Long-Term variability of the indian summer monsoon and related parameters     

G. B. Pant  K. Rupa Kumar  B. Parthasarathy  H. P. Borgaonkar 《大气科学进展》1988,5(4):469-481

The long-term variability of the Indian summer monsoon rain-fall and related regional and global param-eters are studied. The cubic spline is used as a digital filter to smooth the high frequency signals in the time series of the various parameters. The length of the data series varies from 95 to 115 years during the period 1871-1985. The parameters studied within the monsoon system are: (a) monsoon rainfall of the country as a whole; (b) number of break-monsoon days during July and August; (c) number of storms/ depressions in Bay of Bengal and Arabian Sea during summer monsoon season; and (d) dates of onset of summer monsoon over South Kerala Coast. The parameters studied outside the monsoon system are: (a) the Wright’s Southern Oscillation Index (June-July-August); (b) the January mean Northern Hemi-spheric surface air temperature anomaly; and (c) the East-equatorial Pacific sea surface temperature anomaly.In order to examine the variability under various degrees of the smoothing, the series are filtered with splines of 50% variance reduction frequency of one cycle per 10, 20 and 30 years. It is observed that the smoothed time series of the parameters within the monsoon system comprise a common slowly varying com-ponent in an episodic manner distinctly showing the excess and deficient rainfall epochs. The change of intercorrelations between the time series with increasing degree of smoothing throws some light on the time scales of the dominant interactions. The relation between Southern Oscillation and East equatorial Pacific sea surface temperature and the Indian summer monsoon seems to be dominant on the interannual scale. The low frequency variations are found to have significantly contributed to the instability of the correlations of monsoon rainfall with parameters outside the monsoon system.  相似文献   

Some results of night-time scintillations at low latitude     

Sushil Kumar  S K Vijay  A K Gwal 《Journal of Earth System Science》1993,102(2):307-312

Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73°E longitude) at Bhopal from January 1990 to December 1990 have been used to study the characteristic variations of scintillation activity. It is found that scintillation occurrence is essentially a night-time phenomenon and day-time scintillations are very rare. Annual average nocturnal variation of percentage occurrence of scintillations shows maximum at around 2100–2200 hours LT. Seasonally, scintillations are most prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations in the pre-midnight period.  相似文献   

A probability-weighted moment test to assess simple scaling     

Praveen Kumar  Peter Guttarp  Efi Foufoula-Georgiou 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(3):173-183

We present a statistically robust approach based on probability weighted moments to assess the presence of simple scaling in geophysical processes. The proposed approach is different from current approaches which rely on estimation of high order moments. High order moments of simple scaling processes (distributions) may not have theoretically defined values and consequently, their empirical estimates are highly variable and do not converge with increasing sample size. They are, therefore, not an appropriate tool for inference. On the other hand we show that the probability weighted moments of such processes (distributions) do exist and, hence, their empirical estimates are more robust. These moments, therefore, provide an appropriate tool for inferring the presence of scaling. We illustrate this using simulated Levystable processes and then draw inference on the nature of scaling in fluctuations of a spatial rainfall process.  相似文献   

Iterative methods for non-classically damped dynamic systems     

Firdaus E. Udwadia  Ravi Kumar 《地震工程与结构动力学》1994,23(2):137-152

Non-classically damped structural systems do not easily lend themselves to the modal superposition method because these systems yield coupled second-order differential equations. In this paper, a variety of new computationally efficient iterative methods for determining the response of such systems are developed. The iterative approaches presented here differ from those presented earlier in that they are computationally superior and/or are applicable to the determination of the responses of broader classes of structural systems. Numerical examples, which are designed to evaluate the efficacy of these schemes, show the vastly improved rates of convergence when compared to earlier iterative schemes.  相似文献   

Precipitable water over the tropical Indian Ocean derived from NIMBUS 7 satellite data — A case study     

M. R. Ramesh Kumar  P. M. Muralidharan  P. V. Sathe 《Boundary-Layer Meteorology》1993,66(3):325-330

The data from the Scanning Multichannel Microwave Radiometer (SMMR) sensor on board the NIMBUS 7 satellite in the 18 and 21 Ghz channels are used to derive the Precipitable Water (PW) over the tropical Indian Ocean for the period May–September, 1979. The PW values are derived by using both the horizontal and vertical polarization channels. These PW values along with the satellite-derived sea surface temeprature (SST) and the lower tropospheric wind (UW) data reveal the features of the summer monsoon circulation of the tropical Indian Ocean in 1979. Further, the derived PW values from Nimbus 7 SMMR data agree well with features of PW presented by Cadet (1983) inferred from the TIROS—N soundings and FGGE data.  相似文献   

Integrated approach for demarcating the fracture zone for well site location : A case study near Gumla and Lohardaga,Bihar     

