Observations of F‐region Vertical Velocities at Millstone Hill 2. Evidence for Fluxes into and Out of the Protonosphere

Abstract

The vertical flux of O+ in the F region has been obtained from incoherent scatter radar measurements at Millstone Hill. The paper reports an investigation of the altitude variation of the flux during two 24‐hour periods in March taken a year apart. We find that except for a brief period around sunrise the flux is always directed downwards at altitudes below 500 km and its magnitude seems governed simply by the competing processes of production, loss, and diffusion. On the quiet day above 535 km the flux is directed upward in the afternoon when the electron density is not changing with time. This upward flux reached a peak value of ∼108 ions cm−2 sec−1 near 700 km altitude and then decreased at higher altitudes. This decrease is attributed to charge exchange with hydrogen. During the night on this day there is evidence for a downward flux of 3 × 107 O+ ions cm−2 sec−1 from the protonosphere. Additional H+ ions may be diffusing through the 1000‐km level and contributing to the maintenance of the nighttime F layer, but they would not be detected in our observations. On the disturbed day there is no evidence of a flux of ionization into the protonosphere except at sunrise. We suggest that this change is brought about by a large reduction in the abundance of neutral hydrogen, resulting from increased escape either via the polar wind or from the heating of the atmosphere in the vicinity of the auroral zones. Thus, it is suggested that the abundance of neutral hydrogen at the base of the exosphere is reduced at high latitudes during magnetic storms.

Field-aligned plasma diffusive fluxes in the topside ionosphere from radio occultation measurements by CHAMP

“…The altitudinal dependences of the diffusive fluxes are consistent with those from a numerical study by Balan and Bailey (1996). These altitude variations of the plasma diffusive velocities and fluxes have also been observed at Millstone Hill by Evans (1971c), Evans and Holt (1978). In Evans' studies, however, the transition altitudes happened between 450 and 600 km.…”

atmospheric heating by solar EUV radiation

“…However, above 300 km the ion temperature increases above the neutral temperature and thus indicates closer collisional coupling with the electrons and a small magnetospheric heat flow that is a result of the specified upper boundary condition at 800 kin. The neutral gas temperature is obtained from the model of and is in agreement with the neutral temperature deduced from the measurements of Evans [1971b].…”

“…In particular, N atoms in the 2D excited state react rapidly with Os to form NO. We have thus considered the chemistry of odd nitrogen (N4S, NSD, and NO) given in Table 1 N(•'D), and NO are calculated by using the neutral and ion chemistry given in Table 1 when by Evans [1971b] at 14.22 LT. The diurnal variation of the heat flow from the magnetosphere that is required to bring the calculated and observed temperatures at 800 km into agreement is given by Roble [1975].…”

Postsunset observations of ionospheric‐protonospheric coupling at Arecibo

“…cm -2 s -• at Arecibo. Evans [1971] higher L value than that of Arecibo (L = 1.4), some features seen in our data do appear in the model. The magnitudes of our measured velocities were less than those predicted, and the observations appear to be more altitude dependent than the model results for this time period.…”