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1.
Sudden short-duration decreases in cosmic ray flux, known as Forbush decreases (FDs), are mainly caused by interplanetary disturbances. A generally accepted view is that the first step of an FD is caused by a shock sheath and the second step is due to the magnetic cloud (MC) of the interplanetary coronal mass ejection (ICME). This simplistic picture does not consider several physical aspects, such as whether the complete shock sheath or MC (or only part of these) contributes to the decrease or the effect of internal structure within the shock-sheath region or MC. We present an analysis of 16 large (\({\geq}\,8 \%\)) FD events and the associated ICMEs, a majority of which show multiple steps in the FD profile. We propose a reclassification of FD events according to the number of steps observed in their respective profiles and according to the physical origin of these steps. This study determines that 13 out of 16 major events (\({\sim}\,81\%\)) can be explained completely or partially on the basis of the classic FD model. However, it cannot explain all the steps observed in these events. Our analysis clearly indicates that not only broad regions (shock sheath and MC), but also localized structures within the shock sheath and MC have a significant role in influencing the FD profile. The detailed analysis in the present work is expected to contribute toward a better understanding of the relationship between FD and ICME parameters. 相似文献
2.
Manish Kumar Vasim Riyasat Shaikh 《Journal of the Indian Society of Remote Sensing》2013,41(2):417-424
Identification of suitable site for urban development in hilly areas is one of the critical issues of planning. Site suitability analysis has become inevitable for delineating appropriate site for various developmental initiatives, especially in the undulating terrain of the hills. The study illustrates the use of geographic information system (GIS) and multicriteria evaluation (MCE) technique for selection of suitable sites for urban development in Mussoorie municipal area, Dehradun district, Uttarakhand. For this purpose Toposheet and IKONOS satellite data were used to generate various thematic layers using ArcGIS software. Criteria using five parameters, i.e. slope, road proximity, land use/land cover, land values and geological formation were used for site suitability analysis following land evaluation. The generated thematic maps of these criteria were standardized using pairwise comparison matrix known as analytical hierarchy process (AHP). A weight for each criterion was generated by comparing them with each other according to their importance. With the help of these weights and criteria, final site suitability map was prepared. 相似文献
3.
An experimental investigation of the airflow structure in the near surface region over the wind-sheared air–water interface
is reported. The two-dimensional velocity fields in a plane perpendicular to the water surface were measured using particle
image velocimetry (PIV) technique over a wind speed range from 1.5 to 4.4 m s−1. The results show a reduction in the mean velocity magnitudes and the tangential stresses when gravity waves appear on the
surface. An enhanced vorticity layer was observed immediately above the water surface that extended to a height of approximately
2 cm. The vorticity was enhanced by an order of magnitude, and the energy dissipation rate was enhanced by a factor of 7 in
this layer at all wind speeds. The vertical profiles of Reynolds stress, energy production, and dissipation indicate the contribution
of surface waves in the enhanced transfer of momentum and energy between the two fluids. The results in this study show that
the flow dynamics in a layer immediately adjacent to the water surface whose thickness is of the order of the significant
wave height is significantly different from that at greater heights. Thus, it is concluded that the quantitative investigation
of the flow in the immediate vicinity of the interface is vital for an improved understanding of the heat, mass, and momentum
exchange between air and water. The present study demonstrates that PIV is an effective technique to accurately measure the
velocity fields in this region. 相似文献
4.
5.
The flow of an infinitely extending homogenous thermally conducting plasma permeated by a variable magnetic field is considered.
The combined effect of several physical parameters, namely Hall currents, finite conductivity, ion viscosity and thermal conductivity
on plasma instability is studied in the framework of Tsallis statistics. A new Jeans Criterion is derived, which depends explicitly
on the nonextensive parameter q. The standard values are obtained in the limiting case q=1. 相似文献
6.
