EMIC waves around the plasma-pause region     

P. Varma  G. Ahirwar  M.S. Tiwari   《Planetary and Space Science》2008,56(7):1023-1029

Electromagnetic ion-cyclotron (EMIC) instability has been studied using the general loss-cone distribution function by investigating the trajectories of charged particles and using the method of particle aspect analysis. A low β (ratio of plasma pressure to magnetic pressure) plasma consisting of resonant and non-resonant particles has been considered. It is assumed that the resonant particles participate in energy exchange with the wave, whereas non-resonant particles support the oscillatory motion of the wave. The wave is assumed to propagate parallel to the static magnetic field. The effects of steepness of loss-cone distribution with thermal anisotropy are discussed. The growth rate, perpendicular and parallel resonant energies of the particles and marginal instability condition are derived. The effect of general loss-cone distribution function is to enhance the growth rate of EMIC waves. The results are interpreted for the space plasma parameters appropriate to the plasma-pause region of the earth's magnetoplasma. The results of the work is consistent for EMIC emissions observation by SAMPEX and CRRES satellite around the plasma-pause region as reported by Bortnik et al. [Bortnik, J., Thorne, R.M., O’Brien, T.P., Green, J.C., Strongeway, R.J., Shprits, Y.Y., Baker, D.N., 2006. Observation of two distinct, rapid loss mechanisms during the 20 November 2003 radiation belt dropout event. J. Geophys. Res. 111, A12216, doi:10.1029/2006JA011802] and Xinlin et al. [Xinlin, Li., Baker, D.N., O’Brien, T.P., Xie, L., Zong, Q.G., 2006. Correlation between the inner edge of outer radiation belt electrons and the innermost plasmapause location. Geophys. Res. Lett. 33, L14107, doi:10.1029/2006GL026294].  相似文献   

Cylindrical magnetohydrodynamic model of shock waves with radiation heat flux     

S. N. Ojha  V. D. Tiwari 《Astrophysics and Space Science》1989,162(1):57-69

Similarity solutions have been obtained for a cylindrical piston advancing with constant speed into a uniform plasma of infinite electrical conductivity and uniform axial magnetic field with heat radiation. The total energy of the expanding wave has been supposed to remain constant. The plasma is assumed to be a perfect grey gas in local thermodynamic equilibrium. To make the discussions less complicated the simplifying assumptions include transparent shock, cool piston neither an emitter nor a reflector and negligible radiation pressure and energy.This research was partially supported by a grant from U.G.C., India.  相似文献   

Mapping forest biomass in India through aerial photographs and nondestructive field sampling     

A.K. Tiwari  J.S. Singh 《Applied geography (Sevenoaks, England)》1984,4(2):151-165

A method for mapping of forest biomass using black-and-white aerial photographs and nondestructive field sampling is described through a case study of Ladhiya subcatchment in Kumaun Himalaya, India. Forest types were mapped using aerial photographs and field checks. Each forest type was divided into five crown cover classes. Mean crown cover for each class was determined in the field. Density and basal cover were measured on reference sites. Stand biomass was estimated by using biomass estimation equations, mean girth and mean density on the reference sites. Regression equations were developed between crown cover and basal cover, and between crown cover and stand biomass. Mean basal cover and mean stand biomass for each photo-interpreted crown cover class were estimated through these equations. Forest biomass values were substituted for crown cover classes on the interpreted map.  相似文献   

Growing stock with aerial photographs     

K. P. Tiwari 《Journal of the Indian Society of Remote Sensing》1973,1(1-2):35-42

For assessment of growing stock, the role of aerial photographs mairly consists of volume class stratification, knowing proportion of various stratum and in providing layout for ground sample plots along with their precise location on the the ground. Plain Sal stratum was stratified into three volume classes on the basis of volume stereograms and standard deviation in each stratum estimated on the basis of reconnaissance data. 63 ground plots were needed for ± 5 cum (E = ± 5) accuracy for optimum allocation. Volume in 0.1 hectare circular plots was obtained from measurement of all trees above 10 cm dbh. The mean volume was 124 cum per hectare ± 9.55 cum at 95% probability level. A comparison with Working Plan figures revealed a close similarity. Advantage in time and cost for getting information on growing stock by the use of aerial photographs have been highlighted.  相似文献   

Role of the Water Vapour Greenhouse Effect in the Forecasting Of Fog Occurrence     

P. K. Pasricha  B. S. Gera  S. Shastri  H. K. Maini  T. John  A. B. Ghosh  M. K. Tiwari  S. C. Garg 《Boundary-Layer Meteorology》2003,107(2):469-482

Nocturnal measurements of air temperature, relative humidity, temperatureinversion-layer thickness, water vapour path and visibility-through-fog, madeunder non-foggy and foggy conditions in winter over two seasons at Delhi,are analysed to study the decrease in both rate of cooling and temperature inversion-layer thickness during the course of nights followed by fog occurrence.In particular, the decrease in the rate of cooling, compared to that on non-foggynights, is explained as due to the greenhouse warming effect by a layer of excessive,near-saturated water vapour trapped in a temperature inversion. Next, the linearprogramming technique is employed to forecast the occurrence of fog, where thevisibility-through-fog is minimized through its linear regression equation with thepair of variables, mean air temperature and temperature decrease over one hour(measuring rate of cooling at two convenient hours) in the pre-midnight period.This technique provides feasible solutions that enables one to forecast the occurrenceof radiative fog.  相似文献   

