Retrievals of nighttime electron density from Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission Global Ultraviolet Imager (GUVI) measurements

Abstract

[1] In this work we will present a method for retrieving nighttime electron density profiles from OI 135.6 nm limb emissions measured by the Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission spacecraft. The primary mechanism for 135.6 nm radiance in the nighttime thermosphere is recombination of O + ions, and the volume emission rate is approximately proportional to the square of the electron density. Herein we describe a two-step inversion method in which we first determine the volume emission rate as a function of altitude from the radiance measurements and then use the inferred volume emission rates to determine the electron density profile. There are two important factors that we have addressed in constructing the retrieval algorithms for this problem. First, the GUVI instrument was primarily designed for day side measurements. Consequently, the signal levels on the night side are very low, and our retrieval algorithms must therefore be able to function in regions where the signals are weak. Second, since we must take the square root of the volume emission rate, it must be everywhere positive in order for the electron density to be deduced. For this reason, we have imposed nonnegativity constraints (using the methods described by Menke [1989]) on what might otherwise be discrete linear retrievals of volume emission rate. After describing the retrieval method we present an error analysis and a preliminary comparison with coincident measurements by incoherent scatter radars (ISRs). In general, the retrieved electron densities from the GUVI data agree well with the ISR data, although more coincident measurements would increase our confidence in the resulting electron density profiles.

Formation of a plasma depletion shell in the equatorial ionosphere

“…Figure 1a shows the OI 135.6-nm emission observed in successive orbit swaths near 2323 LT on 23 March 2002 by the Global Ultraviolet Imager (GUVI) [Christensen et al, 2003] on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite. Oxygen ions are the dominant ionic constituent near the F peak height, and the emission intensity of OI 135.6 nm is proportional to the line-of-sight integral of the square of the F region electron density up to the satellite altitude (625 km) [DeMajistre et al, 2004]. The image is projected onto the globe by assuming that the altitude of the peak emission is at 350 km.…”

The Global-Scale Observations of the Limb and Disk (GOLD) Mission

“…The 135.6 nm nightglow emission is produced by the relaxation of oxygen atoms in the 5 S state to the ground state, 3 P (DeMajistre et al 2004;Meier 1991 (DeMajistre et al 2004). In addition, the radiance of the 135.6 nm nightglow is enhanced by resonance scattering by ambient oxygen atoms (Qin et al 2015;Meier 1991).…”

<i>F</i>-region Pedersen conductivity deduced using the TIMED/GUVI limb retrievals

“…To investigate the seasonal difference of the growth condition of bubbles we used the EDPs deduced from the GUVI limb retrievals (see DeMajistre et al (2004) for the description of the GUVI limb retrieval). Precession of the TIMED satellite enables GUVI to sample the ionosphere for all local times every 60 days.…”

“…The Global Ultraviolet Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite provides reliable electron density profiles (EDPs) in the altitude range of 200-500 km (Christensen et al, 2003;DeMajistre et al, 2004;Paxton et al, 2004). The equatorial ionization anomaly (EIA) is normally located in this altitude range.…”