Tracking Galaxy Evolution Through Low-Frequency Radio Continuum Observations using SKA and Citizen-Science Research using Multi-Wavelength Data     

Ananda Hota  C. Konar  C. S. Stalin  Sravani Vaddi  Pradeepta K. Mohanty  Pratik Dabhade  Sai Arun Dharmik Bhoga  Megha Rajoria  Sagar Sethi 《Journal of Astrophysics and Astronomy》2016,37(4):41

We present a brief review of progress in the understanding of general spiral and elliptical galaxies, through merger, star formation and AGN activities. With reference to case studies performed with the GMRT, we highlight the unique aspects of studying galaxies in the radio wavelengths where powerful quasars and bright radio galaxies are traditionally the dominating subjects. Though AGN or quasar activity is extremely energetic, it is extremely short-lived. This justify focussing on transitional galaxies to find relic-evidences of the immediate past AGN-feedback which decide the future course of evolution of a galaxy. Relic radio lobes can be best detected in low frequency observations with the GMRT, LOFAR and in future SKA. The age of these relic radio plasma can be as old as a few hundred Myr. There is a huge gap between this and what is found in optical bands. The very first relic-evidences of a past quasar activity (Hanny’s Voorwerp) was discovered in 2007 by a Galaxy Zoo citizen-scientist, a school teacher, in the optical bands. This relic is around a few tens of thousand years old. More discoveries needed to match these time-scales with star formation time-scales in AGN host galaxies to better understand black hole galaxy co-evolution process via feedback-driven quenching of star formation. It is now well-accepted that discovery and characterization of such faint fuzzy relic features can be more efficiently done by human eye than a machine. Radio interferometry images are more complicated than optical and need the citizen-scientists to be trained. RAD@home, the only Indian citizen-science research project in astronomy, analysing TIFR GMRT Sky Survey (TGSS) 150 MHz data and observing from the Giant Meterwave Radio Telescope (GMRT), was launched in April 2013. Unique, zero-infrastructure zero-funded design of RAD@home as a collaboratory of 69 trained e-astronomers is briefly described. Some of the new-found objects like episodic radio galaxies, radio-jet and companion galaxy interaction, radio galaxy bent by motion of the intra-filament medium in a Mpc-scale galaxy filament etc. are briefly presented as demonstration of its potential. Citizen-science has not only opened up a new way for astronomy research but also possibly the only promising way to extract maximum science out of the Big Data in the SKA-era. This possibly can convert the Big Data problem into a prospect. Citizen-science can contribute to the knowledge creation in never-seen-before speed and in approach. As it is based on internet, it can provide an equal opportunity of academic-growth to people even in the under-developed regions where we always need to put our optical and radio telescopes. This can liberate the research-activity of city-based research-institutes out of the four brick walls and alleviate various socio-economic and geo-political constraints on growth of citizens educated in undergraduate-level science but located in remote areas.  相似文献   

Probing Magnetic Fields with Square Kilometre Array and its Precursors     

Subhashis Roy  Sharanya Sur  Kandaswamy Subramanian  Arun Mangalam  T. R. Seshadri  Hum Chand 《Journal of Astrophysics and Astronomy》2016,37(4):42

Origin of magnetic fields, its structure and effects on dynamical processes in stars to galaxies are not well understood. Lack of a direct probe has remained a problem for its study. The first phase of Square Kilometre Array (SKA-I), will have almost an order of magnitude higher sensitivity than the best existing radio telescope at GHz frequencies. In this contribution, we discuss specific science cases that are of interest to the Indian community concerned with astrophysical turbulence and magnetic fields. The SKA-I will allow observations of a large number of background sources with detectable polarization and measure their Faraday depths (FDs) through the Milky Way, other galaxies and their circum-galactic mediums. This will probe line-of-sight magnetic fields in these objects well and provide field configurations. Detailed comparison of observational data (e.g., pitch angles in spirals) with models which consider various processes giving rise to field amplification and maintenance (e.g., various types of dynamo models) will then be possible. Such observations will also provide the coherence scale of the fields and its random component through RM structure function. Measuring the random component is important to characterize turbulence in the medium. Observations of FDs with redshift will provide important information on magnetic field evolution as a function of redshift. The background sources could also be used to probe magnetic fields and its coherent scale in galaxy clusters and in bridges formed between interacting galaxies. Other than FDs, sensitive observations of synchrotron emission from galaxies will provide complimentary information on their magnetic field strengths in the sky plane. The core shift measurements of AGNs can provide more precise measurements of magnetic field in the sub parsec region near the black hole and its evolution. The low band of SKA-I will also be useful to study circularly polarized emission from Sun and comparing various models of field configurations with observations.  相似文献   

