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1.
V. Thapliyal 《Pure and Applied Geophysics》1971,88(1):53-59
Summary The effects of anisotropy and inhomogeneity on the propagation of Love waves in a sedimentary layer, overlying the inhomogeneous and transversely isotropic half space, are studied in this paper. The results of numerical analysis show an appreciable variation of phase- and group-velocity of Love waves in low frequency region compared to high frequency region due to the presence of transverse isotropy and inhomogeneity in the half space. The higher values for phase velocity are found for the increasing values of anisotropy factor as well as for the greater power of density variation. However, the presence of higher anisotropy factor and inhomogeneity in the half space reduce group velocity considerably in the lower frequency region. 相似文献
2.
V. Thapliyal 《Pure and Applied Geophysics》1971,91(1):40-50
Summary The frequency equation is derived for the propagation of Love waves in the earth's crust, composed of transversely isotropic layers and overlying anisotropic and inhomogeneous mantle. The exact boundary value problem is solved for a single layer and extended to multilayered media by generalizing theHaskell's technique. In fact the problem of deriving the frequency equation has been reduced to finding out the solution of the equation of motion subject to the appropriate boundary conditions. To illustrate the method, the author has derived frequency equations of Love waves for linear, exponential and generalized power law variation of vertical shear wave velocity with depth in the half space overlain by transversely isotropic inhomogeneous stratum. 相似文献
3.
P. K. Pal W. J. Prakash P. K. Thapliyal C. M. Kishtawal 《Meteorology and Atmospheric Physics》1999,71(3-4):157-168
Summary ?A methodology has been developed to assimilate satellite-measured rainfall during the initial phase of model integration
for extended range monsoon prediction. The vertical profiles of latent heating corresponding to different rain rates have
been derived from the model statistics. These heating rates have been assimilated through nudging in the thermodynamics equation
of the model. This procedure of assimilating observed heating has corrected the simulation of heating location in the model
and consequently removed the anomalous sinking motion over Indian landmass. With the correction of vertical circulation, both
mean July rainfall over India and the distribution have improved. Interannual variability has been brought out for the years
1987 and 1988. In view of the availability of rainfall profile from Tropical Rain Measuring Mission (TRMM) there is a scope
of adopting this method of assimilating observed rainfall, for extended range monsoon prediction.
Received February 12, 1999/Revised May 4, 1999 相似文献
4.
Zhou Su Han Desheng Gokani Sneha A. Selvakumaran Ravindran Zhang Yongliang 《中国科学:地球科学(英文版)》2020,63(6):891-898
Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause. A global view of the auroral oval with throat aurora will be critical for inferring global processes at the magnetopause, but it has never been achieved. Using imaging spectrograph observations from Defense Meteorological Satellite Program satellites, for the first time, here we show typical throat auroras in a global view and reveal some important observational facts as follows.(1) The throat auroras can be as long as ～8 degrees in latitudinal direction,which is hardly to be fully seen in the ground-based camera.(2) The plasma flows and field aligned currents associated with throat aurora show consistences with previous radar observations, which have been suggested to be the observational evidence of magnetopause reconnection.(3) Most importantly, we confirmed that the electron and ion precipitations associated with throat aurora are always spatially separated, i.e., electrons in the east and ions in the west. The observational results not only establish a new picture of the aurora oval near local noon, but also provide important support to a conceptual model of throat aurora. 相似文献
5.
New Models for Long Range Forecasts of Summer Monsoon Rainfall over North West and Peninsular India 总被引：1，自引：0，他引：1
M. Rajeevan Pulak Guhathakurta V. Thapliyal 《Meteorology and Atmospheric Physics》2000,73(3-4):211-225
Summary New models based on (a) Multivariate Principal Component Regression (PCR) (b) Neural Network (NN) and (c) Linear Discriminant
Analysis (LDA) techniques were developed for long-range forecasts of summer monsoon (June–September) rainfall over two homogeneous
regions of India, viz., North West India and Peninsular India. The PCR and NN models were developed with two different data
sets. One set consisted 42 years (1958–1999) of data with 8 predictors and the other, 49 years (1951–1999) of data with 6
predictors. The predictors were subjected to the Principal Component Analysis (PCA) before model development. Two different
neural networks were designed with 2 and 3 hidden neurons. To avoid the nonlinear instability, 20 ensemble runs were made
while training the network and the ensemble mean results are discussed. The LDA model was developed with 42 years of data
(1958–1999) for classifying three rainfall intervals with equal prior probability of 0.33. Both the PCR and NN models showed
useful forecast skill for NW India and Peninsular India. Models with 8 predictors performed better than the models with only
6 predictors. The NN model with 3 hidden neurons performed better than model with 2 hidden neurons. For NW India, the NN model
performed better than the PCR model. The RMSE of the NN model and PCR model with 8 predictors for NW India (Peninsular India)
during the independent period 1984–99 was 12.5% (12.2%) and 12.6% (11.5%), respectively. Corresponding figures for the models
with 6 predictors are 15.0% (13.0%) and 13.9% (11.4%) respectively. During the independent period, model errors were large
in 1991, 1994, 1997 and 1999. However all the models showed deteriorating predictive skill after 1988, both for NW India and
Peninsular India. The LDA model correctly classified 62% of grouped cases for NW India and Peninsular India. The LDA model
showed better skill in classifying deficient rainfall (< − 8%) over NW India and excess rainfall (> 3%) over Peninsular India.
