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Title |
The thermospheric auroral red line Angle of Linear Polarization |
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Year |
2016 |
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Journal of Geophysical Research: Space Physics |
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Volume |
121 |
Issue |
7 |
Pages |
7125-7134 |
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Keywords |
ionosphere polarization |
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Abstract |
The auroral red line at 630 nm is linearly polarized. Up to now, only its Degree of Linear Polarization had been studied. In this article, we examine for the first time the Angle of Linear Polarization (AoLP) and we compare the measurements to the apparent angle of the magnetic field at the location of the red line emission. We show that the AoLP is a tracer of the magnetic field configuration. This opens new perspectives, both in the frame of space weather and in the field of planetology. |
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1026 |
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2169-9402 |
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yes |
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7644 |
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Author |
F. Pitout, A. Marchaudon, K. J. Trattner, J. Berchem, H. Laakso, C. P. Escoubet |
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Title |
Simultaneous Polar and Cluster Observations in the Northern and Southern Middle-Altitude Polar Cusps Around Equinox |
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Year |
2020 |
Publication |
Journal of Geophysical Research: Space Physics |
Abbreviated Journal |
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Volume |
125 |
Issue |
12 |
Pages |
e2020JA028346 |
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Keywords |
dayside magnetosphere hemispheric asymmetry polar cusp |
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Abstract |
We present an event of simultaneous observations of the northern and southern middle-altitude polar cusps by the Polar spacecraft and Cluster fleet that occurred on 23 September 2004. We examine the possible asymmetries in the fields and plasma parameters, although the proximity of the equinox should limit these asymmetries. Ion sensors reveal two dispersions in both cusps, and data analysis leads to the conclusion that those dispersions are due to pulsed reconnection at a single X-line, which runs along the subsolar magnetopause. While the electromagnetic and particle energy fluxes injected in both cusp are globally very similar, we report significant differences in ion dispersions, width of the low-latitude boundary layer, and peak convection velocities. We ascribe these differences to the dipole tilt that introduces an asymmetry in the magnetosheath flow at the exterior cusps. |
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312 |
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2169-9402 |
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yes |
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6363 |
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Author |
V. Haberle, A. Marchaudon, A. Chambodut, P.-L. Blelly |
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Title |
Direct Determination of Geomagnetic Baselines During Quiet Periods for Low- and Mid-Latitude Observatories |
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Journal |
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Year |
2022 |
Publication |
Journal of Geophysical Research: Space Physics |
Abbreviated Journal |
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127 |
Issue |
8 |
Pages |
e2022JA030407 |
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Keywords |
magnetic baseline magnetic observatory data quiet geomagnetic field Sq current |
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Abstract |
The geomagnetic field is composed of a variety of sources that act on a wide range of timescales and amplitudes. The separation of magnetic storm effects from quiet variations is needed to accurately quantify impacts of space weather events. The extraction of such quiet contributions within geomagnetic measurements is achieved by the determination of baselines, which, ideally, is done by a simple algorithm which captures quiet sources suitably well, while being applicable to an extensive network of magnetic observatories independent of the period of time. In this work, we apply signal filtering techniques on the horizontal components of geomagnetic field measurements from low- and mid-latitude observatories to determine baselines. The variations within the baseline are investigated for magnetically quiet periods between 1991 and 2019, focusing on long-term trends, seasonal and local time dependencies, and day-to-day variability. The analysis confirms that the contributing quiet sources include the secular variation and the solar quiet (Sq) current system. The non-negligible day-to-day variability, that is typical for Sq in low- and mid-latitudes, is embedded within the baseline. Thus, the filter approach extracts quiet magnetic field variations well. Comparisons with other baseline methods show good agreements. We conclude that the filter approach can be used to determine baselines automatically during magnetically quiet periods without the need of further apriori information and is applicable on a wide network of magnetic observatories. It marks the first step for deriving magnetic indices for (near) real-time space weather applications. |
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139 |
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2169-9402 |
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yes |
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Call Number |
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Serial |
8568 |
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Author |
Hubert G., Pazianotto M. T., Federico C. A. |
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Title |
Modeling of ground albedo neutrons to investigate seasonal cosmic ray?induced neutron variations measured at high?altitude stations |
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Journal |
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Year |
2017 |
Publication |
Journal of Geophysical Research: Space Physics |
Abbreviated Journal |
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Volume |
121 |
Issue |
12 |
Pages |
12,186-12,201 |
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Keywords |
albedo neutron cosmic ray spectrometer |
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Abstract This paper investigates seasonal cosmic ray?induced neutron variations measured over a long?term period (from 2011 to 2016) in both the high?altitude stations located in medium geomagnetic latitude and Antarctica (Pic?du?Midi and Concordia, respectively). To reinforce analysis, modeling based on ground albedo neutrons simulations of extensive air showers and the solar modulation potential was performed. Because the local environment is well known and stable over time in Antarctica, data were used to validate the modeling approach. A modeled scene representative to the Pic?du?Midi was simulated with GEANT4 for various hydrogen properties (composition, density, and wet level) and snow thickness. The orders of magnitudes of calculated thermal fluence rates are consistent with measurements obtained during summers and winters. These variations are dominant in the thermal domain (i.e., En??20?MeV) is weakly impacted. The role of hydrogen content on ground albedo neutron generation was investigated with GEANT4 simulations. These investigations focused to mountain environment; nevertheless, they demonstrate the complexity of the local influences on neutron fluence rates. |
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1112 |
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ISSN |
2169-9380 |
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2169-9380 |
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yes |
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Serial |
6722 |
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Author |
Marchaudon A., Blelly P.?L. |
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Title |
A new interhemispheric 16?moment model of the plasmasphere?ionosphere system: IPIM |
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Journal |
