pinecone/core-2020-05-10-deduplication huggingface dataset:
Ionospheric midlatitude electric current density inferred from multiple magnetic satellites

A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data. Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting for estimates of main and crustal magnetic fields. Current density in the range ±0.1 μA/m2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F10.7, which has implications for any future efforts to model their effects. We resolve persistent current intensifications between geomagnetic latitudes of 30 and 50° in the postmidnight, predawn sector, a region typically thought to be relatively free of electric currents. The cause of these unexpected intensifications remains an open issue. We compare our results with current density predictions made by the Coupled Thermosphere-Ionosphere-Plasmasphere model, a self-consistent, first-principles, three-dimensional numerical dynamic model of ionospheric composition and temperatures. This independent validation of our current density estimates highlights good agreement in the broad spatiotemporal trends we identify, which increases confidence in our results
Photoelectrons in the Enceladus plume

The plume of Enceladus is a remarkable plasma environment containing several charged particle species. These include cold magnetospheric electrons, negative and positive water clusters, charged nanograins, and “magnetospheric photoelectrons” produced from ionization of neutrals throughout the magnetosphere near Enceladus. Here we discuss observations of a population newly identified by the Cassini Plasma Spectrometer (CAPS) electron spectrometer instrument—photoelectrons produced in the plume ionosphere itself. These were found during the E19 encounter, in the energetic particle shadow where penetrating particles are absent. Throughout E19, CAPS was oriented away from the ram direction where the clusters and nanograins are observed during other encounters. Plume photoelectrons are also clearly observed during the E9 encounter and are also seen at all other Enceladus encounters where electron spectra are available. This new population, warmer than the ambient plasma population, is distinct from, but adds to, the magnetospheric photoelectrons. Here we discuss the observations and examine the implications, including the ionization source these electrons provide
Solar cycle variations in polar cap area measured by the superDARN radars

We present a long-term study, from January 1996 to August 2012, of the latitude of\ud
the Heppner-Maynard Boundary (HMB) measured at midnight using the northern\ud
hemisphere Super Dual Auroral Radar Network (SuperDARN). The HMB represents the\ud
equatorward extent of ionospheric convection and is used in this study as a measure of the\ud
global magnetospheric dynamics. We ﬁnd that the yearly distribution of HMB latitudes is\ud
single peaked at 64° magnetic latitude for the majority of the 17 year interval. During 2003,\ud
the envelope of the distribution shifts to lower latitudes and a second peak in the distribution\ud
is observed at 61°. The solar wind-magnetosphere coupling function derived by Milan et al.\ud
(2012) suggests that the solar wind driving during this year was signiﬁcantly higher than\ud
during the rest of the 17 year interval. In contrast, during the period 2008–2011, HMB\ud
distribution shifts to higher latitudes, and a second peak in the distribution is again observed,\ud
this time at 68° magnetic latitude. This time interval corresponds to a period of extremely\ud
low solar wind driving during the recent extreme solar minimum. This is the ﬁrst long-term\ud
study of the polar cap area and the results demonstrate that there is a close relationship\ud
between the solar activity cycle and the area of the polar cap on a large-scale,\ud
statistical basis.European Union Seventh Framework Programme\ud
(FP7/2007–2013) under grant agreement 263325Peer-reviewedPublisher Versio
Mars ionospheric response to solar wind variability

At planets with induced magnetospheres, the coupling between the ionosphere, the\ud
weak draped magnetosphere, and the solar wind is very direct in comparison to Earth. The\ud
weak induced magnetosphere itself is created by the prevailing Solar wind conditions and\ud
therefore in its shape and strength dynamically depending on it. In early 2010, Mars was\ud
located behind Earth in the Solar wind; thus, we can use coordinated data from multiple\ud
near-Earth spacecraft (Stereo, Wind) to evaluate what kind of Solar wind disturbances have\ud
passed by Earth and might consecutively hit Mars, and when. We employ plasma data from\ud
the ESA Mars-Express mission, the ASPERA-3 particle instrument, and the MARSIS\ud
Active Ionospheric Sounder (AIS) to investigate, for a number of isolated events in March\ud
and April 2010, how the ionosphere and the induced magnetosphere at Mars develop and\ud
decay in response to Solar wind variability in the magnetic ﬁeld, density, and velocity. In a\ud
dedicated campaign mode, we use frequent long-duration MARSIS AIS operations for\ud
several consecutive orbits, to monitor for the ﬁrst time the long-term development of the\ud
Martian plasma environment during solar wind disturbances. We ﬁnd that the\ud
magnetosphere and ionosphere of Mars can become considerably compressed by solar wind\ud
dynamic pressure variations, which usually are also associated with changes in the magnetic\ud
draping of the interplanetary magneticﬁeld around the planet. These are typically associated\ud
with corotating interaction regions and coronal mass ejections, and can last for several days.\ud
During such episodes of compression, we see signatures of increased plasma transport over\ud
the terminator and enhanced ion outﬂow from the upper atmosphere.Peer-reviewedPublisher Versio
Plasma sheet magnetic fields and flows during steady magnetospheric  convection events

