The Experts below are selected from a list of 7785 Experts worldwide ranked by ideXlab platform
Christine Amory-mazaudier - One of the best experts on this subject based on the ideXlab platform.
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Planetary magnetic signature of the storm wind disturbance dynamo
2015Co-Authors: Currents Ddyn, Minh Le Huy, Christine Amory-mazaudierAbstract:[1] During magnetic storms, Joule heating and ion drag, in Auroral Zones, strongly influence the circulation of thermospheric neutral winds. Joule heating produces equatorward neutral winds at F-region heights with return flow at E-region altitudes around the equator, the so-called Hadley cell. The modified thermospheric circulation produces upwelling of molecule-enriched air at high latitudes and global changes in the atmospheric composition. The equatorward neutral winds extending from the Auroral zone to mid and low latitudes through the Coriolis force create westward storm wind which drives an equatorward dynamo current. In this paper, we detect for the first time, in the three longitude sectors, the planetary magnetic signature (Ddyn) of ionospheric disturbance dynamo with its main features: (1) the decrease of the equatorial electrojet due to a westward electric current flow opposite to the regular eastward current flow and (2) the equatorward ionospheric disturbance dynamo currents at midlatitudes. Citation: Le Huy, M., and C. Amory-Mazaudier (2008), Planetary magnetic signature of the storm wind disturbance dynam
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Planetary magnetic signature of the storm wind disturbance dynamo currents: Ddyn
Journal of Geophysical Research, 2008Co-Authors: Christine Amory-mazaudierAbstract:[1] During magnetic storms, Joule heating and ion drag, in Auroral Zones, strongly influence the circulation of thermospheric neutral winds. Joule heating produces equatorward neutral winds at F-region heights with return flow at E-region altitudes around the equator, the so-called Hadley cell. The modified thermospheric circulation produces upwelling of molecule-enriched air at high latitudes and global changes in the atmospheric composition. The equatorward neutral winds extending from the Auroral zone to mid and low latitudes through the Coriolis force create westward storm wind which drives an equatorward dynamo current. In this paper, we detect for the first time, in the three longitude sectors, the planetary magnetic signature (Ddyn) of ionospheric disturbance dynamo with its main features: (1) the decrease of the equatorial electrojet due to a westward electric current flow opposite to the regular eastward current flow and (2) the equatorward ionospheric disturbance dynamo currents at midlatitudes.
T. Gruner - One of the best experts on this subject based on the ideXlab platform.
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1An Overview of the Fast Auroral SnapshoT (FAST) Satellite
2015Co-Authors: R. Pfaff, C. Carlson, J. Watzin, D. Everett, T. GrunerAbstract:Abstract. The FAST satellite is a highly sophisticated scientific satellite designed to carry out in situ measurements of acceleration physics and related plasma processes associated with the Earth's aurora. Initiated and conceptualized by scientists at the University of California at Berkeley, this satellite is the second of NASA's Small Explorer Satellite program designed to carry out small, highly focused, scientific investigations. FAST was launched on August 21, 1996 into a high inclination (83o) elliptical orbit with apogee and perigee altitudes of 4175 km and 350 km, respectively. The spacecraft design was tailored to take high-resolution data samples (or "snapshots") only while it crosses the Auroral Zones, which are latitudinally narrow sectors that encircle the polar regions of the Earth. The scientific instruments include energetic electron and ion electrostatic analyzers, an energetic ion instrument that distinguishes ion mass, and vector DC and wave electric and magnetic field instruments. A state-of-the-art flight computer (or instrument data processing unit) includes programmable processors that trigger the burst data collection when interesting physical phenomena are encountered and stores these data in a 1 Gbit solid-state memory for telemetry to the Earth at later times. The spacecraft incorporates a light, efficient, and highly innovative design, which blends proven sub-system concepts with the overall scientific instrument and mission requirements. The result is a new breed of space physics mission that gathers unprecedented fields and particles observations that are continuous and uninterrupted by spin effects. In this and other ways, the FAST mission represents a dramatic advance over previous Auroral satellites. This paper describes the overall FAST mission, including a discussion of the spacecraft design parameters and philosophy, the FAST orbit, instrument and data acquisition systems, and mission operations. 1
