We present multi spacecraft measurements in the magnetosheath (MSH) and in the solar wind (SW) by Interball, Cluster and Polar, demonstrating that coherent structures with magnetosonic Mach number up ...to 3 - Supermagnetosonic Plasma Streams (SPS) - generate transient and anomalous boundary dynamics, which may cause substantial displacements of the magnetospheric boundaries and the riddling of peripheral boundary layers. In this regard, for the first time, we describe a direct plasma penetration into the flank boundary layers, which is a candidate for being the dominant transport mechanism for disturbed MSH periods. Typically SPS's have a ram pressure exceeding by several times that of the SW and lead to long-range correlations between processes at the bow shock (BS) and at the magnetopause (MP) on one side and between MSH and MP boundary layers on the other side. We demonstrate that SPS's can be observed both near the BS and near the MP and argue that they are often triggered by hot flow anomalies (HFA), which represent local obstacles to the SW flow and can induce the SPS generation as a means for achieving a local flow balance. Finally, we also discuss other causes of SPS's, both SW-induced and intrinsic to the MSH. SPS's appear to be universal means for establishing a new equilibrium between flowing plasmas and may also prove to be important for astrophysical and fusion applications.
Knowledge of the ion composition in the near-Earth’s magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ...ionospheric origin in the magnetosphere, in particular oxygen (O
+
), influences the plasma sheet bulk properties, current sheet (CS) thickness and its structure. It affects reconnection rates and the formation of Kelvin-Helmholtz instabilities. This has profound consequences for the global magnetospheric dynamics, including geomagnetic storms and substorm-like events. The formation and demise of the ring current and the radiation belts are also dependent on the presence of heavy ions. In this review we cover recent advances in observations and models of the circulation of heavy ions in the magnetosphere, considering sources, transport, acceleration, bulk properties, and the influence on the magnetospheric dynamics. We identify important open questions and promising avenues for future research.
Until now it is still questionable whether ions are accelerated to energies above 100 keV in the near‐Earth current sheet (CS), in the vicinity of a possible near‐Earth neutral line. By using 11 ...years of 3‐D energetic ion flux data for protons, helium, and oxygen (~150 keV–1 MeV) from the RAPID instrument on board Cluster 4, we statistically study the energetic ion acceleration by investigating ion anisotropies in the near‐Earth magnetotail (−20 RE < X <−16 RE). It is found that the earthward (tailward) anisotropy of the energetic (>150 keV) ions (protons, He+, and O+) tend to become higher as the earthward (tailward) plasma bulk flows (measured by Cluster Ion Spectrometry experiment) become stronger. During such periods the presence of a strong acceleration source tailward (earthward) of Cluster spacecraft (S/C) is confirmed by the hardening energy spectra of the earthward (tailward) energetic ion flows. A good statistical correlation between tailward bulk flow, negative Bz, and the tailward anisotropy of energetic ions indicates that the strong ion acceleration might be related to a near‐Earth reconnection, which occurred earthward of the Cluster S/C. The energetic ion anisotropies do not show a clear dependence on the AE index, which may indicate that the acceleration source(s) for the energetic ions could be spatially localized.
Key Points
We present the observational evidence of ion acceleration in the plasma sheet
The acceleration of ions to energies > 150 keV may occur in the near‐Earth CS
The acceleration is a spatially localized process
In this paper, we analyzed the thermal and energy characteristics of the plasma components observed during the magnetic dipolarizations in the near tail by the
Cluster
satellites. It was previously ...found that the first dipolarization the ratio of proton and electron temperatures (
T
p
/
T
e
) was ~6–7. At the time of the observation of the first dipolarization front
T
p
/
T
e
decreases by up to ~3–4. The minimum value
T
p
/
T
e
(~2.0) is observed behind the front during the turbulent dipolarization phase. Decreases in
T
p
/
T
e
observed at this time are associated with an increase in
T
e
, whereas the proton temperature either decreases or remains unchanged. Decreases of the value
T
p
/
T
e
during the magnetic dipolarizations coincide with increase in wave activity in the wide frequency band up to electron gyrofrequency
f
ce
. High-frequency modes can resonantly interact with electrons causing their heating. The acceleration of ions with different masses up to energies of several hundred kiloelectron-volts is also observed during dipolarizations. In this case, the index of the energy spectrum decreases (a fraction of energetic ions increases) during the enhancement of low-frequency electromagnetic fluctuations at frequencies that correspond to the gyrofrequency of this ion component. Thus, we can conclude that the processes of the interaction between waves and particles play an important role in increasing the energy of plasma particles during magnetic dipolarizations.
