K. Kersten

Low-frequency whistler waves and shocklets observed at quasi-perpendicular interplanetary shocks

[1] We present observations of low-frequency waves (0.25 Hz < f < 10 Hz) at five quasi-perpendicular interplanetary (IP) shocks observed by the Wind spacecraft. Four of the five IP shocks had oblique precursor whistler waves propagating at angles with respect to the magnetic field of 20–50 and large propagation angles with respect to the shock normal; thus they do not appear to be phase standing. One event, the strongest in our study and likely supercritical, had low-frequency waves consistent with steepened magnetosonic waves called shocklets. The shocklets are seen in association with diffuse ion distributions. Both the shocklets and precursor whistlers are often seen simultaneously with anisotropic electron distributions unstable to the whistler heat flux instability. The IP shock with upstream shocklets showed much stronger electron heating across the shock ramp than the four events without upstream shocklets. These results may offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

The properties of large amplitude whistler mode waves in the magnetosphere: Propagation and relationship with geomagnetic activity

using waveform capture data from the Wind spacecraft. Weobserved 247 whistler mode waves with at least one electricfield component (105/247 had≥80 mV/m peak!to!peakamplitudes) and 66 whistler mode waves with at least onesearch coil magnetic field component (38/66 had≥0.8 nTpeak!to!peak amplitudes). Wave vectors determined fromevents with three magnetic field components indicate that30/46 propagate within 20° of the ambient magnetic field,though some are more oblique (up to ∼50°). No relationshipwas observed between wave normal angle and GSM lati-tude. 162/247 of the large amplitude whistler mode waveswere observed during magnetically active periods (AE >200 nT). 217 out of 247 total whistler mode waves exam-ined were observed inside the radiation belts. We presenta waveform capture with the largest whistler wave magneticfield amplitude (^8nTpeak!to!peak) ever reported in theradiation belts. The estimated Poynting flux magnitude asso-ciated with this wave is ^300 mW/m

Observation of relativistic electron microbursts in conjunction with intense radiation belt whistler-mode waves

We present multi-satellite observations indicating a strong correlation between large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. The microburst precipitation exhibits a bursty temporal structure similar to that of the observed large amplitude wave packets, suggesting a connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave--particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

Observations of electromagnetic whistler precursors at supercritical interplanetary shocks

] We present observations of electromagnetic precursorwaves, identified as whistler mode waves, at supercriticalinterplanetary shocks using the Wind search coil magneto-meter. The precursors propagate obliquely with respect tothe local magnetic field, shock normal vector, solar windvelocity, and they are not phase standing structures. All areright-hand polarized with respect to the magnetic field(spacecraft frame), and all but one are right-hand polarizedwith respect to the shock normal vector in the normal inci-dence frame. They have rest frame frequencies f

Observations of kinetic scale field line resonances

We identify electromagnetic field variations from the Van Allen Probes which have the properties of Doppler shifted kinetic scale Alfvenic field line resonances. These variations are observed during injections of energetic plasmas into the inner magnetosphere. These waves have scale sizes perpendicular to the magnetic field which are determined to be of the order of an ion gyro-radius (ρi) and less. Cross-spectral analysis of the electric and magnetic fields reveals phase transitions at frequencies correlated with enhancements and depressions in the ratio of the electric and magnetic fields. Modeling shows that these observations are consistent with the excitation of field-line resonances over a broad range of wave numbers perpendicular to the magnetic field (k⊥) extending to k⊥ρi ≫ 1. The amplitude of these waves is such that E/Bo ≳ Ωi/k⊥ (E, Bo, and Ωi are the wave amplitude, background field strength, and ion gyro-frequency, respectively) leading to ion demagnetization and acceleration for multiple transitions through the wave potential.

Interplanetary and interstellar dust observed by the Wind/WAVES electric field instrument

Observations of hypervelocity dust particles impacting the Wind spacecraft are reported here for the first time using data from the Wind/WAVES electric field instrument. A unique combination of rotating spacecraft, amplitude-triggered high-cadence waveform collection, and electric field antenna configuration allow the first direct determination of dust impact direction by any spacecraft using electric field data. Dust flux and impact direction data indicate that the observed dust is approximately micron-sized with both interplanetary and interstellar populations. Nanometer radius dust is not detected by Wind during times when nanometer dust is observed on the STEREO spacecraft and both spacecraft are in close proximity. Determined impact directions suggest that interplanetary dust detected by Wind/WAVES at 1 AU is dominated by particles on bound trajectories crossing Earths orbit, rather than dust with hyperbolic orbits.

