Investigation of Thermosphere Mass Density Perturbations Ascribed by CHAMP Observations

Earth’s thermosphere plays a complex role in balancing dynamic and thermodynamic processes due to its interactions with the ionosphere and external influences. Despite all the ground-based and in-situ measurements taken of the thermosphere, gaps persist in the comprehensive understanding of the thermosphere’s role in the transfer of these energy and momentum sources. This is largely attributed to the limited observational data of thermosphere and ionosphere properties collected in the same volume at the same time. Over the last two decades, on-board accelerometry techniques have been used to extract thermospheric properties of mass density and cross-track winds in the same volume and time. However, the intrinsic response of accelerometers to momentum flux introduces an inherent ambiguity between mass density and in-track winds. This ambiguity is often addressed by either neglecting the in-track winds or modeling the in-track wind using the Horizontal Wind Model. While total accelerations may not be strongly influenced by in-track winds, perturbations in acceleration often ascribed to a thermosphere density enhancement or depletion are more susceptible to in-track winds. Large wind disturbances, such as those found at high latitudes, can account for much of the acceleration perturbation (800 m/s in-track wind produces > 20% in acceleration perturbation), resulting in large mass density errors if presumed to be caused solely by mass density perturbations. An ascending-descending accelerometry (ADA) technique has been developed that takes advantage of the wind’s directionality to discern whether perturbations in accelerometer measurements are due to perturbations in the mass density, wind, or a mixture of the two.

This poster utilizes the ADA technique with CHAMP’s continuous and high-precision accelerometer data to provide a global description of whether the observed perturbations in accelerometer measurements in the upper thermosphere stem from density or wind perturbations. This description is especially important for regions that have competing formation theories (e.g., equatorial dayside and high-latitude regions) and can elucidate the underlying mechanisms responsible for the observed acceleration structures in the thermosphere without the use of supplemental wind models. The goal is to enhance the understanding of coupling of the ionosphere-thermosphere-magnetosphere system by determining which thermosphere property, density or wind, is responsible for the observed accelerations and, consequently, what processes are responsible in producing them.