Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on ...particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L‐shell (MLT‐L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
Key Points
A statistical study of EMIC waves is conducted over all MLATs and MLTs
Off‐equator peaks in wave occurrence are observed in the outer magnetosphere
Wave ellipticity, normal angle, propagation angle, and wave power are also investigated
We use the Solar, Anomalous, and Magnetospheric Particle Explorer to explore the relationship between microbursts and global flux decay of electrons from the outer Van Allen belt during the recovery ...phase of geomagnetic storms. We investigate the correlation between microbursts and global electron loss in each of the quasi‐trapped (drift loss cone), stably trapped, and untrapped electron (bounce loss cone) populations. For the quasi‐trapped electrons, we separately classify the storms as driven by coronal mass ejections or corotating interaction regions and explore their connection to microburst loss. We find that the decay lifetime of electron fluxes, that is, e‐folding times of macroscopic fluxes in the recovery phase is correlated with strong microburst activity. That is, when the microburst activity is high, global flux decay times are short, and vice versa, suggesting a cross‐scale coupling between microloss and macroloss phenomena. Furthermore, we find that the microburst to global loss coupling is predominant in the quasi‐trapped population of radiation belt electrons while having negligible influence on the untrapped and stably trapped populations. We find that microburst activity during storms driven by coronal mass ejections is coupled more strongly with global flux decay as compared with corotating interaction regions. In addition, we find that distance from the plasmapause is likely a better indicator of microburst location than L‐shell, with most microbursts occurring ~0.5–2.0 L from the model plasmapause location.
The solar energetic particle (SEP) populations of electrons and ions are highly variable in space and time, in intensity, energy, and composition. Over the last ~20 years advanced instrumentation ...onboard many spacecraft (e.g. ACE, Coronas, GOES, Hinode, RHESSI, SAMPEX, SDO, SOHO, STEREO, TRACE, Ulysses, Yokoh, to name a few) extended our ability to explore the characteristics of solar energetic particles by in-situ measurements in interplanetary space and by observing their source characteristics near the Sun by remote-sensing observation of electromagnetic emission over a wide frequency range. These measurements provide crucial information for understanding the sources of the particle populations and the acceleration and propagation processes involved. We are now able to measure intensity-time profiles and anisotropies, energy spectra, elemental and isotopic abundances, and the ionic charge of particles over an extended energy range of 0.01 to several 100 MeV/nuc and for a large dynamic range of particle intensities. Furthermore, multi-spacecraft in-situ observations at different solar longitudes and latitudes provide new insight into the acceleration and propagation processes of SEPs near the Sun and in interplanetary space. In this paper we present an overview of SEP observations, their implications for SEP acceleration and propagation processes, and discuss open questions.
We investigate the combined effects of solar energetic particle propagation, parallel and perpendicular to the large-scale magnetic field in the solar wind. Numerical methods employing stochastic ...differential equations are used incorporating pitch-angle diffusion, focusing, and pitch-angle-dependent diffusion perpendicular to the magnetic field. We compute spatial distributions of approx100 keV electrons and 4 MeV protons in the inner heliosphere, assuming impulsive injection near the Sun over a limited range of solar longitude and latitude. In addition, spatial distributions and intensity-time profiles for various combinations of the parallel and perpendicular mean free path, with different assumptions for the dependence of lambda{sub perpendicular} on the radial distance and pitch angle, are investigated. We find that realistic results can be obtained when we assume that the perpendicular mean free path scales in the inner heliosphere with the gyroradius of the particles. Step-like decreases of particle intensities as frequently observed in impulsive events at 1 AU can be reproduced for a ratio of lambda{sub perpendicular}/lambda{sub ||} a few times 10{sup -5}.
