Editorial     

Prabhakar Misra 《Journal of the Indian Society of Remote Sensing》1989,17(3):ii-ii

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Representative abundances of a few positive ions in the innermost coma of comet Halley     

P. P. Saxena  Alka Misra 《Earth, Moon, and Planets》1993,60(1):59-68

The production rate of H₂O molecules at a heliocentric distance of 1 AU for comet Halley and the abundance ratio with respect to water (H₂O) of parent molecules at the cometary nucleus from the paper of Yamamoto (1987) have been used to compute the number densities of positive ions viz. H₃O⁺, H₃S⁺, H₂CN⁺, H₃CO⁺, CH₃OH ₂ ⁺ and NH ₄ ⁺ at various cometocentric distances within 600 kms from the nucleus.The role of proton transfer reactions in producing major ionic species is discussed. A major finding of the present investigation is that NH ₄ ⁺ ion which may be produced through proton transfer reactions is the most abundant ion near the nucleus of a comet unless the abundance of NH₃ as a parent is abnormally low. Using the quoted value of Q(NH₃)/Q(H₂O) for comet Halley and the life times of NH₃ and H₂O molecules, the abundance ratio N(NH₃)/N(H₂O) is found to be one-third of that used in the present paper. The consequent proportionate decrease in the NH ₄ ⁺ ions does not, however, affect its superiority in number density over other ions near the nucleus.The number density of the next most abundant ion viz. H₃O⁺ is found to be 4 × 10⁴ cm^-3 at the nucleus of comet Halley and decreases by a factor of two only upto a distance of 600 K ms from the nucleus. The ionic mass peak recorded by VEGA and GIOTTO spacecrafts atm/q = 18 is most probably composite of the minor ionic species H₂O⁺, as its number density = 10² cm^-3 remains virtually constant in the inner coma and of NH ₄ ⁺ , the number density of which at large cometocentric distances may add to the recorded peak atmlq = 18. The number densities of other major ions produced through proton transfer from H₃O⁺ are also discussed in the region within 600 K ms from the nucleus of comet Halley.  相似文献   

Magnetospheric electric field from low latitude whistlers during magnetic storm     

K.D. Misra  B.D. Singh 《Planetary and Space Science》1980,28(5):449-452

An attempt has been made to estimate the east-west component (E_w) of the magnetospheric equatorial electric field near L = 1.12 during a magnetic storm period from the whistlers observed at our low latitude ground station, Nainital (geomag.lat. 19°1'N), on March 25, 1971 in the 0130–0500 IST sector. The method of measuring E_w from the observed cross L-motions of whistler ducts within the plasmasphere, indicated by changes in nose frequency of whistlers, has been outlined. The nose frequencies of non-nose whistlers under consideration have been deduced from Dowden-Allcock linear Q-technique. The variation of ($\text{?}{}_{\mathrm{n}}\text{)}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ with local time has been shown, the slope of which can be directly related to the convection electric field. The estimated equatorial electric field at L? 1.12 is in the range 0.1–0.5 mV m^?1 (in the 0130–0500 IST sector) during a storm period, which is in agreement with the results reported by earlier workers. The departure from a dipole field and the contribution of an induced electric field from the temporal changes have been discussed. The importance of an electric field study has been indicated.  相似文献   

Target rocks,impact glasses,and melt rocks from the Lonar impact crater,India: Petrography and geochemistry     

Shiloh Osae  Saumitra Misra  Christian Koeberl  Debashish Sengupta  Sambhunath Ghosh 《Meteoritics & planetary science》2005,40(9-10):1473-1492

Abstract— The Lonar crater, India, is the only well‐preserved simple crater on Earth in continental flood basalts; it is excavated in the Deccan trap basalts of Cretaceous‐Tertiary age. A representative set of target basalts, including the basalt flows excavated by the crater, and a variety of impact breccias and impact glasses, were analyzed for their major and trace element compositions. Impact glasses and breccias were found inside and outside the crater rim in a variety of morphological forms and shapes. Comparable geochemical patterns of immobile elements (e.g., REEs) for glass, melt rock and basalt indicates minimal fractionation between the target rocks and the impactites. We found only little indication of post‐impact hydrothermal alteration in terms of volatile trace element changes. No clear indication of an extraterrestrial component was found in any of our breccias and impact glasses, indicating either a low level of contamination, or a non‐chondritic or otherwise iridium‐poor impactor.  相似文献   

