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Found 10 entries in the Bibliography.

Showing entries from 1 through 10

2021

Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24

This work analyzes the geo-effectiveness of Coronal Mass Ejection- (CME-) induced storms by investigating the responses of ionospheric Vertical Total Electron Content (VTEC) and the Equatorial Ionization Anomaly (EIA) over the Indian sector to two storms. One of the storms occurred on February 19, 2014 (SYM-H: −120 nT), while the other occurred on June 23, 2015 (SYM-H: −204 nT). Both storms were driven by full halo CMEs. Global TEC maps were used to characterize VTEC variations during the storms. June 23, 2015 storm was characterized with stronger solar progenitors, right from its origin, although the VTEC response to the storm was not influenced by their strong progenitors. The CMEs that caused the selected storms are large (Halo CMEs). We inferred that irrespective of the strength of solar origin of a storm, the response of ionization distribution over equatorial and low-latitude regions to it depends on the season of storm occurrence, local time of the storm onset, and PPEF orientation. From the VTEC variations for the three Indian stations namely, Trivandrum (geographic latitude: 8.52°N, geographic longitude: 76.94°E, magnetic latitude: 0.37°N), Hyderabad (17.39°N, 78.49°E, 10.15°N) and Delhi (28.70°N, 77.10°E, 22.70°N), we observed that EIA disturbances were more prominent over Hyderabad than over Delhi. The February 19, 2014 storm was characterized by a localized EIA crest at latitude a little above Hyderabad, while in June 23, 2015 storm localized EIA crest was observed directly on Hyderabad. IRI-2016 model generally underestimated VTEC at the three Indian equatorial and low-latitude locations. Solar cycle 24 was characterized with low heliospheric pressure due to its weak polar field strength. The lower pressure allowed CMEs to expand greatly as they transit through space. As they expand, the strengths of the magnetic field inside them decrease, and such lower-strength magnetic fields cause geomagnetic storms that are less geoeffective, even when their solar/interplanetary progenitors are strong and healthy. This associated weak polar field strength of solar cycle 24 caused weak fountain effect with the attendant inability to exhibit storm-time super-fountain effect in the dayside of the equatorial/low-latitude regions.

Simi, K.; Akala, A.; Krishna, Siva; Amaechi, Paul; Ogwala, Aghogho; Ratnam, Venkata; Oyedokun, O.;

Published by: Advances in Space Research Published on: oct

YEAR: 2021 DOI: 10.1016/j.asr.2021.06.013

Coronal mass ejection; Disturbance dynamo electric field; geomagnetic storm; prompt penetration electric field; total electron content

The impact of a stealth CME on the Martian topside ionosphere

Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow coronal mass ejection (CME) that evolved without any low coronal

Thampi, Smitha; Krishnaprasad, C; Nampoothiri, Govind; Pant, Tarun;

Published by: Monthly Notices of the Royal Astronomical Society Published on:

YEAR: 2021 DOI: 10.1093/mnras/stab494

2020

Consequences of a solar wind stream interaction region on the low latitude ionosphere: event of 7 October 2015

In this article, we present a study of the perturbations occurring in the Earth’s environment on 7 October 2015. We use a multi-instrument approach, including space and ground

Molina, Maria; Dasso, S; Mansilla, G; Namour, Jorge; Cabrera, Miguel; Zuccheretti, Enrico;

Published by: Solar Physics Published on:

YEAR: 2020 DOI: 10.1007/s11207-020-01728-7

2018

Solar activity variations of equatorial spread F occurrence and sustenance during different seasons over Indian longitudes: Empirical model and causative mechanisms

A comprehensive analysis using nearly two decades of ionosonde data is carried out on the seasonal and solar cycle variations of Equatorial Spread F (ESF) irregularities over magnetic equatorial location Trivandrum (8.5\textdegreeN, 77\textdegreeE). The corresponding Rayleigh Taylor (RT) instability growth rates (γ) are also estimated. A seasonal pattern of ESF occurrence and the corresponding γ is established for low solar (LSA), medium solar (MSA) and high solar (HSA) activity periods. For LSA, it is seen that the γ maximizes during post sunset time with comparable magnitudes for autumnal equinox (AE), vernal equinox (VE) and winter solstice (WS), while for summer solstice (SS) it maximizes in the post-midnight period. Concurrent responses are seen in the ESF occurrence pattern. For MSA, γ maximizes during post-sunset for VE followed by WS and AE while SS maximises during post-midnight period. The ESF occurrence for MSA is highest for VE (80\%), followed by AE (70\%), WS (60\%) and SS (50\%). In case of HSA, maximum γ occurs for VE followed by AE, WS and SS. The concurrent ESF occurrence maximizes for VE and AE (90\%), WS and SS at 70\%.

The solar cycle variation of γ is examined. γ shows a linear variation with F10.7 cm flux. Further, ESF percentage occurrence and duration show an exponential and linear variation respectively with γ. An empirical model on the solar activity dependence of ESF occurrence and sustenance time over Indian longitudes is arrived at using the database spanning two solar cycles for the first time.

