Inner magnetosphere coupling: Recent advances Usanova, M. E.; Shprits, Y. Y.
Journal of geophysical research. Space physics,
January 2017, 2017-01-00, 20170101, Letnik:
122, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The dynamics of the inner magnetosphere is strongly governed by the interactions between different plasma populations that are coupled through large‐scale electric and magnetic fields, currents, and ...wave‐particle interactions. Inner magnetospheric plasma undergoes self‐consistent interactions with global electric and magnetic fields. Waves excited in the inner magnetosphere from unstable particle distributions can provide energy exchange between different particle populations in the inner magnetosphere and affect the ring current and radiation belt dynamics. The ionosphere serves as an energy sink and feeds the magnetosphere back through the cold plasma outflow. The precipitating inner magnetospheric particles influence the ionosphere and upper atmospheric chemistry and affect climate. Satellite measurements and theoretical studies have advanced our understanding of the dynamics of various plasma populations in the inner magnetosphere. However, our knowledge of the coupling processes among the plasmasphere, ring current, radiation belts, global magnetic and electric fields, and plasma waves generated within these systems is still incomplete. This special issue incorporates extended papers presented at the Inner Magnetosphere Coupling III conference held 23–27 March 2015 in Los Angeles, California, USA, and includes modeling and observational contributions addressing interactions within different plasma populations in the inner magnetosphere (plasmasphere, ring current, and radiation belts), coupling between fields and plasma populations, as well as effects of the inner magnetosphere on the ionosphere and atmosphere.
Key Points
The dynamics of the inner magnetosphere is strongly governed by the interactions between different plasma populations
Our understanding of the coupling processes in the magnetosphere is still incomplete
This special issue contains a collection of papers advancing our knowledge of the processes affecting the inner magnetosphere
We report observations of a Bursty Bulk Flow (BBF) penetrating close to the outer edge of the radiation belt. The turbulent BBF braking region is characterized by ion velocity fluctuations, magnetic ...field (B) variations, and intense electric fields (E). In this event, energetic (>100 keV) electron and ion fluxes are appreciably enhanced. Importantly, fluctuations in energetic electrons and ions suggest local energization. Using correlation distances and other observed characteristics of turbulent E, test‐particle simulations support local energization by E that favors higher‐energy electrons and leads to an enhanced energetic shoulder and tail in the electron distributions. The energetic shoulder and tail could be amplified to MeV energies by adiabatic transport into the radiation belt where |B| is higher. This analysis suggests that turbulence generated by BBFs can, in part, supply energetic particles to the outer radiation belt and that turbulence can be a significant contributor to particle acceleration.
Plain Language Summary
Bursty Bulk Flows are thought to be the earthward‐traveling exhaust from magnetic reconnection events in the Earth's magnetotail. These plasma flows slow and divert as they approach Earth and, in doing so, can generate strong plasma turbulence. The electric field turbulence, in turn, appears to energize electrons and ions. The primary finding of this research is that the electron energization favors electrons that already have high energy, and therefore results in "acceleration" in which a relatively few particles receive a disproportionate share of the energy. Furthermore, turbulent regions of bursty bulk flows are shown to penetrate to the edge of the outer radiation belt. As such, bursty bulk flows are potentially a significant source or seed population for radiation belt electrons.
