pinecone/core-2020-05-10-deduplication huggingface dataset:
Magnetic correlation functions in the slow and fast solar wind in the Eulerian reference frame

Simultaneous multiple point measurements of the magnetic field from seven spacecraft are employed to estimate the Eulerian correlation function and decorrelation time scales in the near Earth solar wind for two different solar wind speed ranges. We find that the Eulerian decorrelation time scale differs significantly in the slow solar wind (<450 km/s), where quasi-two-dimensional turbulence dominates, and in the fast solar (>600 km/s) wind, where slab-type turbulence dominates. In slow solar wind, the decorrelation time is 215 ± 43 min, and in fast solar wind, the decorrelation time scale is 114 ± 23 min, which indicates that<br />decorrelation times vary with the nature of the turbulence. The values reported here are comparable to estimates of decorrelation times based on a number of different models, but do not clearly support or refute any specific solar wind turbulence model. These results may be useful in magnetohydrodynamic modeling of the solar wind and can contribute to our understanding of solar and galactic cosmic ray diffusion in the heliosphere.Fil: Weygand, James M.. University of California; Estados UnidosFil: Matthaeus, W. H.. University of Delaware; Estados UnidosFil: Kivelson M. G.. University of California; Estados UnidosFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Multi-spectral simultaneous diagnosis of Saturns aurorae throughout a
  planetary rotation

From the 27th to the 28th January 2009, the Cassini spacecraft remotely
acquired combined observations of Saturns southern aurorae at radio,
ultraviolet and infrared wavelengths, while monitoring ion injections in the
middle magnetosphere from energetic neutral atoms. Simultaneous measurements
included the sampling of a full planetary rotation, a relevant timescale to
investigate auroral emissions driven by processes internal to the
magnetosphere. In addition, this interval coincidently matched a powerful
substorm-like event in the magnetotail, which induced an overall dawnside
intensification of the magnetospheric and auroral activity. We comparatively
analyze this unique set of measurements to reach a comprehensive view of
kronian auroral processes over the investigated timescale. We identify three
source regions in atmospheric aurorae, including a main oval associated with
the bulk of Saturn Kilometric Radiation (SKR), together with polar and
equatorward emissions. These observations reveal the co-existence of
corotational and sub-corototational dynamics of emissions associated with the
main auroral oval. Precisely, we show that the atmospheric main oval hosts
short-lived sub-corotating isolated features together with a bright,
longitudinally extended, corotating region locked at the southern SKR phase. We
assign the susbtorm-like event to a regular, internally driven, nightside ion
injection possibly triggerred by a plasmoid ejection. We also investigate the
total auroral energy budget, from the power input to the atmosphere,
characterized by precipitating electrons up to 20 keV, to its dissipation
through the various radiating processes. Finally, through simulations, we
confirm the search-light nature of the SKR rotational modulation and we show
that SKR arcs relate to isolated auroral spots. The resulting findings are
discussed in the frame of pending questions
Spectroscopic diagnostics of laboratory air plasmas as a benchmark for spectral rotational (gas) temperature determination in TLEs

13 p.: gráf.We have studied laboratory low pressure (0.1 mbar ≤ p ≤2 mbar) glow air discharges by optical emission spectroscopy to discuss several spectroscopic techniques that could be implemented by field spectrographs, depending on the available spectral resolution, to experimentally quantify the gas temperature associated to transient luminous events (TLEs) occurring at different altitudes including blue jets, giant blue jets, and sprites. Laboratory air plasmas have been analyzed from the near UV (300 nm) to the near IR (1060 nm) with high (up to 0.01 nm) and low (2 nm) spectral resolution commercial grating spectrographs and by an in-house intensified CCD grating spectrograph that we have recently developed for TLE spectral diagnostic surveys with ≃0.45 nm spectral resolution. We discuss the results of lab tests and comment on the convenience of using one or another technique for rotational (gas) temperature determination depending on the altitude and available spectral resolution. Moreover, we compare available low resolution (3 nm ≤Δλ≤7 nm) N2 1PG field recorded sprite spectra at 53 km (≃1 mbar), and resulting vibrational distribution function, with 1 mbar laboratory glow discharge spectrum (Δλ=2 nm) and synthetic sprite spectra from models. We found that while the relative population of N2(B3Πg,v=2−7) in sprites and laboratory produced air glow plasmas are similar, the N2(B3Πg,v=1) vibrational level in sprites is more efficiently populated (in agreement with model predictions) than in laboratory air glow plasmas at similar pressures.Supported by the Spanish Ministry of Science and Innovation, MINECO under projects AYA2011-29936-C05-02, CSD2009-00038, and FIS2010-16455 and by the Junta de Andalucia, Proyecto de Excelencia FQM-5965. MINECO for a FPI grant BES-2010-042367.  support by a Ramón y Cajal contract, code RYC-2011-07801. support by a Juan de la Cierva contract, code\ud
JdC-2009-04949.Peer reviewe
Understanding shock dynamics in the inner heliosphere with modeling and type II radio data: A statistical study

