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Thithonis M.A.,Space Science Office | Achuthan J.,National Atmospheric Research Laboratory
IEEE Geoscience and Remote Sensing Letters | Year: 2013

This letter reports the results of the validation study on Jason-2 (JA2) rain flag and rain rate (RR) estimation over North Indian Ocean for the first time. This study was performed using 12 months of Geophysical Data Record (GDR) and collocated Microwave Imager and Precipitation Radar (PR) observations onboard Tropical Rainfall Measuring Mission (TRMM) employing strict spatial and temporal collocation criteria. The present study brought out that rain flag parameter available in GDR was not triggered during rain events, and an attempt is made to recompute the same using a novel method of differential attenuation between Ku band and C band backscatter. The score of rain detection using recomputed Ku/C mean rain-free relation is found to be about 98%. The high rain detection by JA2 clearly demonstrates the performance of the dual-frequency rain flagging while considering the high temporal and spatial variability of the rain. The comparison of RR estimated from JA2 with TRMM sensors was in good agreement. The results of the present study thus accentuate the need for better rain flagging over regional oceans which is essential to evade erroneous values in altimetric geophysical parameters. © 2013 IEEE.


Poletto G.,National institute for astrophysics | Sterling A.C.,Space Science Office | Pucci S.,University of Florence | Romoli M.,University of Florence
Proceedings of the International Astronomical Union | Year: 2013

Blowout jets constitute about 50% of the total number of X-ray jets observed in polar coronal holes. In these events, the base magnetic loop is supposed to blow open in what is a scaled-down representation of two-ribbon flares that accompany major coronal mass ejections (CMEs): indeed, miniature CMEs resulting from blowout jets have been observed. This raises the question of the possible contribution of this class of events to the solar wind mass and energy flux. Here we make a first crude evaluation of the mass contributed to the wind and of the energy budget of the jets and related miniature CMEs, under the assumption that small-scale events behave as their large-scale analogs. This hypothesis allows us to adopt the same relationship between jets and miniature-CME parameters that have been shown to hold in the larger-scale events, thus inferring the values of the mass and kinetic energy of the miniature CMEs, currently not available from observations. We conclude our work estimating the mass flux and the energy budget of a blowout jet, and giving a crude evaluation of the role possibly played by these events in supplying the mass and energy that feeds the solar wind. © 2013 International Astronomical Union.


Pant T.K.,Vikram Sarabhai Space Center | Sreelatha P.,Vikram Sarabhai Space Center | Mridula N.,Vikram Sarabhai Space Center | Trivedi S.,Space Science Office | And 17 more authors.
Indian Journal of Radio and Space Physics | Year: 2012

This paper presents, for the first time, a few tomograms obtained using India's own Radio Beacon for Ionospheric Tomography (RaBIT) onboard YOUTHSAT, a small satellite dedicated for the terrestrial upper atmospheric studies. The tomograms presented here, were obtained during the beginning of the solar cycle 24, and clearly demonstrate the potential of the tomography technique to investigate the large scale ionospheric processes over the Indian longitude region.


Ramadevi M.C.,Space Astronomy Group | Babu V.C.,Space Astronomy Group | Ashoka B.N.,Space Astronomy Group | Seetha S.,Space Science Office
Experimental Astronomy | Year: 2014

The Scanning Sky Monitor (SSM) on ASTROSAT is a position-sensitive gas-filled proportional counter with a wide field of view. The science objective of SSM is to scan the sky to detect and locate transient X-ray sources in the outburst phase. The energy range of operation of SSM is 2.5 to 10 keV. Gas-filled proportional counters are known to have distorted electric fields at the ends of the anodes inside the detector. The electric field and hence the gas gain is different at the ends of the anodes compared to that of the central region. In SSM, the ends of the anode wires were found to have high electric field values and hence high gas gain initially. These effects had to be minimized as they would result in huge charge collection for incidence of highly energetic photons and charged particles, leading to probable discharge effects which would limit the life time of the detector. They also result in undesirable signals, the amplitude of which may not be proportional to the energy of the incident photon. In this paper, we discuss the technique which we use to reduce the field at the ends of the anodes in SSM detectors. © 2014 Springer Science+Business Media Dordrecht