Geomagnetic storms are primarily driven by stream interaction regions (SIRs) and coronal mass ejections (CMEs). Since SIR and CME storms have different solar wind and magnetic field characteristics, ...the magnetospheric response may vary accordingly. Using FAST/TEAMS data, we investigate the variation of ionospheric O+ and H+ outflow as a function of geomagnetic storm phase during SIR and CME magnetic storms. The effects of storm size and solar EUV flux, including solar cycle and seasonal effects, on storm time ionospheric outflow, are also investigated. The results show that for both CME and SIR storms, the O+ and H+ fluences peak during the main phase, and then declines in the recovery phase. However, for CME storms, there is also significant increase during the initial phase. Because the outflow starts during the initial phase in CME storms, there is time for the O+ to reach the plasma sheet before the start of the main phase. Since plasma is convected into the ring current from the plasma sheet during the main phase, this may explain why more O+ is observed in the ring current during CME storms than during SIR storms. We also find that outflow fluence is higher for intense storms than moderate storms and is higher during solar maximum than solar minimum.
Key Points
Both coronal mass ejection (CME) and stream interaction region (SIR) storms have their maximum O+ and H+ outflow during the main phase, and a decrease during the recovery phase
During CME storms, the outflow increases during the initial phase, while during SIR storms it doesn’t increase until the main phase
This difference in outflow timing may explain why more O+ is observed in the ring current during CME storms than during SIR storms
This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10 years (2001–2010) of Cluster observations. In the first paper, ...an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)‐distance as well as magnetic local time (MLT)‐L frames. This paper focuses on the distribution of EMIC wave‐associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H+ anisotropy, electron and hot H+ density measurements, hot H+ parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well‐known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off‐equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere.
Key Points
A statistical study of EMIC waves is conducted using 10 years of Cluster observations
EMIC wave‐associated plasma conditions along with two wave generation proxies are analyzed
A high L shell region favorable for wave generation is observed for a broad range in MLATs
Solar particle events that are rich in 3He typically also exhibit large overabundances of heavy and ultraheavy ions that increase with the mass of the ions. To explain these observations we apply our ...charge-consistent acceleration model, which takes into account the acceleration efficiency as a function of the charge to mass ratio of the ion, as well as the charge-dependent Coulomb energy losses, to consider the acceleration of ions within a wide range of their nuclear charge. Because the considerations of particle acceleration were restricted so far by tabulated values of ionization and recombination coefficients that were available only for a limited set of ions, we make use of our method developed earlier and calculate the rates of ions resembling the three representative mass groups of ultraheavy ions. We demonstrate that smaller Coulomb losses together with higher acceleration efficiency result in the enhancements of heavy and ultraheavy ions, in accordance with recent observations. We also conclude that the existing measurements of ultraheavy ions in impulsive solar energetic particle events provide evidence in favor of a magnetic turbulence in the acceleration region with spectral index S ≥ 2.
Magnetospheric plasma sheet ions drift toward the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface, and this ...disturbance strongly affects the strength of a magnetic storm. The contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure in the near‐Earth plasma sheet is not always considered. In this study, we evaluate the contribution of low‐energy and energetic ions of different species to the total plasma pressure for the storm observed by the Cluster mission from 27 September until 3 October 2002. We show that the contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure is ≃76–98.6% in the ring current and ≃14–59% in the magnetotail. The main source of oxygen ions, responsible for ≃56% of the plasma pressure of the ring current, is located at distances earthward of XGSE ≃ −13.5 RE during the main phase of the storm. The contribution of the ring current particles agrees with the observed Dst index. We model the magnetic storm using the Space Weather Modeling Framework (SWMF). We assess the plasma pressure output in the ring current for two different ion outflow models in the SWMF through comparison with observations. Both models yield reasonable results. The model which produces the most heavy ions agrees best with the observations. However, the data suggest that there is still potential for refinement in the simulations.
