Hydrogen Escape Flux Research Articles

The diurnal and solar cycle variation of the charge exchange induced hydrogen escape flux

Using ion temperature and density data at specific points and times in June 1969 provided by the OGO 6 satellite, and altitude profiles of the ion and electron temperature and concentration provided by the Arecibo radar facility over the period February 1972–April 1974, the diurnal and solar cycle variation of the charge exchange induced hydrogen escape flux was investigated. It was calculated that for low to moderate solar activity at Arecibo, the diurnal ratio of the maximum-to-minimum charge exchange induced hydrogen escape flux was approximately 6 with a peak around noon and a minimum somewhere between 0100 and 0300 h L.T. This study of a limited amount of OGO 6 and Arecibo data seems to indicate that the charge exchange induced hydrogen escape flux increases as the F 10.7 flux increases for low to moderate solar activity.

Atomic hydrogen escape rate due to charge exchange with hot plasmaspheric ions

Data on ion and electron temperatures and concentrations to several thousand kilometers of altitude were obtained from the Atmosphere Explorer C satellite for 1974 and to 850 km from Arecibo incoherent scatter radar measurements. These data were used to normalize diffusive equilibrium profiles. From these profiles and by using the neutral atmospheric model of Jacchia (1971) and a new hydrogen model, the charge-exchange-induced neutral hydrogen escape fluxes for equatorial and middle latitudes were calculated. The data confirm earlier estimates that the charge exchange loss is more important than Jeans escape for the earth. It is also found that inside the plasmapause this charge exchange process with hot plasmapheric ions is the major production and loss process for the satellite population in the hydrogen geocorona.

The regulation of hydrogen and oxygen escape from Mars

It is shown that under present conditions the Jeans escape flux of hydrogen from Mars in the form of H and H 2 is constrained to be the same as twice the non-thermal ( McElroy, 1972) escape of O atoms. The mediation of the chemical chain that recombines CO 2 plays an essential role in regulating the escape of hydrogen to match that of oxygen, confirming a mechanism postulated by McElroy and Donahue (1972). It is also shown that if the oxygen flux changes, a change in the O 2 mixing ratio results and the consequence is to induce a large change in the odd hydrogen concentration, and consequently in H 2 production and hydrogen escape. The effect is to stabilize the hydrogen escape flux at twice the O flux. It is shown that surface chemistry should not change the operation of this mechanism but has consequences for the eddy coefficient variation at low altitudes. There is a strong correlation between low humidity, large solar zenith angles and large O 3 abundances. The effect of argon in a mixing ratio as large as 0.3 on these results is also investigated.

The aeronomy of the upper atmosphere of Venus

Density profiles for CO, O, and O 2 in the Cytherean atmosphere above 90 km are plotted with eddy diffusion coefficient ( K) as a parameter, subject to the constraint that the mixing ratios of CO and O 2 approach their observed value or values under the observed upper limit at the lower boundary. It is then shown that the value of K puts upper limits on the amount of hydrogen (in the form of H 2O, HCl, and H 2) the atmosphere near 90km can contain. This value is a function of the density and temperature of hydrogen at the critical level and the magnitude of the total escape flux, where unspecified flux mechanisms other than thermal are postulated ad hoc. In general these constraints call for large values of K to accomodate the atomic hydrogen produced by measured mixing ratios of HCl and H 2O. Hence they constrain thee amount of O in the upper atmosphere to values well under 1% at 130 km unless there are very large hydrogen escape fluxes, 10 7 cm −2sec −1 or larger. The freedom to assume arbitrary amounts of H 2 in the atmosphere is also restricted. We suggest either very effective escape mechanisms—despite low exospheric hydrogen densities—or novel excitation mechanisms for O(3 3S) and O(3 5S) in the upper atmosphere.