Lithosphere of the Dharwar craton by joint inversion of P and S receiver functions   总被引：1，自引：0，他引：1  

S. Kiselev  L. Vinnik  S. Oreshin  S. Gupta  S. S. Rai  A. Singh  M. R. Kumar  G. Mohan 《Geophysical Journal International》2008,173(3):1106-1118

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Geomagnetic field variation during winter storm at localized southern and northern high latitude     

Babita Devi  Smita Dubey  Shailendra Saini  Rajni Devi  Rashmi Wahi  Ajay Dhar  S. K. Vijay  A. K. Gwal 《Journal of Astrophysics and Astronomy》2008,29(1-2):275-280

This paper presents the effect of geomagnetic storm on geomagnetic field components at Southern (Maitri) and Northern (Kiruna) Hemispheres. The Indian Antarctic Station Maitri is located at geom. long. 66.03° S; 53.21° E whereas Kiruna is located at geom. long. 67.52° N; 23.38° E. We have studied all the geomagnetic storms that occurred during winter season of the year 2004–2005. We observed that at Southern Hemisphere the variation is large as compared to the Northern Hemisphere. Geomagnetic field components vary when the interplanetary magnetic field is oriented in southward direction. Geomagnetic field components vary in the main phase of the ring current. Due to southward orientation of vertical component of IMF reconnection takes place all across the dayside that transports plasma and magnetic flux which create the geomagnetic field variation.  相似文献   

Effect of interplanetary magnetic field and disturb storm time on H component     

Rajni Devi  Smita Dubey  Shailendra Saini  Babita Devi  Ajay Dhar  S. K. Vijay  A. K. Gwal 《Journal of Astrophysics and Astronomy》2008,29(1-2):281-286

A fluxgate digital magnetometer is used to study the variation of magnitude of H component during geomagnetic storm events of April, July and November 2004 at southern subauroral localized region at “MAITRI” (geom. lat. 62°S, long. 52.8°E). We also study the effect of vertical component of interplanetary magnetic field (IMF) on the variation of the magnitude of H component during storm time of April, July and November 2004. Results show that before sudden storm commencement (SSC) time magnitude of H component and IMF show smooth variation but after SSC of first storm of 22 July 2004, the magnitude of the H component shows fluctuations and at 09:00 UT it increases, but during second storm of 24 July 2004, the magnitude of H component indicates large fluctuations and it increases rapidly at 04:00 UT.  相似文献   

A Comparison of Sea Surface Fluxes over Southern Indian Ocean Cruise Expedition Observation and NCEP Reanalysis     

Avinash C. Pandey  Shailendra Rai  Amitabh Mitra 《Marine Geodesy》2013,36(1):82-92

Surface layer atmospheric and ocean observations have been collected along the cruise track from a special scientific expedition to Antarctica. Bulk estimates of surface momentum flux, sensible heat flux and latent heat flux have been computed applying bulk algorithms from the data collected along cruise track during the time period January 27 to March 31, 2006, and compared the results with National Centre for Environmental Prediction (NCEP) reanalysis. Underestimation of surface momentum flux in roaring forties (40°S–50°S) area of Indian Ocean is seen from NCEP reanalysis. Systemic differences in sensible and latent heat fluxes between observed and NCEP reanalysis have been found. Along the cruise track, the average sensible (latent) heat flux was 9.45 Wm^?2 (67.46 Wm^?2) and 3.75 Wm^?2 (64.45 Wm^?2) from the direct measurement and NCEP reanalysis, respectively. The NCEP reanalysis is being widely used in numerical modeling studies, and the discrepancies shown in the NCEP reanalysis in present study will be of immense use to the modeling community of the Indian Ocean in general and Southern Indian Ocean in particular.  相似文献   

脉冲星射电轮廓中高斯成分在主脉冲和中间脉冲的不同分布          下载免费PDF全文

韩晓红  YUEN Rai 《天文学报》2022,63(3):29-57

研究了高斯辐射成分在可视点所画出轨迹上的分布,这个可视点因脉冲星的转动而作非匀速度运动.通过假设辐射区域围绕磁轴均匀分布,一个高斯辐射成分便对应于可视轨迹划过的一个辐射区域.因为演示辐射区域在可视轨迹上是不均匀的分布,因此高斯成分沿轨迹也是不均匀的,而高斯成分的密度在磁轴与视线距离最近时为最大.高斯成分的分布取决于脉冲星的两个角度:旋转轴和视线之间的夹角,以及磁轴和旋转轴之间的倾角.基于此模型,一个脉冲星平均轮廓中观察到的多个高斯成分便对应于可视轨迹在特定的转动相位范围内的辐射区域.演示了脉冲星旋转的近侧和远侧的相位,分别对应的主脉冲和中间脉冲,两者高斯成分的数量和分布是不同的.而且还发现,沿可视轨迹上的辐射区域总数与围绕磁轴的辐射区域的总数是不同,并且预测的辐射区域数目会因忽略可见点的运动而明显不同.拟合表明脉冲星轮廓的高斯成分的形状和数量可能与实际构成轮廓的成分的形状和数量不同.以PSR B0826–34的辐射为例,并假设辐射来自单一磁极.  相似文献   

Geochemical studies of granitoids from Shyok tectonic zone of Khardung-Panamik section,Ladakh, India     

