Anti-sunward high-speed jets in the subsolar magnetosheath

Using 2008–2011 data from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in Earth's subsolar magnetosheath, we study high-speed jets identified as intervals when the anti-sunward component of the dynamic pressure in the subsolar magnetosheath exceeds half of its upstream solar wind value. Based on our comprehensive data set of 2859 high-speed jets, we obtain the following statistical results on jet properties and favorable conditions: high-speed jets occur predominantly downstream of the quasi-parallel bow shock, i.e., when interplanetary magnetic field cone angles are low. Apart from that, jet occurrence is only very weakly dependent (if at all) on other upstream conditions or solar wind variability. Typical durations and recurrence times of high-speed jets are on the order of tens of seconds and a few minutes, respectively. Relative to the ambient magnetosheath, high-speed jets exhibit higher speed, density and magnetic field intensity, but lower and more isotropic temperatures. They are almost always super-Alfvénic, often even super-magnetosonic, and typically feature 6.5 times as much dynamic pressure and twice as much total pressure in anti-sunward direction as the surrounding plasma does. Consequently, they are likely to have significant effects on the magnetosphere and ionosphere if they impinge on the magnetopause

The global structure and time evolution of dayside magnetopause surface eigenmodes

Theoretical work and recent observations suggest that the dayside magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern and southern ionospheres. These magnetopause surface eigenmodes (MSEs) are a potential source of magnetospheric ultralow‐frequency (ULF) waves with frequencies less than 2 mHz. Here we use the Space Weather Modeling Framework to study the magnetospheric response to impulsive solar wind dynamic pressure increases. Waves with 1.8 mHz frequency are excited whose global properties are largely consistent with theoretical predictions for MSE and cannot be explained by other known ULF wave modes. These simulation results lead to two key findings: (1) MSE can be sustained in realistic magnetic field geometries with nonzero flow shear and finite current layer thickness at the magnetopause and (2) MSE can seed the growth of tailward propagating surface waves via the Kelvin‐Helmholtz instability.Key PointsDayside ULF response to pulse consistent with magnetopause surface eigenmodeMagnetopause surface eigenmodes are a potential source of ULF waves below 2 mHzMagnetopause surface eigenmodes seed tailward propagating surface wave growthPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111803/1/grl52799.pd

Massless, String Localized Quantum Fields for Any Helicity

For any massless, irreducible representation of the covering of the proper, orthochronous Poincar\'e group we construct covariant, free quantum fields that generate the representation space from the vacuum and are localized in semi-infinite strings in the sense of commutation or anti-commutation of the field operators at space-like separation of the strings.Comment: Minor corrections. To be published in Journal of Mathematical Physic

Frequency variability of standing Alfven waves excited by fast mode resonances in the outer magnetosphere

NASA. Grant Number: NAS5-0209

What frequencies of standing surface waves can the subsolar magnetopause support?

STFC. Grant Number: ST/I505713/

How Accurately Can We Measure the Reconnection Rate E M for the MMS Diffusion Region Event of 11 July 2017?

We investigate the accuracy with which the reconnection electric field E M can be determined from in situ plasma data. We study the magnetotail electron diffusion region observed by National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) on 11 July 2017 at 22:34 UT and focus on the very large errors in E M that result from errors in an L M N boundary normal coordinate system. We determine several L M N coordinates for this MMS event using several different methods. We use these M axes to estimate E M. We find some consensus that the reconnection rate was roughly E M = 3.2 ± 0.6 mV/m, which corresponds to a normalized reconnection rate of 0.18 ± 0.035. Minimum variance analysis of the electron velocity (MVA-v e), MVA of E, minimization of Faraday residue, and an adjusted version of the maximum directional derivative of the magnetic field (MDD-B) technique all produce reasonably similar coordinate axes. We use virtual MMS data from a particle-in-cell simulation of this event to estimate the errors in the coordinate axes and reconnection rate associated with MVA-v e and MDD-B. The L and M directions are most reliably determined by MVA-v e when the spacecraft observes a clear electron jet reversal. When the magnetic field data have errors as small as 0.5% of the background field strength, the M direction obtained by MDD-B technique may be off by as much as 35°. The normal direction is most accurately obtained by MDD-B. Overall, we find that these techniques were able to identify E M from the virtual data within error bars ≥20%

Possible coexistence of kinetic Alfvén and ion Bernstein modes in sub-ion scale compressive turbulence in the solar wind

We investigate compressive turbulence at sub-ion scales with measurements from the Magnetospheric MultiScale Mission. The tetrahedral configuration and high time resolution density data obtained by calibrating spacecraft potential allow an investigation of the turbulent density fluctuations in the solar wind and their three-dimensional structure in the sub-ion range. The wave-vector associated with the highest energy density at each spacecraft frequency is obtained by application of the multipoint signal resonator technique to the four-point density data. The fluctuations show a strong wave-vector anisotropy k⊥ k� where the parallel and perpendicular symbols are with respect to the mean magnetic-field direction. The plasma frame frequencies show two populations, one below the proton cyclotron frequency ω<ci consistent with kinetic Alfvén wave (KAW) turbulence. The second component has higher frequencies ω>ci consistent with ion Bernstein wave turbulence. Alternatively, these fluctuations may constitute KAWs that have undergone multiple wave-wave interactions, causing a broadening in the plasma frame frequencies. The scale-dependent kurtosis in this wavevector region shows a reduction in intermittency at the small scales which can also be explained by the presence of wave activity. Our results suggest that small-scale turbulence exhibits linear-wave properties of kinetic Alfvén and possibly ion-Bernstein (magnetosonic) waves. Based on our results, we speculate that these waves may play a role in describing the observed reduction in intermittency at sub-ion scales

Anti-sunward high-speed jets in the subsolar magnetosheath

Peer reviewe

In Situ Observations of a Magnetosheath High-Speed Jet Triggering Magnetopause Reconnection

Magnetosheath high‐speed jets—localized dynamic pressure enhancements typically of ∼1 Earth radius in size—impact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five Time History of Events and Macroscale Interactions during Substorms spacecraft in a string‐of‐pearls configuration on 7 August 2007. The spacecraft recorded magnetopause in‐and‐out motion during an impact of a magnetosheath jet (VN∼−300 km/s along the magnetopause normal direction). There was no evidence for reconnection for the preimpact crossing, yet three probes observed reconnection after the impact. We infer that the jet impact compressed the originally thick (60–70 di), high magnetic shear (140–160° magnetopause until it was thin enough for reconnection to occur. Magnetosheath high‐speed jets could therefore act as a driver for bursty dayside reconnection