Abstract
The whistler-mode wave is an electromagnetic wave that commonly occurs in space plasma and has been extensively studied, especially within the Earth's magnetosphere. They have also been ...reported in the near-Mars space, such as Martian upstream solar wind, crustal magnetic field, ionopause, and the magnetic reconnection ion diffusion region. However, the generation of whistler-mode waves in the Martian magnetotail current sheet is still unclear. Based on observations made by Mars Atmosphere and Volatile Evolution spacecraft, we report whistler-mode waves observed within a train of proton-scale magnetic dips during a Martian magnetotail current sheet crossing. The linear growth rate analyses demonstrate that the whistler-mode waves are locally generated within the magnetic dips. Unlike in Earth's plasma environment, the train of magnetic dips in the Martian plasma sheet is attributed to electron mirror-mode instability. Our finding suggests that the mirror-mode structure in the Martian magnetotail can be an important source region for generating whistler-mode waves. This provides a new insight into how whistler-mode waves are generated in unmagnetized planets.
Using the high‐time‐resolution data from the Magnetospheric Multiscale mission, precursor waves upstream of foreshock transient (FT) shocks are statistically investigated using the four‐spacecraft ...timing method. The wave frequencies and wave vectors determined in the plasma rest frame (PRF) are shown to follow the cold plasma dispersion relation for whistler waves. Combining with the feature of the right‐hand polarization in the PRF, the precursors are identified as whistler‐mode waves around the lower hybrid frequency. The occurrence of whistler precursors is independent of the Alfvén Mach number and the FT shock normal angle. More importantly, all the whistler precursors have group velocities pointing upstream in the shock frame, suggesting the dispersive radiation to be a possible generation mechanism. The study improves the understanding of not only the whistler precursors but also the overall FT shock dynamics.
Plain Language Summary
The characteristics of the precursor waves upstream of foreshock transient (FT) shocks are determined in the plasma rest frame using the multi‐point measurements from the Magnetospheric Multiscale mission with appropriate separation scales. The statistical results demonstrate for the first time that the precursors upstream of FT shocks are lower hybrid frequency whistler‐mode waves. The presence or absence of large amplitude whistler precursors does not depend on the FT shock normal angle and the Alfvén Mach number. These results have important implications on the nature of the whistler precursors and the dynamics of the FT shocks.
Key Points
Precursor waves upstream of foreshock transient shocks are found to follow the whistler wave dispersion relation in the plasma rest frame
The occurrence of whistler precursors is independent of the Alfvén Mach numbers and normal angles of the foreshock transient shocks
The observed wave characteristics are consistent with that the precursors are generated through the dispersive radiation mechanism
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ultra‐low‐frequency (ULF) waves emerge as pivotal factors in elucidating the mechanisms that drive the intricate dynamics of radiation belt electrons within the plasmasphere and plasmaspheric plumes. ...Utilizing THEMIS data from September 2012 to September 2017, we conducted a comprehensive statistical analysis of Pc4‐5 ULF waves within and outside the plasmaspheric plume. Our findings reveal a distinctive dawn‐dusk asymmetry in occurrence rate and wave power of poloidal mode waves in the absence of the plume, resembling the toroidal mode asymmetry observed. Poloidal mode waves exhibit a higher likelihood of formation within the plume, while the toroidal mode waves show the opposite trend, contributing to the elevated dusk‐side occurrence rate of poloidal mode waves. Moreover, both wave modes within the plume demonstrate lower peak frequencies compared to waves outside the plume. The global distribution of wave power within the plume suggests higher power at noon than on the dusk side.
Plain Language Summary
In this work, we report the statistical analysis of Pc4‐5 ULF waves both within and outside the plasmaspheric plume. We discovered a noticeable difference between the dawn and dusk sides in how often and how strongly poloidal and toroidal mode waves occur when the plasmaspheric plume is absent. Intriguingly, poloidal mode waves are more likely to form within the plume, while toroidal mode waves tend to do the opposite. This leads to a higher occurrence of poloidal mode waves on the dusk side. Additionally, both wave types within the plume have lower peak frequencies than those outside the plume. The power of both types of waves within the plasmaspheric plume, the toroidal and poloidal modes, is higher around noon compared to the dusk side. This indicates that the solar wind dynamic pressure and the plasmaspheric plume's connection with the flanks play a crucial role in creating and spreading ULF waves.