Nitrate pollution of ground waters from shallow basaltic aquifers,Deccan Trap Hydrologic Province,India 总被引：2，自引：0，他引：2
Analyses of groundwater samples collected from several locations in a small watershed of the Deccan Trap Hydrologic Province, indicated anomalously higher values of nitrate than the background. However, the NO3 concentrations in water from dug wells under pastureland where the subsurface material consisted of stony waste were minimum. The maximum values were reported for water from dug wells where the principal land use was agricultural. Lowering of NO3 values under shallow water-table conditions suggests denitrification. Higher concentrations of nitrate determined for samples collected from the wells with a deeper water-table indicate that denitrification process is inactive. The high values of nitrate coinciding with agricultural land use indicate fertilizers as the main source of nitrate pollution of ground-water. Decrease in Cl/NO3 ratio for agricultural land use confirms this inference. 相似文献
7.
Deepak M. Maurya Prabhuti Tiwari Mohamedharoon Shaikh Atul K. Patidar Naimisha Vanik Akash Padmalal Laxman S. Chamyal 《地球表面变化过程与地形》2021,46(7):1268-1293
Drainage reorganization on restricted temporal and spatial scales is poorly-documented. We attempt to decode the relatively complicated mechanism of drainage realignment involving two small rivers that show structurally controlled, highly anomalous channel networks. We provide geomorphic and shallow subsurface evidence using ground-penetrating radar (GPR) for the presence of a buried paleo-valley flowing northward through the wind gap and surface faulting along the range bounding Katrol Hill Fault (KHF) which correlates with the previously known three surface faulting events in last ~30 ka bp . Most of the present river channels and the KHF zone are occupied by aeolian miliolite (local name) which is stratigraphic and lithologic equivalent of the Late Quaternary carbonate rich aeolianite deposits occurring in several parts of the globe. The history of drainage evolution in the study area comprises pre-miliolite, syn-miliolite and post-miliolite phases. Geomorphic evidences show that the paleo-Gangeshwar River flowed north through the wind gap and paleo-valley, while the short paleo-Gunawari occupied the saddle zone to the east of Ler dome prior to and during the phase of miliolite deposition which ended by ~40 ka bp . Southward tilting of the Katrol Hill Range (KHR) due to surface faulting cut off the catchment of the paleo-Gangeshwar River. The abandoned catchment stream extended its channel eastward along the strike through top-down process while the paleo-Gunawari River extended its course westward by headward erosion (bottom-up process). As the channels advanced towards each other they joined to produce the “S”-shaped bend which formed the capture point. We conclude that multiple surface faulting events along the KHF in the last ~30 ka bp , resulted in uplift and tilting of the KHR which caused drainage realignment by river diversion, beheading and river capture. Our study shows that the complexity of drainage reorganization processes is more explicit on shorter rather than longer timescales. 相似文献
8.
Gravity data collected by the Geological Survey of Bangladesh are processed and interpreted for imaging of a sediment-basement interface over the northwestern part of Bangladesh. The observed gravity data are processed for discriminating gravitational fields contributed subtly from the shallow basement topographic feature with the twelve nodal piecewise cubic polynomial–based finite–element approach. In spectral analysis, the presence of a widely spread shallow basement feature has been detected and interpretation of gravity data using a two-dimensional gravity inversion technique indicates that its depth ranges from 0.041 km to 0.570 km relative to ground surface. In the northern part of the study area, the inferred basement configuration shows a general depression of the basement in the Takurgaon-Panchagar and Lalmonirhat districts and reaches a maximum depth of about 0.570 km. In the Nilphamari district and its southwestern part, the basement occurs at the most shallow depth due to its upliftment. However, the estimated sediment-basement interface depths are compared with the borehole and other geophysical interpretative information and are found to be consistent. 相似文献
9.
