Plasmasphere electron temperature studies using satellite observations and a theoretical model

Abstract

Electron temperature variations in the Earth's plasmasphere are studied using the Exos D satellite observations and the Sheffield University plasmasphere‐ionosphere model. The observations made during the years 1989–1994 are analyzed to investigate the local time and altitude (1000–8000 km) variations of the electron temperature at magnetic latitudes 0°–45°N. The observed electron temperature Te is almost constant during both day and night and is found to have large day‐to‐night differences that vary with altitude and latitude; the largest day‐to‐night ratio in Te (≈6500 K/2600 K) occurs at the highest altitude at equatorial latitudes and the smallest ratio (≈3300 K/2300 K) at the lowest altitude at midlatitudes. During daytime, Te increases rapidly with altitude in the lower plasmasphere (altitude <2500 km) and slowly in the upper plasmasphere with mean gradients of 1.33 and 0.22 K km−1, respectively. At night, on the other hand, the lower plasmasphere is in thermal equilibrium, and in the upper plasmasphere Te increases slowly with a mean gradient equal to the daytime value. The electron temperature shows maximum latitude variation at medium plasmaspheric altitudes (around 4000 km) and smaller variations at lower and higher altitudes, particularly during daytime. At the altitude of maximum latitude variation, Te increases by about 1200 K between the equator and 40°N during both day and night. The model reproduces the observations reasonably well and is used to explain the occurrence of a prominent morning peak in Te. The morning peak becomes prominent in the lower plasmasphere at low latitudes because of the vertical E × B drift in the equatorial F region, which increases Te during morning hours and decreases Te during daytime hours. The observations and model results also show the occurrence of an afternoon peak in Te, which becomes prominent with increasing altitude and latitude; the peak could be caused by the daytime poleward neutral wind.

Predawn ionospheric heating observed by Hinotori satellite

“…The heating rate at 600 km height (Figure 7) is also greater than that at 300 km height (∼1 to ∼4 K/min), reported using the backscatter radar data from Arecibo [ Carlson , 1966] and Millstone Hill [ Evans , 1967b]. The greater heating rate at the greater height (600 km) can be understood because the efficiency of photoelectron heating increases with increasing altitude [ Balan et al , 1996a].…”

On the possibility of generation of high-power low-frequency radiation as a result of evolution of explosive instability in the flow–nonisothermal plasma system

“…Note that the most difficult task is to measure the electron temperature; therefore, within the framework of the model considered, the ion sound velocity can be most indefinite. Let us assume the following parameters of the flow-nonisothermal plasma system: the proton beam velocity is 3·10 7 cm/s, the ratio of the particle densities in the beam and the background plasma is 10 −3 , the density of plasma particles is 8 · 10 4 cm −3 , and the plasma temperature is 10 6 K (these data correspond to an increase in the temperature which was recorded by the EXOS-D ("Akebono") satellite [21]. Using Eq.…”

Seasonal dependence of the longitudinal variations of nighttime ionospheric electron density and equivalent winds at southern midlatitudes

“…It could be also induced by stronger cooling effects or thermal contraction in the Southern Hemisphere in local summer (Burns et al, 2008;Liu et al, 2010). During later hours close to midnight, the equatorial anomaly disappears and the cooling effects slow down or even stop due to a decreasing temperature gradient with time (Balan et al, 1996;Liu et al, 2010), and thus the above suggested flux from the plasmasphere could be much weaker in those regions where the WSA occurs. However, it is not clear whether the expected weak downward flux around midnight in the Western Hemisphere is still stronger than that of the Eastern Hemisphere at southern midlatitudes.…”