In 2003, water vapor exhaust and iron that ablated during a space shuttle launch reached the lower thermosphere, Earth's neutral atmosphere above 85 km dominated by neutral gas dynamics and driven by diurnal heating. Two to three days later noctilucent clouds appeared in the upper atmosphere, and the iron was detected over the Antarctic [Stevens et al., 2005]. These observations raise an intriguing question: was there structuring in the thermospheric fluid that could have predicted the transport?
Material transport analysis is important for understanding movement of contaminants, products of meteor ablation, and plasma motion in the ionosphere, the charged particle layer embedded in the thermosphere, all of which have space weather impacts. Analysis of coherent structuring provides a way to predict such material transport. However, identification of ionospherethermosphere (IT) structuring requires sustained observation of 2D or 3D flow fields over broad regions, enabled by: distributed remote sensing and data assimilation. Together these provide the means to apply advanced fluid advection analysis for predictive ability in material transport in the upper atmosphere.
In this work, I present recent efforts in distributed sensing and data assimilation of upper atmospheric measurements. The Scintillation Auroral GPS Array (SAGA) consists of six closely spaced Global Positioning System (GPS) receivers designed to monitor fluctuations in signal amplitude and phase. Through spaced-receiver cross-correlation techniques, the array senses motion of the ionospheric irregularities that cause scintillation. The data assimilation method Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) ingests GPS-derived electron densities and Fabry-Perot interferometer (FPI) measurements of line-of-sight thermospheric neutral winds for the first time to provide regional estimates of horizontal neutral winds and ion convection.
Finally, I present a method of fluid analysis gaining widespread attention in geophysical fluid dynamics: Lagrangian Coherent Structures (LCSs). In the Lagrangian frame, which flows with the particles in contrast to an Eulerian fixed mesh frame, barriers in material transport can be numerically and objectively identified. These barriers are LCSs, manifolds of maximal separation in a flow domain. I show that the locations of global thermospheric LCSs are expected to be at mid-to-high latitudes, based on the empirical Horizontal Wind Model (HWM 2014). Such analysis can in future be applied to data-derived flow fields to investigate IT material transport such as that of the space shuttle plume.