An ensemble strategy for high-resolution regional model forecasts     

V. Misra  M. K. Yau 《Meteorology and Atmospheric Physics》2001,78(1-2):61-74

Summary An ensemble methodology is proposed for very high-resolution regional model Quantitative Precipitation Forecasts. To facilitate a systematic study, the model and the boundary conditions are assumed to be perfect. The generation of perturbations is derived on the basis that the largest errors in precipitation forecasts at very high resolutions arise from miss-specified diabatic heat sources and sinks which feedback erroneously to the grid scale variables in the initial state. This methodology is tested in a Proxy Observed System Simulation Experiment (POSSE) involving an intense cyclone over eastern Canada. The perturbations of wind and temperature in this ensemble strategy are obtained as normalized coefficients of a Combined Empirical Orthogonal Function analysis of the difference fields between the control and the diabatically initialized model runs. These perturbations are added to and subtracted from the control initial state to obtain a set of two perturbed initial states. Several such perturbed initial states are obtained from initializing observed rain rates at different times close to the time of the analysis. The results from the POSSE reveal that the Quantitative Precipitation Forecast of the ensemble mean outperforms the control model run. Received August 8, 2000/Revised November 1, 2000  相似文献   

Sphalerite-bearing detrital ‘sand’ bodies in Mississippi Valley-type zinc deposits Mascot-Jefferson City district,Tennessee     

J. F. Matlock  K. C. Misra 《Mineralium Deposita》1993,28(5):344-353

The Mississippi Valley-type sphalerite mineralization in the Mascot-Jefferson City zinc district of East Tennessee occurs as open-space fillings in breccia bodies within the upper part of the Knox Group (Lower Ordovician) which is truncated by a regional unconformity. A lower age limit of mineralization is constrained by the formation of solution-collapse breccia bodies, which are believed to be related to the post-Knox unconformity. The breccias contain irregularly distributed “sand” bodies that represent cavities filled with well-laminated and size-graded, sphalerite-bearing, detrital, internal sediments. The texture, composition, and fluid inclusion characteristics of the sphalerite, are consistent with its local derivation from the wallrocks as detrital grains. The conformability between the laminations in the sediments and the bedding planes of the host carbonate rocks suggests that the sand bodies formed prior to the regional deformation event (Alleghenian orogeny). The stylolitization of carbonate and sphalerite clasts in the internal sediments as well as the deformation of the sphalerite are also consistent with a pre-Alleghenian age for the emplacement of the main-stage sphalerite mineralization in the Mascot-Jefferson City district and, by analogy, in other Lower Ordovician-hosted Mississippi Valley-type districts of the southern Appalachians.  相似文献   

A variable K planetary boundary-layer model     

Prasanta K. Misra 《Boundary-Layer Meteorology》1977,11(1):117-120

The steady-state, homogeneous and barotropic equations of motion within the planetary boundary layer are solved with the assumption that the coefficient of eddy viscosity varies as K(Z) = K _O(1–Z/h) ^p , where h is the height of the bounday layer and p is a parameter which depends on atmospheric stability. The solutions compare favourably with observed velocity profiles based on the Wangara data.  相似文献   

Petrology and sedimentation of the middle siwalik clays at dholkhand,saharanpur district,U.P., India     

Nityananda Bhattacharya  Sarada Saran Misra 《Contributions to Mineralogy and Petrology》1963,9(2):139-147

The Middle Siwalik clays at Dholkhand, Saharanpur district, U. P., in India were studied to investigate the nature of Siwalik (middle Miocene to lower Pleistocene) sedimentation in relation to the tectonism associated with the Himalayan orogenesis. The clays are reddish brown to buff in color containing montmorillonite, expandable mixed-layers, degraded chlorite, and illite. The clays were studied byX-ray diffractometry using standard techniques with copper radiation. The clay mineral distribution of the Middle Siwaliks indicates that the material was deposited under continental conditions in stream channels during periods of minimum current activity. The clays were deposited by slow sedimentation and are little affected by diagenesis. Further work in this area and elsewhere are now under progress to establish the relation of Siwalik sedimentation with the uplift of the Himalayas in the Tertiary period.  相似文献   

Role of remote sensing in demarcation of alluvial fan deposits in Tarai-Bhabar belt of Nainital District (U.P.) and the environmental impact assessment     

C. S. Agarwal  N. K. Choudhary  Ashok K. Misra 《Journal of the Indian Society of Remote Sensing》1996,24(1):53-67

Remotely sensed data has unique advantage aver conventional data collection techniques in the study of geomorphology, as physiographical and geo-structural parameters are mostly discernible on the imagery. In the present study an attempt has been made to identify and evaluate the process of geomorphological evolution and hydrogeological conditions, temporal changes in pattern of geomorphic elements and overall impact on environment in alluvial fan region in Nainital District using multidate satellite data from Landsat (1975, 1986) and IRS (1993), through visual interpretation technique. The landuse changes are quite prominent in alluvial fan of upper and lower zone. As a consequence of deforestation, an area of 16 sq. km. of natural forest cover has been lost over a span of 18 years (1975–1993) leading to the increase in rate of erosion as well as environmental degradation in upstream areas. The study suggests that the ground water utilization in Tarai belt without replenishment of confined aquifers and installation of more tubewells in Bhabar belt may lead to total failure of flowing wells and subsequently disturb the balanced ecosystem.  相似文献   

Reconciling droughts and landfalling tropical cyclones in the Southeastern United States     

Vasubandhu Misra  Satish Bastola 《Climate Dynamics》2016,46(3-4):1277-1286

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