B. K. Sinha  Ashok Kumar  Deepak Shrivastava  Sanjay Srivastava 《Journal of the Indian Society of Remote Sensing》1990,18(3):1-8

In recent years satellite remote sensing techniques have greatly aided identification of fractures/joints/faults in connection with groundwater exploration. However, due to some constraints in filtering out the type of fracture i.e. shear fracture, tensional fracture, mineralised fracture etc. as to their “open or closed” nature from groundwater aspects, there is need of adding geophysical survey, particularly resistivity survey to further enhance the accuracy, and hence minimise drilling failures. The area under study is a part of Ranchi plateau and lithologically comprising of granite-gneiss. The present paper lays stress on an integrated approach for localising well sites through satellite data analysis and resistivity profiling along with vertical electrical sounding which is based on fracture patterns. With this combined effort i.e. firstly considering the surfacial features like drainage, geomorpho-logy, lithology and lineaments, and secondly taking into account geophysical survey aspects, i.e. depth and thickness of fracture zone, lateral extent, different layer parameter, etc., fairly accurate results are achieved. In the presnt study this type of an integrated survey has been carried out in Lohardaga and Gumla districts in Bihar, the results of which are highlighted in the paper.  相似文献   

Air-sea interaction over the tropical Indian Ocean during several contrasting monsoon seasons     

M. R. Ramesh Kumar  J. S. Sastry 《Journal of Earth System Science》1990,99(3):393-404

Monthly mean anomaly fields of various parameters like sea surface temperature, air temperature, wind stress, effective radiation at the surface, heat gain over the ocean and the total heat loss between a good and bad monsoon composite and the evaporation rates over the Arabian Sea and southern hemisphere have been studied over the tropical Indian Ocean. The mean rates of evaporation on a seasonal scale over the Arabian Sea during a good and bad monsoon composites were equal (about 2·48 × 10¹⁰ tons/day). The evaporation rates over the southern hemisphere were greater during all the months. The mean evaporation rates over the southern hemisphere on a seasonal scale for the good and bad monsoon composites were 4·4 × 10¹⁰ and 4·6 × 10¹⁰ tons/day respectively. The maximum evaporation rates over the southern hemisphere were observed in August. The anomalies of wind stress, effective radiation at the surface and the heat gain over the ocean also exhibit large variations in August, as compared to other monsoon months.  相似文献   

Surface wave propagation in a transversely isotropic elastic layer overlying a liquid saturated porous solid half-space and lying under the uniform layer of liquid     

M. D. Sharma  Rajneesh Kumar  M. L. Gogna 《Pure and Applied Geophysics》1990,133(3):523-539

Dispersion of Rayleigh-type surface wave is studied in a homogeneous transversely isotropic elastic layer overlying a nondissipative liquid-saturated porous solid half-space and lying under a uniform layer of homogeneous liquid. The frequency equation in the form of ninth-order determinant is obtained.Special cases have been deduced by reducing the depth of the layers to zero and by changing the transverse isotropic layer to an isotropic layer. Dispersion curves for the phase velocity have been plotted for a particular model.  相似文献   

The Fauna of Different Drinking Water Sources of Bhagalpur,India     

S. Kumar 《洁净——土壤、空气、水》1990,18(6):683-690

In three drinking water sources i. e. river, well and filter water, there were detected 50 taxa of animals: 10 amoebae and 2 ciliates (protozoa), 24 rotifera, 5 cladocerans, and 9 copepods. Chief components of the rotifers population were Brachionus and Keratella, although K. cochlearis is the most common form at all the sites. The presence of Entamoeba histolytica in well water was indicative of faecal contamination which may become a causative agent of amoebiasis in human beings.  相似文献   

Water Quality,Phytoplankton Diversity and Production in G. B. Pant Sagar at Rihand Dam,Pipri     

N. K. Srivastava  R. S. Ambasht  R. Kumar 《洁净——土壤、空气、水》1991,19(5):529-538

The man made reservoir, G. B. Pant Sagar at the dam site (24° 15′ N Lat) in the South Mirzapur district of eastern U. P. was investigated in terms of water quality, phytoplankton diversity and production at monthly intervals between January 1987 and December 1987. The reservoir water showed low to moderate dissolved oxygen (4.3 … 7.5 mg/l) and quite low nutrient contents (0.01-0.2 mg l^?1). Phytoplankton diversity narrowly fluctuated (3.17-3.74) and mean annual production (149.7 g/m³ · aC) showed a meso- to eutrophic condition. A significant positive correlation was obtained between gross production and phytoplankton density (r = 0.79; P < 0.001) Multiple regression equation (GPP = 11.292 + 0.043 BAC + 0.075 CHL + 0.073 CYN) indicates that Chlorophyta contributed more to gross production due to the presence of a higher number of individuals.  相似文献