Received October 2, 1999 Revised December 28, 1999 相似文献
6.
Global structure of the Madden-Julian Oscillations during two recent contrasting summer monsoon seasons over India 总被引：1，自引：0，他引：1
A. D. Vernekar V. Thapliyal R. H. Kripalani S. V. Singh B. Kirtman 《Meteorology and Atmospheric Physics》1993,52(1-2):37-47
Summary The global nature of the Madden-Julian Oscillations (MJOs) have been investigated by applying a frequency filter to daily data for the summer monsoon months (June to September) during two contrasting years—1987, a deficient monsoon year and 1988, an excess monsoon year. Several meteorological parameters at five levels in the troposphere have been examined. Regions with large amplitude of these oscillations are isolated for each year. The results indicate that the global spatial distribution of these oscillations is more in a deficient year than in an excess year, in particular over the Indian subcontinent and the EI Niño Southern Oscillation (ENSO) regions. The principal modes of variability during these two years have been investigated through Empirical Orthogonal Functions (EOFs). The first two eigenmodes of 850 hPa zonal wind explain nearly 50% of the variance. The dipole type of structure between the Indian and the Pacific region is more apparent in 1987 than in 1988. Time-longitude cross sections of the filtered zonal wind over the equatorial regions clearly show that eastward propagation is detected in 1987, but is virtually absent in 1988. It is also seen that the 30–60 day filtered winds are stronger during the monsoon of 1987 than in 1988. 相似文献
7.
P Jindal P K Thapliyal M V Shukla A K Mishra D Mitra 《Journal of Earth System Science》2014,123(6):1265-1271
The present study examines the potential of infrared sounder observations from Indian geostationary satellite INSAT-3D for the estimation of total column integrated ozone over the tropical Indian region. A dataset with diverse profiles was used to create training and testing datasets using forward simulations from a radiative transfer model for infrared sounder channels. A study was carried out for the standard tropical atmospheric profile to examine the sensitivity of ozone band radiance corresponding to the atmospheric temperature, water vapour, and ozone mixing ratios at different atmospheric pressure levels. Further, statistical retrieval technique has been used for the total column ozone estimation using two different approaches: (i) ozone channel observation along with the a-priori estimate of temperature and water vapour profile and (ii) only sounder channels observations. The accuracy of the retrieval algorithms was examined for different errors in the atmospheric profiles for the method (i) and different sensor noise specification for the method (ii). This study has shown that accurate temperature information is very important for ozone estimation and lower instrument noise results in better ozone estimates. 相似文献
8.
Summary The existing methods based on statistical techniques for long range forecasts of Indian monsoon rainfall have shown reasonably
accurate performance, for last 11 years. Because of the limitation of such statistical techniques, new techniques may have
to be tried to obtain better results. In this paper, we discuss the results of an artificial neural network model by combining
two different neural networks, one explaining assumed deterministic dynamics within the time series of Indian monsoon rainfall
(Model I) and other using eight regional and global predictors (Model II). The model I has been developed by using the data
of past 50 years (1901–50) and the data for recent period (1951–97) has been used for verification. The model II has been
developed by using the 30 year (1958–87) data and the verification of this model has been carried out using the independent
data of 10 year period (1988–97). In model II, instead of using eight parameters directly as inputs, we have carried out Principal
Component Analysis (PCA) of the eight parameters with 30 years of data, 1958–87, and the first five principal components are
included as input parameters. By combining model I and model II, a hybrid principal component neural network model (Model
III) has been developed by using 30 year (1958–87) data as training period and recent 10 year period (1988–97) as verification
period. Performance of the hybrid model (Model III) has been found the best among all three models developed. Rootmean square
error (RMSE) of this hybrid model during the independent period (1988–97) is 4.93% as against 6.83%of the operational forecasts
of the India Meteorological Department (IMD) using the 16 parameter Power Regression model. As this hybrid model is showing
good results, it is now used by the IMD for experimental long-range forecasts of summer monsoon rainfall over India as a whole.
Received August 20, 1998/Revised April 20, 1999 相似文献
9.
Tiger conservation often requires local-level support to avoid facing serious political challenges. In order to address the political challenges, the social capital of communities can be utilized to create community action and to help understand local dynamics. We studied the social capital in two villages bordering Corbett Tiger Reserve, India. Our results indicate that social capital of local communities is a significant determinant of potential for community action to support or oppose tiger conservation outcomes. Our results also indicate that specific components of social capital (solidarity, reciprocity and cooperation, networks, and mutual support) were critical in this potential community action. Further, the data suggest that the decline of social capital was led by the financial disparities created by unplanned growth of tourism outside the reserve boundaries. We suggest that policy and management interventions should consider social capital of local communities and ways in which it may support tiger conservation in India. 相似文献
10.