Evolving coronal holes and interplanetary erupting stream disturbances     

Rajendra Shelke 《Journal of Astrophysics and Astronomy》2006,27(2-3):101-112

Coronal holes and interplanetary disturbances are important aspects of the physics of the Sun and heliosphere. Interplanetary disturbances are identified as an increase in the density turbulence compared with the ambient solar wind. Erupting stream disturbances are transient large-scale structures of enhanced density turbulence in the interplanetary medium driven by the high-speed flows of low-density plasma trailing behind for several days. Here, an attempt has been made to investigate the solar cause of erupting stream disturbances, mapped by Hewish & Bravo (1986) from interplanetary scintillation (IPS) measurements made between August 1978 and August 1979 at 81.5 MHz. The position of the sources of 68 erupting stream disturbances on the solar disk has been compared with the locations of newborn coronal holes and/or the areas that have been coronal holes previously. It is found that the occurrence of erupting stream disturbances is linked to the emergence of new coronal holes at the eruption site on the solar disk. A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity. The newborn coronal hole emerges on the Sun, owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into the corona. The fundamental activity for the onset of an erupting stream seems to be a transient opening of pre-existing closed magnetic structures into a new coronal hole, which can support highspeed flow trailing behind the compression zone of the erupting stream for several days.  相似文献   

Jeans instability of partially-ionized self-gravitating viscous plasma with Hall effect FLR corrections and porosity     

Sachin Kaothekar  Ghanshyam D. Soni  R. P. Prajapati  Rajendra K. Chhajlani 《Astrophysics and Space Science》2016,361(6):204

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Ground Based Bistatic Scatterometer Measurement for the Estimation of Growth Variables of Ladyfinger Crop at X-Band     

Ajeet Kumar Vishwakarma  Rajendra Prasad  Dileep Kumar Gupta  Pradeep Kumar  Varun Narayan Mishra 《Journal of the Indian Society of Remote Sensing》2018,46(6):973-980

The present study describes the ground based bistatic scatterometer measurements of ladyfinger crop at its various growth stages in the specular direction with the azimuthal angle (\( \phi = 0 \)) for the angular incidence angle ranging from 20° to 60° at the interval of 10° at HH and VV polarization. An outdoor ladyfinger crop bed of an area 4 × 4 m² was specially prepared for the ground based bistatic scatterometer measurements. The crop growth variables like vegetation water content, leaf area index, fresh biomass, and plant height were also measured at the time of each bistatic scatterometer measurement. The specular bistatic scattering coefficients were found to be decreasing with the crop growth variables up to the maturity stage and then after it increased slightly. The linear regression analysis was carried out between specular bistatic scattering coefficient and crop growth variables at all the incidence angles for HH and VV polarization to select the optimum angle of incidence and polarization for the estimation of crop growth variables. The potential of subtractive clustering based adaptive neuro-fuzzy inference system was applied for the estimation of crop growth variables. The estimated values for different crop growth variables were found almost close to the observed values.  相似文献   

Mapping wetland cover in the greater Himalayan region: a hybrid method combining multispectral and ecological characteristics     

Zhuoqing Li  Jianchu Xu  Rajendra L. Shilpakar  Xing Ma 《Environmental Earth Sciences》2014,71(3):1083-1094

In the greater Himalayan region, wetland ecosystems such as lakes, marshes, and peat lands play an important role in regulating the flow of major rivers. These ecosystems are often overlooked and not well represented on land-use planning and conservation maps. Wetland complexes are partly ephemeral and difficult to map accurately either with digital image processing or visual interpretation. This study developed a hybrid method of extracting spatial patterns of wetland areas which combines month-on-month multispectral classifications of Moderate Resolution Imaging Spectroradiometer data with a sample wetland extraction method based on knowledge of the spectral characteristics of satellite data and wetland ecological systems. The results were compared with the best available sources for lakes and wetlands on global and national scales. It was demonstrated that the method could extract wetlands automatically to a reasonable degree of accuracy and, therefore, reduce the need for extensive ground knowledge. The model was transferred by adjusting parameters through application of high-resolution satellite data (Landsat) in some sub-basin areas. These findings are cognizant with field interviews conducted by wetland experts. The hybrid method and high-altitude wetlands maps will provide decision makers with valuable information about wetland distribution and change in response to global warming and human activities.  相似文献   

