Collisional Joule dissipation in the ionosphere of Venus: The importance of electron heat conduction


J. Geophys. Res., 101, 2279-2295, 1996
(received March 20, 1995; revised August 18, 1995; accepted August 21, 1995.)
Copyright 1996 by the American Geophysical Union.
Paper number 95JA02587.


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Figure Captions

Figure 1.     Electron collision frequencies as a function of electron temperature. The electron-ion collision frequency (solid line) is plotted for electron densities of 10 and 10 cm, while the electron-neutral collision frequency (dashed line) is plotted for neutral oxygen densities of 10 and 10 cm, and neutral CO density of 10 cm Ionospheric electron temperatures typically lie in the range 0.1 to 1 eV [Theis et al., 1980].

thumb2 Figure 2.     Electron heating and cooling rate estimates for the dayside ionopause. Since electron-ion collisions dominate, the rates are given by (9) to (11). The rates are shown (a) as a function of density for T = 1 eV and (b) as a function of temperature for n = 1000 cm. It is also assumed that L = 1000 km, B = 50 nT, E = 10 mV/m, and the ions are O. As an indication of the relative importance of the heating and cooling rates, we include the energy density (nT). The dot on this line marks = 1, where we expect kinetic effects to be important.

Figure 3.     Electron heating and cooling rate estimates for the nightside ionosphere. (a) The rates are shown for an ionospheric hole, altitude ~ 150 km. We assume that L = 10 km, B = 30 nT, T = 0.1 eV, E = 1 mV/m, the ions are O, and the neutrals are O with a density of 4 10 cm. (b) The rates are shown for the bottomside ionosphere, altitude ~ 130 km, where electron-neutral collisions dominate. We assume that L = 2 km, B = 5 nT, n = 1000 cm, E = 10 mV/m, the neutrals are CO and N = 10 cm. In Figure 3b we have also shown the cooling rate due to vibrational excitation of CO (6).

Figures 4a & 4b, Figures 4c & 4d.     Wave propagation through the nightside Venus ionosphere for weakly attenuated 100-Hz signals. (a) Ionospheric parameters: The peak density is 1000 cm, and the ambient magnetic field is 30 nT, corresponding to a deep ionospheric hole. The electron temperature profile has been modified so that (1) is satisfied. (b) Characteristic frequencies: The electron collision frequencies, wave frequency, and electron gyrofrequency are shown. (c) Wave parameters: The wave electric field amplitude and Poynting flux are shown. The real and imaginary parts of the refractive index () are also shown. (d) Heat budget: The Joule dissipation rate, given by minus the divergence of the Poynting flux (-S), the divergence of the heat flux (q), and the elastic collision cooling rate (Q) are shown. Although not included in the heat budget, we have also included the vibrational cooling rate (Q) for reference.

Figures 5a & 5b, Figure 5c & 5d.     Wave propagation through the nightside Venus ionosphere for moderately attenuated 100-Hz signals. Similar in format to Figure 4. The peak density is 5000 cm , and the ambient magnetic field is 20 nT, corresponding to a moderate ionospheric hole.

Figures 6a & 6b, Figures 6c & 6d.     Wave propagation through the nightside Venus ionosphere for strongly attenuated 100-Hz signals. Similar in format to Figure 4. The peak density is 20,000 cm, and the ambient magnetic field is 5 nT, corresponding to the typical ionosphere. In Figure 6d the Joule dissipation is so weak at higher altitudes that we also plot -q, as this balances the cooling due to ions.

Figures 7a & 7b, Figures 7c & 7d.     Heat budget, electron temperature, and wave amplitude as a function of altitude, including vibrational cooling in the heat budget. (a) Weakly attenuated, moderate amplitude signal; (b) weakly attenuated, high amplitude signal; (c) strongly attenuated, moderate amplitude signal; (d) strongly attenuated, high amplitude signal.

Figure A1.     Cooling rates for electron-CO collisions [after Morrison and Greene, 1978]. The symbols give the cooling rates for vibrational (squares), electronic (diamonds), and rotational (triangles) excitation of CO, and for elastic, momentum transfer (circles), collisions. The solid lines give least squares fits used to parameterize the vibrational cooling rate and momentum transfer collision cross section.

Figure A2.     Electron temperature profiles and associated cooling rates for different ionosphere minimum altitudes. The temperature (thick solid line) and collisional cooling rate (thick dashed line) are plotted to the right for an ionospheric density profile that vanishes at 125 km altitude. The peak density is at 140 km, with a value of 20,000 cm. The thin lines show the temperature and cooling rate for the same peak density and altitude, but with the ionospheric minimum altitude at 130 km.


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Text and figures by R.J. Strangeway
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Last modified: Feb. 10,1996