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An Overview of the Fast Auroral SnapshoT (FAST) Satellite
Space Science Reviews, 2001Co-Authors: R. Pfaff, C. Carlson, J. Watzin, D. Everett, T. GrunerAbstract:The FAST satellite is a highly sophisticated scientific satellite designed to carry out in situ measurements of acceleration physics and related plasma processes associated with the Earth's aurora. Initiated and conceptualized by scientists at the University of California at Berkeley, this satellite is the second of NASA's Small Explorer Satellite program designed to carry out small, highly focused, scientific investigations. FAST was launched on August 21, 1996 into a high inclination (83°) elliptical orbit with apogee and perigee altitudes of 4175 km and 350 km, respectively. The spacecraft design was tailored to take high-resolution data samples (or `snapshots') only while it crosses the Auroral Zones, which are latitudinally narrow sectors that encircle the polar regions of the Earth. The scientific instruments include energetic electron and ion electrostatic analyzers, an energetic ion instrument that distinguishes ion mass, and vector DC and wave electric and magnetic field instruments. A state-of-the-art flight computer (or instrument data processing unit) includes programmable processors that trigger the burst data collection when interesting physical phenomena are encountered and stores these data in a 1 Gbit solid-state memory for telemetry to the Earth at later times. The spacecraft incorporates a light, efficient, and highly innovative design, which blends proven sub-system concepts with the overall scientific instrument and mission requirements. The result is a new breed of space physics mission that gathers unprecedented fields and particles observations that are continuous and uninterrupted by spin effects. In this and other ways, the FAST mission represents a dramatic advance over previous Auroral satellites. This paper describes the overall FAST mission, including a discussion of the spacecraft design parameters and philosophy, the FAST orbit, instrument and data acquisition systems, and mission operations.
U. P. Løvhaug - One of the best experts on this subject based on the ideXlab platform.
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Effects of substorm electrojet on declination along concurrent geomagnetic latitudes in the northern Auroral zone
Journal of Space Weather and Space Climate, 2016Co-Authors: Inge Edvardsen, Magnar Gullikstad Johnsen, U. P. LøvhaugAbstract:The geomagnetic field often experiences large fluctuations, especially at high latitudes in the Auroral Zones. We have found, using simulations, that there are significant differences in the substorm signature, in certain coordinate systems, as a function of longitude. This is confirmed by the analysis of real, measured data from comparable locations. Large geomagnetic fluctuations pose challenges for companies involved in resource exploitation since the Earth’s magnetic field is used as the reference when navigating drilling equipment. It is widely known that geomagnetic activity increases with increasing latitude and that the largest fluctuations are caused by substorms. In the Auroral Zones, substorms are common phenomena, occurring almost every night. In principle, the magnitude of geomagnetic disturbances from two identical substorms along concurrent geomagnetic latitudes around the globe, at different local times, will be the same. However, the signature of a substorm will change as a function of geomagnetic longitude due to varying declination, dipole declination, and horizontal magnetic field along constant geomagnetic latitudes. To investigate and quantify this, we applied a simple substorm current wedge model in combination with a dipole representation of the Earth’s magnetic field to simulate magnetic substorms of different morphologies and local times. The results of these simulations were compared to statistical data from observatories and are discussed in the context of resource exploitation in the Arctic. We also attempt to determine and quantify areas in the Auroral zone where there is a potential for increased space weather challenges compared to other areas.
Michel Parrot - One of the best experts on this subject based on the ideXlab platform.
