Paul J. Kellogg

WAVES: The radio and plasma wave investigation on the wind spacecraft

The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace. These processes are then to be interpreted in conjunction with results from the other ISTP spacecraft in order to discern the measurements and parameters for mass, momentum, and energy flow throughout geospace. This investigation will also contribute to observations of radio waves emitted in regions where the solar wind is accelerated. The WAVES investigation comprises several innovations in this kind of instrumentation: among which the first use, to our knowledge, of neural networks in real-time on board a scientific spacecraft to analyze data and command observation modes, and the first use of a wavelet transform-like analysis in real time to perform a spectral analysis of a broad band signal.

Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wave number ranges in a Beta > or approximately = 1 plasma. The k(-5/3) inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfvén speed. At smaller wavelengths krho(i) > or = 1 the electric spectrum is enhanced and is consistent with the expected dispersion relation of short-wavelength kinetic Alfvén waves. Kinetic Alfvén waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluidlike nature of the solar wind.

Bipolar electrostatic structures in the shock transition region: Evidence of electron phase space holes

We present observations of intense, bipolar, electrostatic structures in the transition region of the terrestrial bow shock from the Wind spacecraft. The electric field signatures are on the order of a tenth of a millisecond in duration and greater than 100 mV/m in amplitude. The measured electric field is generally larger on the smaller dipole antenna, indicating a small spatial size. We compare the potential on the two dipole antennas with a model of antenna response to a Gaussian potential profile. This result agrees with a spatial scale determined by convection and gives a characteristic scale size of 2–7 λd. We interpret the observations as small scale convecting unipolar potential structures, consistent with simulations of electron phase space holes and discuss the results in the context of electron thermalization at strong collisionless shocks.

Wind Spacecraft Observations of Solar Impulsive Electron Events Associated with Solar Type III Radio Bursts

We present Wind spacecraft observations of solar impulsive electron events associated with locally generated Langmuir waves during solar type III radio bursts. The solar impulsive electrons had energies from ~600 eV to greater than 300 keV. Local Langmuir emissions associated with these fluxes generally coincided with the arrival of 2-12 keV electrons. A survey of 27 events over 1 yr shows that there were few occurrences of electron distributions (~96 s averaged) that were unstable to Langmuir waves and none that had a substantial growth rate (>3 × 10-2 s-1) or endured for more than 96 s. Intense solar impulsive electron events that occurred on 1995 April 2 are studied in detail. Marginally stable (plateaued) distributions occasionally coincided with a periods of local Langmuir emissions, but the electron distributions were otherwise stable. These observations suggest that kinetic processes were modifying the electron distribution but also suggest that processes other than one-dimensional quasilinear relaxation were involved. We find that solar impulsive electron distributions were often unstable to oblique waves, such as quasi-electrostatic whistler waves or electromagnetic ion cyclotron waves, suggesting that competition between Langmuir and oblique emissions may be important. There are several other features in the Wind spacecraft solar impulsive electron observations that are noteworthy. Nondispersive flux modulations were visible in many of the events (also visible in the published ISEE 3 data) in ~1-4 keV electrons, suggesting that a local hydromagnetic instability may have accompanied the lowest energy solar impulsive electron fluxes. The Wind data differ from the ISEE 3 data in the energy spectra of the electron events. ISEE 3 recorded few events with only high-energy (>10 keV) electron fluxes, whereas a survey of the Wind events shows a substantially higher ratio of high-energy events. The high-energy events were often associated with solar flares that could not have been magnetically well connected with the satellite.

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.

Langmuir waves in a fluctuating solar wind

The Langmuir waves which are resonant with typical type III solar radio burst electrons have a frequency so little above the ambient plasma frequency that they should be strongly affected by known density fluctuations. Some consequences of this observation are worked out, and the expected consequences are demonstrated in the observations of the Langmuir waves from two quite different bursts, of November 4, 1997, and January 19, 1998.

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

Electrostatic Turbulence and Debye-Scale Structures Associated with Electron Thermalization at Collisionless Shocks

We analyze measurements of bipolar, Debye-scale electrostatic structures and turbulence measured in the transition region of the Earths collisionless bow shock. In this region, the solar wind electron population is slowed and heated, and we show that this turbulence correlates well in amplitude with the measured electron temperature change. The observed bipolar structures are highly oblate and longitudinally polarized and may instantaneously carry up to 10% of the plasma energy ψ ≡ e/kbTe ≈ 0.1 before dissipating. The relationship between ψ and the field-aligned scale size Δ∥ of the Gaussian potential suggests that the bipolar structures are BGK trapped particle equilibria or electron hole modes. We suggest a generation scenario and a potential role in dissipation.

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.

Transverse z‐mode waves in the terrestrial electron foreshock

We examine the phase relation between two orthogonal electric field components for several hundred waveform measurements of intense electron plasma waves in the terrestrial electron foreshock. In general, the phase shift at the carrier frequency is not zero or π as would be expected if the waves were purely electrostatic Langmuir waves, but is a function of the angle between the antennas and the interplanetary magnetic field (IMF). When the antennas are field aligned, the phase shift between the components is large; this value recedes smoothly to zero as the antenna is rotated away from the IMF direction. When solar wind density fluctuations are considered, this is consistent with the dispersion of the electromagnetic z-mode and we assert that the electron foreshock is populated by transverse z-mode waves, not purely longitudinal Langmuir waves. This has implications for conversion to freely propagating modes and large-amplitude saturation mechanisms.