Tropospheric biennial oscillation of summer monsoon rainfall over East Asia and its association with ENSO   总被引：1，自引：0，他引：1  

Yunyun Liu  Zeng-Zhen Hu  Arun Kumar  Peitao Peng  Dan C. Collins  Bhaskar Jha 《Climate Dynamics》2015,45(7-8):1747-1759

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Influence of climatic teleconnections on the temporal isotopic variability as recorded in a firn core from the coastal Dronning Maud Land,East Antarctica     

Sushant S Naik  Meloth Thamban  A Rajakumar  Witty D’Souza  C M Laluraj  Arun Chaturvedi 《Journal of Earth System Science》2010,119(1):41-49

Ice and firn core studies provide one of the most valuable tools for understanding the past climate change. In order to evaluate the temporal isotopic variability recorded in ice and its relevance to environmental changes, stable isotopes of oxygen and hydrogen were studied in a firn core from coastal Dronning Maud Land, East Antarctica. The annual δ ¹⁸O profile of the core shows a close relation to the El Niño Southern Oscillation (ENSO) variability. The ENSO indices show significant correlation with the surface air temperatures and δ ¹⁸O values of this region during the austral summer season and support an additional influence related to the Southern Annular Mode (SAM). The correlation between the combined ENSO-SAM index and the summer δ ¹⁸O record seems to have been caused through an atmospheric mechanism. Snow accumulation in this region illustrates a decreasing trend with opposite relationships with δ ¹⁸O data and surface air temperature prior and subsequent to the year 1997. A reorganization of the local water cycle is further indicated by the deuterium excess data showing a shift around 1997, consistent with a change in evaporation conditions. The present study thus illustrates the utility of ice-core studies in the reconstruction of past climate change and suggests possible influence of climatic teleconnections on the snow accumulation rates and isotopic profiles of snow in the coastal regions of east Antarctica.  相似文献   

Prediction and monitoring of monsoon intraseasonal oscillations over Indian monsoon region in an ensemble prediction system using CFSv2   总被引：1，自引：0，他引：1  

S. Abhilash  A. K. Sahai  N. Borah  R. Chattopadhyay  S. Joseph  S. Sharmila  S. De  B. N. Goswami  Arun Kumar 《Climate Dynamics》2014,42(9-10):2801-2815

An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001–2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio of the forecasted rainfall becomes unity by about 18 days. The potential predictability error of the forecasted rainfall saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are found even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of large-scale MISO amplitude as well as the initial conditions related to the different phases of MISO. An analysis of categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead.  相似文献   

Interannual and interdecadal variability of ocean temperature along the equatorial Pacific in conjunction with ENSO   总被引：1，自引：1，他引：0  

Arun Kumar  Zeng-Zhen Hu 《Climate Dynamics》2014,42(5-6):1243-1258

In this paper, the leading modes of ocean temperature anomalies (OTA) along the equatorial Pacific Ocean are analyzed and their connection with El Niño-Southern Oscillation (ENSO) and interdecadal variation is investigated. The first two leading modes of OTA are connected with the different phases of the canonical ENSO and display asymmetric features of ENSO evolution. The third leading mode depicts a tripole pattern with opposite variation of OTA above the thermocline in the central Pacific to that along the thermocline in the eastern and western Pacific. This mode is found to be associated with so-called ENSO-Modoki. Insignificant correlations of this mode with the first two leading modes suggest that ENSO-Modoki may be a mode that is independent to the canonical ENSO and also has longer time scales compared with the canonical ENSO. The fourth mode reflects a warming (cooling) tendency above (below) the thermocline since 2000. Both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979–2012. Also, the analysis also documents that both ENSO and OTA shifted into higher frequency since 2000 compared with that during 1979–1999. Interestingly, the ENSO-Modoki related OTA mode does not have any trend or significant interdecadal shift during 1979–2012. In addition, it is shown that first four EOF modes seem robust before and after 1999/2000, suggesting that the interdecadal shift of the climate system in the tropical Pacific is mainly a frequency shift and the changes in spatial pattern are relatively small, although the mean states over two periods experienced some significant changes.  相似文献   

Enhancing the relevance of Shared Socioeconomic Pathways for climate change impacts,adaptation and vulnerability research   总被引：1，自引：1，他引：0  