Electrical resistivity imaging over natural (in situ) geological samples using physical model studies     

Rajesh Rekapalli  Padmavathi Devi P  V. S. Sarma  P. Rajendra Prasad 《Arabian Journal of Geosciences》2014,7(11):4717-4725

To understand the characteristic responses of natural geological samples, viz., black granite, green marble, and graphite sheet, and to have “an a priori” knowledge of their physical property through electrical resistivity imaging, the physical model laboratory setup has been established to conduct scale model studies over targets of finite dimensions and resistivities. The present experiment involves IRIS make SYSCAL Pro-96 measuring system using 48 electrodes with 2-cm interelectrode separation in the laboratory model tank. In the present communication, we have presented the 2D cross section images using Wenner, Wenner–Schlumberger, and dipole–dipole array configurations over the resistive (granite, marble) and conductive (graphite) sheets. In the case of resistive target (black granite sheet, green marble), the combined usage of dipole–dipole and Wenner–Schlumberger arrays provided more accurate measures on target parameters, i.e., the combined usage of both the arrays is preferable in searching high-resistive targets beneath the low-resistive ones over burden. The shape of the resistive target (green marble sheet) is inappropriate when the thickness of the target is greater than one half of the minimum array separation. As the thickness of the target increases, the signatures of the target become feeble, and hence, the shape of the resistive target is not properly reflected in the corresponding tomogram. The response over graphite sheet indicates that the true parameters of the target are not reflected in the cross section, and the existence of the low-resistive (high-conductive) target in the host medium (water) deviates the resistivity of the medium. The target parameters from the cross section using dipole–dipole array are somewhat correlated with true parameters in the case of thin targets at shallow depths. In the case of the sequence of layers of gravel–marble gravel–sand gravel simulated in a small model tank in the physical model laboratory, the thickness of the high-resistive marble layer beneath the low-resistive gravel layer is enhanced conspicuously because of the significant resistivity contrast between gravel and marble.  相似文献   

Spatial and temporal variability in maximum,minimum and mean air temperatures at Madhya Pradesh in central India   总被引：2，自引：0，他引：2  

Darshana Duhan  Ashish Pandey  Krishan Pratap Singh Gahalaut  Rajendra Prasad Pandey 《Comptes Rendus Geoscience》2013,345(1):3-21

In the present study, an investigation has been made to study the spatial and temporal variability in the maximum, the minimum and the mean air temperatures at Madhya Pradesh (MP), in central India on monthly, annual and seasonal time scale from 1901 to 2002. Further, impact of urbanization and cloud cover on air temperature has been studied. The annual mean, maximum and minimum temperatures are increased by 0.60, 0.60 and 0.62 °C over the past 102 years, respectively. Seasonally, the warming is more pronounced during winter than summer. The temperature decreased during the less urbanized period (from 1901 to 1951) and increased during the more urbanized period (1961 to 2001). It is also found that the minimum temperature increased at higher rate (0.42 °C) followed by the mean (0.36 °C) and the maximum (0.32 °C) temperature during the more urbanized period. Furthermore, cloud cover is significantly negatively related with air temperature in monsoon season and as a whole of the year.  相似文献   

Spatial and temporal variation in the trends of hydrological response of forested watersheds in Thailand     

Jessada Techamahasaranont  Sangam Shrestha  Mukand S. Babel  Rajendra P. Shrestha  Damien Jourdain 《Environmental Earth Sciences》2017,76(12):430

Thailand has undergone significant forest cover changes in recent decades, and this is likely to have altered the hydrological functioning of many watersheds; however, such potential impacts are not fully understood. To contribute towards a better understanding of the potential hydrological impacts of forest cover changes, this study examines the temporal trends of several hydrological indices in eight watersheds of Thailand over the period from 1982 to 2013. A number of hydrological indices (runoff coefficient, baseflow index, flow duration indices, streamflow elasticity, dryness index) were analysed using a combined Thiel–Sen/Mann–Kendall trend-testing approach, to assess the magnitude and significance of patterns in the observed data. These trend tests indicated that the change in the hydrological response of watersheds varied with the change in structure and composition of forest species. A significant increase in runoff (viz. average flow) was observed in those watersheds covered with natural forests, whereas a significant reduction in runoff (viz. baseflow and low runoff) was observed in those watersheds where the land cover was changed to Para rubber plantations and reforested areas. It is also noteworthy that the watersheds covered by natural forest showed more streamflow elasticity than plantations or reforested areas. These results highlight the importance of considering both forest types/dynamics and watershed characteristics when assessing hydrological impacts.  相似文献   

