A climatological perspective of water vapor at the UTLS region over different global monsoon regions: observations inferred from the Aura-MLS and reanalysis data     

K. N. Uma  Subrata Kumar Das  Siddarth Shankar Das 《Climate Dynamics》2014,43(1-2):407-420

The Aura-MLS observations of eight years from 2004 to 2011 have been utilized to understand the hydration and the dehydration mechanism over the northern and the southern hemispheric monsoon (NH and SH) regions. The monsoon regions considered are the Asian Summer Monsoon, East Asian Summer Monsoon, Arizona Monsoon (AM), North African Monsoon, South American Monsoon and the Australian Monsoon. The annual cycle of water vapor as expected shows maxima over the NH during June–August and during December–February over the SH. The time taken by the air parcels over the NH monsoon regions is found to be different compared to that over the SH monsoon regions. The analysis shows the concentration of water vapor in the upper troposphere and the lower stratosphere (UTLS) has not changed over these eight years in both the hemispheres during their respective monsoon seasons. The present analysis show different processes viz., direct overshooting convection, horizontal advection, temperature and cirrus clouds in influencing the distribution of water vapor to the UTLS over these different monsoon regions. Analysis of the UTLS water vapor with temperature and ice water content shows that the AM is hydrating the stratosphere compared to all the other monsoon regions where the water vapor is getting dehydrated. Thus it is envisaged that the present results will have important implications in understanding the exchange processes across the tropopause over the different monsoon regions and its role in stratosphere chemistry.  相似文献   

Geomorphic characterization of seafloor using Digital Elevation Model derivatives – a case study around Bombay High,Western Indian offshore     

Sandeep Narayan Kundu  Durga Shankar Pattnaik 《国际地球制图》2013,28(2):185-197

The present study demonstrates the use of gridded bathymetry in the form of a Digital Elevation Model (DEM) in a geographic information system (GIS) in geomorphic characterization of the seafloor in the Western Indian offshore around Bombay High region and presents the salient findings. The variography of bathymetry and its derivatives and their spatial correlation provides a technique to measure the presence of seafloor features and provides an insight into the processes involved. The current study utilizes tools available within a GIS for processing of a DEM and its derivatives involving spatial techniques like spatial correlation and variography studies for geomorphic characterization. A broad regional analysis for the study area comprising the near shore coast to the deep waters is discussed, followed up by a detailed study limiting to the coastal region around Bombay High.  相似文献   

Flare Prediction Using Photospheric and Coronal Image Data     

Eric Jonas  Monica Bobra  Vaishaal Shankar  J. Todd Hoeksema  Benjamin Recht 《Solar physics》2018,293(3):48

The precise physical process that triggers solar flares is not currently understood. Here we attempt to capture the signature of this mechanism in solar-image data of various wavelengths and use these signatures to predict flaring activity. We do this by developing an algorithm that i) automatically generates features in 5.5 TB of image data taken by the Solar Dynamics Observatory of the solar photosphere, chromosphere, transition region, and corona during the time period between May 2010 and May 2014, ii) combines these features with other features based on flaring history and a physical understanding of putative flaring processes, and iii) classifies these features to predict whether a solar active region will flare within a time period of \(T\) hours, where \(T = 2 \mbox{ and }24\). Such an approach may be useful since, at the present time, there are no physical models of flares available for real-time prediction. We find that when optimizing for the True Skill Score (TSS), photospheric vector-magnetic-field data combined with flaring history yields the best performance, and when optimizing for the area under the precision–recall curve, all of the data are helpful. Our model performance yields a TSS of \(0.84 \pm0.03\) and \(0.81 \pm0.03\) in the \(T = 2\)- and 24-hour cases, respectively, and a value of \(0.13 \pm0.07\) and \(0.43 \pm0.08\) for the area under the precision–recall curve in the \(T=2\)- and 24-hour cases, respectively. These relatively high scores are competitive with previous attempts at solar prediction, but our different methodology and extreme care in task design and experimental setup provide an independent confirmation of these results. Given the similar values of algorithm performance across various types of models reported in the literature, we conclude that we can expect a certain baseline predictive capacity using these data. We believe that this is the first attempt to predict solar flares using photospheric vector-magnetic field data as well as multiple wavelengths of image data from the chromosphere, transition region, and corona, and it points the way towards greater data integration across diverse sources in future work.  相似文献   

