by SrideviJade, T.S. Shrungeshwara and Boddapati Anil
Precipitable Water Vapor (PWV) is estimated using MODIS (Moderate Resolution Imaging Spectro-radio-meter) Terra level 3 data with daily resolution i. e MOD08_D3 at 64 cGPS (continuous Global Positioning System) stations spatially spread over Indian subcontinent between geodetic latitude 5° to 35° N and geodetic longitude of 70° to 96° E. MODIS-PWV is compared with GPS-PWV estimated at these cGPS stations to check the validity of water vapor retrieved from MODIS data in Indian subcontinent. Correlation coefficient (R2) between daily values of MODIS and GPS water vapor is above 0.9 with RMSE (root mean square error) of 2–5 mm for 22 cGPS in peninsular India, above 0.9 with RMSE of 3–6 mm for 5 cGPS in northeast India and above 0.8 with RMSE of 1–9 mm for 26 cGPS in Himalayas. PWV time series at all the cGPS stations indicated distinct seasonal cycle for both MODIS and GPS PWV with high RMSE (~6 mm) in wet months and low RMSE (~3 mm) during dry months. Taking advantage of broad spatial spread of stations and long span of data, model for spatial variability of GPS-PWV for Indian subcontinent is proposed. Inter-annual and seasonal variability of GPS-PWV is discussed in detail for peninsular India, northeast India and Himalayas.
We reconstruct the movement of the India Plate relative to Eurasia at ≈1-Myr intervals from 20 Ma to the present from GPS site velocities and high-resolution sequences of rotations from the India–Somalia Antarctic–Nubia–North America–Eurasia Plate circuit. The plate circuit rotations, which are all estimated using the same data fitting functions, magnetic reversal sampling points, calibrations for magnetic reversal outward displacement, and noise mitigation methods, include new India–Somalia rotations estimated from numerous Carlsberg and northern Central Indian ridge plate kinematic data and high-resolution rotations from the Southwest Indian Ridge that account for slow motion between the Nubia and Somalia plates. Our new rotations indicate that India–Somalia plate motion slowed down by 25–30 per cent from 19.7 to 12.5–11.1 Ma, but remained steady since at least 9.8 Ma and possibly 12.5 Ma. Our new India–Eurasia rotations predict a relatively simple plate motion history, consisting of NNE-directed interplate convergence since 19 Ma, a ≈50 per cent convergence rate decrease from 19.7 to 12.5–11.1 Ma, and steady or nearly steady plate motion since 12.5–11.1 Ma. Instantaneous convergence rates estimated with our new India–Eurasia GPS angular velocity are 16 per cent slower than our reconstructed plate kinematic convergence rates for times since 2.6 Ma, implying either a rapid, recent slowdown in the convergence rate or larger than expected errors in our geodetic and/or plate kinematic estimates. During an acceleration of seafloor faulting within the wide India–Capricorn oceanic boundary at 8– 7.5 Ma, our new rotations indicate that the motions of the India Plate relative to Somalia and Eurasia remained steady. We infer that forces acting on the Capricorn rather than the India Plate were responsible for the accelerated seafloor deformation, in accord with a previous study. India–Eurasia displacements that are predicted with our new, well-constrained rotations are fit poorly by a recently proposed model that attributes the post-60-Ma slowdown in India–Eurasia convergence rates to the steady resistance of a strong lithospheric mantle below Tibet.
This study is about the impact assessment of different land-use data sets on the simulation of an Extreme Rainfall Event (ERE) which is one of the unusually rare events that occurred between 14th to 18th of June 2013 over Uttarakhand in India. In this work, high-resolution (2-km), time ensemble simulations are carried out using Weather Research and Forecasting model (WRFV3.5) with a 3-nest configuration. The sensitivity analysis of the model in simulating rainfall to different land-use data i.e. USGS-24 category (1992–93), ISRO (2004–05) and (2012–13) are carried out. Comparison of simulated rainfall which is averaged over the study region with that of IMD observed station data (averaged over 23 stations) showed that the simulations based on ISRO land-use data are comparatively more accurate with lesser simulation error when compared to simulations with USGS land-use data. The percentage of error in rainfall for the 3 simulations was found to be 24% (USGS), 9.5% (ISRO-2005) and 10% (ISRO-2013) with respect to the IMD observation. During the initial stage, the results have shown maximum convergence and vorticity with a strong updraft. The strong updraft, however, persisted throughout the simulation period. The increasing tendency of positive vorticity both in the simulation and observation suggests an intensification of cyclonic circulation in a vertical direction and hence creates instability in the boundary layer causing ERE over Uttarakhand. This study shows that ISRO land-use data is a relatively more realistic representation of the study region than the USGS data, and found to be useful in reducing the model error in the simulation of such rare events over this kind of mountainous region.
by Stella Jes Varghese, Sajani Surendran, Kavirajan Rajendran and Akio Kitoh
Abstract: Present-day simulations (1983–2003) of a global climate model of 60-km resolution with three deep convection schemes are analysed to find the best scheme for simulation of mean Indian summer monsoon rainfall (ISMR) and its variability. Multiforcing ensemble projections with the best scheme are carried out under multiple Representative Concentration Pathways (RCPs) (based on various socio-economic and technological development at the end of the century), viz. RCP2.6, RCP4.5, RCP6.0 and RCP8.5, forced with four patterns of future sea surface temperature (SST) change for each scenario; one with mean SST changes projected by 28 Coupled Model Intercomparison Project Phase-5 (CMIP5) models and the rest obtained from subgroups of CMIP5 models grouped through cluster analysis of tropical SST changes. These are analysed for future (2079–2099) changes in surface air temperature (Ts ) and rainfall which show overall increase over India except for rainfall reduction over Western Ghats. We find that combination of enhanced atmospheric water vapour content and increased vertically integrated low level moisture transport into the subcontinent as the major contributing factors for future intensification of ISMR. Extreme events show increase in warm days with significant increase in warm nights. Percentage of grid points showing increased extreme rainfall increases from low to high emission scenario. The high-resolution model enables to study projected changes over India at homogeneous zones level. The maximum increase in Ts and rainfall occurs over Western Himalaya and Northeast hilly region respectively. Consistent with future increase in Ts and rainfall, their extreme events also increase over all the homogeneous zones.
by A. K. Nekrasova, V. G. Kossobokov, I. A. Parvez and X. Tao
Abstract
The distribution of the number of seismic events by magnitudes—the Gutenberg–Richter frequency–magnitude relation—is of paramount importance for seismic hazard assessment of a territory. The generalization of the Gutenberg–Richter relation—the Unified Scaling Law for Earthquakes (USLE) proposed in 1988 makes it possible to take into account the pattern of epicentral distribution of seismic events when changing the spatial scale of the analysis. This is extremely important for adequate downscaling of the frequency of occurrence into a smaller area within the territory under study (e.g., in the megalopolis). In 2002, Per Buck suggested a dual formulation of USLE where, instead of the number of earthquakes over a certain period of time, the reciprocal of their frequency of occurrence—the time between seismic events—is used. The same year, the Institute of Earthquake Prediction Theory and Mathematical Geophysics of the Russian Academy of Sciences developed a modified algorithm for robust estimation of USLE parameters referred to as Scaling Coefficients Estimation (SCE) for producing seismic hazard maps of territories prone to seismic effects. This brief review is focused on the use of the USLE approach to the assessment of seismic hazard and associated risk.
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