The Occultation Wave Limb Sounder (OWLS): Science Goals and Instrumentation

Gravity waves (GWs) are atmospheric waves that commonly arise from irregularities in the fluid motion, such as wind flow over topography or from deep atmospheric convection. It is generally accepted that GWs play an important role in the energy budget of Earth's thermosphere, but the degree to which GW forcing influences the thermosphere is still poorly understood. Much of the current understanding of the influence of GWs on the thermosphere comes from numerical modeling, and the topic has become an area of increasing focus over the past decade. Although numerical GW models are only sparsely constrained by observations, both models and observations show a tendency for GWs to deposit energy at high latitudes and altitudes. However, different modeling frameworks have yielded substantially different results, creating some degree of controversy regarding the extent of GW influence on thermospheric temperature that remains unresolved due to a dearth of observations.
The Occultation Wave Limb Sounder (OWLS) is designed to address disparities in the current understanding of GW effects on the thermosphere by answering two science questions: (1) Are regions of high GW 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 GWs in the middle thermosphere from those reported in the Mesosphere/Lower Thermosphere (MLT) region, and does this vary with season and local time? OWLS measures thermospheric parameters via solar occultations, where the absorption of sunlight by atmospheric gases is used to infer atmospheric properties. OWLS consists of two instruments built by the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP), the Extreme Ultraviolet Occultation Photometers (EUV-OP) and the Compact SOLSTICE (CSOL) that, when combined, provide the needed measurements for characterizing the influence of GWs on upper atmospheric temperature. Simply put, CSOL measures GW activity in the lower and middle thermosphere and EUV-OP measures thermospheric temperature in the middle and upper thermosphere. When combined, the influence of GWs on thermospheric temperature can be directly measured. OWLS is a ~6U instrument payload flying on the INSPIRESat-3 MicroSat to be launched into a polar orbit by the Indian Space Research Organization (ISRO). The orbit will be optimized in order to observe high latitude thermospheric GWs, with a minimum mission duration of 1 year. This presentation will provide an overview of the OWLS science goals, instruments and expected performance.