Evidence for injection of relativistic electrons into the Earth's outer radiation belt via intense substorm electric fields

Observation and model results accumulated in the last decade indicate that substorms can promptly inject relativistic ‘killer’ electrons (≥MeV) in addition to 10–100 keV subrelativistic populations. Using measurements from Cluster, Polar, LANL, and GOES satellites near the midnight sector, we show in two events that intense electric fields, as large as 20 mV/m, associated with substorm dipolarization are associated with injections of relativistic electrons into the outer radiation belt. Enhancements of hundreds of keV electrons at dipolarization in the magnetotail can account for the injected MeV electrons through earthward transport. These observations provide evidence that substorm electric fields inject relativistic electrons by transporting magnetotail electrons into the outer radiation belt. In these two events, injected relativistic electrons dominated the substorm timescale enhancement of MeV electrons as observed at geosynchronous orbit.

Electromagnetic waves and electron anisotropies downstream of supercritical interplanetary shocks

We present waveform observations of electromagnetic lower hybrid and whistler waves with f_ci 1.01. Thus, the whistler mode waves appear to be driven by a heat flux instability and cause perpendicular heating of the halo electrons. The lower hybrid waves show a much weaker correlation between \partialB and normalized heat flux magnitude and are often observed near magnetic field gradients. A third type of event shows fluctuations consistent with a mixture of both lower hybrid and whistler mode waves. These results suggest that whistler waves may indeed be regulating the electron heat flux and the halo temperature anisotropy, which is important for theories and simulations of electron distribution evolution from the sun to the earth.

Van Allen Probes investigation of the large-scale duskward electric field and its role in ring current formation and plasmasphere erosion in the 1 June 2013 storm

Using the Van Allen Probes, we investigate the enhancement in the large-scale duskward convection electric field during the geomagnetic storm (Dst similar to-120nT) on 1 June 2013 and its role in ring current ion transport and energization and plasmasphere erosion. During this storm, enhancements of similar to 1-2mV/m in the duskward electric field in the corotating frame are observed down to L shells as low as similar to 2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90 degrees pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earths nightside, given the strength and duration of the convection electric field. The calculation based on this simple model indicates that the enhanced duskward electric field is of sufficient intensity and duration to transport ions from a range of initial locations and initial energies characteristic of (though not observed by the Van Allen Probes) the earthward edge of the plasma sheet during active times (L similar to 6-10 and similar to 1-20keV) to the observed location of the 58-267keV ion population, chosen as representative of the ring current (L similar to 3.5-5.8). According to the model calculation, this transportation should be concurrent with an energization to the range observed, similar to 58-267keV. Clear coincidence between the electric field enhancement and both plasmasphere erosion and ring current ion (58-267keV) pressure enhancements are presented. We show for the first time nearly simultaneous enhancements in the duskward convection electric field, plasmasphere erosion, and increased pressure of 58-267keV ring current ions. These 58-267keV ions have energies that are consistent with what they are expected to pick up by gradient B drifting across the electric field. These observations strongly suggest that we are observing the electric field that energizes the ions and produces the erosion of the plasmasphere.

Chorus waves and spacecraft potential fluctuations: Evidence for wave‐enhanced photoelectron escape

Chorus waves are important for electron energization and loss in Earths radiation belts and inner magnetosphere. Because the amplitude and spatial distribution of chorus waves can be strongly influenced by plasma density fluctuations and spacecraft floating potential can be a diagnostic of plasma density, the relationship between measured potential and chorus waves is examined using Van Allen Probes data. While measured potential and chorus wave electric fields correlate strongly, potential fluctuation properties are found not to be consistent with plasma density fluctuations on the timescales of individual chorus wave packets. Instead, potential fluctuations are consistent with enhanced photoelectron escape driven by chorus wave electric fields. Enhanced photoelectron escape may result in potential fluctuations of the spacecraft body, the electric field probes, or both, depending on the ambient plasma and magnetic field environment. These results differ significantly from prior interpretations of the correspondence between measured potential and wave electric fields.