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Browsing by Author "Kunduri, B. S. R."

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    First Observation of Ionospheric Convection From the Jiamusi HF Radar During a Strong Geomagnetic Storm
    Zhang, J. J.; Wang, W.; Wang, C.; Lan, A. L.; Yan, J. Y.; Xiang, D.; Zhang, Q. H.; Ruohoniemi, J. Michael; Kunduri, B. S. R.; Nishitani, Nozomu; Shi, X.; Qiu, H. B. (2019-12-11)
    The Super Dual Auroral Radar Network (SuperDARN) is an international low-power high-frequency (HF) radar network, which provides continuous observations of the motion of plasma in the ionosphere. Over the past 15 years, the network has expanded dramatically in the middle latitudes of the Northern Hemisphere to improve the observation capabilities of the network during periods of strong geomagnetic disturbance. However, a large coverage gap still exists in the middle latitudes. A newly deployed middle-latitude HF radar in China (the Jiamusi radar) is about to join the network. This paper presents the first observation of the ionospheric convection from the Jiamusi radar during the strong geomagnetic storm on 26 August 2018. The Jiamusi measurements are compared with the simultaneous measurements from the SuperDARN Hokkaido East radar. The features of the high-velocity westward flows including the equatorward expansion and variation tendency of the line-of-sight velocities observed by the two radars are consistent with each other. According to joint analysis with auroral images, we can confirm that the westward flows observed by the two radars are sunward return flows of the duskside convection cell in the auroral region. The impact the Jiamusi data had on the calculation of SuperDARN convection patterns is also examined. The results show that the inclusion of the Jiamusi data can increase the number of gridded line-of-sight velocity measurements by up to 24.42%, the cross-polar cap potential can be increased by up to 13.90% during the investigated period.
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    GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm
    Prikryl, P.; Ghoddousi-Fard, R.; Kunduri, B. S. R.; Thomas, E. G.; Coster, A. J.; Jayachandran, P. T.; Spanswick, E.; Danskin, D. W. (Copernicus Publications, 2013)
    The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs) from L1 signal recorded at the rate of 50 Hz. The scintillation indices S-4 and sigma(Phi) are stored in real time from an array of high-rate scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN). Ionospheric phase scintillation was observed at high latitudes during a moderate geomagnetic storm (Dst = -61 nT) that was caused by a moderate solar wind plasma stream compounded with the impact of two coronal mass ejections. The most intense phase scintillation (sigma(Phi) similar to 1 rad) occurred in the cusp and the polar cap where it was co-located with a strong ionospheric convection, an extended tongue of ionisation and dense polar cap patches that were observed with ionosondes and HF radars. At sub-auroral latitudes, a sub-auroral polarisation stream that was observed by mid-latitude radars was associated with weak scintillation (defined arbitrarily as sigma(Phi) < 0.5 rad). In the auroral zone, moderate scintillation coincided with auroral breakups observed by an all-sky imager, a riometer and a magnetometer in Yellowknife. To overcome the limited geographic coverage by GISTMs other GNSS data sampled at 1 Hz can be used to obtain scintillation proxy indices. In this study, a phase scintillation proxy index (delta phase rate, DPR) is obtained from 1-Hz data from CHAIN and other GPS receivers. The 50-Hz and 1-Hz phase scintillation indices are correlated. The percentage occurrences of sigma(Phi) > 0.1 rad and DPR > 2mm s(-1), both mapped as a function of magnetic latitude and magnetic local time, are very similar.
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    A study of interhemispheric magnetic conjugacy and large scale magnetosphere-ionosphere coupling using SuperDARN radars
    Kunduri, B. S. R. (Virginia Tech, 2013-12-30)
    Ionospheric convection dynamics is an important window for understanding the coupling of the solar wind and interplanetary magnetic field to the Earth's ionosphere and upper atmosphere. In this study, we use measurements of ionospheric convection made by the SuperDARN radars to investigate the role of interhemispheric magnetic conjugacy in magnetosphere-ionosphere coupling and study the large-scale interactions between the magnetosphere and ionosphere. SuperDARN radars cover large geographic regions in both hemispheres and have a dataset spanning more than a decade, making them ideal for such studies. We begin in chapter 2 with an analysis of the degree of interhemispheric conjugacy exhibited in a Sub-Auroral Polarization Stream (SAPS). We present simultaneous observations of a SAPS event in both hemispheres made by mid-latitude SuperDARN radars with magnetically conjugate fields-of-view. An interhemispheric comparison of the characteristics of the SAPS channel reveals that the channel was conjugate in terms of potential variations across the channel even though substantial differences in latitudinal width and electric fields were observed in the channel. In chapter 3, we use interhemispheric SuperDARN observations of high latitude ionospheric convection in the noon-dusk sector to investigate the effects of IMF By penetrating into the closed magnetic field line region. The observations support the existence of an IMF By associated interhemispheric potential difference and field-aligned current system resulting in the generation of the interhemispheric asymmetries in ionospheric convection. Four events are analyzed in this study and the strength of interhemispheric currents associated with IMF By are estimated. Moreover, the strength of the interhemispheric currents is found to depend on the magnitude of IMF By, proximity of the currents to open-closed field line boundary, ionospheric conductivity and magnetic local time. In chapter 4, we use data from the mid-latitude SuperDARN radars between Jan-2011 and Aug-2012 to compile a database of SAPS events spanning about six hours in magnetic local time. The event database is used to analyze the average spatial variations in the occurrence rate and velocities of the SAPS channel under different geomagnetic conditions. An empirical model based on Dst-index is then developed to estimate the occurrence rate of SAPS at a given latitude and magnetic local time.