Key Points
A bursty bulk flow near the outer radiation belt displays turbulent electric fields and enhanced fluxes of energetic ions and electrons
Electrons appear to be locally accelerated by turbulent electric fields forming an energetic shoulder in the distribution
Turbulent electric fields in the Bursty Bulk Flow braking region favors energization of the highest energy electrons
On 11 October 2012, during the recovery phase of a moderate geomagnetic storm, an extended interval (> 18 h) of continuous electromagnetic ion cyclotron (EMIC) waves was observed by Canadian Array ...for Real‐time Investigations of Magnetic Activity and Solar‐Terrestrial Environment Program induction coil magnetometers in North America. At around 14:15 UT, both Van Allen Probes B and A (65° magnetic longitude apart) in conjunction with the ground array observed very narrow (ΔL ~ 0.1–0.4) left‐hand polarized EMIC emission confined to regions of mass density gradients at the outer edge of the plasmasphere at L ~ 4. EMIC waves were seen with complex polarization patterns on the ground, in good agreement with model results from Woodroffe and Lysak (2012) and consistent with Earth's rotation sweeping magnetometer stations across multiple polarization reversals in the fields in the Earth‐ionosphere duct. The narrow L‐widths explain the relative rarity of space‐based EMIC occurrence, ground‐based measurements providing better estimates of global EMIC wave occurrence for input into radiation belt dynamical models.
Key Points
Continuous EMIC waves confined to narrow L‐shells near plasma density gradients
The narrow L‐widths explains low in‐situ EMIC occurrence
Ground measurements provide better estimates of global EMIC wave occurrence
Up until recently, signatures of the ultrarelativistic electron loss driven by electromagnetic ion cyclotron (EMIC) waves in the Earth's outer radiation belt have been limited to direct or indirect ...measurements of electron precipitation or the narrowing of normalized pitch angle distributions in the heart of the belt. In this study, we demonstrate additional observational evidence of ultrarelativistic electron loss that can be driven by resonant interaction with EMIC waves. We analyzed the profiles derived from Van Allen Probe particle data as a function of time and three adiabatic invariants between 9 October and 29 November 2012. New local minimums in the profiles are accompanied by the narrowing of normalized pitch angle distributions and ground‐based detection of EMIC waves. Such a correlation may be indicative of ultrarelativistic electron precipitation into the Earth's atmosphere caused by resonance with EMIC waves.
Key Points
Formation of local minimums in phase space density profiles of ultrarelativistic electrons coincides with EMIC wave occurrence
New local minimums are accompanied by narrowing of normalized pitch angle distributions
The local minimums are indicative of EMIC wave‐induced loss in the heart of the outer belt
The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror ...structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies.
Physical mechanisms of compressional EMIC wave growth McCollough, J. P.; Elkington, S. R.; Usanova, M. E. ...
Journal of Geophysical Research: Space Physics,
October 2010, Letnik:
115, Številka:
A10
Journal Article
Recenzirano
Odprti dostop
On 29 June 2007, electromagnetic ion cyclotron (EMIC) waves were observed on the ground by the Canadian Array for Realtime Investigations of Magnetic Activity (CARISMA) network of magnetometers ...between L = 4 and L = 6 in response to a significant magnetospheric compression. Here a new MHD/particle method for studying EMIC wave growth in the magnetosphere is used to provide a detailed study of the compression event. We compare equatorial field line crossings of NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and CARISMA observation sites to frequency‐integrated wave growth rates from the MHD/particle method. Simulated temperatures were constant in time, suggesting an absence of energizing processes during this event. Many particles experienced so‐called Shabansky orbits during this event, in which their drift motion was confined to high latitudes in the dayside magnetosphere. We propose a new nonenergizing process, driven by ions undergoing Shabansky orbits, for generating ion temperature anisotropies. In addition, the fundamental role of the plasmasphere in generating EMIC waves from the free energy of warm ion temperature anisotropies is discussed.
Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on ...properties of these waves and present events from the main phase of two storms on 1 November 2012 and 17 March 2013 and associated dropouts of a few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 to several Hz, and amplitude ~0.1 to a few nT in magnetic and ~0.1 to a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron waves, which are believed to contribute to loss of ring current ions and radiation belt electrons and therefore can be also important for inner magnetosphere dynamics.