Numerical modelling-based pillar strength estimation for an increased height of extraction     

Ashok Kumar  Rakesh Kumar  Arun K. Singh  Sahendra Ram  Pradeep K. Singh  Rajendra Singh 《Arabian Journal of Geosciences》2017,10(18):411

Underground extraction of total thickness of a thick coal seam in single lift by bord and pillar method increases pillar height during retreat. Field studies found that the increase in pillar height affects the depillaring operation adversely, especially, during caving of the strong/massive roof strata. Dilution in strength due to the increased pillar height caused catastrophic failure of barrier pillars and goaf overriding. This warrants a systematic study of pillar strength variation for the different heights of pillar. A review of different pillar strength estimation approaches for an analysis of the dilution in strength of the heightened pillar suggested that numerical modelling provides a better option for such a systematic study. Accordingly, investigations are conducted on simulated models in laboratory adopting a recognised numerical modelling procedure. The observed nature of variations in pillar strengths with the increase in its height in the numerical models and empirical formula is found to be matched. But a mismatch is found between the strength values of the two approaches with an increase in height of the pillar. Considering validity of the empirical formulation in Indian coalfields, a relationship is developed to incorporate a correction in the strength values of the numerical models. The suggested correction on the basis of this simple study of the pillar strength variation would be helpful for the use of the established simulation tool during the depillaring of a thick coal seam.  相似文献   

Activity of radon (<Superscript>222</Superscript>Rn) in the lower atmospheric surface layer of a typical rural site in south India     

K Charan Kumar  T Rajendra Prasad  M Venkat Ratnam  Kamsali Nagaraja 《Journal of Earth System Science》2016,125(7):1391-1397

Analysis of one year measurements of in situ radon (²²²Rn) and its progenies along with surface air temperature, relative humidity and pressure near to the Earth’s surface has been carried out for the first time at the National Atmospheric Research Laboratory (NARL, 13.5^°N and 79.2^°E) located in a rural site in Gadanki, south India. The dataset was analysed to understand the behaviour of radon in relation to the surface air temperature and relative humidity at a rural site. It was observed that over a period of the 24 hours in a day, the activity of radon and its progenies reaches a peak in the morning hours followed by a remarkable decrease in the afternoon hours. Relatively, a higher concentration of radon was observed at NARL during fair weather days, and this can be attributed to the presence of rocky hills and dense vegetation surrounding the site. The high negative correlation between surface air temperature and activity of radon (R = – 0.70, on an annual scale) suggests that dynamical removal of radon due to increased vertical mixing is one of the most important controlling processes of the radon accumulation in the atmospheric surface layer. The annual averaged activity of radon was found to be 12.01±0.66 Bq m^?3 and 4.25±0.18 Bq m^?3 for its progenies, in the study period.  相似文献   

Validation of a satellite-based cyclogenesis technique over the North Indian Ocean     

Suman Goyal  M Mohapatra  Ashish Kumar  S K Dube  Kushagra Rajendra  P Goswami 《Journal of Earth System Science》2016,125(7):1353-1363

Indian region is severely affected by the tropical cyclones (TCs) due to the long coast line of about 7500 km. Hence, whenever any low level circulation (LLC) forms over the Indian Seas, the prediction of its intensification into a TC is very essential for the management of TC disaster. Satellite Application Centre (SAC) of Indian Space Research Organization (ISRO), Ahmedabad, has developed a technique to predict TCs based on scatterometer-derived winds from the polar orbiting satellite, QuikSCAT and Oceansat-II. The India Meteorological Department (IMD) has acquired the technique and verified it for the years 2010–2013 for operational use. The model is based on the concept of analogs of the sea surface wind distribution at the stage of LLC or vortex (T1.0) as per Dvorak’s classifications, which eventually leads to cyclogenesis (T2.5). The results indicate that the developed model could predict cyclogenesis with a probability of detection of 61% and critical success index of 0.29. However, it shows high over-prediction of the model is better over the Bay of Bengal than over Arabian Sea and during post-monsoon season (September–December) than in pre-monsoon season (March–June).  相似文献