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Technique for determining midlatitude O + /H + transition heights from topside ionograms
Author(s) -
Webb Phillip A.,
Benson Robert F.,
Grebowsky Joseph M.
Publication year - 2006
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/2005rs003391
Subject(s) - plasmasphere , electron density , ionosphere , f region , atomic physics , electron temperature , middle latitudes , ion , physics , altitude (triangle) , electron , atmospheric sciences , magnetosphere , plasma , mathematics , geophysics , geometry , quantum mechanics
The midlatitude O + /H + transition height (where the H + and O + number densities are equal) is of importance because it is where the topside altitude distribution of the dominant ions transitions from the ionospheric F region into the plasmasphere, which is considered the inner region of the magnetosphere. This transition height can be determined by fitting ionospheric topside sounder–derived electron density ( N e ) profiles to analytical H + and O + functions. There are four variables involved in this process, two involving ion number densities and two involving the electron temperature T e . The density variables are the H + density at the height of the satellite and the O + density at the base of the profile (taken as 400 km). The temperature variables have been treated using different approaches. In an earlier investigation, diffusive equilibrium ion density profiles, based on an earlier Titheridge height‐varying electron temperature function, were used to fit the N e profiles in which the electron temperature T e and the T e altitude gradient at a base height of 400 km, denoted by T 0 and G 0 , respectively, were free variables. In the present work, T 0 and G 0 are constrained by using a later Titheridge empirical temperature model. Alternatively, when in situ Langmuir probe T e determinations are available, the problem reduces to one with only one free temperature variable. All three of these approaches, using Titheridge's revised height‐varying electron temperature function, are applied to a sequence of midlatitude ISIS 2–derived N e profiles obtained during a period of prolonged high magnetic activity. The results indicate that in the inner plasmasphere, where the transition height is slowly varying, the approach based on the two free T e parameters ( T 0 and G 0 ) agrees well with the one using the Langmuir probe input. In the region where the transition height is rapidly increasing, however, the approach based on the empirical temperature model produced the most consistent results for the O + /H + transition height.