We study two methods of predicting interplanetary shock location and strength in the inner heliosphere: (1) the ENLIL simulation and (2) the kilometric type II (kmTII) prediction. To evaluate differences in the performance of the first method, we apply two sets of coronal mass ejections (CME) parameters from the cone-model fitting and flux-rope (FR) model fitting as input to the ENLIL model for 16 halo CMEs. The results show that the ENLIL model using the actual CME speeds from FR-fit provided an improved shock arrival time (SAT) prediction. The mean prediction errors for the FR and cone-model inputs are 4.90±5.92 h and 5.48±6.11 h, respectively. A deviation of 100 km s−1 from the actual CME speed has resulted in a SAT error of 3.46 h on average. The simulations show that the shock dynamics in the inner heliosphere agrees with the drag-based model. The shock acceleration can be divided as two phases: a faster deceleration phase within 50 Rs and a slower deceleration phase at distances beyond 50 Rs. The linear-fit deceleration in phase 1 is about 1 order of magnitude larger than that in phase 2. When applying the kmTII method to 14 DH-km CMEs, we found that combining the kmTII method with the ENLIL outputs improved the kmTII prediction. Due to a better modeling of plasma density upstream of shocks and the kmTII location, we are able to provide a more accurate shock time-distance and speed profiles. The mean kmTII prediction error using the ENLIL model density is 6.7±6.4 h; it is 8.4±10.4 h when the average solar wind plasma density is used. Applying the ENLIL density has reduced the mean kmTII prediction error by ∼2 h and the standard deviation by 4.0 h. Especially when we applied the combined approach to two interacting events, the kmTII prediction error was drastically reduced from 29.6 h to −4.9 h in one case and 10.6 h to 4.2 h in the other. Furthermore, the results derived from the kmTII method and the ENLIL simulation, together with white-light data, provide a valuable validation of shock formation location and strength. Such information has important implications for solar energetic particle acceleration.Fil: Xie, H.. NASA. Goddard Space Flight Center; Estados Unidos. Department of Physics. Catholic University of America; Estados UnidosFil: St. Cyr, O.C.. NASA. Goddard Space Flight Center; Estados UnidosFil: Gopalswamy, N.. NASA. Goddard Space Flight Center; Estados UnidosFil: Odstrcil, D.. George Mason University. Department of Computational and Data Sciences; Estados UnidosFil: Cremades Fernandez, Maria Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional de Mendoza; Argentin
The free escape continuum of diffuse ions upstream of the Earth's quasi-parallel bow shock

The Earth's bow shock is very efficient in accelerating ions out of the incident solar wind distribution to high energies (≈ 200 keV/e). Fluxes of energetic ions accelerated at the quasi-parallel bow shock, also known as diffuse ions, are best represented by exponential spectra in energy/charge, which require additional assumptions to be incorporated into these model spectra. One of these assumptions is a so-called "free escape boundary" along the interplanetary magnetic field into the upstream direction. Locations along the IBEX orbit are ideally suited for in situ measurements to investigate the existence of an upstream free escape boundary for bow shock accelerated ions. In this study we use 2 years of ion measurements from the background monitor on the IBEX spacecraft, supported by ACE solar wind observations. The IBEX Background Monitor is sensitive to protons > 14 keV, which includes the energy of the maximum flux for diffuse ions. With increasing distance from the bow shock along the interplanetary magnetic field, the count rates for diffuse ions stay constant for ions streaming away from the bow shock, while count rates for diffuse ions streaming toward the shock gradually decrease from a maximum value to ~1/e at distances of about 10 RE to 14 RE. These observations of a gradual decrease support the transition to a free escape continuum for ions of energy >14 keV at distances from 10 RE to 14 RE from the bow shock
Ionospheric density perturbations recorded by DEMETER above intense thunderstorms