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Ionospheric density perturbations recorded by DEMETER above intense thunderstorms
Journal of Geophysical Research Space Physics, 2013Co-Authors: Michel Parrot, Jean-andré Sauvaud, S Soula, Jean-louis Pinçon, O Van Der VeldeAbstract:[1] DEMETER (Detection of Electromagnetic Emissions Transmitted From Earthquake Regions) was a three-axis stabilized Earth-pointing spacecraft launched on 29 June 2004 into a low-altitude (710 km) polar and circular orbit that was subsequently lowered to 650 km until the end of the mission in December 2010. DEMETER measured electromagnetic waves all around the Earth, except in the Auroral Zones (invariant latitude >65°). The frequency range for the electric field was from DC up to 3.5 MHz, and for the magnetic field, it was from a few hertz up to 20 kHz. At its altitude, the phenomena observed on the E field and B field spectrograms recorded during nighttime by the satellite in the very low frequency range are mainly dominated by whistlers. In a first step, the more intense whistlers have been searched. They correspond to the most powerful lightning strokes occurring below DEMETER. Then, it is shown that this intense lightning activity is able to perturb the electron and ion densities at the satellite altitude (up to 133%) during nighttime. These intense lightning strokes are generally associated with transient luminous events, and one event with many sprites recorded on 17 November 2006 above Europe is reported. Examining the charged particle precipitation, it is shown that this density enhancement in the high ionosphere can be related to the energetic particle precipitation induced by the strong whistlers emitted during a long-duration thunderstorm activity at the same location. Citation: Parrot, M., J. A. Sauvaud, S. Soula, J. L. Pinc¸n , and O. van der Velde (2013), Ionospheric density perturbations recorded by DEMETER above intense thunderstorms,
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Satellite observations of banded VLF emissions in conjunction with energy-banded ions during very large geomagnetic storms
Journal of Geophysical Research: Atmospheres, 2012Co-Authors: Christopher A. Colpitts, Cynthia A. Cattell, Janet U. Kozyra, Michel ParrotAbstract:[1] Frequency-banded electromagnetic VLF waves up to 2000 Hz are observed concurrently with warm (10 s to 10,000 s of eV) energy-banded ions in the low latitude Auroral and sub-Auroral Zones during every large geomagnetic storm encountered by the FAST and DEMETER satellites. The banded ions and waves persist for several FAST or DEMETER orbits, lasting up to 12 h, in both dawn and dusk sectors, in both the northern and southern hemispheres. If the waves are generated at harmonics of the proton gyrofrequency, the inferred source region would be $4000 km altitude. Previous investigations have shown that such waves can propagate from this source region to the locations of both spacecraft. An investigation into the growth of waves at harmonics of f ci in the inferred source region suggests that these emissions could be generated by ion bands similar to those observed at the same time as the waves. Magnetospheric waves such as these play a role in energy transfer between distinct particle populations and may contribute to ion heating and ion outflow as well as electron energization. All of these phenomena occur during the strongest magnetic storms. The appearance of the banded ions and associated wave activity suggests that there may be distinct changes in the geospace system that characterize large magnetic storms. Citation: Colpitts, C. A., C. A. Cattell, J. U. Kozyra, and M. Parrot (2012), Satellite observations of banded VLF emissions in conjunction with energy-banded ions during very large geomagnetic storms,
J.l. Rauch - One of the best experts on this subject based on the ideXlab platform.
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DEMETER observations of EM emissions related to thunderstorms
Space Science Reviews, 2008Co-Authors: Marc Parrot, R. Treumann, Jean-pierre Lebreton, Jean-jacques Berthelier, J.l. RauchAbstract:Abstract. The paper is related to specific emissions at frequency <3 MHz observed by the low altitude satellite DEMETER in relation with the thunderstorm activity. At its altitude (∼700 km), the phenomena observed on the E-field and B-field spectrograms recorded by the satellite are mainly dominated by whistlers. Particular observations performed by DEMETER are reported. It concerns multiple hop whistlers and interaction between whistlers and lower hybrid noise. Two new phenomena discovered by the satellite are discussed. First, V-shaped emissions up to 20 kHz are observed at mid-latitude during night time. They are centered at the locations of intense thunderstorm activity. By comparison with VLF saucers previously observed by other satellites in the Auroral Zones it is hypothesized that the source region is located below the satellite and that the triggering mechanism is due to energetic electrons accelerated during sprite events. Second, emissions at frequency ∼2 MHz are observed at the time of intense whistlers. These emissions are produced in the lower ionosphere in probable relation with Transient Luminous Events (TLEs).