Key Points
The Pc4‐5 ULF waves in the presence and absence of plasmaspheric plume at L ∼ 6–12 are statistically studied by THEMIS satellites
The majority of waves within the plasmaspheric plume are poloidal waves, and the majority of waves outside the plasmaspheric plume are toroidal waves
The plasmaspheric plume has a significant effect on the wave properties of poloidal mode waves and toroidal mode waves
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
NASA’s Magnetospheric Multi-Scale (MMS) mission is designed to explore the proton- and electron-gyroscale kinetics of plasma turbulence where the bulk of particle acceleration and heating ...takes place. Understanding the nature of cross-scale structures ubiquitous as magnetic cavities is important to assess the energy partition, cascade and conversion in the plasma universe. Here, we present theoretical insight into magnetic cavities by deriving a self-consistent, kinetic theory of these coherent structures. By taking advantage of the multipoint measurements from the MMS constellation, we demonstrate that our kinetic model can utilize magnetic cavity observations by one MMS spacecraft to predict measurements from a second/third spacecraft. The methodology of “observe and predict” validates the theory we have derived, and confirms that nested magnetic cavities are self-organized plasma structures supported by trapped proton and electron populations in analogous to the classical theta-pinches in laboratory plasmas.
The Moon is exposed to a variety of complex space environments during its 29.5-d orbiting around Earth, of which one-quarter in Earth’s magnetosphere. The collection of particles in Earth’s ...magnetosphere is called Earth wind, which consists of the solar wind particles entering into the magnetosphere and the ions upflowing from the ionosphere and the upper atmosphere into the magnetosphere. The interaction between Earth wind and the Moon provides insights into understanding the evolution of the whole Earth–Moon system and other planet–moon systems such as Mars, Jupiter, Saturn, and their satellites. The key scientific questions on the Earth wind and the Moon are reviewed and summarized. Finally, the several unaddressed issues and the possible resolution in the Earth wind–Moon interactions are discussed.
•Geomagnetic field reversal substantially weakens the protection for the atmosphere.•Solar wind energizes more oxygen ions to escape when geomagnetic field is weakened.•Oxygen escape may explain the ...drop of atmospheric level during mass extinction.•The causal relation between reversal and mass extinction should be “many-to-one”.•The simulated oxygen escape rate based on knowledge of Mars support our hypothesis.
The evolution of life is affected by variations of atmospheric oxygen level and geomagnetic field intensity. Oxygen can escape into interplanetary space as ions after gaining momentum from solar wind, but Earth's strong dipole field reduces the momentum transfer efficiency and the ion outflow rate, except for the time of geomagnetic polarity reversals when the field is significantly weakened in strength and becomes Mars-like in morphology. The newest databases available for the Phanerozoic era illustrate that the reversal rate increased and the atmospheric oxygen level decreased when the marine diversity showed a gradual pattern of mass extinctions lasting millions of years. We propose that accumulated oxygen escape during an interval of increased reversal rate could have led to the catastrophic drop of oxygen level, which is known to be a cause of mass extinction. We simulated the oxygen ion escape rate for the Triassic–Jurassic event, using a modified Martian ion escape model with an input of quiet solar wind inferred from Sun-like stars. The results show that geomagnetic reversal could enhance the oxygen escape rate by 3–4 orders only if the magnetic field was extremely weak, even without consideration of space weather effects. This suggests that our hypothesis could be a possible explanation of a correlation between geomagnetic reversals and mass extinction. Therefore, if this causal relation indeed exists, it should be a “many-to-one” scenario rather the previously considered “one-to-one”, and planetary magnetic field should be much more important than previously thought for planetary habitability.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Coronal mass ejection (CME)‐driven or corotating interaction region (CIR)‐driven storms can change the electron distributions in the radiation belt dramatically, which can in turn affect the ...spacecraft in this region or induce geomagnetic effects. The Van Allen Probes twin spacecraft, launched on 30 August 2012, orbit near the equatorial plane and across a wide range of L∗ with apogee at 5.8 RE and perigee at 620 km. Electron data from Van Allen Probes MagEIS and REPT instruments have been binned every 6 h at L∗=3 (defined as 2.5 < L∗<3.5), 4 (3.5 < L∗<4.5), 5 (4.5 < L∗<5.5). The superposed epoch analysis shows that (1) CME storms induce more electron flux enhancement at L∗=3 for energy channels below 1 MeV than CIR storms; (2) CME storms induce more electron flux enhancement at L∗=4 and 5 in the energy channels above 1 MeV than CIR storms; (3) CIR storms induce more electron flux enhancement at L∗=4 and 5 in the energy channels below 1 MeV than CME storms; (4) intense CME induce more than 50 times flux enhancement for the energy channel around 400 keV at L∗=3; (5) intense CIR induce more than 50 times flux enhancement for the energy channel around 200 keV at L∗=4. These results are consistent with a general picture of enhanced convection over a longer period for CIR storms which increased flux closer to geosynchronous orbit consistent with earlier studies, while CME storms likely produce deeper penetration of enhanced flux and local heating which is greater at higher energies at lower L∗.
