An experimental test of the ionosphere electron gas cooling rate by excitation of the fine structure of the ground state of atomic oxygen

Abstract

Excitation of the fine structure levels of the ground state of atomic oxygen, O (³P), is currently believed to be the dominant cooling mechanism for the electron gas of the bottomside ionosphere (roughly, below 250 km). Recent refinements in theoretical excitation cross section calculations have reduced its magnitude by about a factor of 3. This cooling rate, however, has never been measured. The work reported here presents the results of the first experiment designed to measure this cooling rate. The technique is to measure the time relaxation rate of the temperature of the lower F region electron gas, after it is artifically heated by radio waves from a ground‐based high‐power HF transmitter. The experimental measurements presented favor the cooling rate corresponding to the lowest of the currently available theoretical excitation cross sections. The measurements do not, however, exclude the possibility that even this rate might still be too high by a considerable factor.

Rise and fall of electron temperatures: Ohmic heating of ionospheric electrons from underdense HF radio wave pumping

“…After Shoucri et al [1984] where z is aligned with the local magnetic field, e is the electron heat conductivity, Q HF is the HF pump wave energy deposition to the electrons, Q 0 is the background electron heating (mainly from photoelectrons), and L is the electron cooling rate. The dominant cooling processes in the HF-heated ionosphere are excitation of vibrational states in N 2 [Pavlov, 1998a], excitation of fine structure levels in atomic oxygen [Dalgarno, 1968;Carlson and Mantas, 1982], excitation of vibrational states in O 2 [Pavlov, 1998b], and elastic electron-ion collisions [e.g., Rees and Roble 1975], as shown in Figure 3. If we take into account the very low field aligned plasma drift measured by EISCAT the convective terms are found to be insignificantly small and equation (1) For underdense conditions Q HF will consist of ohmic heating only, since there can be no pump-wave-driven instabilities because f 0 will be well above both f p and f UH at all altitudes.…”

Cooling rate of thermal electrons by electron impact excitation of fine structure levels of atomic oxygen

“…where the constants e ij , f ij , g ij , and q ij are given in Table 1 of Carlson and Mantas (1982). In the approximation of Eq.…”

“…Schunk and Nagy (1978) have reviewed the theory of these processes and presented the generally accepted electron cooling rates. Pavlov (1998a, c) has revised and evaluated the electron cooling rates by vibrational and rotational excitation of N 2 and O 2 and concluded that the generally accepted electron cooling rates of Prasad and Furman (1973) The thermal electron impact excitation of the ®ne structure levels of the 3 ground state of atomic oxygen is presently believed to be one of the dominant electron cooling processes in the F region of the ionosphere (Dalgarno and Degges, 1968;Hoegy, 1976;Schunk and Nagy, 1978;Carlson and Mantas, 1982;Richards et al, 1986;Richards and Khazanov, 1997). To evaluate the energy loss rate for this process, Dalgarno and Degges (1968) have employed the theoretical O 3 excitation cross sections given by Breig and Lin (1966).…”

“…To evaluate the energy loss rate for this process, Dalgarno and Degges (1968) have employed the theoretical O 3 excitation cross sections given by Breig and Lin (1966). The electron cooling rates of Hoegy (1976) and Carlson and Mantas (1982) which are currently used in models of the ionosphere are based on the excitation cross sections calculated by Henry (1974, 1976) and Le Dourneuf and Nesbet (1976). The shortcomings of the theoretical approach of Henry (1974, 1976) and Le Dourneuf and Nesbet (1976) were summarised by Berrington (1988) and Bell et al (1998) Bell et al (1998) improved the work of Berrington (1988) and presented the numerical calculations of the rate coecient of this electron cooling rate for the electron temperature, e 200, 500, 1000, 2000, and 3000 K and the neutral temperature, n 100, 300, 1000, and 2000 K. The primary object of this study is to use the theoretical O 3 excitation cross sections of Bell et al (1998) to calculate and to ®t to a new analytical expression for atomic oxygen ®ne structure cooling rate of thermal electrons.…”

Comment on “Are observed broadband plasma wave amplitudes large enough to explain the enhanced electron temperatures of the high‐latitude E Region?” by J.‐P. St.‐Maurice and Russ Laher

“…Recently, however, Carlson and Mantas 1-1982] have measured electron cooling rates using the technique of observing the time relaxation rate of the temperature, after the electron gas is subjected to a radio wave heating pulse of 2 min duration from a ground-based high-power HF transmitter [Carlson and Mantas, 1982 …”