The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Ronald R. Ilma - One of the best experts on this subject based on the ideXlab platform.
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generation of a severe convective Ionospheric Storm under stable rayleigh taylor conditions triggering by meteors
Annales Geophysicae, 2016Co-Authors: M C Kelley, Ronald R. IlmaAbstract:Abstract. Here we report on four events detected using the Jicamarca Radio Observatory (JRO) over an 18-year period, in which huge convective Ionospheric Storms (CISs) occur in a stable ionosphere. We argue that these rare events could be initiated by meteor-induced electric fields. The meteor-induced electric fields map to the bottomside of the F region, causing radar echoes and a localized CIS. If and when a localized disturbance reaches 500 km, we argue that it becomes two-dimensionally turbulent and cascades structure to both large and small scales. This leads to long-lasting structure and, almost certainly, to scintillations over a huge range of latitudes some ±15° wide and to 3 m irregularities, which backscatter the VHF radar waves. These structures located at high altitudes are supported by vortices shed by the upwelling bubble in a vortex street.
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Generation of a severe convective Ionospheric Storm under stable Rayleigh–Taylor conditions: triggering by meteors?
Annales Geophysicae, 2016Co-Authors: Michael C. Kelley, Ronald R. IlmaAbstract:Abstract. Here we report on four events detected using the Jicamarca Radio Observatory (JRO) over an 18-year period, in which huge convective Ionospheric Storms (CISs) occur in a stable ionosphere. We argue that these rare events could be initiated by meteor-induced electric fields. The meteor-induced electric fields map to the bottomside of the F region, causing radar echoes and a localized CIS. If and when a localized disturbance reaches 500 km, we argue that it becomes two-dimensionally turbulent and cascades structure to both large and small scales. This leads to long-lasting structure and, almost certainly, to scintillations over a huge range of latitudes some ±15° wide and to 3 m irregularities, which backscatter the VHF radar waves. These structures located at high altitudes are supported by vortices shed by the upwelling bubble in a vortex street.
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C/NOFS and radar observations during a convective Ionospheric Storm event over South America
Geophysical Research Letters, 2009Co-Authors: Michael C. Kelley, John M. Retterer, Fabiano S. Rodrigues, Jonathan J. Makela, Roland T. Tsunoda, Patrick A. Roddy, Donald E. Hunton, O. De La Beaujardiere, E. R. De Paula, Ronald R. IlmaAbstract:[1] The development of a convective Ionospheric Storm is studied using three radars, the C/NOFS satellite, airglow instrumentation, and a numerical model. First detected in the form of convective plumes over the Eastern Pacific, plasma irregularities, airglow signatures, plumes, and irregularities were also detected over Brazil and then Peru. Dynamo conditions were such that a modest prereversal enhancement was recorded at both Christmas Island and Peru and probably over Brazil as well. No prereversal enhancement occurred during the next two days and no plumes were detected. The numerical model reproduced the results quite well over Peru. Evidence for seeding by both gravity waves and the Kelvin-Helmholtz instability is presented.
Michael C. Kelley - One of the best experts on this subject based on the ideXlab platform.
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Generation of a severe convective Ionospheric Storm under stable Rayleigh–Taylor conditions: triggering by meteors?
Annales Geophysicae, 2016Co-Authors: Michael C. Kelley, Ronald R. IlmaAbstract:Abstract. Here we report on four events detected using the Jicamarca Radio Observatory (JRO) over an 18-year period, in which huge convective Ionospheric Storms (CISs) occur in a stable ionosphere. We argue that these rare events could be initiated by meteor-induced electric fields. The meteor-induced electric fields map to the bottomside of the F region, causing radar echoes and a localized CIS. If and when a localized disturbance reaches 500 km, we argue that it becomes two-dimensionally turbulent and cascades structure to both large and small scales. This leads to long-lasting structure and, almost certainly, to scintillations over a huge range of latitudes some ±15° wide and to 3 m irregularities, which backscatter the VHF radar waves. These structures located at high altitudes are supported by vortices shed by the upwelling bubble in a vortex street.
