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41.
Granulometric analysis of nineteen sediment samples has been carried out for their statistical and textural parameters. The
samples are collected from the northern and southern margins of Schirmacher Oasis extending below the polar ice sheet and
grading to coastal area respectively and main rocky land of Schirmacher including lakes. The analysis shows that most of the
sediments are of medium grain size and fall in poor to very poor sorted category.
An attempt has been made to interpret the depositional set-up by plotting the scatter patterns between various textural parameters,
including C-M plot and arithmetic log-probability curves. The influence of physical parameters viz. low to high velocity winds,
ice and meltwater on sediment characteristics has been discussed. 相似文献
42.
X-ray emissions from Young Stellar Objects (YSO) are detected by many X-ray missions that are providing important information about their properties. However, their emission processes are not fully understood. In this research note, we propose a model for the generation of emissions from a YSO on the basis of a simple interaction between the YSO and its surrounding circumstellar accretion disc containing neutral gas and charged dust. It is assumed that the YSO has a weak dipole type magnetic field and its field lines are threaded into the circumstellar disc. Considering the motion of ions and charged dust particles in the presence of neutral gas, we show that the sheared dust-neutral gas velocities can lead to a current along the direction of ambient magnetic field. Magnitude of this current can become large and is capable of generating an electric field along the magnetic field lines. It is shown how the particles can gain energy up to MeV range and above, which can produce high-energy radiations from the YSO. 相似文献
43.
Pramoda Kumar Samal Rajib Saha Pankaj Jain John P. Ralston 《Monthly notices of the Royal Astronomical Society》2008,385(4):1718-1728
We introduce new symmetry-based methods to test for isotropy in cosmic microwave background (CMB) radiation. Each angular multipole is factored into unique products of power eigenvectors, related multipoles and singular values that provide two new rotationally invariant measures mode by mode. The power entropy and directional entropy are new tests of randomness that are independent of the usual CMB power. Simulated Galactic plane contamination is readily identified. The ILC– WMAP data maps show seven axes well aligned with one another and the direction Virgo. Parameter free statistics find 12 independent cases of extraordinary axial alignment, low power entropy, or both having 5 per cent probability or lower in an isotropic distribution. Isotropy of the ILC maps is ruled out to confidence levels of better than 99.9 per cent, whether or not coincidences with other puzzles coming from the Virgo axis are included. Our work shows that anisotropy is not confined to the low l region, but extends over a much larger l range. 相似文献
44.
We study the magnetic and velocity field evolution in the two magnetically complex active regions NOAA 10486 and NOAA 10488 observed during October–November 2003. We have used the available data to examine net flux and Doppler velocity time profiles to identify changes associated with evolutionary and transient phenomena. In particular, we report detection of rapid moving features observed in NOAA 10486 during the maximum phase of the X17.2/4B superflare of October 28, 2003. The velocity of this moving feature is estimated around 40 km/s, i.e., much greater than the usual Hα flare-ribbons’ separation speed of 3–10 km/s, but similar to the velocity of seismic waves, i.e., ~ 45 km/s reported earlier by Kosovichev & Zharkova (1998). 相似文献
45.
We reinvestigate the problem of Hα intensity oscillations in large flares, particularly those classified as X-class flares. We have used high spatial and temporal resolution digital observations obtained from Udaipur Solar Observatory during the period 1998–2006 and selected several events. Normalized Lomb-Scargle periodogram method for spectral analysis was used to study the oscillatory power in quiet and active chromospheric locations, including the flare ribbons. 相似文献
46.
This study characterizes the black carbon in Agra, India home to the Taj Mahal—and situated in the Indo-Gangetic basin.The mean black carbon concentration is 9.5 μg m~(-3)and, owing to excessive biomass/fossil fuel combustion and automobile emissions, the concentration varies considerably. Seasonally, the black carbon mass concentration is highest in winter, probably due to the increased fossil fuel consumption for heating and cooking, apart from a low boundary layer. The nocturnal peak rises prominently in winter, when the use of domestic heating is excessive. Meanwhile, the concentration is lowest during the monsoon season because of the turbulent atmospheric conditions and the process of washout by precipitation. The ratio of black carbon to brown carbon is less than unity during the entire study period, except in winter(December). This may be because that biomass combustion and diesel exhaust are major black carbon contributors in this region, while a higher ratio in winter may be due to the increased consumption of fossil fuel and wood for heating purposes. ANOVA reveals significant monthly variation in the concentration of black carbon; plus, it is negatively correlated with wind speed and temperature. A high black carbon mass concentration is observed at moderate(1–2 m s~(-1)) wind speed, as compared to calm or turbulent atmospheric conditions. 相似文献
47.
