Characteristics of Magnetosheath Plasma Observed at Low Altitudes in the Dayside Magnetospheric Cusps

At high latitudes, top side ionospheric spread F is observed over a very large latitude range. Within this spread F region there is a severe top side irregularity zone (stiz) in which irregularities have larger amplitudes than elsewhere. Top side ionograms obtained within the stiz exhibit very severe frequency spread (≳1 MHz) at zero range. The stiz occurs up to altitudes of at least 3000 km. Its equatorward edge is quite abrupt and is a good reflector of HF radio waves. Echoes from the stiz boundary have been observed by satellites as far as 2500 km equatorward. Comparisons of simultaneous top side sounder and particle data indicate that on the day side of the earth the equatorward boundaries of the stiz and of ≲ 300‐eV electron precipitation coincide. It is clear that the ionizing and heating effects of the particle precipitation produce irregularities, but other processes may also contribute. Usually, the stiz extends beyond the poleward boundary of the particle precipitation. This feature is probably due to magnetospheric convection transporting irregularities poleward of the region of production.

Section: Comparison Of Stiz and Particle Precipitationsupporting

confidence: 70%

Top side ionospheric spreadFand particle precipitation in the day side magnetospheric clefts

Dyson¹,

Winningham²

1974

“…cm -'•. The region in which low-energy electron This would imply that, during the first part flux is accompanied by a detectable flux of of encounter 2, the interplanetary field at the 0.1-to 10-kev protons at low altitudes is more magnetopause was northward and, during the limited in extent [Winningham, 1972] but is last part of encounter 2, the interplanetary field . contained within the region that we denote was southward.…”

supporting

confidence: 76%

Dependence of the polar cusp on the north-south component of the interplanetary magnetic field

Kivelson¹,

Russell²,

Neugebauer

et al. 1973

Ogo 5 observations of the polar cusp on November 1, 1968, show that the north‐south component of the interplanetary field exhibits control over both the location of and the physical processes occurring in the polar cusp. When the interplanetary field turned from north to south, the polar cusp moved equatorward. During intervals when the interplanetary field was southward, the electron temperature in the polar cusp was lower and the currents were stronger than when the interplanetary field was northward. Also during these intervals of southward field, regions of apparently rapidly varying currents were encountered within the cusp. Associated with these regions were enhanced VLF electric field levels. When the interplanetary field was northward, quasi‐monochromatic Pc 1 waves close to but below the proton gyrofrequency and energetic electrons (E > 50 kev) were observed. Most of these observations are consistent with the existence of merging of the interplanetary magnetic field with the dayside magnetospheric field when the interplanetary field is southward and the absence of merging when it is northward. The dependence of electron temperature on field direction remains unexplained.

“…This behavior is in contrast to Carpenter's bulge at 2000 hours and midday plasmapause at about L=4, as shown in Figure 16. It seems likely that Muldrew's trough was related in part to the movements of the auroral oval, particularly on the dayside where the cusp is found at about L=15-20 at midday and drifts equatorward at both dawn and dusk (Winningham 1972).…”

Section: Relationship Of the Plasmapause To Ionosphere Troughsmentioning

confidence: 99%

The behavior of the plasmapause at mid-latitudes: Isis 1 Langmuir probe measurements

Brace

Theis

1974

Observations of the electron concentration, Ne, and temperature, Te, from the electrostatic probes on the ISIS-I satellite were used to examine the location and behavior of the plasmapause at about 3000 kilometers altitude in the vicinity of L=4. At these altitudes, the Ne measurements are equivalent to measurements of H + since the satellite is well into the protonosphere. The plasmapause is evident as a sharp drop in Ne by a factor of 10 to 100 as the satellite passes into the polar cap, and a corresponding increase is observed as it enters the plasmasphere on the opposite side of the Earth. An enhancement of Te is also observed at the plasmapause, an effect that is most visible at night when the temperatures at latitudes above and below the plasmapause are usually very low. The position of the plasmapause, Lpp, decreases with magnetic activity but is found to be somewhat less sensitive to kp than is the equatorial plasmapause. Also unlike its equatorial behavior, the mid-latitude plasmapause exhibits no detectable late afternoon bulge. These differences imply rather complex coupling of the thermal plasma along the field lines that link these two regions of the plasmasphere.An additional factor may be the recently observed axial asymmetry in the geomagnetic field at high altitudes.iii PRECEDING PAGE BLANK NOT FILMED CONTENTS