What auroral electron and ion beams tell us about magnetosphere-ionosphere coupling

The Viking wave electric field and density fluctuation measurements together with simultaneous particle observations are used to study waves at frequencies below the local proton gyrofrequency. Such waves were observed during about 20% of nightside auroral field line crossings by Viking at altitudes between 2000 and 10,000 km. The observations are different from earlier spacecraft observations of similar waves in such a way that the center frequency in about one out of four of the observed events was below the gyrofrequency of singly charged helium, which has not been reported previously. The waves were well correlated with precipitating electrons of energies of a few keV and with VLF auroral hiss. Detailed investigations of simultaneously observed wave emissions, particles, and total densities strongly suggest that secondary peaks at keV energies in the distributions of downgoing electrons can cause the emissions. INTRODUCTION Waves below the local proton gyrofrequency, fc•,, were frequently observed by the Swedish Viking satellite when it crossed auroral field lines at altitudes between 2000 and 10,000 km. The emissions were observed in regions where the precipitating auroral electrons of a few keV and VLF auroral hiss were present. Similar wave modes have been reported earlier from several spacecraft on orbits in corresponding regions, e.g., INJUN 5 [Gurnett and Frank, 1972], S3-3 [Lysak and Ternerin, 1983; Ternerin and Lysak, 1984], and ISIS 1 and 2 [Saito et al., 1987]. The first report on observations of narrow-banded ELF noise, that was closely associated with the so-called inverted-V auroral electron precipitation, was published by Gurnett and Frank [1972] based on INJUN 5 measurements. The ELF waves had frequencies from 100 to 300 Hz. The wave electric field amplitudes were 3-10 mV/m, and the magnetic field amplitudes 10-30 my. The authors did not directly associate the emission with the precipitating electrons. Because of the spectral similarities with the previously reported OGO 5 observations of the so-called lion's roar in the magnetosheath [Smith et al., 1969], they proposed that the wave would propagate along auroral field lines down to the topside ionosphere. The INJUN 5 observations were confirmed by Ternerin and Lysak [1984] from the S3-3 measurements of ELF wave emissions on the auroral field lines. They argued that the inverted-V auroral electrons generate the waves locally within and below the field-aligned acceleration region. The proposed generation mechanism is analogous to the mecha-nism producing VLF hiss by auroral electrons [Maggs, 1976; Lotko and Maggs, 1979; Maggs and Lotko, 1981]. The whistler mode resonance cone above the local lower hybrid frequency, flh, is replaced by a similar resonance cone between the proton gyrofrequency, fc•,, and the local ion-ion hybrid frequency, fii. Clearly, the mechanism by Ternerin and Lysak [1984] requires the presence of heavier ions. The most extensive statistical investigation so far of the ELF emissions was based on 1122 orbits from ISIS 1 and 2...

Section: Ell(vii ) = • F(v)v ñ DV ñ (1)mentioning

confidence: 57%

Section: Specific Examplesmentioning

confidence: 99%

On waves below the local proton gyrofrequency in auroral acceleration regions

Gustafsson¹,

André²,

Matson³

et al. 1990

“…Upflowing ions that originated in the dense atmosphere will be expected to appear in region 3, their restricted pitch angle range produced by the mirror effect although transverse acceleration may move them into region 2b, producing conics [Ungstrup et al, 1979;Klumpar, 1979], or an electrostatic potential may give them additional parallel energy, further restricting their pitch angles and producing beams. However, ion beams often have pitch angle widths considerably wider than the loss cone [Coilin et al, 1981], possibly because of additional perpendicular heating [Singh et al, 1983] or diffusion [Kaufmann, 1984]. Alternatively, a structured electrostatic potential may itself give rise to conics [Lennartsson, 1980;Borovsky, 1983].…”

Section: B-• (1)mentioning

confidence: 99%

The magnitude and composition of the outflow of energetic ions from the ionosphere

Collin¹,

Sharp²,

Shelley³

1984

Data from the Lockheed ion mass spectrometer on the polar-orbiting satellite S3-3 were used to determine the outflow from the high-latitude ionosphere of terrestrial ions in the energy range of 0.5 to 16 keV during magnetically quiet times (Kp < 3) and magnetic storms (minimum Dst < -80nT). Populations of ions with different histories were separated on a statistical basis to allow the use of all available data rather than just data in which outflowing ions were conspicuous. The major constituents of the outflow were H + and O + . A small component (<5%) of He + could be detected but was too weak to be measured reliably. Both the intensity of the outflow and its composition showed marked dependence on magnetic activity. During quiet times the total outflow in this energy range from both hemispheres was --•1.3 x 1025 s -• with the ratio O+/H + = 0.25. During storms the total outflow was higher, --•7.2 x 10 25 s -1 with a much larger O + component, O+/H + = 1.4.

