In this Letter we introduce a generalization of the Lorenz dynamical system using fractional derivatives. Thus, the system can have an effective noninteger dimension Sigma defined as a sum of the ...orders of all involved derivatives. We found that the system with Sigma<3 can exhibit chaotic behavior. A striking finding is that there is a critical value of the effective dimension Sigma(cr), under which the system undergoes a transition from chaotic dynamics to regular one.
The Val66Met, G196A (rs6265) polymorphism in the brain‐derived neurotrophic factor gene, BDNF, located at 11p13, has been associated with a wide range of cognitive functions. Yet, the pattern of ...results is complex and conflicting. In this study, we conducted a meta‐analysis that included 23 publications containing 31 independent samples comprised of 7095 individuals. The phenotypes that were examined in this analysis covered a wide variety of cognitive functions and included indicators of general cognitive ability, memory, executive function, visual processing skills and cognitive fluency. The meta‐analysis did not establish significant genetic associations between the Val66Met polymorphism and any of the phenotypes that were included.
The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial ...distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn‐dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (Pdyn) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near‐Earth duskside during disturbed geomagnetic conditions, enhanced SW Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near‐Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models.
Key Points
The spatial distributions of energetic O+ and H+ are established
Effective inductive acceleration is located at the near‐Earth duskside
Higher energetic ion losses in the day plasma sheet under disturbed conditions
An asymmetrical pileup of the interplanetary magnetic field leads to an additional draping of the field lines in the opposite direction to the motional electric field. Such a draping and the ...associated magnetic field forces push the ionosphere plasma in the transverse direction opening a passage for an ion trail which contains dense and slowly moving plasma. We found that wrapping of the field lines around Mars starts in the hemisphere pointing in the direction of the motional electric field and propagates to the opposite hemisphere where the cross‐flow component of the draped interplanetary magnetic field changes sign in a broad area accompanied by the formation of loops of closed field lines. Reconnection near Mars accompanied by the generation of plasma vortices imposes serious constraints on the ion dynamics and their escape through the tail. The existence of all these features is confirmed by hybrid simulations.
Key Points
Additional draping of the field lines in the opposite direction to the motional electric field appears
Ion trail that contains dense and slowly moving tailward plasma arises
Wrapping of the field lines is accompanied by the formation of loops of closed field lines and plasma vortices
Using burst mode Magnetospheric Multiscale (MMS) observations in the plasma sheet (PS), we study the dynamics of electron anisotropy and its relation to quasi‐parallel narrowband whistler bursts in ...37 dipolarization fronts (DFs) propagating in the Earth's magnetotail along with fast flows at −25 RE ≤ X ≤ −17 RE. The bursts were observed at the DFs and behind them in the dipolarizing flux bundle (DFB) region with frequencies fpeak ~ (0.1–0.6) fce ( fce is electron gyrofrequency) and durations approximately a few seconds. The majority of the whistler waves were associated with perpendicular electron temperature anisotropy TPER/TPAR > 1, and the value of this anisotropy decreased by the end of the bursts suggesting electron scattering by the waves. We found that the major contribution to the growth rate of whistler waves is made by resonant electrons with energies Wres ~ 1–5 keV and pitch angles αres ~ 40–75° and ~100–135°. In the majority of cases, the largest Wres was observed at the DF and immediately behind it, while in the DFB the Wres decreased. The sources of the majority of whistler bursts were not confined near the neutral plane but could be extended into the PS where the perpendicular anisotropy of the local electron distribution provided the positive growth rate of the whistler waves. We show that the observed whistler waves play a significant role in the dynamics of electron velocity distribution in DFs, leading to energy exchange between various parts of electron population and constraining temperature anisotropy of electron distribution.
