Time-Variations of D-Region Electron Densities, and Comparisons With Model Computations     

Suman Ganguly  John Zinn 《Studia Geophysica et Geodaetica》1998,42(4):500-510

An extensive series of incoherent scatter studies of the ionospheric D-region was carried out at the Arecibo radar facility during 1978 and 1979. They included several full-day sequences of electron density measurements over a range of altitudes, and also included a sequence during the serendipitous occurrence of a large solar flare. For the solar flare event simultaneous data on solar X-ray fluxes in several wavelength bands were available from the GOES-2 and ISEE-3 satellites. In the course of development of a large ionospheric computer model at Los Alamos we have used the solar flare data as a reality check. The solar X-ray flux data were used as inputs for computing ionization rates. The model computer includes 999 chemical reactions, and also includes diffusion and transport processes. In the course of the flare studies we used the data comparisons to adjust the values of three chemical rate coefficients that were poorly known. With those adjustments the model computations fitted the data quite well. Subsequent to the flare analysis we have been using the same model with some minor updates to compute the expected diurnal variations of the ambient D-region under conditions chosen to match those existing at the times of the incoherent scatter measurements. Comparisons of the computations and the data will be shown, and the relative importance of the several separate ionization processes will be discussed. We also compare model results with experimental data on concentrations of NO.  相似文献   

Luminescence chronology of late Holocene extreme hydrological events in the upper Penner River basin,South India     

Puthusserry J. Thomas  Navin Juyal  Vishwas S. Kale  Ashok K. Singhvi 《第四纪科学杂志》2007,22(8):747-753

Field stratigraphy, sedimentology and optically stimulated luminescence (OSL) dating have been used to reconstruct the southwest monsoon variability in the semi‐arid region of southern India during the late Holocene. Facies architecture and OSL dating of the water‐lain sediment suggest prevalence of a weak hydrological regime around 3 ka. Following this, a progressive strengthening of monsoon occurred till 2 ka. After 2 ka and until 1 ka fluvial activity was nearly dormant, indicating weakening of the monsoon. Presence of high‐magnitude flood deposits, overbank sedimentation and pedogenesis during 1–0.6 ka indicate intensification of the southwest monsoon in the basin. The onset of aridity was associated with episodic storm surge events that are manifested in the pond sedimentation and localised aeolian accretion. This phase is bracketed between 0.5 ka and 0.2 ka. A renewed phase of monsoonal activity was observed in the form of floodplain aggradation between 180 and 90 years ago. In the past 70 years no significant change in the monsoon performance has been observed. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Spatial pattern of languages in India: A culture-historical analysis     

Ashok K. Dutt  Chandrakanta C. Khan  Chandralekha Sangwan 《GeoJournal》1985,10(1):51-74

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Possibility of Excitation of Low-ℓ P-Modes by Energetic Solar Transients     

Ashok Ambastha  H. M. Antia 《Solar physics》2006,238(2):219-230

We examine the temporal variation of power in low-ℓ modes using GONG data for the period of May 1995–October 2005 and compare this with disk-integrated flare and CME indices. A poor correlation between the running means of Flare Index and mode power is found. A similar result is found for CME Index also. Variations in the running mean mode power corresponding to ℓ = 0 modes with different radial orders are generally stochastic in nature. This behaviour is also reflected in the distribution of mode power.  相似文献   

Erratum to: Comparative Analysis of Phytoplankton Composition and Abundance over a Two-Decade Period at the Land<Emphasis Type="Italic">–</Emphasis>Ocean Boundary of a Tropical Mangrove Ecosystem     

Haimanti Biswas  Mitali Dey  Dipnarayan Ganguly  Tarun K. De  Sandip Ghosh  Tapan K. Jana 《Estuaries and Coasts》2010,33(2):395-398

Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′ N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007. Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered by long-term changes in climate.  相似文献   

Decadal changes in the relationship between the Indian and Australian summer monsoons     

Karumuri Ashok  C. Nagaraju  A. Sen Gupta  D. S. Pai 《Climate Dynamics》2014,42(3-4):1043-1052

