A dynamo model with double diffusive convection for Mercury's core

A recent dynamo model for Mercury assumes that the upper part of the planet's fluid core is thermally stably stratified because the temperature gradient at the core–mantle boundary is subadiabatic. Vigorous convection driven by a superadiabatic temperature gradient at the boundary of a growing solid inner core and by the associated release of light constituents takes place in a deep sub-layer and powers a dynamo. These models have been successful at explaining the observed weak global magnetic field at Mercury's surface. They have been based on the concept of codensity, which combines thermal and compositional sources of buoyancy into a single variable by assuming the same diffusivity for both components. Actual diffusivities in planetary cores differ by a large factor. To overcome the limitation of the codensity model, we solve two separate transport equations with different diffusivities in a double diffusive dynamo model for Mercury. When temperature and composition contribute comparable amounts to the buoyancy force, we find significant differences to the codensity model. In the double diffusive case convection penetrates the upper layer with a net stable density stratification in the form of finger convection. Compared to the codensity model, this enhances the poloidal magnetic field in the nominally stable layer and outside the core, where it becomes too strong compared to observation. Intense azimuthal flow in the stable layer generates a strong axisymmetric toroidal field. We find in double diffusive models a surface magnetic field of the observed strength when compositional buoyancy plays an inferior role for driving the dynamo, which is the case when the sulphur concentration in Mercury's core is only a fraction of a percent.     

A micromorphological record of contemporary and relict pedogenic processes in soils of the Indo‐Gangetic Plains: implications for mineral weathering,provenance and climatic changes

Micromorphology has important application in earth surface process and landform studies particularly in alluvial settings such as the Indo‐Gangetic Plains (IGP) with different geomorphic surfaces to identify climatic changes and neotectonic events and their influence on pedogenesis. The soils of the IGP extending from arid upland in the west to per humid deltaic plains in the east developed on five geomorphic surfaces namely QIG1 to QIG5 originating during the last 13.5 ka. Four soil‐geomorphic systems across the entire IGP are identified as: (i) the western Yamuna Plains/Uplands, (ii) the Yamuna‐Ganga Interfluve, (iii) the Ganga‐Ghaghara Interfluve, and (iv) the Deltaic Plains. Thin section analysis of the soils across the four soil‐geomorphic systems provides a record of provenance, mineral weathering, pedogenic processes and polygenesis in IGP. The soils over major parts of the IGP dominantly contain muscovite and quartz and small fraction of highly altered feldspar derived from the Himalayas. However, soils in the western and eastern parts of the IGP contain large volumes of fresh to weakly altered plagioclase and smectitic clay derived from the Indian craton. The soils in western Yamuna Plains/Uplands dominated by QIG2–QIG3 geomorphic surfaces and pedogenic carbonate developed in semi‐arid climate prior to 5 ka. However, soils of the central part of the IGP in the Yamuna‐Ganga Interfluve and Ganga‐Ghaghara Interfluve regions with dominance of QIG4–QIG5 surfaces are polygenetic due to climate change over the last 13.5 ka. The clay pedofeatures formed during earlier wet phase (13.5–11 ka) show degradation, loss of preferred orientation, speckled appearance in contrast with the later phase of wet climate (6.5–4 ka). The soils over the deltaic plains with dominance of vertic features along with clay pedofeatures suggest that illuviation of fine clay is an important pedogenic process even in soils with shrink‐swell characteristics. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluation and implications of seismic events in Garhwal-Kumaun region of Himalaya

The Garhwal-Kumaun region continues to accumulate the built-up of strain energy like the other regions of the Himalaya. But this sector unlike the other sectors is yet to release this accumulated strain energy which can be in the form of great earthquake. The region has sufficient strain energy to generate earthquake of M>8. The analysis of seven hundred ten local events recorded by ten station broad band network between August’07 to February’10 shows that most of the seismic events recorded in this region continue to occur from shallow depths (< 25 km). The evaluation of source parameters from p-wave spectral analysis indicates that the events have low stress drop values. The region continues to release energy in the form of smaller magnitude earthquakes. The epicentral location map indicates that Munsiari Thrust, which is located south of the Main Central Thrust is more active.     

Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge — northernmost part of the Chagos-Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs).     

Rainstorm-generated sediment yield model based on soil moisture proxies (SMP)

This study develops improved Soil Moisture Proxies (SMP) based suspended sediment yield (SMPSY) models corresponding to three antecedent moisture conditions (AMCs) (i.e., AMC-I-AMC-III) by coupling the improved initial abstraction (I_a-λ) model, the SMA procedure and the SMP concept for modelling the rainfall generated suspended sediment yield. The SMPSY models specifically incorporate a watershed storage index (S) model to accentuate the transformation from storm to storm and to avoid the sudden jumps in sediment yield computation. The workability of the SMPSY models is tested using a large dataset of rainfall and sediment yield (98 storm events) from twelve small watersheds and a comparison has been made with the existing MSY model. The goodness-of-fit (GOF) statistics is evaluated in terms of the Nash Sutcliffe efficiency (NSE), and error indices, i.e., root mean square error (RMSE), normalized root mean square error (nRMSE), standard error (SE), mean absolute error (MAE), and RMSE-observations standard deviation ratio (RSR). The NSE values vary from 74.31% to 96.57% and from 75.21% to 91.78%, respectively for the SPMSY and MSY model. The NSE statistics indicate that the SMPSY model has lower uncertainty in simulating sediment yield as compared to the MSY model. The error indices are lower for the SMPSY model than the MSY model for most of the watersheds. These results show that the SMPSY model has less uncertainty and performs better than the MSY model. A sensitivity analysis of the SMPSY model shows that the parameter β is most sensitive followed by parameter S, α and A. Overall, the results show that the characterization of soil moisture variability in terms of SMPs and incorporation of improved delivery ratio and runoff coefficient relationship improves the simulation of the erosion and sediment yield generation process.     

Empirical assessment of adaptation to climate change impacts of mountain households: development and application of an Adaptation Capability Index

The present study proposes an index to assess the potential for adaptation to climate change for households in the mountainous regions. The index provides a realistic approach to recognize social and natural factors which contribute to successful adaptation and addresses several household functions, such as social networking, livelihood strategy, adjustment strategies, resource availability and accessibility. The proposed Adaptation Capability Index (ACI) is analytically defined, mathematically formulated and field tested on mountainous households in urban and semi-urban regions of the Uttarakhand Himalaya in India. To gather data on the topic relevant to the ACI, a household scale questionnaire was developed and administered to 120 heads of households through face-to-face interviews. The results highlight higher adaptive capability of urban households and low adaptation capacity of rural households due to poor farm productivity, low accessibility and availability of resources and technological input. Future programs and policies must include and implement regulations to remedy attributive factors responsible for higher adaptation. This paper may be applicable to other mountainous regions and may provide insights for effective adaptation strategies to climate change.     

Estimation of Natural Radionuclides and Exhalation Rate in Surface Soils of Four Districts of Haryana,India

A fossil wood of Lagerstroemia L. from the Upper Siwalik sediments of Arunachal Pradesh is described. The genus is recorded for the first time from this state. The modern analog of the fossil species i.e. L. tomentosa C. Presl is not found in the fossil locality at present.. The most plausible reason for the disappearance of the species from the fossil locality is an increase in temperature seasonality caused by the upheaval of the Himalaya during the Pleistocene.