Thermospheric hydrogen: The long‐term solar influence

Abstract

We describe an investigation of the long‐term behavior of neutral hydrogen in the thermosphere as influenced by changes associated with the solar cycle. Hydrogen concentrations are derived from application of charge exchange equilibrium to ionospheric measurements in the low‐latitude F region with the AE‐C and AE‐E satellites. The adopted data base spans the years, 1974–1979, of increasing solar activity and daily average exospheric temperatures ranging between 700° and 1300°K. Statistical analyses yield the diurnal relative variations and mean concentrations of hydrogen at a reference height of 300 km. These mean concentrations generally agree with other measurements over smaller temperature intervals, with minor differences at the higher temperatures. The associated daily average evaporative escape flux tends toward a constant value above ∼1000°K; this behavior is consistent with theory for the total vertical flux, but the magnitude, near 108 cm−2 s−1, is smaller by a factor of ∼3 than values deduced by other means. The observed diurnal variation has an average near 2.5 at the low temperatures, decreasing to about 2 as the temperature increases, in agreement with some but generally larger than most reported measurements. Current theoretical models require the presence of neutral winds and/or diurnally varying charge exchange fluxes into and out of the plasmasphere to provide diurnal ratios as large as those reported here.

The importance of neutral hydrogen for the maintenance of the midlatitude winter nighttime ionosphere: Evidence from IS observations at Kharkiv, Ukraine, and field line interhemispheric plasma model simulations

“…Similar results are obtained by us for 1996. Dependence of hydrogen density on exospheric temperature determined from 1969 to 1972 IS measurements conducted at Saint‐Santin, France (44.7°N, 2.2°E 40.4 ILAT) [ Derieux et al ., ; Breig et al ., ], is also on line with our results. Higher neutral hydrogen densities are also supported by recent measurements of the H‐alpha airglow [ Nossal et al ., ].…”

Particle tomography of the inner magnetosphere

“…Several factors may contribute to this discrepancy. For one, the hydrogen geocorona is not as stationary as treated by the Chamberlain model but rather known to have a local time [e.g., Hodges , 1994] and a solar cycle dependency [e.g., Breig et al , 1985], which are not considered by the model. Furthermore, the Rairden et al [1986] parameterization of the Chamberlain model utilizes four years of Ly α photon data measured by three imaging photometers aboard the DE 1 spacecraft.…”

Geocoronal hydrogen studies using Fabry–Perot interferometers, part 1: Instrumentation, observations, and analysis

“…Until recently, the full utilization of ground-based Balmer a nightglow measurements to extract parameters of more general aeronomic interest (i.e., [H], H(z), and f(H)) has been hampered by apparent inconsistencies with satellite Lyman a data sets (Donahue, 1966;Tinsley and Meier, 1971;Anderson et al, 1987) and in situ atomic hydrogen density measurements (e.g., Breig et al, 1985). Recent radiative transport analysis of satellite and ground-based data by Bishop (2001) and Bishop et al (2001), using the spherical nonisothermal radiative transport code LYAO_RT (Bishop, 1999), thermospheric atomic hydrogen density profiles ARTICLE IN PRESS E.J.…”