—A ten-level axi-symmetric primitive equation model with cylindrical coordinates is used to simulate the tropical cyclone evolution from a weak vortex for the Bay of Bengal region. The physics of the model comprises the parameterization schemes of Arakawa-Schubert cumulus convection (Lord et al., 1982) and Deardorff’s (1972) planetary boundary layer. The initial conditions have been taken from the climate mean data for November of Port Blair (92.4 E, 11.4 N) in the Bay of Bengal, published by the India Meteorological Department. An initial vortex has been designed to have tangential wind maximum of 10 m/s at 120-km radius with a central surface pressure of 1008 hPa. As a control experiment, referred to as ASBB1, the model is integrated for 240 h maintaining the sea-surface temperature (SST) constant at 301 K. The results of the control experiment reveal a slow decrease of the Central Surface Pressure (CSP) from the initial value of 1008 hPa to 970 hPa at 156 h. After 156 h the CSP decreased sharply until 186 h, attaining 890 hPa. The tangential wind at 1 km level attained the Cyclone Threshold Intensity (CTI) of 17 m/s around 78 h and a maximum of 87 m/s was found at 210 h. These features indicate a predeveloping stage up to 156 h, a deepening stage of 30 h from 156–186 h followed by the mature stage. The mature stage is characterized by the simulation of the central eye region, warm core, strong cyclonic circulation in the central 300 km with low-level inflow; strong vertical motion at the eye wall and outflow aloft. The convection features of the different cloud types conform with the circulation features. The control experiment clearly indicates the evolution of a cyclone with hurricane intensity from a weak vortex. In part two of the paper, results from sensitivity experiments with respect to variations in latitude, SST and initial thermodynamic state have been presented. 相似文献
48.
D. K. Singh Ashok K. Singh R. P. Patel R. P. Singh A. K. Singh 《Annales Geophysicae》1999,17(10):1260-1267
The morphology of ELF hiss events observed at low-latitude ground station Varanasi (L = 1.07, geomagnetic latitude 14°55′N) are reported, which consist of two types: (1) events which propagated in ducted mode along the geomagnetic field line corresponding to observing station Varanasi and (2) events which propagated in ducted mode along higher L-values (L = 4–6), after reaching the lower edge of ionosphere excite the Earth-ionosphere wave guide and propagate towards equator to be received at Varanasi. To understand the generation mechanism of ELF hiss, incoherent Cerenkov radiated power from the low latitude and middle latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave-particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF hiss. 相似文献
49.
Analysis of fractures inferred from DBTM and remotely sensed data for groundwater development in godavari sub-watershed, Giridih, Bihar 总被引:2,自引:2,他引:0
Ashok Kumar Savita Tomar Lal Bihari Prasad 《Journal of the Indian Society of Remote Sensing》1999,27(2):105-114
Godavari sub-watershed is a part of buried pediplain developed over ‘Chotanagpur’ granite gneiss. Aquifer is unconfined in nature and groundwater occurs under water table condition. In the study area, groundwater is being exploited only through dugwells which are not capable of sustaining long duration pumping. Groundwater exploration involves the investigation of depth and nature of weathered and fractured horizon. To understand the groundwater storage and retrieval in the area, the basement topography derived from Digital Basement Topography Modelling (DBTM), the lineaments identified on remotely sensed data and geohydrological and physiographic data have been analysed. From DBTM, fracture zones have also been inferred. Lineaments (probable fractures) identified with the help of remotely sensed data are linear features representated on a planner surface. Lineaments in the area are subtle in expression due to deeply buried pediplian. Correlation of lineaments with DBTM reveals that a few lineaments/fractures are deep seated and a few have no sub-surface extensions. Also some sub-surface fractures inferred from DBTM have no expressions on the image. Attempt has been made to delineate more authentic lineaments/fractures with the help of remotely sensed data and DBTM. Correlation of probable fractures inferred from remotely sensed data and fracture zones inferred from DBTM indicated that 40 per cent of lineaments seems to be real fractures. Higher correlation may be achieved where lineaments are prominent and reproducible. It has also been observed that those lineaments which correlate with the fracture zones inferred from DBTM, are also not completely traceable in their linear extent. The exaggeration in length of lineaments may be due to subtle nature of lineaments. Correlation shows that remotely sensed lineaments are improtant for groundwater exploration and its authenticity can be further ascertained with DBTM. 相似文献
50.
Ashok Kumar 《Journal of the Indian Society of Remote Sensing》1999,27(1):13-22
Alaunja watershed, located on ‘Chotanagpur’ plateau of Bihar, is mainly under single cropping. The area receives more than 1000 mm of rainfall but it has not been utilised properly to increase the agricultural output. The remote sensing, geophysical, DBTM (Digital Basement Terrain Model) and GIS (Geographic information System) techniques were used for providing scientific database for sustainable utilisation of water resources in watershed perspective. The landuse, soil and surface water body maps have been prepared using remotely sensed data. DBTM has been generated based on depth of basement information derived from geophysical data to provide information regarding aquifer geometry, fracture zones and sub-surface basins. Analysis indicated that surface and groundwater resources have potential to irrigate 53 per cent of geographical area of the watershed. But at present, this available potential has been utilised only to irrigate 7.03 per cent area of the watershed. Feasibility for large scale development of groundwater through dugwell is possible only in 2 per cent area of the watershed. The available groundwater potential to irrigate 28 per cent area of watershed can not be utilised through dugwells. The surface water potential is also poorly utilised. The present study also helped in prioritising the water resource development activities. 相似文献