Exosphere and thermosphere density measurements from GOES for space weather operations

The Earth’s thermosphere plays a critical role in the Earth’s response to space weather and satellite drag in particular. The relationship between thermospheric variability and satellite drag is relatively straightforward: A hotter thermosphere results in higher densities at all altitudes, directly increasing satellite drag. Despite its crucial role in space weather, there are presently no operational direct measurements of the thermospheric state. Instead, today, the thermospheric state can only be estimated by driving numerical models with known space weather drivers, or by assimilating spatiotemporally averaged satellite drag data into such models.

The NOAA GOES satellites include a suite of measurements for space weather operations including magnetic field, energetic particle flux, solar soft x-ray and EUV irradiance and solar corona imagery, but historically have not provided measurements of the upper atmosphere. This may soon change. Recent NASA and NOAA funded projects have derived upper atmospheric densities from GOES solar measurements during solar occultations, which include measurements of exospheric hydrogen density from ~1000 km to 40,000 km using the GOES EXIS instrument and thermospheric O and N₂ density from ~180 km to 400 km using the GOES SUVI instrument.  In this presentation, we review the new datasets, discuss their capabilities and limitations, and provide examples of both longer-term (solar cycle) and transient (geomagnetic storm) variability. Additionally, we discuss what improvements could be made for future sensors intended for thermospheric measurements.