Simulation of Indian summer monsoon: experiments with SSTs

Summary Hindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from an ensemble of numerical simulations performed with a global model by changing SST. Two sets of ensemble simulations have been produced without vegetation: (i) by prescribing the weekly observed SST from ECMWF (European Centre for Medium Range Weather Forecasting) analyses, and (ii) by adding weekly SST anomalies (SSTA) of April to the climatological SST during the simulation period from May to August. For each ensemble, 10 simulations have been realized with different initial conditions that are prepared from ECMWF data with five each from April and May analyses of both the years. The predicted June–July monsoon rainfall over the Indian region shows good agreement with the GPCP (observed) pentad rainfall distribution when 5 member ensemble is taken from May initial conditions. The All-India June–July simulated rainfall time series matches favourably with the observed time series in both the years for the five member ensemble from May initial condition but drifts away from observation with April initial conditions. This underscores the role of initial conditions in the seasonal forecasting. But the model has failed to capture the strong intra-seasonal oscillation in July 2002. Heating over equatorial Indian Ocean for June 2002 in a particular experiment using 29th May 12 GMT as initial conditions shows some intra-seasonal oscillation in July 2002 rainfall, as in observation. Further evaluation of the seasonal simulations from this model is done by calculating the empirical orthogonal functions (EOFs) of the GPCP rainfall over India. The first four EOFs explain more than 80% of the total variance of the observed rainfall. The time series of expansion coefficients (principal components), obtained by projecting on the observed EOFs, provide a better framework for inter-comparing model simulations and their evaluation with observed data. The main finding of this study is that the All-India rainfall from various experiments with prescribed SST is better predicted on seasonal scale as compares to prescribed SST anomalies. This is indicative of a possible useful seasonal forecasts from a GCM at least for the case when monsoon is going to be good. The model responses do not differ much for 2002 and 2003 since the evolution of SST during these years was very similar, hence July rainfall seems to be largely modulated by the other feedbacks on the overall circulation.     

A cyclone over Saudi Arabia on 5 January 2002: A case study

Summary A shallow and short-lived subsynoptic cyclone is discussed as one of typical events causing natural disasters over Saudi Arabia on 5 January 2002 using the Japan Meteorological Agency global analysis dataset. The main cause for its formation was vorticity stretching. On the same day widespread rainfall over Saudi Arabia with enhanced precipitation over the mountainous Jeddah region was also observed using the Global Precipitation Climatology Project dataset. Owing to eastward-moving wintertime synoptic-scale Mediterranean disturbances, this rainfall was associated with frontal activity, modified by the local orography.     

Role of Triad Kinetic Energy Interactions for Maintenance of Upper Tropospheric Low Frequency Waves during Summer Monsoon 1988

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Mg tracer diffusion in synthetic forsterite and San Carlos olivine as a function of P,T and fO2

We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo₁₀₀) and San Carlos olivine (Fo₉₂) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ/mol (96 kcal/mol) and 275 (±25) kJ/mol (65 kcal/ mol) in forsterite and San Carlos olivine, respectively, along [001] at a fO₂ of 10^–12 bars. There is no change in activation energy of Mg tracer diffusion within this temperature range. Mg tracer diffusion in a nominally pure forsterite is found to be anisotropic (D_c > D_a > D _b) and a function of fO₂. This fO₂ dependence is different from that in olivine containing Fe as a major element, which suggests that the diffusion mechanism of Mg in forsterite is different from that in Fe-bearing olivine at least over some range of fO₂. The diffusion mechanism in nominally pure forsterites may involve impurities present below the limits of detection or alternately, Si or Fe³⁺ interstitial defects, Fe being present as impurity (ppm level) in forsterite. Pressure dependence of Mg tracer diffusivity in forsterite measured to 10 GPa in a multianvil apparatus yields an activation volume of approximately 1–3.5 cm³/ mol. It is found that presence of small amounts of hydrogen bearing species in the atmosphere during diffusion anneal (f_H2 0.2 bars, f_H20 0.24 bars) do not affect Mg tracer diffusion in forsterite within the resolution of our measurement at a total pressure of 1 bar. The observed diffusion process is shown to be extrinsic; hence extrapolation of the diffusion data to lower temperatures should not be plagued by uncertainties related to change of diffusion mechanism from intrinsic to extrinsic.     

Depositional Record of Tidal-Flat Sedimentation in the Permian Coal Measures of Central India: Barakar Formation, Mohpani Coalfield, Satpura Gondwana Basin

The Permian Barakar Formation in the Mohpani coalfield, Satpura Gondwana basin, is composed of three broad lithologies that occur repetitively and are iterdigitated: (1) several metres thick coarse- to medium-grained sandstone bodies with scoured bases, (2) 5-20 m thick medium- to fine-grained sandstone bodies and (3) 5-20 m thick mudstone-dominated packages with variable proportions of centimetre- to decimetre-scale, fine- to medium-grained sandstone, carbonaceous shale and coal. The Barakar strata were previously interpreted as deposits of braided rivers and associated inter-channel flood basin in a continental setting. However, this study recognizes signatures of tidal current from the mudstone-dominated packages implying marine influence during Barakar sedimentation.