Inner magnetosphere magnetic field and plasma flow data are examined during 228 steady magnetospheric convection events. We find that the BZ component of the magnetic field around geostationary orbit is weaker than during average conditions and the plasma flow speeds are higher than average in the dusk sector just beyond geostationary orbit. The steady magnetospheric convection periods include more enhanced earthward and tailward flow intervals than during average conditions. The steady convection period magnetic field is not steady: The near-geostationary nightside field grows increasingly taillike throughout the steady convection period. In the midtail, earthward flows are enhanced in a wide region around the midnight sector, which leads to enhanced magnetic flux transport toward the Earth during the steady convection periods. Compared to well-known characteristics during magnetospheric substorms, the inner tail evolution resembles that during the substorm growth phase, while the midtail flow characteristics during steady convection periods are similar to those found during substorm recovery phases.Peer reviewe
Solar Energetic Particle drifts in the Parker spiral

Drifts in the Parker spiral interplanetary magnetic field are known to be an
important component in the propagation of galactic cosmic rays, while they are
thought to be negligible for Solar Energetic Particles (SEPs). As a result they
have so far been ignored in SEP propagation modelling and data analysis. We
examine drift velocities in the Parker spiral within single particle
first-order adiabatic theory, in a local coordinate system with an axis
parallel to the magnetic field. We show that, in the presence of scattering in
interplanetary space, protons at the high end of the SEP energy range
experience significant gradient and curvature drift. In the scatter-free case,
drift due to magnetic field curvature is present. The magnitude of drift
velocity increases by more than an order of magnitude at high heliographic
latitudes compared to near the ecliptic; it has a strong dependence on radial
distance r from the Sun, reaching a maximum at r~1 AU at low heliolatitudes and
r~10 AU at high heliolatitudes. Due to the mass over charge dependence of drift
velocities, the effect of drift for partially ionised SEP heavy ions is
stronger than for protons. Drift is therefore likely to be a considerable
source of cross field transport for high energy SEPs.Comment: 7 pages, 4 figures, submitted to Journal of Geophysical Research -
  Space Physic
A new diffusion matrix for whistler mode chorus waves

Global models of the Van Allen radiation belts usually include resonant wave-particle interactions as a diffusion process, but there is a large uncertainty over the diffusion rates. Here we present a new diffusion matrix for whistler mode chorus waves that can be used in such models. Data from seven satellites are used to construct 3,536 power spectra for upper and lower band chorus for 1.5 ≤ L∗ ≤ 10, MLT, magnetic latitude 0o ≤ |λm| ≤ 60o and five levels of Kp. Five density models are also constructed from the data. Gaussian functions are fitted to the spectra and capture typically 90% of the wave power. The frequency maxima of the power spectra vary with L∗ and are typically lower than that used previously. Lower band chorus diffusion increases with geomagnetic activity and is largest between 21:00 and 09:00 MLT. Energy diffusion extends to a few MeV at large pitch angles > 60o and at high energies exceeds pitch angle diffusion at the loss cone. Most electron diffusion occurs close to the geomagnetic equator (< 12o). Pitch angle diffusion rates for lower band chorus increase with L∗ and are significant at L∗ = 8 even for low levels of geomagnetic activitywhile upper band chorus is restricted to mainly L∗ < 6. The combined drift and bounce averaged diffusion rates for upper and lower band chorus extend from a few keV near the loss cone up to several MeV at large pitch angles indicating loss at low energies and net acceleration at high energies
A re-examination of latitudinal limits of substorm-produced energetic electron precipitation

The primary sources of energetic electron precipitation (EEP) which affect altitudes <100 km (>30 keV) are expected to be from the radiation belts, and during substorms. EEP from the radiation belts should be restricted to locations between L = 1.5-8, while substorm produced EEP is expected to range from L = 4-9.5 during quiet geomagnetic conditions. Therefore, one would not expect any significant D-region impact due to electron precipitation at geomagnetic latitudes beyond about L = 10. In this study we report on large unexpectedly high latitude D-region ionization enhancements, detected by an incoherent scatter radar at L ≈ 16, which appear to be caused by electron precipitation from substorms. We go on to reexamine the latitudinal limits of substorm produced EEP using data from multiple low-Earth orbiting spacecraft, and demonstrate that the precipitation stretches many hundreds of kilometers polewards of the previously suggested limits. We find that a typical substorm will produce significant EEP over the IGRF L-shell range L = 4.6 ± 0.2-14.5 ± 1.2, peaking at L = 6-7. However, there is significant variability from event to event; in contrast to the median case, the strongest 25% of substorms have significant EEP in the range spaning L = 4.1 ± 0.1-20.7 ± 2.2, while the weakest 25% of substorms have significant EEP in the range spaning L = 5.5 ± 0.1-10.1 ± 0.7. We also examine the occurrence probability of very large substorms, focusing on those events which appear to be able to disable geostationary satellites when they are located near midnight MLT. On average these large substorms occur approximately 1-6 times per year, a significant rate given the potential impact on satellites
Modification of continental lithosphere by tectonic processes: A tomographic image of central North America

