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1.
Having recognized that it is the tropospheric temperature (TT) gradient rather than the land–ocean surface temperature gradient that drives the Indian monsoon, a new mechanism of El Niño/Southern Oscillation (ENSO) monsoon teleconnection has been unveiled in which the ENSO influences the Indian monsoon by modifying the TT gradient over the region. Here we show that equatorial Pacific coralline oxygen isotopes reflect TT gradient variability over the Indian monsoon region and are strongly correlated to monsoon precipitation as well as to the length of the rainy season. Using these relationships we have been able to reconstruct past Indian monsoon rainfall variability of the first half of the 20th century in agreement with the instrumental record. Additionally, an older coral oxygen isotope record has been used to reconstruct seasonally resolved summer monsoon rainfall variability of the latter half of the 17th century, indicating that the average annual rainfall during this period was similar to that during the 20th century. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
2.
We have analyzed the solar irradiance data from the Earth Radiation Budget Satellite(ERBS)during the time period from 1984 October 15 to 2003 October 15.By first filtering the data by Simple Exponential Smoothing,we have applied the periodogram method to the processed data in order to search for its time variation.The study exhibits multi-periodicities on these data around 110,118,574 and 740d with very high confidence levels(more than 99%).These periods are significantly similar to the periods of other solar activities which may suggest that solar irradiance may be associated with other solar activities. 相似文献
3.
Koushik Sen Ruchika Sharma B. R. Arora Vikram Gupta 《Journal of the Geological Society of India》2010,76(5):322-330
Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show
good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic
lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively.
Both Vp and Vs show positive correlation with the SiO2 content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility
(Km) having ‘r’ value of 0.86. The correlation between Vs-Km, Vp-P′, Vp-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested
that, in paramagnetic granites, Vp is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other
hand, Vs is more dependent on the mineralogy alone. 相似文献
4.
Koushik Sen Ruchika Sharma B. R. Arora Vikram Gupta 《Journal of the Geological Society of India》2010,76(4):322-330
Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO2 content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (Km) having ‘r’ value of 0.86. The correlation between Vs-Km, Vp-P′, Vp-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, Vp is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone. 相似文献
5.
Koushik N. Kumar K. Kishore Ramkumar Geetha Subrahmanyam K. V. Kishore Kumar G. Hocking W. K. He Maosheng Latteck Ralph 《Climate Dynamics》2020,54(9):4059-4074
Climate Dynamics - In the present communication, characteristics of mean winds and planetary waves in the mesosphere lower thermosphere (MLT) region during sudden stratospheric warming (SSW) events... 相似文献
6.
Information on geographic distribution, population and threat status of most globally red listed species in the Indo Burma zone are inadequate. Given the increase in the prevalence of isolated forest patches in the part of this hotspot, evaluation is necessary on how size of the remnant forest patches and on-going disturbances affects structure and diversity of remaining habitats including the population of some globally threatened tree species. Quantitative vegetation inventory by 500 m long and 10 m wide (0.5 ha) line transects were randomly set in nine fragmented tropical semi-evergreen forest patches in Tripura, Northeast India. The studied forests patches grouped into small, medium and large based on their respected sizes. Spatial variability was analysed in woody species diversity and structure along the patch size gradients and their response to both patch size and anthropogenic disturbances. Out of 167 species, 13 identified as red-listed species by IUCN under the present inventory. Most of the diversity and structural parameters showed statistically significant positive response with the forest patch size, except for stand dominance, disturbance, sapling density and number of aggregated distribution pattern decreased when patch size increased. In addition, most of the diversity and structural attributes showed negative response with disturbances. Present baseline data would serve as an effective tool for management and protection of this important forest type. Future habitat restoration programme and strategies for relocation of additional population and re-introduction of those globally threatened trees are recommended. 相似文献
7.