“…Also, accurate correction to the approximate pitch angle values in individual data samples is straightforward given an approximate knowledge of Z. where j(rn, E, ]•) is the ion intensity, ]• < 90 ø in the downward hemisphere and fire < 90ø (northern hemispheric notation); fire is energy dependent if A V :• 0. It is not possible to equate the upward flux in the (upward) loss cone with the net terrestrial ion flux, since ion beams may undergo pitch angle diffusion [Kaufman, 1984]…”

Section: Introductionmentioning

confidence: 99%

Energetic auroral and polar ion outflow at DE 1 altitudes: Magnitude, composition, magnetic activity dependence, and long‐term variations

Yau¹,

Shelley²,

Peterson³

et al. 1985

262

166

were used to determine the mass composition, magnitude, magnetic activity dependence, long-term variations, and topology (MLT-invariant latitude distribution) of energetic (0.01-17 keV/el) terrestrial outflow. The September 1981 to May 1984 period coincided with the declining phase of the current solar cycle (cycle 21), when the monthly average of the solar radio flux at 10.7 cm, Fxo.v, decreased from a high of 222 ( x 10 -22 W m -2 Hz-X) in September 1981 to a low of 93 in November 1983. At both magnetically quiet and active times, the O* outflow rate exhibited long-term variations which correlated with the declining solar radio flux. Overall, the O* outflow rate in the 1981-1982 period was a factor of 2 larger than the 1983-1984 rate. Any corresponding variation in the H* outflow rate, if present, was much smaller and not statistically significant. At solar maximum (in 1981-1982), the total ion outflow rate (H f and O f) was 1.5 x 1026 ions s-• at active times (3 < Kp < 5) and 5 x 1025 ions s -• at quiet times (Kp < 2). The active time flow was predominantly O f; the Of/H f ratio was 3. At quiet times, H f and O f flows were comparable, and the ratio was 0.9. In 1983-1984, a period of reduced solar activity, the total ion outflow rate was 1.0 x 10 26 ions s -x at active times and 4 x 1025 ions s-• at quiet times. The O f/H f ratio was 1.1 and 0.6, respectively. In both H f and O f, the outflow was dominated by < 1-keV ions. Ions of 1-17 keV/el constituted less than 10% of the total ion outflow. The O f ion outflow rate increased exponentially with the Kp index, the rate at very disturbed times (Kp > 6) being a factor of 30 larger than the quiet time (Kp = 0) value. The increase in the H f outflow rate with Kp was more modest, the disturbed time (Kp > 6) rate being a factor of 5 larger than the quiet time value. At quiet times (Kp = 0-2), 10-20% of H f and 20-25% of O f ion outflow occurs above 80 ø invariant. At active times (Kp = 3-5), 20-30% of H f and 30-35% of O f outflows occur above 76 ø invariant. Defining the polar cap as the latitude region above 80 ø invariant at low Kp and above 76 ø invariant at high Kp, the ratio of polar cap to auroral ion outflow is 0.2-0.3 at quiet times and 0.4-0.5 at active times. In other words, the polar cap ion outflow is smaller than, but nevertheless nonnegligible compared with, the auroral ion outflow, particularly at active times. For both H f and O f, the distributions of upward ion fluxes peak near 78 ø invariant in the noon sector. The averaged quiet time H f upward flux at the peak invariant latitude, normalized to 1000-km altitude, is 2-3 x 108 cm -2 s-•. The corresponding quiet time O f upward flux is --• 2 x 108 cm -2 s -• at solar maximum and increases to --• 5 x 108 cm -2 s -• at active times (Kp = 3-5). In the night side the upward ion flux peaks at lower latitude. At quiet times the peak flux in the midnight sector is a factor of 3-5 smaller than the peak flux in the noon sector. At active times it is a factor of 2 smaller. Over 95% of the quiet time (energet...