International audience[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
Simpson's paradox in trend analysis: An example from El Leoncito airglow data

We use our mesopause region temperature data from El Leoncito (31.8°S, 69.3°W) to illustrate how the increased length of the dataset alone does not simplify trend analysis. This is because the adequate interpretation of trend results does not only depend on the statistical characteristics of the data time-series. A longer dataset may make unexpected features stand out, which require an explanation before definite conclusions on long-term trends can be drawn. While the rotational temperatures derived at El Leoncito from the OH(6-2) airglow band appear rather homogeneous at first sight, the O2 temperatures measured with the same instrument and optical filter exhibit features strongly reminiscent of Simpson´s classical statistical paradox, in that straight-forward trends derived from parts show signs opposite to those of the complete data set. The resolution of this paradox requires more efforts to diagnose and remove the impact of instrumental artifacts besides taking any other geophysical variation that does not directly contribute to long-term change into account. Intercomparison with other instruments is certainly useful, but may warrant the elimination of new uncertainties discovered in the act.Fil: Scheer, Jurgen. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Reisin, Esteban Rodolfo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity

International audience[1] We use VLF electromagnetic wave data measured by the DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by 2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes. Citation: Píša, D., F. Němec , O. Santolík, M. Parrot, and M. Rycroft (2013), Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity
On the spatial distribution of decameter-scale subauroral ionospheric irregularities observed by SuperDARN radars

The midlatitude Super Dual Auroral Radar Network (SuperDARN) radars\ud
regularly observe nighttime low-velocity Sub-Auroral Ionospheric Scatter (SAIS) from\ud
decameter-scale ionospheric density irregularities during quiet geomagnetic conditions.\ud
To establish the origin of the density irregularities responsible for low-velocity SAIS, it is\ud
necessary to distinguish between the effects of high frequency (HF) propagation and\ud
irregularity occurrence itself on the observed backscatter distribution. We compare range,\ud
azimuth, and elevation data from the Blackstone SuperDARN radar with modeling results\ud
from ray tracing coupled with the International Reference Ionosphere assuming a uniform\ud
irregularity distribution. The observed and modeled distributions are shown to be very\ud
similar. The spatial distribution of backscattering is consistent with the requirement that\ud
HF rays propagate nearly perpendicular to the geomagnetic ﬁeld lines (aspect angle ≤ 1°).\ud
For the ﬁrst time, the irregularities responsible for low-velocity SAIS are determined to\ud
extend between 200 and 300 km altitude, validating previous assumptions that\ud
low-velocity SAIS is an F-region phenomenon. We ﬁnd that the limited spatial extent of\ud
this category of ionospheric backscatter within SuperDARN radars’ ﬁelds-of-view is a\ud
consequence of HF propagation effects and the ﬁnite vertical extent of the scattering\ud
irregularities. We conclude that the density irregularities responsible for low-velocity\ud
SAIS are widely distributed horizontally within the midlatitude ionosphere but are\ud
conﬁned to the bottom-side F-region.Peer-reviewedPublisher Versio
Do magnetospheric shear Alfvén waves generate sufficient electron energy flux to power the aurora?

