Absolute Measurements of Neutral Winds and Ion Drifts in Earth’s Mesosphere and Thermosphere

Abstract

The height range from approximately 80 km to several hundred km in Earth's atmosphere is a transition region from mostly neutral dynamics at the lower altitudes to space-weather driven plasma dynamics at the top. It is an important region for many modern technological systems that either depend on spacecraft orbiting within it, or on radio signals passing through it. Traditional scale analysis of the governing equations for fluid dynamics in this region suggest that flows above about 110 km altitude should be smooth, laminar, and largely horizontal, with little spatial structure at shorter than synoptic length scales. However, when winds in this region are actually measured, such placid behavior is not observed. Understanding and accounting for this greater than expected dynamism requires measurements that are sampled locally and derived with absolute accuracy. Here it is argued that the best-known way to obtain such measurements is by trigonometric tracking of chemical tracer clouds deployed at altitude by a sounding rocket. We present a brief review of the technique, show some recent results, and discuss examples of important physical phenomena that require these measurements in order to advance current understanding. Finally, we note that the rocket-borne chemical tracer program is currently at risk of losing expertise gained over the previous several decades, and we encourage NASA to take steps to ensure that this expertise is preserved.