Exploring the Limitations of Observing the ETA

Since its discovery in the 1970s, the Equatorial Thermosphere Anomaly (ETA), also known as the Equatorial Temperature and Wind Anomaly (ETWA), has been observed by several satellite missions with many researchers trying to explain this phenomenon. The ETA is a persistent, neutral feature that appears at the equatorial dayside region between ±50° in latitude. This feature can be observed at altitudes between 350-550 km, a region of the thermosphere where ion-neutral coupling is strongest. This feature appears to be magnetically aligned, suggestive of ion-neutral coupling, and it can be easily recognized by its double-hump spikes in the neutral density, with peaks at ±20-30° in geographic latitude and a trough at the magnetic equator. While it is important to understand the full coupling mechanisms/processes occurring in this region, it is also crucial to address the limitations of the observational data. There have been several missions that have captured the ETA, the most successful being the Challenging Minisatellite Payload (CHAMP) mission. CHAMP observed the ETA by deriving density measurements using its on-board accelerometer and has observed seasonal changes, longitudinal changes, and other aspects of the feature over the course of a decade. However, there were also missions that did not capture the ETA, while taking measurements in the same region.

This poster focuses on the challenges in observing features of the ETA and the associated ionospheric properties thought to be connected to its formation. It is important that measurements capture the neutral (mass density, composition, wind, and temperature) and plasma (electron density, plasma motion) properties with sufficient precision to resolve the expected spatial and temporal gradients. Additional observational challenges include the large changes in altitude throughout the orbit, the lack of simultaneously measured parameters, and the inconsistent sampling of the target region. This poster will explore these challenges by conducting satellite fly-through schemes using NCAR’s high resolution TIEGCM (HR-TIEGCM). The goal is to specify the properties and the measurement requirements to accurately describe the formation and evolution of the ETA.