Temperature of interstellar warm ionized medium     

Sanjay K. Mishra  Mahendra Singh Sodha  Sweta Srivastava 《Astrophysics and Space Science》2013,344(1):193-203

This investigation on the temperature of the interstellar warm ionized medium (WIM) is characterized by the number and energy balance of the constituents of the WIM complex plasma viz. H plasma (electrons/ions/neutral atoms) and graphite dust, having a size distribution, characterized by the MRN (Mathis, Rumpl and Nordsieck) power law. Ionization of neutral atoms, electron–ion recombination, photoemission of electrons from and accretion on the dust and cooling through electron collisional excitation, followed by radiative decay of atoms has been included in the analysis. An appropriate expression for the rate of emission and mean energy of photoelectrons emitted from the surface of positively charged dust particles has been used which takes into account the dependence of absorption efficiency on wavelength of the radiation, radius of the particle and spectral irradiance distribution. The results of the parametric analysis have been displayed graphically. It is seen that the consensus values of temperature, surface potential on the dust particles and electron/ion/neutral atom densities, characteristic of interstellar warm ionized medium can be explained on the basis of plausible combinations of the dust particle density n _d and the parameter f _ex α _ex , where f _ex is the fraction of the energy of the neutral gas atoms which gets irradiated, α _ex n _e n _n is the number of the neutral atoms, which get excited per unit volume per unit time and n _e (n _n ) correspond to the density of electrons (neutral atoms).  相似文献   

Luminescence chronology of river adjustment and incision of Quaternary sediments in the alluvial plain of the Sabarmati River, north Gujarat, India   总被引：1，自引：0，他引：1  

Pradeep Srivastava  Navin Juyal  Ashok K. Singhvi  Robert J. Wasson  Mark D. Bateman 《Geomorphology》2001,36(3-4)

River adjustment and incision in the Sabarmati basin, Gujarat, India have been examined at a site near Mahudi. Towards this, the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated. The upper fluvial sequence, along with the overlying aeolian sand and riverbed scroll plains, provide clues to the evolution of the present Sabarmati River. Sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase. Luminescence chronology bracketed this sequence to between 54 and 30 ka, which corresponds to Oxygen Isotope Stage-3, during which the SW monsoon was enhanced. The overlying aeolian sand has been dated to 12 ka, indicating that dune accretion occurred simultaneously with the strengthening of the SW monsoon during the Early Holocene. Adjustment of the Sabarmati along a N–S transect is placed around 12 ka and the incision is bracketed between 12 and 4.5 ka. River adjustment could have been tectonic; however, the incision was facilitated by the availability of continuous flow in the river caused by the SW monsoon. The basin experienced two tectonic events at about 3 and 0.3 ka, as demonstrated by the morphology of the scroll plains.  相似文献   

Anisotropy of magnetic susceptibility and petrofabric studies in the Garhwal synform, Outer Lesser Himalaya: Evidence of pop-up klippen     

Upasana  Devrani  Ashok K.  Dubey 《Island Arc》2009,18(3):428-443

Abstract   Geological field, petrographic, and anisotropy of magnetic susceptibility studies help in understanding the evolutionary history of the Garhwal synform that lies in the western Outer Lesser Himalaya. Orientations of the magnetic susceptibility axes reveal large variations at short distances as a result of superimposed deformation, and predominant stress conditions favorable for normal faulting. Rocks forming the outer limbs of the Garhwal Synform are metamorphosed up to the lower greenschist facies. The metamorphic grade increases to chlorite zone in the inner limb and the core is characterized by chlorite–biotite to garnet zones. The different grades of metamorphism are separated by thrusts and the structure is described as a pop-up klippen.  相似文献   

Drought characterization: a probabilistic approach   总被引：4，自引：0，他引：4  

A. K. Mishra  V. P. Singh  V. R. Desai 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(1):41-55

Using the alternative renewable process and run theory, this study investigates the distribution of drought interval time, mean drought interarrival time, joint probability density function and transition probabilities of drought events in the Kansabati River basin in India. The standardized precipitation index series is employed in the investigation. The time interval of SPI is found to have a significant effect of the probabilistic characteristics of drought.  相似文献   

In-situ measurement of dielectric parameter of soil at microwave frequencies     

Uma Shankar Mishra  Jitendra Behari 《Journal of the Indian Society of Remote Sensing》2000,28(1):1-7

Knowledge of dielectric permittivity of the soil provides direct measure of soil moisture content. A methodology to determine soil moisture based on the reflection coefficient measurement by a pseudo vector method using a horn antenna has been presented. To verify the efficacy of the method, measurements have been carried out at S, C & X band frequencies at two moisture levels and the corresponding emissivity parameters computed. Results so obtained are in good agreement with the already reported data and the direct moisture measurements. This method is expected to be of interest to agricultural scientists and to those involved in the application of remote sensing in crop studies.  相似文献   

