New sources for the hot oxygen geocorona: Solar cycle, seasonal, latitudinal, and diurnal variations

Abstract

This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low-and middle-latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of 02 + and NO +. All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of 02 + and NO + are the most important sources. Quenching of vibrationally excited N 2 (Nf) by O is the most important metastable source at night. Above 300 kin, hot O sources increase by an order of magnitude between solar minimum and solar maximum. For a given level of solar activity, the high-altitude total production rate of hot O kinetic energy is greater during winter than during summer, indicaring a dominance of cooler hot O sources during summer. The N• source dominates at low altitudes. At high altitudes it is almost negligible at solar minimum, but increases to become the dominant source at solar maximum. Atomic oxygen quenching of N(•D) is a large source at solar minimum and is still important at solar maximum. Overall, seasonal variations are small compared to solar cycle, diurnal and latitudinal variations. While quenching of roetastable species is more important at midlatitudes than at low latitudes, there is little latitudinal variation in + hot O production due to dissociative recombination of NO + and O 2 . 1. Introduction The possibility of a hot oxygen geocorona was originally discussed by Rohrbaugh and Nisbet [1973]. They calculated the flux of energetic atoms resulting from the dissociative recombination of O2 + and NO + in the F region of the Earth's ionosphere, and found that the hot atoms can ascend to altitudes of several thousand kilometers and can travel horizontally to distances of the order of the Earth's radius. Following the work of Rohrbaugh and Nisbet [1973], Torr et al. [1974] suggested that energetic oxygen atoms can also be produced by precipitating energetic O + ions during magnetically disturbed periods. Such energetic O + fluxes have been reported by Shelley et al. [1972]. Torr et al. [1974] investigated the angular and energy distributions of the energetic oxygen atoms. Later theoretical calculations were performed by Yee and Hays [1980] and Ishimoto et al. [ 1986, 1992]. The possibility of the existence of hot O coronas in other planetary atmospheres has also received attention. Theoretical studies of the hot O corona of Mars began with the suggestion of Copyright 1995 by the American Geophysical Union. Paper number 95JA00895. 0148-0227/95/95JA-00895505.00 McElroy [1972] that the dissociative recombination of 02 + would produce fast O atoms with a kinetic energy of 2.5 eV. Later, hot O calculations were performed by Knudsen [1973], while more recently, Ip [1990] and Fox [1993] have accounted for the different channels by which the dissociative recombination can occur...

Modeling the behavior of hot oxygen ions

“…6 with the production rates for hot O calculated in Richards et al (1994) and Hickey et al (1995) reveals that the loss rate is comparable to the hot O production rate of from the dominant production reaction considered, N 2 (ν=1)+O−→N 2 (ν=0)+O hot .…”

“…Comparison of figure 6 with the production rates for hot O calculated in Richards et al (1994) and Hickey et al (1995) reveals that the loss rate is comparable to the hot O production rate of from the dominant production reaction considered, distribution function can be calculated in terms of the moments of the separate species by using this distribution function:…”

“…The profile shape of the hot O density has not been determined conclusively; hot O could form a layer shape (Cotton et al, 1993;Schoendorf et al, 2000), it could approximate diffusive equilibrium (Oliver, 1997), or it could form some other type of exponential shape (Yee et al, 1980;Shematovich et al, 1994). Research has shown that hot O can be produced in numerous reactions (Richards et al, 1994;Hickey et al, 1995) and can have a potentially large effect on the energy dynamics of the ionosphere (Oliver, 1997;Alcaydé et al, 2001). Hot O ionizes in the same ways as thermal oxygen: via photoionization and charge exchange chemistry.…”

Origins and variation of terrestrial energetic neutral atoms outflow

“…There are three possible mechanisms by which energetic oxygen neutrals (>1 eV) can be produced near the Earth. These are (1) exothermic reactions in the lower ionosphere/thermosphere [Hickey et al, 1995], (2) charge exchange and energy degradation of precipitating energetic oxygen ions [Ishimoto et al, 1992;Bisikalo et al, 1995], and (3) charge exchange of energized, outflowing oxygen ions. Process 1 would be operating all of the time and should always be apparent in the data.…”

“…The second route is the so-called oxygen backsplash process of Ishimoto et al [1992] where precipitating energetic oxygen ions eject low-energy oxygen atoms and N 2 molecules from the thermosphere. The third process for producing low-energy ENA near the Earth, consists of a set of exothermic reactions that produce oxygen atoms with energies of 1 to 5 eV [Hickey et al, 1995]. These lower-energy oxygen neutrals could be visible to the LENA instrument when their energy in the spacecraft frame is boosted by the ram effect.…”