Ionospheric outflow is believed to be a significant contribution to the magnetospheric plasma population. Ions are extracted from the ionosphere and transported downtail by the large‐scale convection ...motion driven by dayside reconnection. In this paper, we use a comprehensive data set of cold ion (total energy less than 70 eV) measurements combined with simultaneous observations from the solar wind to investigate the fate of these ions. By tracing the trajectories of the ions, we are able to find out where in the magnetotail ions end up. By sorting the observation according to geomagnetic activity and solar wind parameters, we then generate maps of the fate regions in the magnetotail and investigate the effects of these drivers. Our results suggest that, on overall, for about 85% of the cases, the outflowing ions are transported to the plasma sheet. The region where the ions are deposited into the plasma sheet is larger during geomagnetic quiet time than during disturbed conditions. A persistent dawn‐dusk asymmetry in the plasma sheet deposition is also observed.
Key Points
First map of cold ion transport to plasma sheet
Comparison of the deposition regions in geomagnetic activities
Asymmetry in magnetotail is demonstrated
We present Cluster multisatellite observations of accelerated electrons in the near‐Earth magnetotail associated with substorms. We found that the hardest electron energy spectra appear in the ...earliest stage of substorm expansion in the near‐Earth tail region and that they gradually become softer during the events. Enhancement of the high‐energy electron flux occurs generally associated with the bulk acceleration of ions (fast flow) and electrons. It is also shown that the high‐energy electrons sometimes show preferential perpendicular acceleration associated with the temporal enhancement of the normal component of the magnetic field, and then the anisotropic distribution quickly becomes isotropic. During the dipolarization interval, in which no convection signature is observed, perpendicular flux drops to less than the initial value, and the parallel flux is more than the perpendicular flux. The results suggest that the electron acceleration mechanism is mostly consistent with adiabatic betatron acceleration, while Fermi acceleration is not clear in the high‐energy part. The effect of the pitch angle scattering is also important. The dispersive signature of the high‐energy electron flux indicates fast dawnward drift loss, namely, the three‐dimensional effect of the limited plasma acceleration region.
Characteristics of particles and fields in the flow‐bouncing region are studied based on multipoint observations from Cluster located at 13–15RE downtail during a substorm event around 12:50 UT on 7 ...September 2007. The Cluster spacecraft were separated by a distance of up to 10,000 km and allowed to determine the mesoscale evolution of the current sheet as well as the development of the dipolarization front. We show that the flow bouncing took place associated with a tailward‐directed j × B force in a disturbed current sheet in addition to an enhanced tailward pressure gradient force. Multiple Earthward propagating dipolarization fronts accompanied by enhanced flux of energetic electrons were observed before the flow bouncing. The sequence of events started with a localized dipolarization front and ended with a large scale (>10RE) dipolarization front accompanied by a major increase in energetic electrons at all spacecraft and immediately followed by flow bouncing. Multiple dipolarization fronts result in the formation of compressed magnetic field with a plasma bulge bounded by thin ion‐scale current layers, a favorable condition for flow bouncing. These observations suggest that to understand the flow bouncing and related acceleration of plasma in the near‐Earth tail, both the large‐scale MHD properties and the transient and small‐scale effect of the plasma interaction with the Earth‐dipole field need to be taken into account.
Key Points
Dusk‐to‐dawn current identified during the flow bouncingPlasma bulge region with a few ion scale boundaries in flow braking regionElectron injection related to dipolarization front and flow braking
The radiation belts of the Earth, filled with energetic electrons, comprise complex and dynamic systems that pose a significant threat to satellite operation. While various models of electron flux ...both for low and relativistic energies have been developed, the behavior of medium energy (120–600 keV) electrons, especially in the MEO region, remains poorly quantified. At these energies, electrons are driven by both convective and diffusive transport, and their prediction usually requires sophisticated 4D modeling codes. In this paper, we present an alternative approach using the Light Gradient Boosting (LightGBM) machine learning algorithm. The Medium Energy electRon fLux In Earth's outer radiatioN belt (MERLIN) model takes as input the satellite position, a combination of geomagnetic indices and solar wind parameters including the time history of velocity, and does not use persistence. MERLIN is trained on >15 years of the GPS electron flux data and tested on more than 1.5 years of measurements. Tenfold cross validation yields that the model predicts the MEO radiation environment well, both in terms of dynamics and amplitudes o f flux. Evaluation on the test set shows high correlation between the predicted and observed electron flux (0.8) and low values of absolute error. The MERLIN model can have wide space weather applications, providing information for the scientific community in the form of radiation belts reconstructions, as well as industry for satellite mission design, nowcast of the MEO environment, and surface charging analysis.
Plain Language Summary
The radiation belts of the Earth, which are the zones of charged energetic particles trapped by the geomagnetic field, comprise complex and dynamic systems posing a significant threat to a variety of commercial and military satellites. While the inner belt is relatively stable, the outer belt is highly variable and depends substantially on solar activity; therefore, accurate and improved models of electron flux in the outer radiation belt are essential to understand the underlying physical processes. Although many models have been developed for the geostationary orbit and relativistic energies, prediction of electron flux in the 120–600 keV energy range still remains challenging. We present a data‐driven model of the medium energies (120–600 keV) differentialelectron flux in the outer radiation belt based on machine learning. We use 17 years of electron observations by Global Positioning System (GPS) satellites. We set up a 3D model for flux prediction in terms of L‐values, MLT, and magnetic latitude. The model gives reliable predictions of the radiation environment in the outer radiation belt and has wide space weather applications.