The Kwinana Coastal Fumigation Study: III – Meteorological and Turbulence Modelling on Selected Days     

Peter J. Hurley  Ashok K. Luhar 《Boundary-Layer Meteorology》2000,94(1):115-138

The Kwinana Coastal Fumigation Study took place inearly 1995 at Kwinana near Perth in Western Australia.The study involved surface and elevated meteorologicaland plume fumigation measurements in sea-breeze flowsnear the coast, and has yielded a comprehensive dataset that is suitable for assessing meteorological andplume dispersion models. In this paper, wesimulate the meteorology and turbulence on four casestudy days, and compare model results with thedetailed surface and aircraft measurements takenduring the study. These days had surface synopticwinds ranging from southerly to northeasterly, witheither stable or near-neutral temperature profilesover the sea.The model used was based on that developed by Hurley(Boundary-Layer Meteorol. 83, 43–73, 1997), but extended here to allow domain nesting,optional non-hydrostatic simulations, and a vegetativecanopy at the surface. The model was forced bystandard weather service synoptic data, and thesimulations have captured the essential features ofthe strong sea-breeze circulation observed on thesedays. The boundary-layer structure over the sea waspredicted to be near-neutral or stable in agreementwith the observations on the particular day. The windspeed and direction in the sea-breeze flow weregenerally predicted well, although the predictedmaximum inflow speed over the land was a little toohigh. The potential temperature was generallyover-predicted, but temperature gradients agreed well.Predicted turbulence levels in the bottom-half of thethermal internal boundary layer compared well to theobservations, but under-estimated the observations inthe in the upper half of this layer. Near-surfacemeasurements of meteorological variables werepredicted well over the entire diurnal cycle, althoughthe predicted sea-breeze onset was generally tooearly. A quantitative model evaluation for thenear-surface sites showed the model performance to bebetter than that from other studies, with Index ofAgreement (IOA) values of 0.8 (wind speed) and 0.96(temperature), compared with values of 0.5–0.6 (windspeed) and 0.33 (temperature) obtained from otherstudies.The availability of new higher resolution synopticanalyses should obviate the lack of spatial andtemporal resolution in synoptic inputs. Theincorporation of these higher resolution synopticinputs and new parameterisation schemes should improvefuture model performance.  相似文献   

Directional spread parameter at intermediate water depth     

V. Sanil Kumar  M. C. Deo  N. M. Anand  K. Ashok Kumar 《Ocean Engineering》2000,27(8):93

The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information.  相似文献   

Magnetic field gradient and flare: study of a small flare in NOAA 8038     

Mathew  Shibu K.  Ambastha  Ashok 《Solar physics》2000,197(1):75-84

Active region NOAA 8038 was observed from 10 to 13 May, 1997 using the USO solar video magnetograph. During this period, the active region was mostly inactive, and gave rise to only a single notable flare of 1N/C1.3 class on May 12, 1997/04:45 UT. The flare occurred in a weak field location, but new emerging fluxes were observed prior to the flare onset. Horizontal motions of the network photospheric magnetic fluxes were inferred using USO and SOHO magnetograms, and velocities in the range 300–800 m s^–1 were estimated. The initial flare brightening was observed at the flux cancellation site where magnetic field gradients were found to increase. Detailed analyses of flux motions, cancellation and their relation with the flare are presented.  相似文献   

Relationship of non-potentiality and flaring: Intercomparison for an M-class flare     

Ashok Ambastha  Shibu K. Mathew 《Journal of Astrophysics and Astronomy》2000,21(3-4):271-274

We have made an attempt to obtain relationship of magnetic shear and vertical currents in NOAA AR7321. Intercomparison of changes observed at several flaring and non-flaring sites associated with an M4/2B flare observed on October 26, 1992 is reported.  相似文献   

A rapidly evolving active region NOAA 8032 observed on April 15th, 1997     

Shibu K. Mathew  Ashok Ambastha 《Journal of Astrophysics and Astronomy》2000,21(3-4):233-236

The active region NOAA 8032 of April 15, 1997 was observed to evolve rapidly. The GOES X-ray data showed a number of sub-flares and two C-class flares during the 8–9 hours of its evolution. The magnetic evolution of this region is studied to ascertain its role in flare production. Large changes were observed in magnetic field configuration due to the emergence of new magnetic flux regions (EFR). Most of the new emergence occured very close to the existing magnetic regions, which resulted in strong magnetic field gradients in this region. EFR driven reconnection of the field lines and subsequent flux cancellation might be the reason for the continuous occurrence of sub-flares and other related activities.  相似文献