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C/NOFS and radar observations during a convective Ionospheric Storm event over South America
Geophysical Research Letters, 2009Co-Authors: Michael C. Kelley, John M. Retterer, Fabiano S. Rodrigues, Jonathan J. Makela, Roland T. Tsunoda, Patrick A. Roddy, Donald E. Hunton, O. De La Beaujardiere, E. R. De Paula, Ronald R. IlmaAbstract:[1] The development of a convective Ionospheric Storm is studied using three radars, the C/NOFS satellite, airglow instrumentation, and a numerical model. First detected in the form of convective plumes over the Eastern Pacific, plasma irregularities, airglow signatures, plumes, and irregularities were also detected over Brazil and then Peru. Dynamo conditions were such that a modest prereversal enhancement was recorded at both Christmas Island and Peru and probably over Brazil as well. No prereversal enhancement occurred during the next two days and no plumes were detected. The numerical model reproduced the results quite well over Peru. Evidence for seeding by both gravity waves and the Kelvin-Helmholtz instability is presented.
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First successful prediction of a convective equatorial Ionospheric Storm using solar wind parameters
Space Weather, 2008Co-Authors: Michael C. Kelley, John M. RettererAbstract:[1] One of the major challenges of the National Space Weather Program in the United States is to predict the generation of intense turbulence in the equatorial and low-latitude ionosphere. We term this a convective equatorial Ionospheric Storm since, much like a thunderStorm, low-density media erupt upward, releasing stored gravitational energy. This is an important phenomenon since both communication and navigational systems can be severely affected by the associated turbulence. Here, for the first time, we use solar wind data obtained upstream of the Earth and a physics-based assimilative model to successfully predict such an event during a strong magnetic Storm in November 2004.
Moonbeom Heo - One of the best experts on this subject based on the ideXlab platform.
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a new algorithm for high integrity detection and compensation of dual frequency cycle slip under severe Ionospheric Storm conditions
Sensors, 2018Co-Authors: Donguk Kim, Junesol Song, Changdon Kee, Moonbeom HeoAbstract:Many strategies for treating dual-frequency cycle slip, which can seriously affect the performance of a carrier-phase-based positioning system, have been studied over the years. However, the legacy method using the Melbourne-Wubbena (MW) combination and ionosphere combination is vulnerable to pseudorange multipath effects and high Ionospheric Storms. In this paper, we propose a robust algorithm to detect and repair dual-frequency cycle slip for the network-based real-time kinematic (RTK) system which generates high-precision corrections for users. Two independent and complementary carrier-phase combinations, called the Ionospheric negative and positive combinations in this paper, are employed for avoiding insensitive pairs. In addition, they are treated as second-order time differences to reduce the impact of Ionospheric delay even under severe Ionospheric Storm. We verified that the actual error distributions of these monitoring values can be sufficiently bounded by the normal Gaussian distribution. Consequently, we demonstrated that the proposed method ensures high-integrity performance with a maximum probability of missed detection of 7.5 × 10-9 under a desired false-alarm probability of 10-5. Furthermore, we introduce a LAMBDA-based cycle slip compensation method, which has a failure rate of 1.4 × 10-8. Through an algorithm verification test using data collected under a severe Ionospheric Storm, we confirmed that artificially inserted cycle slips are successfully detected and compensated for. Thus, the proposed method is confirmed to be effective for handling dual-frequency cycle slips of the network RTK system.
Jing Liu - One of the best experts on this subject based on the ideXlab platform.
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profiles of Ionospheric Storm enhanced density during the 17 march 2015 great Storm
Journal of Geophysical Research, 2016Co-Authors: Jing Liu, A. G. Burns, Y Zhang, Xinan Yue, Wenbin Wang, Shunrong Zhang, Chaosong HuangAbstract:Ionospheric F2 region peak densities (NmF2) are expected to have a positive correlation with total electron content (TEC), and electron densities usually show an anticorrelation with electron temperatures near the Ionospheric F2 peak. However, during the 17 March 2015 great Storm, the observed TEC, NmF2, and electron temperatures of the Storm-enhanced density (SED) over Millstone Hill (42.6°N, 71.5°W, 72° dip angle) show a quiet different picture. Compared with the quiet time ionosphere, TEC, the F2 region electron density peak height (hmF2), and electron temperatures above ~220 km increased, but NmF2 decreased significantly within the SED. This SED occurred where there was a negative Ionospheric Storm effect near the F2 peak and below it, but a positive Storm effect in the topside ionosphere. Thus, this SED event was a SED in TEC but not in NmF2. The very low Ionospheric densities below the F2 peak resulted in a much reduced downward heat conduction for the electrons, trapping the heat in the topside in the presence of heat source above. This, in turn, increased the topside scale height so that even though electron densities at the F2 peak were depleted, TEC increased in the SED. The depletion in NmF2 was probably caused by an increase in the density of the molecular neutrals, resulting in enhanced recombination. In addition, the Storm time topside Ionospheric electron density profiles were much closer to diffusive equilibrium than the nonStorm time profiles, indicating less daytime plasma flow between the ionosphere and the plasmasphere.
