Numerical simulation of cyclonic storms FANOOS, NARGIS with assimilation of conventional and satellite observations using 3-DVAR

In this work, the impact of assimilation of conventional and satellite data is studied on the prediction of two cyclonic storms in the Bay of Bengal using the three-dimensional variational data assimilation (3D-VAR) technique. The FANOOS cyclone (December 6?C10, 2005) and the very severe cyclone NARGIS (April 28?CMay 2, 2008) were simulated with a double-nested weather research and forecasting (WRF-ARW) model at a horizontal resolution of 9?km. Three numerical experiments were performed using the WRF model. The back ground error covariance matrix for 3DVAR over the Indian region was generated by running the model for a 30-day period in November 2007. In the control run (CTL), the National Centers for Environmental Prediction (NCEP) global forecast system analysis at 0.5° resolution was used for the initial and boundary conditions. In the second experiment called the VARCON, the conventional surface and upper air observations were used for assimilation. In the third experiment (VARQSCAT), the ocean surface wind vectors from quick scatterometer (QSCAT) were used for assimilation. The CTL and VARCON experiments have produced higher intensity in terms of sea level pressure, winds and vorticity fields but with higher track errors. Assimilation of conventional observations has meager positive impact on the intensity and has led to negative impact on simulated storm tracks. The QSCAT vector winds have given positive impact on the simulations of intensity and track positions of the two storms, the impact is found to be relatively higher for the moderate intense cyclone FANOOS as compared to very severe cyclone NARGIS.     

Isotopic fractionation of methane in the martian atmosphere

The existence of methane in the martian atmosphere may be an indicator of subsurface life. Biological processes are known to fractionate the common isotopologues of methane, and hence measuring these isotopic ratios may yield constraints on the nature of the methane source. Any measurement of the isotopic ratios of atmospheric methane must consider the additional fractionation due to photochemistry in order to quantify the isotopic ratios of the source. Using a one-dimensional photochemical model, we find that photochemistry has a small (4.5‰) contribution to δ¹³C(CH₄) but has a large (114‰) contribution to δD(CH₄). Confirmation of these fractionation values will require additional laboratory data on key model inputs, particularly the ultraviolet absorption cross sections of ¹³CH₄ and kinetic rate coefficients for the reactions of ¹³CH₄ and CH₃D with OH and O(¹D) at pressures and temperatures relevant to the martian atmosphere.     

Analysis of snow cover and climatic variability in Bhaga basin located in western Himalaya

Bhaga Basin has complex mountainous terrain; little study has been done on the spatial and temporal characteristics of snow cover in the region. The Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day snow cover products between 2001 and 2012 for winter period (November–April) have been used to study the variation in snow cover area (SCA). The statistical analysis based on non-parametric Mann Kendall and Sen’s slope methods have been used for detecting and estimating trends for climatic variables (temperature and snowfall) and SCA for winter period. Results of statistical analysis indicate rise in minimum temperature (0.02 °C year^?1) and fall in maximum temperature (0.17 °C year^?1). It also shows decrease in mean seasonal snowfall (0.07 cm year^?1). The seasonal SCA was found to decrease at the rate of 0.002% year^?1. This study indicates that the climate change is probably one of the major causes for depleting SCA.     

Transition in Late Quaternary Paleoclimate in Schirmacher Region,East Antarctica as Revealed from Lake Sediments

The lacustrine sediments are one of the best sources to provide information on climate change, specially in peri-glacial climatic region. Schirmacher Oasis, located on the Princess Astrid Coast in Queen Maud Land, is one of the few areas in East Antarctica that provides valuable information on paleoclimate of the region with various depositional features formed due to deglaciation process. This Oasis is dotted with more than 100 lakes of proglacial, land-locked and epi-shelf type. The multi-proxy sedimentological data, generated from the sediment cores from land-locked lakes and grab sample from a proglacial lake, lying in the same drainage line in the central part of Schirmacher region has provided better insight into the paleoclimatic evolution of the region. The immature and chemically unaltered lake sediments have shown restricted drainage pattern. Different phases of warmer and cooler intervals are highlighted by the patterns of fluctuations in different sedimentological and statistical parameters. The dominance of glacial signatures is very clear on the lake sediments as revealed by the surface textures of quartz grains. Physical weathering has mainly controlled the overall sediments and the composition of clay fraction. The clay minerals indicate a gradual shift in the weathering regime and therewith in climate from strongly glacial to fluvioglacial specially around 42 ka. This indicates beginning of warming of the area much before the LGM. But the warm period is not strong enough to alter the overall clay chemistry. Proxy records indicate short-period climatic oscillations during late Quaternary.     

