We present a statistical analysis of >2,100 bipolar electrostatic solitary waves (ESWs) collected from 10 quasi‐perpendicular Earth's bow shock crossings by Magnetospheric Multiscale spacecraft. We developed and implemented a correction procedure for reconstruction of actual electric fields, velocities, and other properties of ESW, whose spatial scales are typically comparable with or smaller than spatial distance between voltage‐sensitive probes. We found that more than 95% of the ESW are of negative polarity with amplitudes typically below a few Volts and 0.1
We present analysis of electrostatic waves around the ramp of a quasi‐perpendicular Earth's bow shock observed by the Magnetospheric Multiscale spacecraft. The electrostatic waves have amplitudes up to 800 mV/m, which is the largest value ever reported in the Earth's bow shock. In contrast to previous studies, the electrostatic waves have large amplitudes of the electrostatic potential, up to 20 V or 20% of local electron temperature. The wavelengths are from 150 m to 3 km, that is from 15 to 300 Debye lengths and typically from 0.4 to 1.5 thermal electron gyroradii. Importantly, these waves can propagate not only quasi‐parallel or oblique, but also almost perpendicular to local magnetic field. The electrostatic waves are interpreted in terms of ion‐acoustic waves, although the presence of electron cyclotron harmonic waves cannot be entirely ruled out. These results suggest that electrostatic waves may strongly affect the dynamics of electrons in collisionless shocks.
more » « less- Award ID(s):
- 2026680
- NSF-PAR ID:
- 10444480
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 11
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract T e (5–30 V or 0.1–0.3T e for a few percent of ESW), spatial scales of 10–100 m orλ D –10λ D , and velocities from a few tens to a few hundred km/s that is on the order of local ion‐acoustic speed. The spatial scales of ESW are correlated with local Debye lengthλ D . The ESW have electric fields generally oblique to magnetic field and they propagate highly oblique to shock normalN ; more than 80% of ESW propagate within 30° of the shock planeLM . In the shock plane, ESW typically propagates within a few tens of degrees of local magnetic field projectionB LMand preferentially opposite toN ×B LM. We argue that the ESW of negative polarity are ion holes produced by ion‐ion streaming instabilities. We estimate ion hole lifetimes to be 10–100 ms, or 1–10 km in terms of traveling distance. The revealed statistical properties will be useful for quantitative studies of electron thermalization in the Earth's bow shock. -
more » « less
Abstract We present Magnetospheric Multiscale observations of electrostatic double layers in quasi‐perpendicular Earth's bow shock. These double layers have predominantly parallel electric field with amplitudes up to 100 mV/m, spatial widths of 50–700 m, and plasma frame speeds within 100 km/s. The potential drop across a single double layer is 2%–7% of the cross‐shock potential in the de Hoffmann‐Teller frame and occurs over the spatial scale of 10 Debye lengths or one tenth of electron inertial length. Some double layers can have spatial width of 70 Debye lengths and potential drop up to 30% of the cross‐shock potential. The electron temperature variation observed across double layers is roughly consistent with their potential drop. While electron heating in the Earth's bow shock occurs predominantly due to the quasi‐static electric field in the de Hoffmann‐Teller frame, these observations show that electron temperature can also increase across Debye‐scale electrostatic structures.
-
more » « less
Abstract We present the first observations of electrostatic solitary waves with electrostatic potential of negative polarity around a fast plasma flow in the Earth's plasma sheet. The solitary waves are observed aboard four Magnetospheric Multiscale spacecraft, which allowed accurately estimating solitary wave properties. Based on a data set of 153 solitary waves, we show that they are locally one‐dimensional Debye‐scale structures with amplitudes up to 20% of local electron temperature and they propagate at plasma frame speeds ranging from a tenth to a few ion‐acoustic speeds at arbitrary angles to the local magnetic field. The solitary waves are associated with multi‐component proton distributions and their velocities are around those of a beam‐like proton population. We argue that the solitary waves are ion holes, nonlinear structures produced by ion‐streaming instabilities, and conclude that once ions are not magnetized, ion holes can propagate oblique to local magnetic field.
-
more » « less
Abstract The nature of the 3‐s ultralow frequency (ULF) wave in the Earth's foreshock region and the associated wave‐particle interaction are not yet well understood. We investigate the 3‐s ULF waves using Magnetospheric Multiscale (MMS) observations. By combining the plasma rest frame wave properties obtained from multiple methods with the instability analysis based on the velocity distribution in the linear wave stage, the ULF wave is determined to be due to the ion/ion nonresonant mode instability. The interaction between the wave and ions is analyzed using the phase relationship between the transverse wave fields and ion velocities and using the longitudinal momentum equation. During the stage when ULF waves have sinusoidal waveforms up to |
dB |/|B 0| ~ 3, wheredB is the wave magnetic field andB 0is the background magnetic field, the wave electric fields perpendicular toB B V ×B B -
more » « less
Abstract The propagation characteristics of hot flow anomalies (HFAs) near the Earth's bow shock are investigated, using observations from the Cluster spacecraft. A data set comprised of 19 classic HFAs (associated with tangential discontinuities, TDs) and 23 spontaneous HFAs (SHFAs, formed in the absence of solar wind discontinuities) was analyzed. For each event, the propagation velocity and normal of leading and trailing HFA edges were calculated using multiple multi‐point satellite analysis methods. For classic HFAs, 93% of the events have leading edge (LE) normal directions within 30° of the normal direction of the driving TDs. For SHFAs, in 74% of the events, the angle between the normal of an SHFA's edges and background magnetic field is in the range of 70°–110° and no angle is in the ranges of 0°–20° and 160°–180°. These results indicate that the LEs of the classic HFAs propagate along the same direction as the driving TDs and most SHFAs propagate quasi‐perpendicular to the background magnetic field and no SHFAs propagate parallel or anti‐parallel to the background magnetic field. Moreover, according to the velocity of HFAs' edges, we find that all classic HFAs and SHFAs' edges propagate toward the Earth in the spacecraft frame as expected and 5 out of 7 SHFAs are contracting and no expanding SHFAs are found. This study provides key parameters to help understand how HFAs disturb the magnetosphere.