Key Points
CME‐ and CIR‐driven storm time outer radiation belt evolutions are studied during Van Allen Probe era
Van Allen Probe measures wide energy span of the belt near the equatorial plane
Differences of trapped RB electrons evolutions during CME‐ and CIR‐driven storms have been concluded at wide energy span and L shells
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here we statistically analyze ~1 eV ...to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L shells except for dawn sector; (2) a bidirectional field‐aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly, and isotropic distributions depending on their energy, MLT, and L shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L shell increases, which is primarily caused by adiabatic transport. Furthermore, energetic H+ (>10 keV) PADs become more isotropic following the substorm injections, indicating wave‐particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
Key Points
We performed a statistics of H+ PADs based on 4 years VAP data and identified four distinct populations in energy range of 1 eV to 600 keV
Plasmaspheric H+ shows pancake PADs at low L; warm plasma cloak are field aligned; more energetic H+ PADs depend on energy, MLT, and L shell
Energetic H+ PADs become more isotropic following the substorm injections, indicating wave‐particle interactions
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Kelvin‐Helmholtz waves (KHWs), which have been widely observed at the magnetopause in the region near the Earth, play an essential role in the transport of solar wind plasma and energy into the ...magnetosphere under dominantly northward interplanetary magnetic field (IMF) conditions. In this study, we present simultaneous observations of KHWs under the northward IMF observed by both the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft in the Earth's magnetotail around the lunar orbit (at X ~ −50RE, Y ~ 30RE, dusk side) and the Geotail in the near‐Earth space (at X ~ −5RE, Y ~ −10RE, dawn side). The KHWs are quantitatively characterized by their dominant period, phase velocity, and wavelength, utilizing wavelet analysis and an approximation of their center‐of‐mass velocity. Our results suggest that the phase velocity and spatial scale of KHWs may increase as they propagate along the boundary layer toward the tail. Alternatively, the differences between the ARTEMIS and Geotail observations may indicate the possibility of dawn‐dusk asymmetry in the excited KHWs in this study. Our results strongly evidence the existence of the development of KHWs in terms of their wave frequency and scale size in the magnetotail and provide insight to the time evolution of KHWs along the magnetopause.
Key Points
Simultaneous observations of KHWs in the midtail and the near‐Earth space
KHWs possibly increase their sizes toward the tail
Potential evidence of dawn‐dusk asymmetry in the KHWs
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
The solar wind can directly interact with the lunar surface and provide an important source for surface space weathering and water generation. Here we study the solar wind implantation flux ...on the lunar surface with global Hall MHD simulations. The shielding effects of both the Earth’s magnetosphere and lunar magnetic anomalies are considered. It is found that a large-scale lunar mini-magnetosphere can be caused by the solar wind interaction with the magnetic anomalies on the lunar far side, which causes a large shielding area on the surface. In addition, the Earth’s magnetosphere brings a longitudinal variation in the implantation flux, with minimum fluxes at 0° longitude. With the integrated flux over a lunation, we find that there are some local cavities on the implantation flux map, which are colocated with both the magnetic anomalies and the lunar swirls. Further studies show that there is a south–north asymmetry in the implantation flux, which can be used to explain the lower water content observed in the southern hemisphere. Our results provide a global map of the solar wind implantation flux on the lunar surface and are useful for evaluating the large-scale effect of solar wind implantation and sputtering on the space weathering and the water or gas generation of the surface.
PDF