Bas J. van Ruijven  Marc A. Levy  Arun Agrawal  Frank Biermann  Joern Birkmann  Timothy R. Carter  Kristie L. Ebi  Matthias Garschagen  Bryan Jones  Roger Jones  Eric Kemp-Benedict  Marcel Kok  Kasper Kok  Maria Carmen Lemos  Paul L. Lucas  Ben Orlove  Shonali Pachauri  Tom M. Parris  Anand Patwardhan  Arthur Petersen  Benjamin L. Preston  Jesse Ribot  Dale S. Rothman  Vanessa J. Schweizer 《Climatic change》2014,122(3):481-494

This paper discusses the role and relevance of the shared socioeconomic pathways (SSPs) and the new scenarios that combine SSPs with representative concentration pathways (RCPs) for climate change impacts, adaptation, and vulnerability (IAV) research. It first provides an overview of uses of social–environmental scenarios in IAV studies and identifies the main shortcomings of earlier such scenarios. Second, the paper elaborates on two aspects of the SSPs and new scenarios that would improve their usefulness for IAV studies compared to earlier scenario sets: (i) enhancing their applicability while retaining coherence across spatial scales, and (ii) adding indicators of importance for projecting vulnerability. The paper therefore presents an agenda for future research, recommending that SSPs incorporate not only the standard variables of population and gross domestic product, but also indicators such as income distribution, spatial population, human health and governance.  相似文献   

Nine years of GPS measurements of crustal deformation at Imphal,Indo-Burmese wedge     

Laishram Sunil Singh  V. K. Gahalaut  Arun Kumar 《Journal of the Geological Society of India》2014,83(5):513-516

We report results of 9 years of GPS measurements of crustal deformation at Imphal, Manipur, a site located in the Indo-Burmese wedge of northwest Sunda arc. The analysis of these measurements suggests that the site moves at a rate of about 36.3±0.5 mm/year towards N55° in the ITRF2008. With respect to the Indian plate it moves at a rate of 16.7 mm/year towards N222°, i.e., predominantly towards southwest. The site is located about 15 km east of the Churachandpur Mao fault (CMF), which is reported to accommodate part of the India-Sunda motion. The site motion is not significantly affected by the earthquakes that occurred in the nearby region. However, the 2004 Sumatra-Andaman earthquake caused a coseismic displacement of ～ 3–5 mm predominantly towards southwest. The site motion is almost linear, with some seasonal variation, and does not show any evidence of accelerated slip or slow earthquake on the CMF or along the plate boundary.  相似文献   

Some Bianchi-type cosmological models in a new scalar-tensor theory     

T. Singh  Anil Kumar Agrawal 《Astrophysics and Space Science》1991,182(2):289-312

Bianchi type I, III, V, VI₀, and Kantowski-Sachs type models have been investigated in a scalar tensor theory developed by Saez and Ballester (1985) and Saez (1985). The dynamical behaviour of the models has also been analyzed.  相似文献   

Accuracy Assessment of Digital Elevation Model Generated by SAR Stereoscopic Technique Using COSMO-Skymed Data     

Ritesh Agrawal  Anup Das  A. S. Rajawat 《Journal of the Indian Society of Remote Sensing》2018,46(10):1739-1747

Radargrammetry technique using the stereoscopic synthetic aperture radar (SAR) images is used for the generation of a digital elevation model (DEM) of a region requires only the amplitude images. SAR stereoscopic technique is analogous to the stereo-photogrammetric technique where the optical stereoscopic images are used for DEM generation. While the advantages of the SAR images are their indifference to atmospheric transparency and solar illumination conditions, the side-looking geometry of the SAR increases the complexity in the SAR stereo analysis. The availability of high spatial and temporal resolution SAR data in recent years has facilitated generation of high-resolution DEM with greater vertical accuracy using radargrammetric technique. In the present study, attempt has been made to generate the DEM of Dehra Dun region, India, from the COSMO-Skymed X-band SAR data-pair acquired at 8 days interval through the radargrammetry technique. Here, radargrammetric orientation approach has been adopted to generate the DEM and various issues and processing steps with the radargrammetry technique have been discussed. The DEM was validated with ground measured elevation values using a differential global positioning system and the root-mean-square error of the DEM was found as 7.3 m. The DEM was compared with the reference DEM of the study area generated from the Cartosat-1 stereo data with a model accuracy of 4 m.  相似文献