Pucci S.,University of Florence | Poletto G.,National institute for astrophysics | Sterling A.C.,Space Science Office | Romoli M.,University of Florence
AIP Conference Proceedings | Year: 2013

Hinode observations of polar coronal holes revealed a larger population of X-ray jets than previously reported. Some of these comply with the standard reconnection model suggested by Shibata et al. (1992), others, likely analogous to CME eruptions and referred to as blow-out jets (e.g. Moore et al., 2010), show a more structured morphology. We present here two events, representative of the two jet categories, that have been observed by HINODE and STEREO in polar coronal holes. Their outward speed has been evaluated from high resolution images; also, because the jets have been observed in multiple filters, we have been able to derive, via spectroscopic techniques, their temperature and density evolution, both along the jets and in time. Knowledge of these parameters allows us to estimate the mass flux that jets of the two types transport to the solar wind and, assuming a given frequency of events, to infer a value for the wind mass loading contributed by polar jets. Because there are insufficient data to establish the percentage of ejections which eventually fall back to the Sun and because the jets we analyzed are probably among the more energetic within their respective class of events, the estimate we give is an upper limit to the jet wind mass loading. © 2013 AIP Publishing LLC.


Kumar P.N.,Osmania University | Rasool N.,Osmania University | Krishna K.M.,Osmania University | Sarma A.D.,Osmania University | And 7 more authors.
Indian Journal of Radio and Space Physics | Year: 2013

The Indian small satellite, YOUTHSAT, was launched mainly for the study of the ionosphere-thermosphere region over the Indian longitudes. The ionospheric processes play an important role in influencing the position accuracies while using the GPS applications. Ionospheric tomography is an effective way of investigating the spatio-temporal variabilities of these ionospheric processes. The RaBIT (Radio Beacon for Ionospheric Tomography) is one of the three payloads on-board the YOUTHSAT. In this paper, first a case, viz. the analysis of the slant total electron content (STEC) variation measured at the three southern RaBIT stations, namely Trivandrum (8.5°N, 77.0°E), Bangalore (13°N, 77.6°E) and Hyderabad (17.8°N, 78.0°E) on 9 May, 7 and 10 June and 6 July 2011 is presented. It is found that the overall STEC variations measured at each station are different for different days. These variations are attributed to the day-to-day changes in the distribution of ionosphere owing to prevailing electrodynamic processes. To highlight this aspect, the RaBIT tomograms are presented, as case 2, for three different days for five stations, one each for the May, June and July months of 2011 to highlight the day and night differences in the overall distribution of the electron density. The tomograms, unambiguously, reveal the marked differences in the ionization distribution on these days not just during daytime but night time also. These differences are attributed to the overall evolution of the electrodynamics and the neutral dynamics over the equatorial region.


Radhika D.,Space Astronomy Group | Radhika D.,University of Calicut | Nandi A.,Space Astronomy Group | Agrawal V.K.,Space Astronomy Group | Seetha S.,Space Science Office
Monthly Notices of the Royal Astronomical Society | Year: 2016

In this paper, we attempt to find out the 'spectro-temporal' characteristics during the jet ejection, of several outbursting Galactic black hole sources based on RXTE-Proportional Counter Array (PCA)/High Energy X-ray Timing Experiment (HEXTE) data in the energy band of 2-100 keV. We present results of detailed analysis of these sources during the rising phase of their outburst, whenever simultaneous or near-simultaneous X-ray and radio observations are 'available'. We find that before the peak radio flare (transient jet) a few of the sources (in addition to those reported earlier) exhibit 'local' softening within the soft intermediate state itself. Except the duration, all the properties of the 'local' softening (Quasi Periodic Oscillation (QPO) not observed, reduction in total rms, soft spectra) are observed to be similar to the canonical soft state. We find similar 'local' softening for the recent outburst of V404 Cyg also based on SWIFT observations. Fast changes in the 'spectro-temporal' properties during the 'local' softening imply that it may not be occurring due to change in Keplerian accretion rate. We discuss these results in the framework of the magnetized two component advective flow model. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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