Soundings of Thermospheric Wind, Temperature, and Density for Space-Weather Research Using OI Fine Structure Emissions

In this paper, we present an instrument concept and new remote sensing technique capable of providing critically-needed pole-to-pole thermospheric wind, temperature, and atomic oxygen density measurements during both day and night from a low earth orbit. Today, detailed understanding of the global thermospheric composition/dynamical/thermal structures and processes governing their changes is still lacking due to limited global observations at all local times under all geophysical conditions. Specifically, the key dynamical variables, neutral wind and temperature, have not been measured well with sufficient spatial and local time coverages. The instrument, THz Limb Sounder (TLS), is aimed to provide, for the first time, these currently lacking, but critical measurements, with a focus at altitudes of 100-400 km where most of the solar and magnetospheric energies are deposited and ion-neutral energy/momentum couplings take place. This instrument- is an ambient-temperature Schottky diode based all solid-state heterodyne spectrometer designed to measure the Doppler line shape of atomic oxygen (OI) fine structure emission at 2.06 and 4.7 THz. These atomic oxygen line emissions are very bright and distributed uniformly globally (at all latitudes including high latitude spatially structured, but intense aurora particle precipitation and joule heating regions) and temporally (at all local times during both day and night and across the terminator), thus ideal for remote sensing of thermospheric thermal/dynamical structures. The TLS sensing technique, measurement methodology, a conceptual instrument design, and its expected measurement capability will be presented and discussed in this paper. Comparisons with other existing and potential sensing techniques will also be discussed.