D. Rameshwar Rao  Hakim Rai 《Journal of the Geological Society of India》2009,73(4):553-566

The Shyok tectonic zone lies to the north of Ladakh magmatic arc or the Ladakh batholith in the Trans-Himalaya of Ladakh district, J & K. Investigations were carried out on the granitoids exposed along Leh-Siachan highway between Khardung and Panamik villages. The granitoid bodies under study are: Khardung granite (KG), Tirit granite (TG) and Panamik granite (PG) belonging to Ladakh batholith, Shyok ophiolitic mélange and Karakoram batholith respectively. Though the granitoids belong to different litho-tectonic units, yet they have subduction related geochemical characters typical of Andean-type granitoids. Re-melting of crustal rocks of volcanic arc affinity has played an important role for the origin of KG rocks which are more evolved, while the TG and PG rocks represent transitional tectonic environment from primitive to mature arc.  相似文献   

Framboidal — colloform — recrystallised pyrite in the granitoids of Wahkyn area,West Khasi hills,Meghalaya     

N. Ranganath  Ashok Kumar Padhi  Ajoy Kumar Padhi  Ashwini Kumar Rai 《Journal of the Geological Society of India》2009,74(5):591-596

Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities. The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests their sedimentary origin.  相似文献   

Vertical structure of orographic precipitating clouds observed over south Asia during summer monsoon season     

Shailendra Kumar  G S Bhat 《Journal of Earth System Science》2017,126(8):114

Orography profoundly influences seasonal rainfall amount in several places in south Asia by affecting rain intensity and duration. One of the fundamental questions concerning orographic rainfall is nature of the associated precipitating clouds in the absence of synoptic forcing. It is believed that these clouds are not very deep, however, there is not much information in the literature on their vertical structure. The present study explores the vertical structure of precipitating clouds associated with orographic features in south Asia using data collected with the precipitation radar on board the Tropical Rainfall Measuring Mission satellite. Two types of precipitating clouds have been defined based on cloud echo top height, namely, shallow echo-top cloud and medium echo-top cloud. In both, radar reflectivity factor is at least 30 dBZ at 1.5 km altitude, and tops of shallow and medium echo-top clouds lie below 4.5 km and between 4.5 and 8 km, respectively. The Western Ghats contains the highest fraction of the shallow echo-top clouds followed by the adjacent eastern Arabian Sea, while the Khasi Hills in Meghalaya and Cardamom Mountains in Cambodia contain the least fraction of them. Average vertical profiles of shallow echo-top clouds are similar in different mountainous areas while regional differences are observed in the medium echo-top clouds. Below 3 km, precipitation liquid water content in medium echo-top clouds is the highest over the Western Ghats and the eastern Arabian Sea. The average precipitation liquid water content increases by \(0.16\,\hbox { gm m}^{-3}\) for shallow echo-top clouds between 3 and 1.5 km altitude, while the corresponding increase for medium echo-top clouds is in 0.05–0.08 \(\hbox { gm m}^{-3}\) range.  相似文献   

Palaeoweathering,composition and tectonics of provenance of the Proterozoic intracratonic Kaladgi–Badami basin,Karnataka, southern India: Evidence from sandstone petrography and geochemistry     

Sukanta Dey  A.K. Rai  Anjan Chaki 《Journal of Asian Earth Sciences》2009,34(6):703-715

Petrographic and geochemical data on the sandstones of the Proterozoic intracratonic Kaladgi–Badami basin, southern India are presented to elucidate the palaeoweathering pattern, and composition and tectonics of their provenance. The Kaladgi–Badami basin, hosting the Kaladgi Supergroup, occupies an E–W trending area. The Supergroup unconformably overlies Archaean basement TTG gneisses, granites and greenstones, comprises a cyclic arenite–pelite–carbonate association and is divided into the Bagalkot and Badami Groups. The immature arkosic character of the basal Saundatti Quartzite Member (Bagalkot Group) containing fresh and angular feldspars, along the northern margin of the basin, suggests that during the initial stage of deposition, this part of the basin received sediments from a restricted, uplifted and less weathered source dominated by K-rich granites occurring to the north. In contrast, the Saundatti Quartzite along the southern margin displays a mostly mature, quartz-rich character with less abundant but severely weathered feldspars, and higher SiO₂ and CIA but lower Al₂O₃, TiO₂, Rb, Sr, Ba, K₂O, K₂O/Na₂O, Zr/Ni and Zr/Cr. This is interpreted in terms of a tectonically stable, considerably weathered mixed source (Archaean gneisses, granites and greenstones) along the southern fringe of the basin. The highly mature (quartz arenite) Muchkundi Quartzite Member (also of the Bagalkot Group), occurring higher up in the succession, exhibits minor but severely altered feldspars, and higher SiO₂, Na₂O, CIA, Cr and Ni with lower K₂O, Al₂O₃, TiO₂ and K₂O/Na₂O. This reflects that with the passage of time the source evolved to a uniform, extensively weathered, tectonically stable peneplained provenance which consisted of less evolved TTG gneisses and greenstones. This was followed by closure, deformation and upliftment of the basin hosting the Bagalkot Group and subsequent deposition of the Badami Group. Sandstone Members of this younger Group (Cave-Temple Arenite and Belikhindi Arenite) range widely in mineralogy (quartz arenite to arkose) and chemistry (including CIA), and point to a source that varied from uplifted, less weathered K-rich granites to less evolved, peneplained TTG gneisses and greenstones or even Bagalkot sediments. Variable alteration of feldspars in the Kaladgi sandstones and severe depletion of Ca, Na and Sr in the associated shales indicate a humid tropical (tropical and subtropical) climate facilitating chemical weathering.  相似文献   

Plane symmetric inhomogeneous cosmological models with a perfect fluid in General Relativity II     

Anirudh Pradhan  Anju Rai 《Astrophysics and Space Science》2008,314(1-3):225-229

We investigate a class of solutions of Einstein equations for the plane symmetric perfect fluid case. If these solutions have shear, they must necessarily be non-static. Some physical and geometric properties of the models are also discussed.   相似文献