Modeling of Anisotropy Dynamics of the Proton Pitch Angle Distribution in the Earth’s Magnetosphere

Last years the attention to research of anisotropy of the charged particle pitch angle distribution has considerably increased. Therefore for research of anisotropy dynamics of the proton pitch angle distribution is used the two-dimensional Phenomenological Model of the Ring Current (PheMRC 2-D), which includes the radial and pitch angle diffusions with consideration of losses due to wave-particle interactions. Experimental data are collected on the Polar/MICS satellite during the magnetic storm on October 21–22, 1999. Solving the non-stationary two-dimensional equation of pitch angle and radial diffusions, numerically was determined the proton pitch angle distribution anisotropy index (or parameter of the proton pitch angle distribution) for the pitch angle of 90 degrees during the magnetic storm, when the geomagnetic activity Kp-index changed from 2 in the beginning of a storm up to 7+ in the end of a storm. Dependence of the perpendicular proton pitch angle distribution anisotropy index with energy E = 90 keV during the different moments of time from the McIlwain parameter L (2.26 < L < 6.6) is received. It is certain at a quantitative level for the magnetic storm on October 21–22, 1999, when and where on the nightside of the Earth’s magnetosphere (MLT = 2300) to increase in the geomagnetic activity Kp-index there is a transition from normal (pancake) proton pitch angle distributions to butterfly proton pitch angle distributions. That has allowed to determine unequivocally and precisely the anisotropy dynamics of the proton pitch angle distribution in the given concrete case. It is shown, that with increase of the geomagnetic activity Kp-index the boundary of isotropic proton pitch angle distribution comes nearer to the Earth, reaching L ≈ 3.6 at Kp = 7+

SEP spectra derived from neutron monitor data and from EPHIN space detector data during recent GLEs and sub-GLEs

The Electron Proton Helium Instrument (EPHIN) aboard the Solar Heliospheric Observatory (SOHO) observed several SEP events with protons accelerated to energies E>500 MeV, whereas no neutron monitor (NM) of the worldwide network showed a significant increase in their counting rate. For instance, the SEP event on 8 November 2000 with maximum proton intensity at 500 MeV of >0.1 (cm2 s sr MeV)-1 is outstanding, as this maximum pro-ton flux is comparable with the GLEs on 14 July 2000 and on 15 April 2001 (max. count rate increase in 5-min data of 225% at South Pole NM). In a first step we applied a forward modelling approach of the SEP event on 8 November 2000, i.e. we computed the expected NM count rate increases for selected NM stations, utilizing as input para-meters the SEP spectra determined from EPHIN data as well as anticipated pitch angle distribution and apparent source direction. The simulated count rate increases for selected NM stations showed that this SEP event should have be seen as a clear GLE. To further understand this situation, we investigated in a next step recent GLEs and sub-GLEs. Consequently, a total of four SEP events were selected, two clearly identified GLEs and two sub-GLEs. We performed a “GLE analysis” based on the data of the worldwide network of NMs for each of the four SEP events and then compared the derived SEP spectra with the proton spectra as determined from EPHIN measurements.