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Year |
2015 |
Publication |
Journal of Geophysical Research: Space Physics |
Abbreviated Journal |
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Volume |
120 |
Issue |
7 |
Pages |
5728-5745 |
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Keywords |
centrifugal acceleration interhemispheric exchanges mirror force temperature anisotropy |
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Abstract |
Abstract We present a new interhemispheric numerical model: the IRAP plasmasphere?ionosphere model (IPIM). This model describes the transport of the multispecies ionospheric plasma from one hemisphere to the other along convecting and corotating magnetic field lines, taking into account source processes at low altitude such as photoproduction, chemistry, and energization through the coupling with a kinetic code solving the transport of suprathermal electron along the field line. Among the new developments, a 16?moment?based approach is used for the transport equations in order to allow development of strong temperature anisotropy at high altitude and we consider important but often neglected effects, such as inertial acceleration (centrifugal and Coriolis). In this paper, after presenting in detail the principle of the model, we focus on preliminary results showing the original contribution of this new model. For these first runs, we simulate the convection and corotation transport of closed flux tubes in the plasmasphere for tilted/eccentric dipolar magnetic field configuration in solstice and equinox conditions. We follow different flux tubes between 1.2 and 6 Earth Radii (RE) and demonstrate the capability of the model to describe a wide range of density (above 15 orders of magnitude). The relevance of the mathematical approach used is highlighted, as anisotropies can develop above 3000?km in the plasmasphere as a result of the mirroring effect related to the anisotropic pressure tensor. Moreover, we show that the addition of inertial acceleration may become critical to describe plasma interhemispheric transport above 4RE. The ability of the model to describe the external plasmasphere is demonstrated, and innovative studies are foreseen, regarding the dynamics of the plasma along the magnetic field lines (in particular interhemispheric exchanges and ?opening?/?closure? of a flux tube). |
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312 |
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2169-9380 |
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2169-9380 |
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yes |
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6855 |
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2014 |
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Journal of Geophysical Research: Solid Earth |
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119 |
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6 |
Pages |
4666-4683 |
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316 |
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2169-9356 |
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yes |
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5377 |
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Author |
Neala Creasy, Maureen D. Long, Heather A. Ford |
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Title |
Deformation in the lowermost mantle beneath Australia from observations and models of seismic anisotropy |
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Journal |
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2017 |
Publication |
Journal of Geophysical Research: Solid Earth |
Abbreviated Journal |
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Volume |
122 |
Issue |
7 |
Pages |
5243-5267 |
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Keywords |
anisotropy lowermost mantle mantle dynamics postperovskite shear wave splitting |
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Abstract |
Observations of seismic anisotropy near the core-mantle boundary may yield constraints on patterns of lowermost mantle flow. We examine seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces. We combined measurements of differential splitting of SKS-SKKS and S-ScS phases sampling our study region over a range of azimuths, using data from 10 long-running seismic stations. Observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle. We identified two subregions for which we have robust measurements of D?-associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations. We tested a variety of elastic tensors and orientations, including single-crystal elasticity of lowermost mantle minerals (bridgmanite, postperovskite, and ferropericlase), tensors based on texture modeling in postperovskite aggregates, elasticity predicted from deformation experiments on polycrystalline MgO aggregates, and tensors that approximate the shape preferred orientation of partial melt. We find that postperovskite scenarios are more consistently able to reproduce the observations. Beneath New Zealand, the observations suggest a nearly horizontal [100] axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models. Our modeling results further suggest that dominant slip on the (010) plane in postperovskite aggregates provides a good fit to the data but the solution is nonunique. Our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow. |
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2169-9356 |
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2169-9356 |
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yes |
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7324 |
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Title |
Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties |
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Year |
2018 |
Publication |
Journal of Geophysical Research: Solid Earth |
Abbreviated Journal |
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Volume |
123 |
Issue |
7 |
Pages |
5831-5852 |
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Keywords |
global earthquake seismology radiated energy seismic coupling source time functions stress drop subduction earthquakes |
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133 |
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2169-9356 |
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2169-9356 |
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yes |
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7383 |
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Author |
Kiwamu Nishida, Takuto Maeda, Yoshio Fukao |
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Title |
Seismic Observation of Tsunami at Island Broadband Stations |
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2019 |
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Journal of Geophysical Research: Solid Earth |
Abbreviated Journal |
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124 |
Issue |
2 |
Pages |
1910-1928 |
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Keywords |
broadband seismometer tsunami propagation |
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133 |
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2169-9356 |
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2169-9356 |
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yes |
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7508 |
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Author |
B. Lauer, R. Grandin, Y. Klinger |
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Title |
Fault Geometry and Slip Distribution of the 2013 Mw 7.7 Balochistan Earthquake From Inversions of SAR and Optical Data |
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Journal |
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Year |
2020 |
Publication |
Journal of Geophysical Research: Solid Earth |
Abbreviated Journal |
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Volume |
125 |
Issue |
7 |
Pages |
e2019JB018380 |
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Keywords |
Balochistan earthquake earthquake rupture modeling earthquake source processes InSAR optical data shallow slip deficit |
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133 |
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2169-9356 |
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7664 |
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