The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed. The review is divided into three basic parts. In the first part the theory concerning electron heating, cooling, and energy transport processes is reviewed, and all the relevant expressions are updated. In the second part the behavior of F region electron temperatures, as measured by satellites, rockets, and incoherent scatter radars, is discussed. This portion covers electron temperature variations with altitude, latitude, local time, season, geomagnetic activity, and solar cycle. The third part is primarily devoted to a discussion of the various attempts to compare measured and calculated F region electron temperatures.

Electron temperatures in the F region of the ionosphere - Theory and observations

We have obtained solutions of the coupled continuity, momentum, and energy equations for NO(+), O(+), and O2(+) ions for conditions appropriate to the daytime high-latitude E and F regions. Owing to the rapid increase of the reaction O(+) + N2 yielding NO(+) + N with ion energy, high-latitude electric fields and consequent perpendicular-E x B drifts deplete O(+) in favor of NO(+). For electric field strengths less than about 10 mV/m the depletion of O(+) is small, and the altitude profiles of ion density are similar to those found at mid-latitudes. However, for moderate electric field strengths (50 mV/m), NO(+) is substantially increased in relation to O(+) and becomes an important ion throughout the F region. For large electric fields (200 mV/m), NO(+) completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overall F region electron density decreases markedly with increasing electric field strength, it appears that high-latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields.

Effect of electric fields on the daytime high-latitude E and F regions

A comparison of the temperature and density structure in high and low speed thermal proton flows

Seasonal and solar cyclical variations in the limiting H(+) flux are compared over the solar minimum-to-maximum interval 1974-80. The comparisons are made on the bases of values derived with the MSIS-83 and -77 models, which in turn are based on Atmospheric Explorer-E O(+) and H(+) data from the ionosphere. The H(+) flux is obtained by integration of the H(+) continuity equation along magnetic flux tubes. The seasonal and cyclical variations are dominated by the neutral hydrogen density, although the O(+) boundary density, scale height and O(+)-H reaction somewhat ameliorate the changes caused by the density variations. Finally, the plasmasphere experienced an order of magnitude decrease in H(+) in going from solar minimum to maximum, which could have been caused by longer limiting flux escapes through more, longer-lived, shorter flux tubes.

Seasonal, diurnal, and solar cyclical variations of the limiting H+ flux in the Earth's topside ionosphere

The theory for the drift of ions in the F region is briefly reviewed, and it is shown that, for the restricted case of no external electric fields or neutral air motion, the velocity of the ions along the magnetic field lines in the upper part of the F2 region can be derived from the continuity equation. Experimental results for the electron density, electron and ion temperatures, and O+ vertical velocity obtained by the incoherent (Thomson) scatter technique at Millstone Hill are presented for two 24-hour periods taken a year apart in March 1969 and 1970. The largest vertical velocities encountered occur around sunrise and sunset and give rise to vertical fluxes of the order of 5 × 108 ions/cm2/sec through 600-km altitude. It is shown that these fluxes are a result primarily of the growth or decay of the layer, though in the case of sunset the thermal contraction resulting from the decrease in the electron temperature with time assists in establishing the observed fluxes. The vertical velocity observed near 300 km is compared with the expected ambipolar diffusion velocity that should result from the observed pressure gradients in the plasma and from acceleration due to gravity. The difference between the observed and computed velocities is attributed to thermospheric neutral winds which have diurnal behavior similar to those determined by Vasseur (1969a, b) from incoherent scatter observations in France.

Observation of f-region vertical velocities at millstone hill. i. evidence for drifts due to expansion, contraction, and winds.

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E.G Fontheim

Papers

A theoretical model of the ionosphere dynamics with interhemispheric coupling