Early Observations from the Solar Orbiter SWA/Electron Analyser System

&lt;p&gt;Solar Orbiter carries a total of 10 instrument suites making up the payload for the mission. &amp;#160;One of these, the Solar Wind Analyser (SWA) instrument, is comprised of 3 sensor units which are together served by a central DPU unit. &amp;#160;Of particular focus in this presentation are the early measurements from one of these sensors, the Electron Analyser System (EAS). &amp;#160;EAS is a dual-head, top-hat electrostatic analyser system that is capable of making 3D measurements of solar wind electrons at energies below ~5 keV from a vantage point at the end of a 4-metre boom extending into the shadow of the spacecraft. &amp;#160;The sensor was accommodated in this location to both maximise the unobstructed field of view and to minimise the effect of spacecraft related disturbances on the low-energy (less than a few tens of eV) electrons expected the core population of the solar wind.&lt;/p&gt;&lt;p&gt;To date the SWA instrument sensors have operated sporadically during the mission cruise phase, which began in June 2020. &amp;#160;This is due to a number of operational issues faced by the SWA team, which mean we have not been able to take data in a continuous manner. &amp;#160;However, the data that has been taken shows the clear promise of the SWA measurements, in general, once these issues can be overcome. &amp;#160;For example, EAS is using a novel sample steering mechanism in burst mode which, with reference to a magnetic field vector shared onboard by the MAG instrument, allows the capture of the electron pitch angle distribution at unusually high time resolution. &amp;#160;We discuss these observations here, and illustrate the potential science returns from the burst mode. &amp;#160;We also present results from the new EAS observations in the vicinity of reconnecting current sheets in the solar wind, to more generally illustrate the capability of the sensor.&amp;#160;&lt;/p&gt;

MMS observations of explosive filamentary current within two adjacent ion scale flux ropes

&lt;p&gt;Flux ropes have attracted extensive attention due to their importance in studying instantaneous magnetic reconnection&amp;#160;over the past years. Recently, with the improvement of high spatio-temporal resolution measurements, kinetic-scale flux ropes have been detected. However, their generation&amp;#160;and energy energization are still unclear. In this study, electron-scale filamentary&amp;#160;currents&amp;#160;within&amp;#160;two adjacent ion scale flux ropes&amp;#160;are observed&amp;#160;using MMS data. We find that:&lt;/p&gt;&lt;p&gt;1. Intense and explosive filamentary currents in parallel and perpendicular directions are found inside the flux ropes.&lt;/p&gt;&lt;p&gt;2. The electron pitch angle distribution appears &quot;X&quot; like shape, and could be caused by the electron acceleration.&lt;/p&gt;&lt;p&gt;3. The filamentary current appears in the center of the &quot;X&quot; distribution.&lt;/p&gt;&lt;p&gt;The filamentary currents are important and are considered to be the evidence of secondary reconnection&amp;#160;[Wang et al.,&amp;#160;2020]. The&amp;#160;observations in our study are&amp;#160;important&amp;#160;to reveal the particle acceleration&amp;#160;and energy dissipation in&amp;#160;magnetic reconnection.&lt;/p&gt;

Ring Current Proton Dynamics Driven by Wave-Particle Interactions During a Nonstorm Period

Modeling of pitch angle scattering of ring current protons at interaction with electromagnetic ion cyclotron waves during a nonstorm period was considered very seldom. Therefore it is used correlated observation of enhanced electromagnetic ion cyclotron (EMIC) waves and dynamic evolution of ring current proton flux collected by Cluster satellite near the location L = 4.5 during March 26–27, 2003, a nonstorm period (Dst > –10 nT). Energetic (5–30 keV) proton fluxes are found to drop rapidly (e.g., a half hour) at lower pitch angles, corresponding to intensified EMIC wave activities. As mathematical model is used the non-stationary one-dimensional pitch angle diffusion equation which allows to compute numerically density of phase space or pitch angle distribution of the charged particles in the Earth’s magnetosphere. The model depends on time t, a local pitch angle and several parameters (the mass of a particle, the energy, the McIlwain parameter, the magnetic local time or geomagnetic eastern longitude, the geomagnetic activity index, parameter of the charged particle pitch angle distribution taken for the 90 degrees pitch angle at t = 0, the lifetime due to wave–particle interactions). This model allows numerically to estimate also for different geophysical conditions a lifetime due to wave–particle interactions. It is shown, that EMIC waves can yield decrements in proton flux within 30 minutes, consistent with the observational data. The good consent is received. Comparison of results on full model for the pitch angle range from 0 up to 180 degrees and on the model for the 90 degrees pitch angle is lead. For a perpendicular differential flux of the Earth’s ring current protons very good consent with the maximal relative error approximately 3.23 % is received