Key Points
Electron distribution function is highly variable on time scales of short narrowband quasi‐parallel whistler bursts at and behind DFs
Electrons with energies 1–5 keV and pitch angles ~40–75° and 100–135° make the major contribution to the growth rate of these waves
The source of the wave bursts is spread out in space and not confined near the neutral plane
According to various orientation of the interplanetary magnetic field (IMF), the planetary shock can be either quasi‐parallel or quasi‐perpendicular. Under quasi‐parallel conditions a significant ...number of solar wind suprathermal particles are reflected from the shock and drift along IMF, forming an extended and highly turbulent region called the foreshock where various nonlinear plasma phenomena are observed. In this research, a case study of the structures in the foreshock region at Mars as observed by Mars Atmosphere and Volatile Evolution is performed close to Martian aphelion, when the foreshock wave activity is usually low. Data from plasma analyzer STATIC and magnetometer MAG is used to analyze ion beams angular spectrum and magnetic field dynamics. It is shown that the observed structures are consistent with Short Large‐Amplitude Magnetic Structures (SLAMS), commonly detected in foreshock regions of magnetized and unmagnetized bodies throughout the Solar system. Finally, the Alfven Mach number is calculated to analyze characteristics of the observed foreshock structures. The analysis shows that the observed SLAMS‐like structures at Mars are steepened waves formed by the ion cyclotron resonance between plasma waves propagating along the IMF and the back‐streaming scattered solar wind H+ and exospheric O+ and O2+ ions, with the dominant impact of O+ ions. The steepening process is accompanied with observation of gradients in the diffuse ion density near the bowshock, like it has been previously reported near the Earth (e.g., Scholer, 1993, https://doi.org/10.1029/92JA01875; Tsubouchi & Lembege, 2004, https://doi.org/10.1029/2003JA010014).
Key Points
SLAMS‐like structures are for the first time reported to be observed in the Martian foreshock close to planetary aphelion
Fluxes of back‐streaming O+ and O2+ ions accelerated up to ∼650 eV are observed between the structures
Magnetic field frequency spectra in the region shows maximum close to O+ gyro frequency
The dissipation processes which transform electromagnetic energy into kinetic particle energy in space plasmas are still not fully understood. Of particular interest is the distribution of the ...dissipated energy among different species of charged particles. The Jovian magnetosphere is a unique laboratory to study this question because outflowing ions from the moon Io create a high diversity in ion species. In this work, we use multispecies ion observations and magnetic field measurements by the Galileo spacecraft. We limit our study to observations of plasmoids in the Jovian magnetotail, because there is strong ion acceleration in these structures. Our model predicts that electromagnetic turbulence in plasmoids plays an essential role in the acceleration of oxygen, sulfur, and hydrogen ions. The observations show a decrease of the oxygen and sulfur energy spectral index γ at ∼30 to ∼400 keV/nuc with the wave power indicating an energy transfer from electromagnetic waves to particles, in agreement with the model. The wave power threshold for effective acceleration is of the order of 10 nT2Hz−1, as in terrestrial plasmoids. However, this is not observed for hydrogen ions, implying that processes other than wave‐particle interaction are more important for the acceleration of these ions or that the time and energy resolution of the observations is too coarse. The results are expected to be confirmed by improved plasma measurements by the Juno spacecraft.
Key Points
Ions are accelerated effectively by plasmoids in the Jovian magnetosphere
Plasmoids with higher electromagnetic turbulence lead to stronger acceleration of oxygen and sulfur ions
Acceleration of hydrogen ions is not correlated with wave power, possibly because of limitations in observations
The Magnetospheric Multiscale spacecraft observations in the burst mode allow the determination of the characteristics of resonant electrons interacting with quasi‐parallel whistler waves during ...prolonged dipolarizations in the near Earth magnetotail at −22 RE < X ≤ −8 RE. We have detected 163 whistler bursts observed during 48 dipolarization events. The bursts were registered within ∼13 min following the dipolarization onset when the burst mode observations were available. In the majority of events, electrons with energies Wres ≥ 10 keV and pitch angles αres ∼ 100°–130° and αres ∼ 50°–80°made the maximum positive contribution to the growth rate of whistler waves propagating quasi‐parallel and antiparallel to the ambient magnetic field, respectively. Our analysis shows that electrons with Wres ∼ 10–20 keV could potentially be scattered into the loss cone by the low frequency whistler waves with fw ∼ (0.05–0.2)fce (fw is the wave frequency and fce is the electron gyrofrequency). The electrons that are scattered into the loss cone can contribute to electron precipitation within ∼13 min following the dipolarization onset. We suggest that whistler waves that are excited due to cyclotron instability driven by the temperature anisotropy of suprathermal electrons (≥2 keV) may, in turn, affect electron distribution in this energy range. Specifically, lower energy resonant electrons transfer a part of their kinetic energy to waves, while more energetic electrons absorb wave energy increasing their kinetic energy. This may lead to the transformation of higher‐energy part of electron distribution from Maxwellian to the power law shape.
