The inflatable sphere: A technique for the accurate measurement of middle atmosphere temperatures

Abstract

In recent years there has been increasing interest in the utilization of the inflatable falling sphere technique for middle atmosphere studies. The falling sphere technique uses radar position information and the equation of motion to calculate density data from which temperature information is derived. Through theoretical derivation, simulation, and measurements it is demonstrated that the temperatures derived from falling spheres are not significantly affected by linear bias in the density measurements that originate from uncertainties in sphere mass, volume, or cross‐sectional area. This study illustrates the sphere's capability to produce accurate temperatures up to 85 km and higher, given that the necessary reduction initialization conditions are met. At heights below 60 km, comparison of sphere temperatures with in situ thermistor measurements obtained close in space and time shows good agreement. Comparison with OH‐radical rotational temperatures also confirms excellent agreement at 86 km. It is concluded that the sphere technique is an independent and highly accurate source of temperature measurement, is unique in being the only low‐cost source of in situ measurement of temperature throughout the mesosphere and lower thermosphere, and qualifies as an intrinsic method to establish the accuracy of other atmospheric measurement systems.