The Occultation Wave Limb Sounder

The Occultation Wave Limb Sounder (OWLS) is a hosted instrument package designed to investigate how Earth’s thermosphere responds to atmospheric gravity waves. Gravity waves, commonly arising from irregularities in the fluid motion of the atmosphere introduced by flow over topography, such as mountains, or deep atmospheric convection, such as occurs in thunderstorms, play an important role in atmospheric dynamics by coupling the lower and upper atmosphere. The propagation of gravity waves allows for energy and momentum to be transported into the thermosphere, typically at high latitudes. The dissipation of gravity waves in the thermosphere has the potential to both heat and cool the atmosphere, with different published simulation results reaching conflicting conclusions on whether gravity wave heating or cooling dominates. Comprised of two instruments, the Extreme Ultraviolet Occultation Photometers (EUV-OP) and Compact Spectrograph for Occultations on the Limb (CSOL), OWLS will seek to resolve this controversy by making the measurements necessary to answer the two primary science questions of the mission: (1) Are regions of high gravity wave potential energy in the high latitude thermosphere positively correlated with regions of temperature increase or decrease? And (2) Is there a transition in dominant vertical wavelengths of gravity waves in the middle thermosphere from those reported in the mesosphere / lower thermosphere (MLT) region, and does this vary with season and local time? Properties of the atmosphere will be retrieved by both instruments by utilizing the technique of solar occultations. The occultation technique measures the absorption of sunlight as the instrument line of sight passes through the atmosphere, enabling the measurement of vertical profiles of atmospheric properties. EUV-OP will be responsible for retrieving thermospheric temperatures using this technique, while CSOL will make measurements of gravity wave activity in the MLT as observed through perturbations in the vertical profile of molecular oxygen density.