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a case study of Ionospheric Storm effects during long lasting southward imf bz driven geomagnetic Storm
Journal of Geophysical Research, 2014Co-Authors: Baiqi Ning, Libo Liu, Biqiang Zhao, Jing Liu, Takuji Nakamura, Akimasa YoshikawaAbstract:Multiple instrumental observations including GPS total electron content (TEC), foF2 and hmF2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound Ionospheric disturbances at midlatitude and low latitude during the 14–17 July 2012 geomagnetic Storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below −10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial Ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient Ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by Storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) Bz in the recovery phase and were responsible for enhanced the EIA and equatorial Ionospheric uplift around sunset.
Matthias Förster - One of the best experts on this subject based on the ideXlab platform.
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Unprecedented Hemispheric Asymmetries During a Surprise Ionospheric Storm: A Game of Drivers
Journal of Geophysical Research Space Physics, 2020Co-Authors: Elvira Astafyeva, Mala Bagiya, Matthias Förster, Nozomu NishitaniAbstract:The geomagnetic Storm occurred on 25-26 August 2018 as a surprise to forecasters. The arrival of a weak coronal mass ejection did not show a sudden impulse in the magnetic data, however, when the IMF Bz turned southward, it intensified and further remained unchangeably negative for the next 9 hours, causing a major Storm with the minimum SYM-H excursion of –205 nT. In this work, we study the thermospheric, Ionospheric and electrodynamic behavior during this Storm. We use a set of space-borne (the Swarm constellation, GUVI/TIMED) and ground-based (GPS receivers, magnetometers, SuperDARN) instruments. We particularly focus on Storm effects in the American and East Pacific sectors, where unprecedented hemispheric asymmetries occurred in the thermosphere and ionosphere during the main and the recovery phases of the Storm. At the beginning of the Storm, a strong positive Ionospheric Storm was observed in the Northern Hemisphere (NH), while in the Southern Hemisphere (SH), surprisingly, no Storm effect occurred. During the recovery phase, the thermospheric composition ratio O/N2 showed an extreme expansion of the bulge into the opposite hemisphere. Our analysis shows that in each asymmetry was produced by a unique combination of drivers that actioned at particular moment of time and in particular place. The seasonal asymmetry in the high-latitude plasma and neutral mass density distributions along with the asymmetries in the geomagnetic field and the timing of these impacts played the decisive role.
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Ionospheric response to the 2015 st patrick s day Storm a global multi instrumental overview
Journal of Geophysical Research, 2015Co-Authors: Elvira Astafyeva, Irina Zakharenkova, Matthias FörsterAbstract:We present the first multi-instrumental results on the Ionospheric response to the geomagnetic Storm of 17–18 March 2015 (the St. Patrick's Day Storm) that was up to now the strongest in the 24th solar cycle (minimum SYM-H value of A233 nT). The Storm caused complex effects around the globe. The most dramatic positive Ionospheric Storm occurred at low latitudes in the morning (~100–150% enhancement) and postsunset (~80–100% enhancement) sectors. These significant vertical total electron content increases were observed in different local time sectors and at different universal time, but around the same area of the Eastern Pacific region, which indicates a regional impact of Storm drivers. Our analysis revealed that this particular region was most concerned by the increase in the thermospheric O/N 2 ratio. At midlatitudes, we observe inverse hemispheric asymmetries that occurred, despite the equinoctial period, in different longitudinal regions. In the European-African sector, positive Storm signatures were observed in the Northern Hemisphere (NH), whereas in the American sector, a large positive Storm occurred in the Southern Hemisphere, while the NH experienced a negative Storm. The observed asymmetries can be partly explained by the thermospheric composition changes and partly by the hemispherically different nondipolar portions of the geomagnetic field as well as by the IMF By component variations. At high latitudes, negative Ionospheric Storm effects were recorded in all longitudinal regions, especially the NH of the Asian sector was concerned. The negative Storm phase developed globally on 18 March at the beginning of the recovery phase.