A document by Ian James Cohen. Click on the document to view its contents.

This paper introduces a modernized application of the falling spheres technique for measurement of neutral winds and densities in the mesosphere and lower thermosphere (MLT) region regardless of time of day or tropospheric conditions, using an Observing System Simulation Experiment (OSSE) of falling spheres equipped with commercial-off-the-shelf (COTS) Global Navigation Satellite Systems (GNSS) receivers. The modernization of this technique is crucial since current techniques to measure the neutral winds in the MLT are often tied to the location of a certain instrument or heavily dependent on clear nighttime skies. We show how state-of-the-art COTS inertial measurement units (IMUs) and GNSS receivers enable precise retrieval of neutral wind and density profiles under various atmospheric conditions represented both by wind profiles measured during the Super Soaker and Auroral Jets sounding rocket missions and by wind profiles simulated via the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). Even under highly conservative conditions (e.g., relatively extreme position uncertainty of $\sigma =\sim$100 m, a low sampling rate of 100~Hz, and strong vertical winds of 25 m/s) the estimated neutral densities exhibit errors of less than 1\%, while estimated neutral wind errors typically do not exceed 2 m/s. The latter errors are largest where the shears maximize in the lower thermosphere. The significance of this work lies in its potential to enhance our understanding of the dynamics within the MLT region, including in situ processes and the interaction with the lower atmosphere.

Collisionless shocks in astrophysical plasmas are important thermalizers, converting some of the incident flow energy into thermal energy, and non-thermalizers, partitioning that energy in unequal ways to different particle species, sub-populations thereof, and field components. This partition problem, or equivalently the shock equation of state, lies at the heart of shock physics. Here we employ systematically a framework to capture all the incident and downstream energy fluxes at two example traversals of the Earth's bow shock by the Magnetospheric Multiscale Mission. Here and traditionally such data has to be augmented by information from other spacecraft, e.g., to provide more accurate measurements of the cold solar wind beam. With some care and fortuitous choices, the energy fluxes are constant, including instantaneous measurements through the shock layer. The dominant incident proton ram energy is converted primarily into downstream proton enthalpy flux, the majority of which is actually carried by a small fraction of suprathermal protons. Fluctuations include both real and instrumental effects. Separating these, resolving the solar wind beam, and other considerations point the way to a dedicated mission to solve this energy partition problem across a full range of plasma and shock conditions.

We present a statistical study of energetic heavy ion acceleration in the near-Earth magnetotail using observations from the Energetic Ion Spectrometer (EIS) onboard the Magnetospheric Multiscale (MMS) spacecraft. Although the EIS instrument does not measure ion charge state directly, we have inferred the dominant charge state of the suprathermal heavy ions (i.e., ~60-1000 keV He and C-N-O), using a previously-developed correlation analysis of the time-dependent flux response between different energy channels of different ion species. For specific events we have also distinguished adiabatic (charge-dependent) energization from non-adiabatic (mass-dependent) energization. This work uses observations from the MMS “Bursty Bulk Flows (BBF) Campaign” in August 2016, when high-energy-resolution “burst”-mode data are more frequently available, to examine the relative occurrence of adiabatic energization versus preferential energization of heavy ions. The results of this study demonstrate the utility and limitations of the cross-correlation technique that was applied. We find that the technique is consistently able to discern coarse charge states for heavy ions such as O+/6+, He+/++ (i.e., ionospheric versus solar wind sources), but that the more subtle job of uniquely determining adiabatic versus non-adiabatic behaviors for the ionospheric component (O+) is only sometimes achievable. The dynamics of Earth’s magnetotail are apparently too complex and variable to consistently accommodate our simple assumption for adiabatic behavior of energy/charge-ordered transport from a common source of particles.

Understanding the physical mechanisms responsible for the cross-scale energy transport and plasma heating from solar wind into the Earth’s magnetosphere is of fundamental importance for magnetospheric physics and for understanding these processes in other places in the universe with comparable plasma parameter ranges. This paper presents observations from Magnetosphere Multi-Scale (MMS) mission at the dawn-side high-latitude dayside boundary layer on 25th of February, 2016 between 18:55-20:05 UT. During this interval MMS encountered both inner and outer boundary layer with quasi-periodic low frequency fluctuations in all plasma and field parameters. The frequency analysis and growth rate calculations are consistent with the Kelvin-Helmholtz Instability (KHI). The intervals within low frequency wave structures contained several counter-streaming, low- (0-200 eV) and mid-energy (200 eV-2 keV) electrons in the loss cone and trapped energetic (70-600 keV) electrons in alternate intervals. Wave intervals also showed high energy populations of O+ ions, likely of ionospheric or ring current origin. The counter-streaming electron intervals were associated with a large-magnitude field-aligned Poynting fluxes. Burst mode data at the large Alfven velocity gradient revealed a strong correlation between counter streaming electrons, enhanced parallel electron temperatures, strong anti-field aligned wave Poynting fluxes, and wave activity from sub-proton cyclotron frequencies extending to electron cyclotron frequency. Waves were identified as Kinetic Alfven waves but their contribution to parallel electron heating was not sufficient to explain the > 100 eV electrons, and rapid non-adiabatic heating of the boundary layer as determined by the characteristic heating frequency, derived here for the first time.

A dipolarization of the background magnetic field was observed during a conjunction of the Magnetospheric Multiscale (MMS) spacecraft and Van Allen Probe B on 22 September 2018. The spacecraft were located in the inner magnetosphere at L~6-7 just before midnight magnetic local time (MLT). The separation between MMS and Probe B was ~1 Re. Gradual dipolarization or an increase of the northward component Bz of the background field occurred on a timescale of minutes. Since both MMS and Probe B measured similar gradual increases, the spatial scale was of the order of the separation between these two. On top of that, there were Bz increases, and a decrease in one case, on a timescale of seconds, accompanied by large electric fields with amplitudes > several tens of mV/m. Spatial scale lengths were of the order of the ion inertial length and the ion gyroradius. The inertial term in the momentum equation and the Hall term in the generalized Ohm’s law were sometimes non-negligible. These small-scale variations are discussed in terms of the ballooning/interchange instability (BICI) and kinetic Alfven waves. It is inferred that physics of multiple scales was involved in the dynamics of this dipolarization event.

The present paper demonstrates the first observations by the Magnetospheric Multiscale (MMS) mission of the counter-streaming energetic electrons and trapped energetic protons, localized in the magnetic field depressions between the mirror mode peaks, in the Earth’s dusk sector high-latitude magnetosphere. This region is characterized by high plasma beta, strong ion temperature anisotropy and intermediate plasma density between magnetospheric and magnetosheath plasma. We show that these plasma conditions are unstable for the drift mirror instability. The counter-streaming electron feature resembles those of the previously reported energetic electron microinjections, but without the energy-time dispersion signature. This suggests that MMS is passing through one of the potential microinjection source regions. The energetic ion data in the present study is mainly used to estimate the scale size of the mirror mode structures.