The assembly of Laurentia by Precambrian accretion is also believed to have formed the underlying lithosphere. Accretionary signatures are detectable by seismic observations but subject to modification by later processes, e.g., orogeny, rifting, and plumes. We examine the Archean Superior Province (SP) and environs using a set of teleseismic P wave arrivals from Canadian and American instruments. The resulting tomographic model has high resolution beneath the Dakotas and Minnesota, provides a first look at the lithosphere beneath Manitoba, and sharpens previously documented features in Ontario. From the model and previous anisotropy observations, we detect (i) a large high-velocity feature beneath the western SP, associated with elevated lithospheric anisotropy. The high-velocity feature does not match crustal boundaries; notably, its western edge lies approximately 200 km east of the contact with the Proterozoic Trans-Hudson Orogen (THO). (ii) A low-velocity channel-shaped feature strikes northwest through Minnesota and the Dakotas, associated with weakening anisotropy. (iii) High velocities southwest of (ii), beneath the Minnesota River Valley terrane (MRVT), associated with low anisotropy. We interpret (i) to be accretionary, and contemporaneous with Superior assembly; similar velocity but weaker anisotropy of the MRVT is consistent with vertical-tectonic mechanisms. The inboard location of the THO contact may indicate modification of the Superior root. The low-velocity channel has no obvious crustal expression but connects to an offset in the Proterozoic Mid-Continent Rift (MCR) and may be rift related. The MCR is not well imaged but will be examined via the temporary Superior Province Rifting EarthScope Experiment, in progress
The 2011 Mw 7.1 Van (Eastern Turkey) earthquake

[1] We use interferometric synthetic aperture radar (InSAR), body wave seismology, satellite imagery, and field observations to constrain the fault parameters of the Mw 7.1 2011 Van (Eastern Turkey) reverse-slip earthquake, in the Turkish-Iranian plateau. Distributed slip models from elastic dislocation modeling of the InSAR surface displacements from ENVISAT and COSMO-SkyMed interferograms indicate up to 9 m of reverse and oblique slip on a pair of en echelon NW 40 °–54 ° dipping fault planes which have surface extensions projecting to just 10 km north of the city of Van. The slip remained buried and is relatively deep, with a centroid depth of 14 km, and the rupture reaching only within 8–9 km of the surface, consistent with the lack of significant ground rupture. The up-dip extension of this modeled WSW striking fault plane coincides with field observations of weak ground deformation seen on the western of the two fault segments and has a dip consistent with that seen at the surface in fault gouge exposed in Quaternary sediments. No significant coseismic slip is found in the upper 8 km of the crust above the main slip patches, except for a small region on the eastern segment potentially resulting from the Mw 5.9 aftershock on the same day. We perform extensive resolution tests on the data to confirm the robustness of the observed slip deficit in the shallow crust. We resolve a steep gradient in displacement at the point where the planes of the two fault segments ends are inferred to abut at depth, possibly exerting some structural control on rupture extent
Acoustic-gravity waves from the source region of the 2011 great Tohoku earthquake (Mw=9.0)

Atmospheric pressure waves were recorded within 5 h after the 2011 great Tohoku earthquake (Mw = 9.0) by sensitive microbarographs at four regional stations and eight International Monitoring System stations at distances up to 6700 km. While its apparent phase velocity between the regional stations is 341 m/s, the global stations indicate weak dispersive wave trains with low frequencies between 1.6 and 4.8 mHz, propagating with an average phase velocity around 364 m/s. The low-frequency waves may be interpreted as acoustic-gravity waves excited by upheaval and depression of the sea surface in the source region due to coseismic uplift and subsidence of the sea bottom during this great thrust earthquake. Assuming the source dimension and the average coseismic vertical displacements of the sea surface, with reference to tsunami observations, we calculate synthetic waveforms for some of the far-field stations by incorporating a standard sound velocity structure in the atmosphere up to an altitude of 220 km. The synthetics provide reasonable explanations for the general features of the observed waveforms, suggesting possible ranges for the source parameters generating these acoustic-gravity waves. Our analysis suggests that the average initial upheaval of the sea surface in the central zones of the source region may exceed 4–6 m and that the risetime of the coseismic deformation may be in the range between 3 and 4 min. In the eastern narrow zone adjacent to the Japan Trench, the deformation has significantly higher initial amplitude and shorter risetime
Seismic anisotropy in the Sumatra subduction zone

