability for various purposes. This stepwise procedure categorized the regions, and the same can be adopted for any regional hydrogeochemical studies.  相似文献   

On the Correlation Between the he ii λ304 Network Brightening and the Photospheric Magnetic Field     

Ravindra  B.  Venkatakrishnan  P. 《Solar physics》2003,214(2):267-285

Near simultaneous coronal EUV images were used to show that the He ii 304 network brightening is independent of coronal EUV radiation. We studied the quantitative relation between the intensity of He ii 304 network brightening with the associated magnetic elements. An almost linear relationship was found between the He ii 304 network brightening and the magnetic field for a field strength higher than 10 G with exceptions at neutral lines and in the intra-network. We also calculated the most probable formation height of He ii 304 network elements using the potential extrapolation of the photospheric magnetic field. The results show that He ii 304 network elements form at or around 3000 km above the height of the layer at which the sources of magnetic flux are deployed.  相似文献