Active tectonics in the Assam seismic gap between the meizoseismal zone of AD 1934 and 1950 earthquakes along eastern Himalayan front,India

The Assam Seismic Gap has witnessed a long seismic quiescence since the \({ Mw}{\sim }8.4\) great Assam earthquake of AD 1950. Owing to its improper connectivity over the last decades, this segment of the Himalaya has long remained inadequately explored by geoscientists. Recent geodetic measurements in the eastern Himalaya using GPS document a discrepancy between the geologic and geodetic convergence rates. West to east increase in convergence rate added with shorter time span earthquakes like the 1697 Sadiya, 1714 (\({ Mw}{\sim }8\)) Bhutan and 1950 (\({ Mw}{\sim } 8.4\)) Tibet–Assam, makes this discrepancy more composite and crucial in terms of seismic hazard assessment. To understand the scenario of palaeoearthquake surface rupturing and deformation of youngest landforms between the meizoseismal areas of \({ Mw}{\sim }8.1\) 1934 and 1950 earthquakes, the area between the Manas and Dhanshiri Rivers along the Himalayan Frontal Thrust (HFT) was traversed. The general deformation pattern reflects north-dipping thrust faults. However, back facing scarps were also observed in conjugation to the discontinuous scarps along the frontal thrust. Preliminary mapping along with the published literature suggests that, in the eastern Himalayan front the deformation is taking place largely by the thrust sheet translation without producing a prominent fault-related folds, unlike that of the central and western Himalayas.     

Machine learning for graph-based representations of three-dimensional discrete fracture networks

Structural and topological information play a key role in modeling flow and transport through fractured rock in the subsurface. Discrete fracture network (DFN) computational suites such as dfnWorks (Hyman et al. Comput. Geosci. 84, 10–19 2015) are designed to simulate flow and transport in such porous media. Flow and transport calculations reveal that a small backbone of fractures exists, where most flow and transport occurs. Restricting the flowing fracture network to this backbone provides a significant reduction in the network’s effective size. However, the particle-tracking simulations needed to determine this reduction are computationally intensive. Such methods may be impractical for large systems or for robust uncertainty quantification of fracture networks, where thousands of forward simulations are needed to bound system behavior. In this paper, we develop an alternative network reduction approach to characterizing transport in DFNs, by combining graph theoretical and machine learning methods. We consider a graph representation where nodes signify fractures and edges denote their intersections. Using random forest and support vector machines, we rapidly identify a subnetwork that captures the flow patterns of the full DFN, based primarily on node centrality features in the graph. Our supervised learning techniques train on particle-tracking backbone paths found by dfnWorks, but run in negligible time compared to those simulations. We find that our predictions can reduce the network to approximately 20% of its original size, while still generating breakthrough curves consistent with those of the original network.     

Numerical model and flume experiments of single- and two-layered hillslope flow related to slope failure

A hillslope flow model is developed considering 3D saturated and unsaturated flow of water during rainfall events. A finite difference-based numerical model of hillslope flow processes is developed. Four different experiments are done to see the effects of a single- and double-layered soil in pore-water pressure dynamics and slope failure. Results from the numerical model are verified with experimental results. The numerical and experimental values of the pore-water pressure and moisture contents are in good agreement. The results show that the hillslope heterogeneity caused by multiple layers of soil has greater influence on hillslope pore-pressure dynamics and slope failure patterns. The depth of slope failure shows high dependency on layering characteristics of the soil slope and pattern of rainfall. The proposed model provides a perspective on failure mechanism of a single- or double-layered slope under rainfall infiltration.     

Flare-associated high-speed solar plasma streams

Characteristics of flare-associated high-speed solar plasma streams are investigated using measurements from space probes and Earth-orbiting spacecraft for the period 1964–1982. The maximum observed velocity (V _m) of these streams range from 400 to 850 km s^–1} with peak probability for 600 km s^–1}. These remain for the period of 1–10 days with the peak occurrence 3 days. The difference between the pre-stream velocity (V ₀) and the maximum velocity (V _m) of any high-speed stream serves as the measure of its intensity. For about 60% of the flare associated streams, (V _m-V ₀) is well in excess of 200 km s^–1} and in some cases becomes as large as 450 km s^–1}. The yearly percentage occurrence, total duration and the product of mean (V _m - V ₀) with total duration of the high-speed streams during the year correlates well with solar activity, e.g., maximum during high solar activity period and minimum during low solar activity. The study suggests that presence of sunspots plays a significant role in the generation of flare associated high-speed solar streams.     

Strain determination from concentric folds

A new technique to determine flattening strain from initially concentric folds is described in this paper. The proposed method is simple and involves direct measurements on fold profiles. It requires measurement of the distance between the center of the fold to the middle of the layer, and this is plotted as a function of line orientation. The method needs few measurements at fixed angular spacing resulting in quick estimation of strain.     

On the origin of ringing irregularities—A meteor hypothesis

Journal of Earth System Science - Isolated ionospheric irregularities produce oscillating (ringing) diffraction patterns on the ground. Typical physical properties such as density, size, etc. of...