Kapila Dahanayake Nayomi Kulasena G. V. Ravi Prasad Koushik Dutta D. K. Ray 《Natural Hazards》2012,63(1):197-209
After the 2004 Sumatra?CAndaman tsunamigenic earthquake, waters from the ocean moved upstream along rivers, bays, harbors, and lagoons and inundated many coastal and inland locations in the southern, eastern, and northern parts of Sri Lanka. The tsunami waters were observed to move upwards inland and then recede downwards to the ocean after varying inundation periods in different coastal areas. Subsequent massive tsunami waves came with the wave height varying from 3 to 8?m inland with speed of about 30?C40?kmph. The oceanic waves carrying heterogeneous sediments with water deposited them in coastal as well as inland locations about 1?km from the present coastline. Given the chaotic nature of tsunami oceanic waves, pre-tsunami deposits, such as beach sands, debris from coral reefs and buildings, parts of vehicles and ships, and tree trunks are found incorporated in authentic tsunami sediments. Thus, the texture, structure, and composition of sediments deposited by tsunami waters differed from one location to another. Therefore, in identifying paleo-tsunami sediments, care was taken to compare them with diagnostic unmixed uncontaminated recent tsunami sediments having characteristic textures and marine microfossil assemblages, such as foraminifera, radiolarians, and diatoms where preserved in coastal depressions. The radiocarbon ages of the carbonate and the organic fractions of these sediments are stratigraphically inconsistent, indicating mixing of sediments by the tsunami waves. The concentrations of organic carbon and nitrogen and their isotopic signatures confirm marine origin of these sediments. 相似文献
8.
Prasad Amrita Roy Soumya Ghosh Koushik Panja Subhash Chandra Patra Sankar Narayan 《Solar System Research》2021,55(2):169-182
Solar System Research - In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar... 相似文献
9.
Kavita Tripathi Koushik Sen A. K. Dubey 《International Journal of Earth Sciences》2012,101(3):761-772
The present day South Tibetan Detachment (STD) of Higher Himalaya is a system of low-angle normal faults. In the Himachal
High Himalaya, the STD hanging wall is characterized by the presence of S-type per-aluminous Paleozoic (~475 Ma) granite called
the Kinnaur Kailash Granite (KKG). This granite is later intruded by Cenozoic leucogranites (~18 Ma) in vicinity of the STD
zone. In this work, microstructures, anisotropy of magnetic susceptibility (AMS), and U–Pb geochronology were carried out
on the KKG and the leucogranites with an aim to (a) understand the conditions of fabric development and (b) decipher the tectonic
relationship between deformation along the STD and the evolution of these granites. Microstructural features and magnetic
anisotropy indicate that the granites are intensely deformed in vicinity of the STD and preserve their emplacement-related
fabric in the interior parts. It is inferred that close to the STD zone, fabrics of both the KKG and the leucogranite are
tectonic and are modified by the Cenozoic (~20 Ma) right-lateral slip and extensional tectonics. Magnetic fabric in the interior
parts of the KKG is related to its emplacement indicating that original fabric was preserved. U–Pb geochronology of zircons
from two samples of the KKG yields crystallization age of 477.6 ± 3.4 and 472 ± 4 Ma. The leucogranite gives a crystallization
age of 18.5 ± 0.6 Ma. Zircons from the KKG also reveal signatures of a deformation event (20.6 ± 2.3 Ma) at its rim. It is
inferred that deformation of the external rim of the KKG and crystallization of the leucogranites are synchronous and triggered
by ductile deformation along the STD. 相似文献
10.
Sankar Narayan Patra Koushik Ghosh Subhash Chandra Panja 《Astrophysics and Space Science》2011,334(2):317-323
In the present paper we have analyzed the daily Forbush decrease indices from January 1, 1967 to December 31, 2003. First
filtering the time series by Simple Exponential Smoothing, we have applied Scargle Method of Periodogram on the processed
time series in order to search for its time variation. Study exhibits periodicities around 174, 245, 261, 321, 452, 510, 571,
584, 662, 703, 735, 741, 767, 774, 820, 970, 1062, 1082, 1489, 1715, 2317, 2577, 2768, 3241 and 10630 days with confidence
levels higher than 90%. Some of these periods are significantly similar to the observed periodicities of other solar activities,
like solar filament activity, solar electron flare occurrence, solar-flare rate, solar proton events, solar neutrino flux,
solar irradiance, cosmic ray intensity and flare, spectrum of the sunspot, solar wind, southern coronal hole area and solar
cycle, which may suggest that the Forbush decrease behaves similarly to these solar activities and these activities may have
a common origin. 相似文献