Using a self-consistent drift-kinetic simulation code, we investigate whether electron acceleration owing to shear Alfvén waves in the plasma sheet boundary layer is sufficient to cause auroral brightening in the ionosphere. The free parameters used in the simulation code are guided by in situ observations of wave and plasma parameters in the magnetosphere at distances >4 RE from the Earth. For the perpendicular wavelength used in the study, which maps to ∼4 km at 110 km altitude, there is a clear amplitude threshold which determines whether magnetospheric shear Alfvén waves above the classical auroral acceleration region can excite sufficient electrons to create the aurora. Previous studies reported wave amplitudes that easily exceed this threshold; hence, the results reported in this paper demonstrate that auroral acceleration owing to shear Alfvén waves can occur in the magnetosphere at distances >4 RE from the Earth
Relativistic electron microbursts due to nonlinear pitch angle scattering by EMIC triggered emissions

We show that the anomalous cyclotron resonance between relativistic electrons and electromagnetic ion cyclotron (EMIC) triggered emissions takes place very effectively near the magnetic equator because of the variation of the ambient magnetic field. Efficient precipitations are caused by nonlinear trapping of relativistic electrons by electromagnetic wave potentials formed by EMIC triggered emissions. We derive the necessary conditions of the wave amplitude, kinetic energies, and pitch angles that must be satisfied for the nonlinear wave trapping. We have conducted test particle simulations with a large number of relativistic electrons trapped by a parabolic magnetic field near the magnetic equator. In the presence of coherent EMIC-triggered emissions with increasing frequencies, a substantial amount of relativistic electrons is trapped by the wave, and the relativistic electrons at high pitch angles are guided to lower pitch angles within a short time scale much less than a second, resulting in rapid precipitation of relativistic electrons or relativistic electron microbursts
Variations of electric field and electric resistivity of air caused by dust motion

International audienceWe report results of a field campaign conducted in the Nevada desert with a suite of electric field instruments consisting of a field mill (FM) and a short dipole antenna (SDA). Further, we show that a combination of the measurements of these two instruments allows the estimation of the electric resistivity of air, an important quantity that is extremely difficult to measure near the Earth's surface. The electric resistivity of air is found to vary between 1.5 · 10<sup>13</sup> and 6⋅10<sup>13</sup> Ω m and to correlate with changes in electric field. Vertical DC electric fields with amplitudes up to 6 kV m<sup>-1</sup> were observed to correspond to clouds of dust blowing through the measurement site. Enhanced DC and AC electric fields are measured during periods when horizontal wind speed exceeds 7 m s<sup>-1</sup>, or around twice the background value. We suggest that low frequency emissions, below ~200 Hz, are generated by the motion of electrically charged particles in the vicinity of the SDA electrode and propose a simple model to reproduce the observed spectra. According to this model, the spectral response is controlled by three parameters, (i) the speed of the charged particles, (ii) the charge concentration and (iii) the minimum distance between the particle and the electrode. In order to explain the electric fields measured with the FM sensors at different heights, we developed a multi-layer model that relates the electric field to the charge distribution. For example, a non-linear variation of the electric field observed by the FM sensors below 50 cm is simulated by a near surface layer of tens of cm that is filled with electrically charged particles that carry a predominantly negative charge in the vicinity of the soil. The charge concentration inside this layer is estimated to vary between 10<sup>12</sup> and 5 · 10<sup>13</sup> electrons m<sup>-3</sup>
Tracing magnetic separators and their dependence on IMF clock angle in
  global magnetospheric simulations

A new, efficient, and highly accurate method for tracing magnetic separators
in global magnetospheric simulations with arbitrary clock angle is presented.
The technique is to begin at a magnetic null and iteratively march along the
separator by finding where four magnetic topologies meet on a spherical
surface. The technique is verified using exact solutions for separators
resulting from an analytic magnetic field model that superposes dipolar and
uniform magnetic fields. Global resistive magnetohydrodynamic simulations are
performed using the three-dimensional BATS-R-US code with a uniform
resistivity, in eight distinct simulations with interplanetary magnetic field
(IMF) clock angles ranging from 0 (parallel) to 180 degrees (anti-parallel).
Magnetic nulls and separators are found in the simulations, and it is shown
that separators traced here are accurate for any clock angle, unlike the last
closed field line on the Sun-Earth line that fails for southward IMF. Trends in
magnetic null locations and the structure of magnetic separators as a function
of clock angle are presented and compared with those from the analytic field
model. There are many qualitative similarities between the two models, but
quantitative differences are also noted. Dependence on solar wind density is
briefly investigated.Comment: 10 pages, 10 figures, Presented at 2012 AGU Fall Meeting and 2013
  Geospace Environment Modeling (GEM) Worksho