Key Points
A machine learning model is created to predict electron flux at MEO for energies 120–600 keV
The model requires solar wind parameters and geomagnetic indices as input and does not use persistence
MERLIN model yields high accuracy and high correlation with observations (0.8)
The effects of condensed tannins on N dynamics in ruminants have been a topic of research for some time, but much less work has focused on their impacts on other nutrients in manure. A 4 × 4 Latin ...square trial was used to determine if intake of sericea lespedeza (; SL; a condensed tannin source), at 0, 10, 20, or 40% of the diet (as-fed basis), would affect concentrations of nutrients in manure and patterns of total excretion when offered with alfalfa (; ALF) to sheep. With SL additions, average daily manure production increased linearly ( ≤ 0.01), from 40 to 50% of the diet mass. The concentrations of total C, total N, soluble P, total and soluble Na, total and soluble S, total and soluble Mn, and total and soluble B in feces increased ( ≤ 0.05) while soluble N, total Ca, total and soluble Mg, soluble Zn, total and soluble Fe, total and soluble Cu decreased ( ≤ 0.02). Total P, total and soluble K, soluble Ca, and total Zn were less affected ( > 0.05). Comparing diets containing 0 to 40% SL, average daily outputs of total C, total N, soluble P, soluble K, total and soluble Na, and total Mn increased linearly ( ≤ 0.01) by 42.0, 71.2, 93.3, 45.2, 111, 148, and 52.4 percentage points, respectively. Total K, total and soluble S, soluble Mn, and total and soluble B increased quadratically ( ≤ 0.02) by 26.1, 52.3, 26.7, 147, 100, and 19.5 percentage points, respectively. Conversely, outputs of soluble Zn and total Fe decreased linearly ( ≤ 0.01), by -51.5 and -24.8 percentage points, while total Ca, total and soluble Mg, soluble Fe, and soluble Cu decreased quadratically ( ≤ 0.05) by -15.7, -12.3, -40.0, -89.9, and -60.3 percentage points, respectively. Outputs of soluble N, total P, soluble Ca, total Zn, and total Cu remained unchanged ( ≥ 0.14). Ratios of manure outputs to feed inputs for C, N, K, and B increased ( ≤ 0.02) but those for P and Mg were unchanged ( ≥ 0.10). Ratios of soluble to total manure outputs (S:O) increased ( ≤ 0.01) for P, Ca, Na, Mn; decreased ( ≤ 0.05) for N, S, Mg, Zn, Fe, Cu, and B; and were unaffected by treatment ( ≤ 0.16) for K. Decreasing S:O ratios are consistent with the formation of complexes that adsorb these nutrients to insoluble fiber fractions of manure and could thus affect mineralization rates. This study suggests that dietary tannins, found in forages like SL, can alter the concentrations, total excretion rates and throughput efficiency of nutrients in manure.
The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma
sheet (PS) (at X ∼ −7–−9 RE) allowed for the multipoint
analysis of properties and spectra of electron and proton ...injections. The
injections were observed during dipolarization and substorm current wedge
formation associated with braking of multiple bursty bulk flows (BBFs). In the
course of dipolarization, a gradual growth of the BZ magnetic field
lasted ∼ 13 min and it was comprised of several
BZ pulses or dipolarization fronts
(DFs) with duration ≤ 1 min. Multipoint observations have shown that the
beginning of the increase in suprathermal (> 50 keV) electron fluxes –
the injection boundary – was observed in the PS simultaneously with the
dipolarization onset and it propagated dawnward along with the onset-related
DF. The subsequent dynamics of the energetic electron flux was similar to the
dynamics of the magnetic field during the dipolarization. Namely, a gradual
linear growth of the electron flux occurred simultaneously with the gradual
growth of the BZ field, and it was comprised of multiple short (∼
few minutes) electron injections associated with the BZ pulses. This
behavior can be explained by the combined action of local betatron
acceleration at the BZ pulses and subsequent gradient drifts of
electrons in the flux pile up region through the numerous braking and
diverting DFs. The nonadiabatic features occasionally observed in the
electron spectra during the injections can be due to the electron
interactions with high-frequency electromagnetic or electrostatic
fluctuations transiently observed in the course of dipolarization. On the contrary, proton injections were detected only in the vicinity of the strongest BZ pulses. The front thickness of these pulses was less than a
gyroradius of thermal protons that ensured the nonadiabatic acceleration of
protons. Indeed, during the injections in the energy spectra of protons the
pronounced bulge was clearly observed in a finite energy range
∼ 70–90 keV. This feature can be explained by the
nonadiabatic resonant acceleration of protons by the bursts of the dawn–dusk
electric field associated with the BZ pulses. Keywords. Magnetospheric physics (Magnetotail; plasma sheet) – Space plasma physics (Transport processes)
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