Key Points
Oxygen cyclotron harmonic waves are often observed during the main phase of geomagnetic storms
For the first time, we report observations of parallel propagating oxygen harmonic waves with properties similar to those of EMIC waves
These waves can contribute to loss of energetic particles in the ring current and radiation belts
Ionospheric irregularities associated with horizontal magnetic fields below 200 km altitude are observed at Mars. Plasma density modulations of up to 200% are observed during such events and appear ...correlated with fluctuations in the magnetic field. The observed fluctuations are likely Doppler shifted and represent spatial structures at length scales of 15–20 km or less. Conditions in the Martian ionosphere below 200 km are synonymous with the terrestrial E region, where ionospheric irregularities have been extensively studied. Interestingly, the irregularities at Mars appear to be electromagnetic in nature, in contrast to the electrostatic nature of irregularities at Earth. It is currently unclear what the primary drivers of these irregularities at Mars are, and further study is needed to explain these important phenomenon within the Martian ionosphere.
Key Points
Example of ionospheric irregularities in the Martian ionosphere below 200 km altitude is presented
Statistical analysis of similar events shows peak occurrences at dawn and dusk
Cause of irregularities is unclear, particularly as irregularities appear to be electromagnetic in nature
This study presents analysis of very low frequency (VLF) transmitter signal measurements on the Very‐Low‐Frequency Propagation Mapper (VPM) CubeSat in low‐Earth orbit. Six months of satellite ...operation provided good data coverage, used to build global statistical maps of VLF power distribution. The power distribution above four powerful transmitters is used as input for ray tracing to study signal propagation to the conjugate hemisphere in two plasmaspheric density models. The ray tracing results are further compared with VPM measurements to determine which model provides better agreement with observations. As ray propagation largely depends on the background plasma density distribution, this indirect method can be used for plasmaspheric density model validation as an alternative to multipoint in situ plasma measurements that may not be readily obtainable. In addition, it can be used to investigate Landau damping and ducted versus non‐ducted propagation of VLF signals.
Plain Language Summary
Very low frequency (VLF) transmitter signals at frequencies in the tens of kHz, used for military communication with submerged submarines, can be used to determine the plasma density distribution in near‐Earth space. Here we demonstrate how a combination of VLF antenna measurements from low‐Earth orbit and numerical modeling of VLF signal propagation can be applied to constrain plasma density profiles in the magnetosphere. This is an indirect method that can be used for plasmaspheric density model validation as an alternative to multipoint in situ plasma measurements that may not be readily obtainable.
Key Points
At L < 3, the Diffusive Equilibrium plasmasphere model provides much better agreement with observations than the Global Core Plasma Model
Signals from selected transmitters at L = 1.17–2.87 propagate primarily in a non‐ducted mode
Landau damping is insignificant for the selected transmitters
Near‐Earth plasma surges sunward during enhanced magnetospheric convection (driven by dayside magnetic reconnection) to form a pathway feature called a plasmaspheric plume. This study uses ...Magnetospheric Multiscale (MMS) observations to investigate the heating of warm ions (H+ and He+) inside plumes. We identify 287 plume events using targeted in‐situ‐observational criteria and plasmapause test particle simulations. One plume‐crossing event by MMS shows that the scalar temperatures of warm He+ increase from ∼10 to ∼40 eV during simultaneous observations of helium‐band electromagnetic ion cyclotron (EMIC) waves, while H+ temperature is almost constant. Next, we analyze all individual observations to investigate warm‐ion heating and its possible association with EMIC waves. The statistical results show that EMIC waves associated with the plume have left‐hand polarizations and small normal angles and the temperatures of warm He+ are always higher than those of warm H+. Also, the minimum resonant energies for H+ are mostly above 100 eV, whereas 17% of warm He+ observations show that they can interact with the H+‐band EMIC waves via cyclotron resonance. These observations suggest that while EMIC waves play a role, there is an unknown mechanism for warm‐ion heating inside the plume that requires more investigation.
Key Points
Warm He+ heating inside the plasmaspheric plume results from the interaction with electromagnetic ion cyclotron (EMIC) waves
Coincident with plumes and EMIC waves, warm He+ is more heated than warm H+
Statistical results indicate that resonant interactions with EMIC waves are insufficient to account for all the observed warm ion heating
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