Mafic alkalic magmatism in central Kachchh,India: a monogenetic volcanic field in the northwestern Deccan Traps 总被引：1，自引：0，他引：1
Magmatism in Kachchh, in the northwestern Deccan continental flood basalt province, is represented not only by typical tholeiitic
flows and dikes, but also plug-like bodies, in Mesozoic sandstone, of alkali basalt, basanite, melanephelinite and nephelinite,
containing mantle nodules. They form the base of the local Deccan stratigraphy and their volcanological context was poorly
understood. Based on new and published field, petrographic and geochemical data, we identify this suite as an eroded monogenetic
volcanic field. The plugs are shallow-level intrusions (necks, sills, dikes, sheets, laccoliths); one of them is known to
have fed a lava flow. We have found local peperites reflecting mingling between magmas and soft sediment, and the remains
of a pyroclastic vent composed of non-bedded lapilli tuff breccia, injected by mafic alkalic dikes. The lapilli tuff matrix
contains basaltic fragments, glass shards, and detrital quartz and microcline, with secondary zeolites, and there are abundant
lithic blocks of mafic alkalic rocks. We interpret this deposit as a maar-diatreme, formed due to phreatomagmatic explosions
and associated wall rock fragmentation and collapse. This is one of few known hydrovolcanic vents in the Deccan Traps. The
central Kachchh monogenetic volcanic field has >30 individual structures exposed over an area of ∼1,800 km2 and possibly many more if compositionally identical igneous intrusions in northern Kachchh are proven by future dating work
to be contemporaneous. The central Kachchh monogenetic volcanic field implies low-degree mantle melting and limited, periodic
magma supply. Regional directed extension was absent or at best insignificant during its formation, in contrast to the contemporaneous
significant directed extension and vigorous mantle melting under the main area of the Deccan flood basalts. The central Kachchh
field demonstrates regional-scale volcanological, compositional, and tectonic variability within flood basalt provinces, and
adds the Deccan Traps to the list of such provinces containing monogenetic- and/or hydrovolcanism, namely the Karoo-Ferrar
and Emeishan flood basalts, and plateau basalts in Saudi Arabia, Libya, and Patagonia. 相似文献
10.
Geology of the saucer-shaped sill near Mahad, western Deccan Traps, India, and its significance to the Flood Basalt Model 总被引：1，自引：0，他引：1
An ～22-m-thick saucer-shaped sill occurs near Mahad and is exposed as a curvilinear, miniature ridge within the Deccan Traps. The sill has variable dips (42–55°). It has a 7.1-km long axis and 5.3 km short axis (aspect ratio of 1.4) and is larger than the MV sill of the Golden Valley sill complex, South Africa and the Panton sill, Australia. The sill has distinct glassy upper and lower chilled margins with a coarse-grained highly jointed core. The samples from the margin are invariably fractured and iron stained because of deuteric alteration. The rock from the sill is plagioclase-phyric basalt. At least three thick sill-like apophyses emanate from the base of the main sill. The apophyses change direction because of bending and thinning from a horizontal concordant sheet at the top to a discordant inclined form that bends again to pass into a lower horizontal concordant sheet. We interpret such features as ‘nascent saucer-shaped sills’ that did not inflate to form nested sills. Geochemically, the sill consists of poorly differentiated tholeiitic basalt that has a restricted geochemical range. Critical trace element ratios and primitive mantle normalised trace and REE patterns indicate that the sills have geochemical affinities to the Poladpur chemical type and that the pahoehoe flow they intrude belongs to the Bushe Formation. Calculated magmatic overpressures during sill emplacement range from 8.4 to 11.3 MPa (for Young’s modulus E?=?5 GPa) and 16.7 to 22.5 MPa (for E=10 GPa) and depth to magma chamber ranges from 8.5 to 11.5 km (E?=?5 GPa) and 17.1 to 22.9 km (E?=?10 GPa), consistent with petrological and gravity modelling. The volume of the Mahad sill is approximately 276 km3 and is constant irrespective of the variations in the values of host-rock Young’s modulus. In 1980, Cox (J Petrol 21:629–650, 1980) proposed a conceptual model of the crust–mantle section beneath the Karoo CFB which is considered as the fundamental model for flood basalt volcanism. Our paper confirms the presence of a sill plus the inferred substructure beneath Mahad that are compatible with predictions of that model. In LIPS, saucer-shaped sills are formed in areas experiencing extensional tectonics where processes such as the Cook–Gordon delamination and Dundurs elastic extensional mismatch between layered sedimentary rocks or lava flows are responsible for the deflection of dykes into sills. A similar process is envisaged for the formation of the Mahad sill. 相似文献