The mudstone-dominated sediment bodies are the focus of this paper and comprise of three lithofacies that bear imprints of tidal processes during Barakar sedimentation: (1) heterolith, (2) sandstone, and (3) coal-carbonaceous shale, which alternate with one another within individual bodies. The heterolithic facies show interlayering of sandstone and claystone resembling flaser, wavy and lenticular bedding, as well as pinstripe stratification. Successive sandstone-mudstone couplets indicate periodic waxing and waning of flows. Within individual heterolithic packages, the sandstone:claystone ratio along with the bedding style, varies cyclically upwards giving rise to alternate sandstone-dominated and claystone-dominated intervals suggesting tidal velocity fluctuation reflective of spring-neap lunar cycle. Thickness plots of successive sand-mud couplets also reveal cyclic variation with a conspicuous periodicity of around 12 couplets per cycle, which corroborates the spring-neap-spring (or neap-spring-neap) lunar cycle. Presence of abundant desiccation cracks indicates periodic emergence and points towards an intertidal setting. The sandstone facies is characterized by a variety of wave-generated features such as bundled and chevron upbuilding of lamina, bi-directional foreset orientations, offshooting and draping laminae, scour-and-drape feature, swollen lens-like geometries suggesting their emplacement under storm-induced combined-flow on the tidal-flat. The coal-carbonaceous shale facies represent supratidal marsh environment.     

Using GIS to Assess the Environmental Justice Consequences of Transportation System Changes

Although environmental justice research has typically focused on locations of industrial toxic releases or waste sites, recent developments in GIS and environmental modeling provide a foundation for developing measures designed to evaluate the consequences of transportation system changes. In this paper, we develop and demonstrate a workable GIS-based approach that can be used to assess the impacts of a transportation system change on minorites and low-income residents. We focus specifically on two adverse affects: vehicle-generated air pollution and noise. The buffer analysis capabilities of GIS provide a preliminary assessment of environmental justice. We integrate existing environmental pollution models with GIS software to identify the specific locations where noise and air pollution standards could be violated because of the proposed system change. A comparison of the geographic boundaries of these areas with the racial and economic characteristics of the underlying population obtained from block level census data provides a basis for evaluating disproportionate impacts. An existing urban arterial in Waterloo, Iowa, is used to illustrate the methods developed in this research.     

Interannual variability and characteristics of the East India Coastal Current associated with Indian Ocean Dipole events using a high resolution regional ocean model

The characteristics and variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal (BoB) during the Indian Ocean Dipole (IOD) years between 2006 and 2012 have been investigated using the high-resolution Regional Ocean Modeling System (ROMS). The evolution of temperature, mixed layer depth (MLD), and seasonal basin scale circulation in the upper ocean simulated by the model agrees well with the observations. The EICC in BoB is characterized by a seasonal reversal flow: the poleward EICC during February?May and the equatorward EICC during August?December. A long-term simulation from 2006 to 2012 suggest that the circulation pattern, boundary current structure, and transport in the western BoB are completely different in positive and negative IOD years. As IOD is mainly phase-locked to the seasonal cycle with most significant influence in the Borel autumn, the equatorward EICC is affected during the IOD years. It is found that the strength of this EICC is ~?5 Sv in October 2010 and a weaker EICC dominated by the presence of eddies is observed in October 2006. We also quantified the local and remote forcing effects on the variability of EICC and found that the seasonal coastal Kelvin waves (KWs) play a dominant role in the development of the EICC. During positive IOD year 2006, due the absence of second downwelling KW, the EICC is completely disorganized and dominated by the eddies, whereas in the negative IOD year 2010, the strong second downwelling KW plays a key role in developing organized and stable EICC in the western BoB.     

Changes in daily maximum temperature extremes across India over 1951–2014 and their relation with cereal crop productivity

This study used gridded daily maximum temperature data (1°?×?1°) for 1951–2014 period to analyze the trend in monthly extreme warm days (ExWD) and changes in its probability distribution in each grid. It also analyzed the trend in spatial spread of annual ExWD over the study period at four exceedance levels and further related the number of ExWDs with cereal crop productivity of India. Extreme warm days have increased throughout India but were statistically significant in 42% grids. The increase was consistent over all the months in north-eastern region, southern plateau and both the coastal plains. It also increased significantly over north-western and central India during April to June summer period. The probability distribution of ExWD also changed significantly in many grids, especially in southern plateau and both the coastal plains. The changes indicated increased frequency in the existing levels of extremes and new occurrences of higher frequency of extremes. The analysis of land area affected by different levels of extremes indicated significant increase, with the rate being highest for higher extremes. In terms of extreme warm day temperatures, the study identified southern plateau, east and west coast plains, and north-eastern India as highly vulnerable. Using copula probability model, study showed that increase in ExWD from 20 to 60% may increase the probability of 5% or more yield loss from 17 to 53% for Kharif cereals, 11 to 43% for Rabi cereals and 19 to 63% for wheat crop. The results may be used for devising zone specific adaptation strategies.     

A Tiered Approach to Evaluating Salinity Sources in Water at Oil and Gas Production Sites

A suspected increase in the salinity of fresh water resources can trigger a site investigation to identify the source(s) of salinity and the extent of any impacts. These investigations can be complicated by the presence of naturally elevated total dissolved solids or chlorides concentrations, multiple potential sources of salinity, and incomplete data and information on both naturally occurring conditions and the characteristics of potential sources. As a result, data evaluation techniques that are effective at one site may not be effective at another. In order to match the complexity of the evaluation effort to the complexity of the specific site, this paper presents a strategic tiered approach that utilizes established techniques for evaluating and identifying the source(s) of salinity in an efficient step‐by‐step manner. The tiered approach includes: (1) a simple screening process to evaluate whether an impact has occurred and if the source is readily apparent; (2) basic geochemical characterization of the impacted water resource(s) and potential salinity sources coupled with simple visual and statistical data evaluation methods to determine the source(s); and (3) advanced laboratory analyses (e.g., isotopes) and data evaluation methods to identify the source(s) and the extent of salinity impacts where it was not otherwise conclusive. A case study from the U.S. Gulf Coast is presented to illustrate the application of this tiered approach.     

Seismic response analysis of a hydraulic fill dam

Acta Geotechnica - The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the natural frequencies of the first and second modes of vibration and analyzing the...