Plain Language Summary
Magnetospheric plasma sheet ions drift toward the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface and strongly affects the strength of a magnetic storm. The contribution of energetic ions and of heavy ions to the total plasma pressure in the near‐Earth plasma sheet is not always considered. In this study, we evaluate the input of these components for the storm observed from 27 September until 3 October 2002 using observations by the Cluster mission. We compare the results with simulations from the Space Weather Modeling Framework which take into account ionospheric ion outflow. We show that neglecting the contribution of energetic ions and of heavy ions to the total plasma pressure can lead to the pressure underestimations of 76–98.6% in the ring current and 14–59% in the magnetotail. We find that it is important to consider heavy ions, especially ionospheric oxygen, and include the energetic part of the ion distribution in the simulations of the ring current and the magnetotail during the magnetic storm.
Key Points
The contribution of ions of different species to the total plasma pressure in the near‐Earth magnetosphere is estimated
The ability of the Space Weather Modeling Framework to reproduce the plasma pressure during a magnetic storm is tested
The main source of oxygen ions is located at distances closer than XGSE = −13.5 RE during the main phase
We have used the ion composition data from the CIS/CODIF instrument on Cluster to determine how the O+ population in the plasma sheet and the adjacent lobes changes during geomagnetic storms. The ...Cluster trajectory, which moves over the polar cap, into the lobe, and then into the plasma sheet on each orbit, allows us to track the changes in O+ in these regions for a prestorm orbit, main‐phase orbit, and recovery phase orbit. We find that changes in the O+ density and pressure in the plasma sheet are similar to those commonly observed in the ring current during a storm. The O+ is low prestorm. It increases by about a factor of 10 just prior to or during the early main phase of the storm, and is reduced, but usually not down to prestorm levels, in the recovery phase. The lobes contain tailward streaming O+ which originates in the “cleft ion fountain”. During the storms main phase, this population also increases. A detailed look at the main‐phase passes shows that a significant increase in the O+/H+ ratio is observed when this lobe population reaches the plasma sheet, and the tailward streaming O+ is observed continuously as the spacecraft moves from the lobe into the plasma sheet. The enhanced O+ in the lobe and the plasma sheet is observed for many hours during the storm. The inward convection of this population is likely a significant contributor to the storm time ring current.
In this work, we review the results of observations by the Cluster/Research with Adaptive Particle Imaging Detectors (RAPID) energetic charged particle detector (∼>40 keV–∼1 MeV). The origin of ...energetic ions in the region upstream of the Earth's bow shock is compared under different solar wind conditions. We give a brief overview of the acceleration mechanisms of charged particles in the plasma sheet. Effective acceleration is associated with (multiple) interaction(s) of charged particles with multiscale magnetic structures and/or electromagnetic fluctuations, which are the consequences of reconnection or other plasma instabilities. The necessity of such acceleration mechanisms to reproduce the distributions of energetic particles on closed magnetic field lines is discussed. We review empirical models describing the distributions of charged particles. Several aspects of the dynamics of energetic particles during substorms and their influence on the dynamics of magnetic storms are shown. We advise to consider including the energetic particles at >40 keV in calculations of the plasma temperature and pressure during these dynamic processes.
Plain Language Summary
A fundamental scientific question is how plasma in the universe is heated up and accelerated. Understanding acceleration at supernovae shocks, of cosmic jets or laboratory plasmas still has many open questions. Near‐Earth space environment is an excellent laboratory to investigate plasma dynamics and to reveal the fundamental laws it obeys. Energetic plasmas are also hazardous for space satellites and play a key role in space weather. It is, therefore, necessary to study the energization of space plasmas, their distribution and consequences on the magnetospheric dynamics. In situ observations in the near‐Earth space by the Cluster satellites and the energetic particle detector, Research with Adaptive Particle Imaging Detectors (RAPID), reveal new insights in plasma acceleration, unexpected features in its distributions, and effects on substorm and geomagnetic storm dynamics. These observations also help space weather applications to determine the level of energetic particle intensities.
Key Points
Energetic particles at energies >40 keV have to be considered for the plasma temperature and pressure calculations
Effective acceleration is due to interaction of charged particles with multiscale magnetic structures and/or electromagnetic fluctuations
Direction of Interplanetary Magnetic Field leads to ion distribution asymmetries between Northern and Southern hemispheres
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