Plain Language Summary
Magnetic dipolarization is an important process in the magnetotail dynamics which manifests in transformation of initially stretched tail‐like configuration into the dipole‐like configuration. The dipolarization is followed by various processes of energy dissipation and transformation including plasma heating and acceleration as well as generation of different wave modes. In collisionless plasma, wave‐particle interactions play a key role in energy exchange between different populations of plasma particles. Also particle interactions with waves may cause particle scattering into the loss cone and their precipitation in the auroral region. The processes of wave‐particle interactions usually occur at very short time scales, and their investigation “in situ” requires observations with high time resolution. In this study, we use the Magnetospheric Multiscale spacecraft observations in burst mode and determine the characteristics of resonant electrons interacting with quasi‐parallel whistler waves at time scales of the order of a few seconds. We have found that quasi‐parallel whistler waves can be generated in the course of dipolarization due to cyclotron instability driven by the temperature anisotropy of suprathermal electrons (≥2 keV). Once have been generated, these waves, in turn, affect electron distribution in this energy range. Specifically, lower energy resonant electrons transfer a part of their kinetic energy to waves, while more energetic electrons absorb wave energy increasing their kinetic energy. We also found that some fraction of suprathermal electrons can be potentially scattered into the loss cone by the low‐frequency whistler waves. Such electrons can contribute to electron precipitation within ∼13 min following the dipolarization onset.
Key Points
Perpendicular anisotropy of electrons with energies more than 10 keV is responsible for whistler waves generation during dipolarizations
Whistler waves play an important role in energy exchange between different parts of electron spectrum in energy range more than 2 keV
Electrons with energies 10–20 keV can be scattered into the loss cone due to their interaction with the low‐frequency whistler waves
Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the ...magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter’s magnetotail provides an almost ideal environment to study high‐energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high‐energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts.
Key Points
Eighty‐seven prominent dipolarization front signatures are observed in the MAG data during Juno's prime mission during 21:00–05:30 local time
Less than half of the identified events are accompanied by an increase of the ion intensities
In 40% of the events observed on the dawn side a significant decrease of the energy spectral index indicates ion acceleration by the fronts
We study energetic spectra of H+, He+, and O+ ion fluxes in the energy range ≥130 keV measured by Cluster/Research with Adaptive Particle Imaging Detectors (RAPID) instruments during 37 intervals of ...the tailward bulk flow propagation in the near‐Earth tail (at X ≤ −19 RE). In all events from our database, the plasmoid‐like magnetic structures with the superimposed low‐frequency magnetic and electric field fluctuations were observed along with the tailward bulk flows. The plasmoid‐like structures were associated with the enhancements of energetic ion fluxes and the hardening of energy spectra of H+ and He+ ion components in 80% of events and of O+ ion component in 64% of events. The hardening of energy spectra was more pronounced for heavy ions than for protons. The analysis of the magnetic structures and power spectral density (PSD) of the magnetic and electric field fluctuations from our database revealed the following factors favorable for the ion energization: (1) the spatial scale of a plasmoid should exceed the thermal gyroradius of a given ion component in the neutral plane inside the plasmoid; (2) the PSD of the magnetic fluctuations near the gyrofrequency of a particular ion component should exceed ~ 50.0 nT2/Hz for oxygen ions; while the energization of helium ions and protons takes place for much lower values of the PSD. The kinetic analysis of ion dynamics in the plasmoid‐like magnetic configuration similar to the observed one with the superimposed turbulence confirms the importance of ion resonant interactions with the low‐frequency electromagnetic fluctuations for ion energization inside plasmoids.
Key Points
Spectra of energetic H+, He+, O+ fluxes were studied tailward of X line
Strong ion acceleration occurs in turbulent region inside plasmoids
Ions are accelerated due to resonant interaction with EM fluctuations
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