SARAS 2: a spectral radiometer for probing cosmic dawn and the epoch of reionization through detection of the global 21-cm signal     

Saurabh Singh  Ravi Subrahmanyan  N. Udaya Shankar  Mayuri Sathyanarayana Rao  B. S. Girish  A. Raghunathan  R. Somashekar  K. S. Srivani 《Experimental Astronomy》2018,45(2):269-314

The global 21-cm signal from Cosmic Dawn (CD) and the Epoch of Reionization (EoR), at redshifts \(z \sim 6-30\), probes the nature of first sources of radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the signal is predicted to be extremely weak, of wide fractional bandwidth, and lies in a frequency range that is dominated by Galactic and Extragalactic foregrounds as well as Radio Frequency Interference, detection of the signal is a daunting task. Critical to the experiment is the manner in which the sky signal is represented through the instrument. It is of utmost importance to design a system whose spectral bandpass and additive spurious signals can be well calibrated and any calibration residual does not mimic the signal. Shaped Antenna measurement of the background RAdio Spectrum (SARAS) is an ongoing experiment that aims to detect the global 21-cm signal. Here we present the design philosophy of the SARAS 2 system and discuss its performance and limitations based on laboratory and field measurements. Laboratory tests with the antenna replaced with a variety of terminations, including a network model for the antenna impedance, show that the gain calibration and modeling of internal additive signals leave no residuals with Fourier amplitudes exceeding 2 mK, or residual Gaussians of 25 MHz width with amplitudes exceeding 2 mK. Thus, even accounting for reflection and radiation efficiency losses in the antenna, the SARAS 2 system is capable of detection of complex 21-cm profiles at the level predicted by currently favoured models for thermal baryon evolution.  相似文献   

Transient three-dimensional modeling of riverbank filtration at Grind well field, Germany     

Vijay Shankar  Paul Eckert  Chandra Ojha  Christoph M. König 《Hydrogeology Journal》2009,17(2):321-326

Riverbank filtration (RBF) is a proven treatment step in a multi-barrier method of drinking-water supply at many sites. RBF wells induce a large amount of river water to infiltrate the river base and travel towards the wells, giving the opportunity for mixing of infiltrated surface water and groundwater. Assessment of raw water quality plays an important role in planning and operating a RBF well field. In this context, the determination of the catchment area (and land uses within the catchment) and the ratio of bank filtrate (BF) to raw groundwater (GW) are two prior steps. Transient model simulations were performed in order to study the hydraulic conditions at the RBF well field at Grind near Düsseldorf, Germany. The BF/GW ratio was determined to be 75/25. The flood events in winter, in particular, showed the BF/GW ratio to have high variation. Transient path lines in the well field were used for delineation of the catchment area.  相似文献   

Hydrography and water masses in the southeastern Arabian Sea during March–June 2003     

S. S. C. Shenoi  D. Shankar  G. S. Michael  J. Kurian  K. K. Varma  M. R. Ramesh Kumar  A. M. Almeida  A. S. Unnikrishnan  W. Fernandes  N. Barreto  C. Gnanaseelan  R. Mathew  K. V. Praju  V. Mahale 《Journal of Earth System Science》2005,114(5):475-491