Haridas, M.K.; Manju, G.; Arunamani, T.;

Published by: Advances in Space Research Published on: 05/2018

YEAR: 2018 DOI: 10.1016/j.asr.2018.02.040

2017

Detection of ionospheric anomalies during intense space weather over a low-latitude GNSS station

The operational availability of Global Navigation Satellite System is affected by large-scale irregularities of the ionosphere. The space weather events induce several intense irregularities and cause the non-linear distribution of ionospheric electron density. Monitoring of ionospheric responses due to extreme space weather events plays a key role in trans-ionospheric radio wave propagation. In the present analysis, a novel technique based on wavelet transform has been implemented for the analysis and detection of ionospheric anomalies during two intense space weather events that occurred in 2013. The investigations have been carried out using the ionospheric observable, Total Electron Content (TEC), derived from the Global Positioning System (GPS) receiver located at an Equatorial Ionisation Anomaly region, KL University, Guntur, India (Geographic Lat.16.37\textdegreeN, Geographic Long. 80.37\textdegreeE). The effects of geomagnetic storms (Sym-H\ <=\ -100\ nT) on the perturbations of ionospheric TEC have been investigated. The algorithm of Continuous wavelet transform has been used to study and characterise the presence of ionospheric anomalies in the local time-scale plane. It can detect spatial and temporal details of ionospheric anomaly intensity during strong solar-terrestrial and geophysical events. It is observed that during the main phase of the geomagnetic storm that occurred during 17 March 2013, TEC enhanced by 7 TECU, while a suppression of 10 TECU in the GPS-TEC can be noticed during the main phase of the 29 June 2013 storm. The variation in the intensity of ionospheric TEC anomalies during storm time has been detected and compared to the intensity of the space weather events measured through solar and geomagnetic indices (F10.7, Sym-H, IMF Bz and IEF Ey).

Sivavaraprasad, G.; Ratnam, Venkata; Padmaja, Sree; Sharvani, V.; Saiteja, G.; Mounika, Y.; Harsha, Babu;

Published by: Acta Geodaetica et Geophysica Published on: 12/2017

YEAR: 2017 DOI: 10.1007/s40328-016-0190-4

2014

Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp

Describing the day-to-day variability of Equatorial Plasma Bubble (EPB) occurrence remains a significant challenge. In this study we use the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM), driven by solar (F_10.7) and geomagnetic (Kp) activity indices, to study daily variations of the linear Rayleigh-Taylor (R-T) instability growth rate in relation to the measured scintillation strength at five longitudinally distributed stations. For locations characterized by generally favorable conditions for EPB growth (i.e., within the scintillation season for that location), we find that the TIEGCM is capable of identifying days when EPB development, determined from the calculated R-T growth rate, is suppressed as a result of geomagnetic activity. Both observed and modeled upward plasma drifts indicate that the prereversal enhancement scales linearly with Kp from several hours prior, from which it is concluded that even small Kpchanges cause significant variations in daily EPB growth.

Carter, B.; Retterer, J.; Yizengaw, E.; Groves, K.; Caton, R.; McNamara, L.; Bridgwood, C.; Francis, M.; Terkildsen, M.; Norman, R.; Zhang, K.;

Published by: Geophysical Research Letters Published on: 08/2014

YEAR: 2014 DOI: 10.1002/2014GL060953

Equatorial ionosphere; plasma bubbles; TIEGCM

2013

Signatures of equatorial plasma bubbles in VHF satellite scintillations and equatorial ionograms

Since their discovery in the 1970s, equatorial plasma bubbles (EPBs) have been invoked to explain the propagation of VHF signals on trans-equatorial circuits at night, and blamed for highly detrimental scintillation of VHF and GHz trans-ionospheric communications signals in equatorial regions. Over the last four decades, the properties of EPBs have been deduced by multiple techniques such as incoherent scatter radar, 630 nm airglow, depletions in GPS total electron content observations, VHF and GHz scintillations, and HF observations by ionosondes. The initiation and evolution of EPBs have by now been successfully modeled and a good understanding developed of the underlying physics. However, different communities tend to concentrate on a single observing technique, without regard to whether the different techniques provide a consistent physical picture. In contrast, this paper discusses two very different types of observations made on a night-by-night basis during the COPEX campaign of late 2002 in Brazil, namely, VHF scintillations and ionograms, and shows that the two methods of observation can provide a consistent interpretation of the properties of EPBs. For example, an EPB seen as an eastward drifting scintillation event can also be seen as an extra ionogram reflection trace that moves closer to and then away from the ionosonde site. The scintillations are attributed to strong gradients across the walls of an EPB, whereas the extra ionogram traces are attributed to oblique reflection of the ionosonde signals from the walls of the EPB.

McNamara, L.; Caton, R.; Parris, R.; Pedersen, T.; Thompson, D.; Wiens, K.; Groves, K.;

Published by: Radio Science Published on: 03/2013

YEAR: 2013 DOI: 10.1002/rds.v48.210.1002/rds.20025

Equatorial ionosphere; equatorial plasma bubbles

2010

Program of transient UV event research at Tatiana-2 satellite

Garipov, G.; Khrenov, B.; Klimov, P.; Morozenko, V.; Panasyuk, M.; Petrova, S.; Tulupov, V.; Shahparonov, V.; Svertilov, S.; Vedenkin, N.; Yashin, I.; Jeon, J.; Jeong, S.; Jung, A.; Kim, J.; Lee, J.; Lee, H; Na, G.; Nam, J.; Nam, S.; Park, I.; Suh, J.; Jin, J; Kim, M.; Kim, Y.; Yoo, B.; Park, Y.-S.; Yu, H.; Lee, C.-H.; Park, J.; Salazar, H.; Martinez, O.; Ponce, E.; Cotsomi, J.;