Weathering impact on the colour of building stones of the ‘Gateway of India’ monument     

L. B. Tiwari  C. J. Jahagirdar  V. D. Deshpande  R. Srinivasan  G. Parthasarathy 《Environmental Geology》2005,48(6):788-794

To understand the effect of monsoon and marine environment on the colour of building stones of the ‘Gateway of India’ monument, 133 samples from different areas were assessed. Colour changes were evaluated using Microflash 200d colour spectrophotometer over a period of 1 year. The alteration in the stones effecting the colour change was studied by petrographic thin section, which shows that the colour change is associated with weathering of the feldspars.  相似文献   

Seasonal inhomogeneity of soot particles over the central Indo-Gangetic Plains,India: Influence of meteorology     

B. P. Singh  S. Tiwari  Philip K. Hopke  R. S. Singh  D. S. Bisht  A. K. Srivastava  R. K. Singh  U. C. Dumka  A. K. Singh  B. N. Rai  Manoj K. Srivastava 《Acta Meteorologica Sinica》2015,29(6):935-949

Black carbon (BC) particles play a unique and important role in earth’s climate system. BC was measured (in-situ) in the central part of the Indo-Gangetic Plains (IGP) at Varanasi, which is a highly populated and polluted region due to its topography and extensive emission sources. The annual mean BC mass concentration was 8.92 ± 7.0 µg m ^-3, with 34% of samples exceeding the average value. Seasonally, BC was highest during the post-monsoon and winter periods (approximately 18 µg m ^-3) and lower in the premonsoon/ monsoon seasons (approximately 6 µg m ^-3). The highest frequency (approximately 46%) observed for BC mass was in the interval from 5 to 10 µg m ^-3. However, during the post-monsoon season, the most common values (approximately 23%) were between 20 and 25 µg m ^-3. The nighttime concentrations of BC were approximately twice as much as the daytime values because of lower boundary layer heights at nighttime. The Ångström exponent was significantly positively correlated (0.55) with ground-level BC concentrations, indicating the impact of BC on the columnar aerosol properties. The estimated mean absorption Ångström exponent was 1.02 ± 0.08 µg m ^-3, indicating that the major source of BC was from fossil fuel combustion. Significant negative correlations between BC mass and meteorological parameters indicate a pronounced effect of atmospheric dynamics on the BC mass in this region. The highest mean BC mass concentration (18.1 ± 6.9 µg m ^-3) as a function of wind speed was under calm wind conditions (38% of the time).  相似文献   

Western Ghats: Evolution and Environmental Issues – An Overview     

V.M. Tiwari  D. Padmalal  T.N. Prakash 《Journal of the Geological Society of India》2018,92(5):515-516

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Gravity Anomalies and Crustal Thickness Variations over the Western Ghats     

C. P. Dubey  V. M. Tiwari 《Journal of the Geological Society of India》2018,92(5):517-522

The Western Ghats (WG), a topographic scarp facing towards the west coast of India and extending over diverse geological terranes – Deccan Volcanic Province (DVP), Dharwar Craton (DC) and Southern Granulite Terrain (SGT), is an enigmatic geomorphic feature. WG is characterized by low gravity anomalies. In order to decipher the sources of gravity anomalies, we have decomposed the gravity anomalies using wavelength filter and have obtained estimates of the depth to crust-mantle boundary (CMB) under WG and surrounding regions from the inversion of gravity data, which is compared with seismically determined CMB estimates. Overall, the CMB depth varies from 33 to 50 km, which is consistent with seismically determined values, except in the region of shear zones between DC and SGT probably indicating a different density contrast at CMB. The major source of gravity low is found to be the deepening of CMB under the WG compared to adjacent regions regardless of surface lithology. The CMB depths under WG and surrounding region generally approximate the CMB depths estimated for low strength flexural isostatic models, which suggests that flexural compensation of uplifted topography, later modified by tectonic and denudation processes, is a likely development model for the Western Ghats.  相似文献   

Shifting dynamics of nature,society and agriculture in the Hindu Kush Himalayas: Perspectives for future mountain development     

BHATTA Laxmi Dutt  SHRESTHA Anil  NEUPANE Nilhari  JODHA Narpat Singh  WU Ning 《山地科学学报》2019,(5)

Current approaches for sustainable mountain development have several persisting warning signals. Economic globalization, profitoriented market development, and infrastructure development have significantly altered traditional nature-society interactions, increased environmental pressures, and challenged agricultural sustainability in the mountains. Some of the effects of globalization could also be beneficial. Social differentiation and disintegration of mountain communities' have weakened their collective stakes on natural resources resulting in decline in initiatives such as community forestry, collective water management, domestication of rapidly disappearing herbal species, and balancing of economic and ecological concerns. Population growth, food insecurity, unemployment, and increasing economic gaps between rich and poor have led to out-migration of youth. Sustained action promoting ownership of new initiatives for rehabilitating degraded mountain landscapes through macro-level global/national initiatives, mountain specific planning and development efforts is severely lacking in many areas on the Hindu Kush Himalayan region. Therefore, there is an urgent need for widening the scope of efforts directed to help mountain areas and communities, and a future thinking approach to enhance the sustainability of mountain areas as they are a valuable natural resource for humankind. This paper discusses the issues, opportunities, and provides suggestions for the future of mountain development.  相似文献