This paper describes the hydrographic observations in the southeastern Arabian Sea (SEAS) during two cruises carried out in March–June 2003 as part of the Arabian Sea Monsoon Experiment. The surface hydrography during March–April was dominated by the intrusion of low-salinity waters from the south; during May–June, the low-salinity waters were beginning to be replaced by the highsalinity waters from the north. There was considerable mixing at the bottom of the surface mixed layer, leading to interleaving of low-salinity and high-salinity layers. The flow paths constructed following the spatial patterns of salinity along the sections mimic those inferred from numerical models. Time-series measurements showed the presence of Persian Gulf and Red Sea Waters in the SEAS to be intermittent during both cruises: they appeared and disappeared during both the fortnight-long time series.  相似文献   

Geochemistry of two sediment cores from the west coast of India   总被引：2，自引：0，他引：2  

A. R. Karbassi  R. Shankar 《International Journal of Environmental Science and Technology》2005,1(4):307-316

Copper, Pb, Zn, Ni, Co, Mn, AI, Ca, magnetic susceptibility and loss on ignition of sediments from two cores near Mangalore along the western continental shelf of India have been studied. The sediments have high Al and organic matter contents due to the high sedimentation rate and their proximity to river mouths. Down-core variations of elements indicate a decrease of lithogenous component during probably the past few centuries. While abundance of calcareous shells in some zones has lead to the dilution of most of the metals, it appears that Pb and Mn are associated with this phase. Copper, Zn and Fe are associated with organic matter and detrital particles, whereas Ni and Co are predominantly associated with the insoluble fraction. Oxides/hydroxides of Fe and Mn are absent because of the reducing conditions and the high terrigenous influx. Geochemically, Mn and Fe are present in different phases of sediments (in the insoluble fraction and organic matter respectively). The Fe content of one of the cores is positively correlated with magnetic susceptibility.  相似文献   

Experimental (clay) models of inversion structures   总被引：3，自引：0，他引：3  

Shankar Mitra  Quazi T. Islam 《Tectonophysics》1994,230(3-4):211-222

Experimental modeling is used to study the geometry and evolution of inversion structures. Two main types of inversion structures are analyzed:

1. (1) structures formed by fault-propagation folding; and

2. (2) structures formed by fault-bend folding on listric faults.

Fault-propagation inversion structures initially develop as broad drape folds with possible fault breakthrough during an early extensional phase. Syn-extensional strata deposited in the hanging wall typically thicken away from the fault. Compressional reactivation results in reversal of slip on the master and secondary faults, their rotation to shallower dips, and the development of a compressional fault-propagation fold. Key features of the fault-propagation fold are basinward thickening of syn-extensional units and resulting steep dips of the front limb of the structure. Fault-bend inversion structures initiate as rollover folds within extensional half-graben. Deformation is primarily localized along a system of antithetic faults. Syn-extensional strata typically thicken across the fault but also thin basinward away from the fault. During compression, the extensional rollover folds are folded into compressional fault-bend folds. Key features of this structure are thinning of syn-extensional units into the basin. Inversion of more symmetric graben results in a doubly-convex geometry of syn-extensional units. These observations of bed geometry and thickness provide predictive models for interpreting the geometries of inversion structures in areas of poor data quality.  相似文献   

A comprehensive and quantitative assessment of Raunthi Gad flash flood,Rishi Ganga catchment,central Himalaya,Uttarakhand, India     

Nainwal  Harish Chandra  Shankar  R.  Mishra  Aditya  Mishra  Sumit  Pandey  Ankit  Shah  Sunil Singh  Chauhan  Gambhir Singh  Kumar  Deepak 《Natural Hazards》2022,113(1):157-184

Natural Hazards - Drought severity is increasing in Southern Africa which is affecting rain-fed agriculture, the main source of livelihood in most countries in this region. The study assessed the...  相似文献   

Thermally altered coals from bore core EBM-1, East Bokaro coal field,Damodar Valley,India: A petrographic inference     

S. Mahesh  Srikanta Murthy  Vikram Partap Singh  Jyoti Shankar Roy 《Journal of the Geological Society of India》2015,86(5):535-546

  相似文献