An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore-arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore-arc islands exhibit trench-parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/trench parallel, while in the back-arc region it is trench perpendicular. The trench-perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault-parallel measurements are similar to the fault-parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW-SSE fast direction with delay times of 0.8–3.0 s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo-Australian Plate. The small delay times exhibited by the local SWS (0.05–0.45 s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab
Did the Paleo-Asian Ocean between North China Block and Mongolia Block exist during the Late Paleozoic? First paleomagnetic evidence from central-eastern Inner Mongolia, China

International audienceThe tectonic evolution of the Paleo-Asian Ocean between the North China Block (NCB) and the Mongolia Block (MOB) is a contentious issue, and geodynamic models remain speculative. In an effort to puzzle out this controversy, a paleomagnetic study was carried out on the Silurian to Permian formations in central- eastern Inner Mongolia (China). More than 680 sedimentary and volcanic samples were collected from 86 sites. We have established titanium-poor magnetite and hematite as the principal magnetic carriers. AMS measurements demonstrate negligible deformation of the majority of study rocks with sedimentary fabrics. From primary magnetizations, a Late Devonian and a Permian pole are calculated for IMB at: λ = 46.8°N, φ = 349.1°E, dp = 14.6°, dm = 27.3° with N = 3 and λ = 48.7°N, φ = 3.7°E, dp = 5.2°, dm = 9.1° with N = 6, respectively. Two stages of secondary magnetization are also identified probably due to Early Permian and Early Cretaceous magmatic events. As preliminary results, the comparison of our new paleomagnetic poles with available data from NCB, MOB and Siberia indicates that (1) the paleolatitude of IMB, NCB and MOB are consistent between Late Devonian and Permian, suggesting pre-Late Devonian closure of the Paleo-Asian Ocean and further evaluation of these three blocks as a single entity; (2) post-Permian intracontinental deformation was significant and characterized by block rotations, which are due to strike-slip faulting within the welded NCB-IMB-MOB block
Earthquake Cycle Deformation in the Tibetan Plateau with a Weak Mid-Crustal Layer

Geodetic observations of interseismic deformation across the Tibetan plateau contain information about both tectonic and earthquake cycle processes. Time-variations in surface velocities between large earthquakes are sensitive to the rheological structure of the subseismogenic crust, and, in particular, the viscosity of the middle and lower crust. Here we develop a semianalytic solution for time-dependent interseismic velocities resulting from viscoelastic stress relaxation in a localized midcrustal layer in response to forcing by a sequence of periodic earthquakes. Earthquake cycle models with a weak midcrustal layer exhibit substantially more near-fault preseismic strain localization than do classic two-layer models at short (<100 yr) Maxwell times. We apply both this three-layer model and the classic two-layer model to geodetic observations before and after the 1997 \(M_W = 7.6\) Manyi and 2001 \(M_W = 7.8\) Kokoxili strike-slip earthquakes in Tibet to estimate the viscosity of the crust below a 20 km thick seismogenic layer. For these events, interseismic stress relaxation in a weak \((viscosity \leq10^{18.5} Pa⋅s)\) and thin (height ≤20 km) midcrustal layer explains observations of both preseismic near-fault strain localization and rapid (>50 mm/yr) postseismic velocities in the years following the coseismic ruptures. We suggest that earthquake cycle models with a localized midcrustal layer can simultaneously explain both preseismic and postseismic geodetic observations with a single Maxwell viscosity, while the classic two-layer model requires a rheology with multiple relaxation time scales.Earth and Planetary Science
A Domain Decomposition Approach to Implementing Fault Slip in
  Finite-Element Models of Quasi-static and Dynamic Crustal Deformation

We employ a domain decomposition approach with Lagrange multipliers to
implement fault slip in a finite-element code, PyLith, for use in both
quasi-static and dynamic crustal deformation applications. This integrated
approach to solving both quasi-static and dynamic simulations leverages common
finite-element data structures and implementations of various boundary
conditions, discretization schemes, and bulk and fault rheologies. We have
developed a custom preconditioner for the Lagrange multiplier portion of the
system of equations that provides excellent scalability with problem size
compared to conventional additive Schwarz methods. We demonstrate application
of this approach using benchmarks for both quasi-static viscoelastic
deformation and dynamic spontaneous rupture propagation that verify the
numerical implementation in PyLith.Comment: 14 pages, 15 figure