In this study, we investigate a long-term modulation in the relationship between Indian summer monsoon rainfall with the subsequent Australian summer monsoon rainfall. The two monsoon rainfall time series are significantly correlated at 0.3 at the 99 % confidence level. However, the relationship weakens during the 1932–1966 period, with the inter-monsoon correlation for the period falling below statistical significance. We find that this modulation is consistent with a breakdown of the typical El Niño-Southern Oscillation (ENSO) influence on sea surface temperature in the northern region of Australia, during this period. In addition, a change in the relative influences of ENSO and Indian Ocean Basin-wide Warming sea surface temperature anomalies on the Australian summer monsoon rainfall is also apparent across different time periods.  相似文献   

Analysing the spatio-temporal evolution of an active debris slide in Eastern Himalaya,India   总被引：1，自引：0，他引：1  

Saibal Ghosh  Anjan Bora  Sudipta Nath  Ashok Kumar 《Journal of the Geological Society of India》2014,84(3):292-302

Landslide is one of the prominent geohazards in the Himalayas where loss of lives and property are common. Owing to the complicated geomorphic and tectono-stratigraphic setting of this active Fold-thrust belt (FTB), landsliding of all possible types and spatial scales observed exhibit conspicuous spatio-temporal signatures and evolution. This evolution of landslides is commonly studied by regional assessment and by examining the multi-temporal landslide inventories of a particular area. The success of creating such multi-temporal landslide inventory depends on (i) the availability of relevant past source data (e.g., images, post event maps, air photos etc.) of suitable resolution, scale and quality, (ii) time of generation of source data with respect to the time of landsliding event, (iii) skill of the investigators in interpreting the old images, air photos etc. However, this method is of restricted use in studying the spatio-temporal evolution of a single landslide which is perennially active in the Himalayan terrain, where rapid changes in land use and land cover patterns readily obliterate the signatures of past landsliding. Moreover because of scale constraints, subtle and frequent changes in the spatial dimensions of these individual landslides, and their temporal activity become difficult to identify in such regional assessment carried out over a larger area. In this study therefore, a different approach is adopted whereby the spatio-temporal activity and style of Lanta Khola landslide, a perennially active and large (0.25 km²) debris flow in the Eastern Himalayas, has been studied in detail through detailed scale (1:1000) site-specific geological mapping in phases during the last 28 years (1983–2011). Such site-specific geological observations coupled with numerical slope stability analysis utilising the limit equilibrium method facilitate in detailed understanding of the temporal and spatial evolution and inherent mechanism of this perennial landslide.  相似文献   

The excitation mechanism of [Fe XIV] 5303 å line in the inner regions of solar corona     

K. P .Raju  J. N. Desai  T. Chandrasekhar  N. M. Ashok 《Journal of Astrophysics and Astronomy》1991,12(4):311-317

The line intensity of the green coronal line and the continuum intensity are derived from the filter and white light photographs of the solar corona obtained during the 1980 total solar eclipse. Ratio of the line to continuum intensity is plotted against the radial distancer(=R/R₀,R ₀ is the solar radius), in various position angles. A simple model assuming an electron density dependence of the line and continuum intensities suggests a dominant collisional mechanism for the excitation of the line in the innermost regions (～ 1.4R ₀). The measured line to continuum ratio tends to a constant value at different radial distances in different position angles. The constancy of the measured line to continuum ratio indicates significant radiative excitation beyond 1.4 R₀, in some of the position angles.  相似文献   

A multivariate statistical study of copper mineralization in the central section of Mosaboni Mine, Eastern Singhbhum, India     

A. K. Saha  S. N. Sarkar  Swapna Basu  Dhruba Ganguly 《Mathematical Geology》1986,18(2):215-235

A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (>0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones.  相似文献   

Stochastic finite-fault modeling of M w 5.4 earthquake along Uttarakhand–Nepal border     

Mittal  Himanshu  Kumar  Ashok 《Natural Hazards》2015,78(2):1145-1161

Natural Hazards - In this work, an attempt has been made to simulate strong ground motion of M w 5.4 earthquake in Kumaun region of Uttarakhand. The simulation is based on modified stochastic...  相似文献