Resolving the strange behavior of extraterrestrial potassium in the upper atmosphere

Abstract

It has been known since the 1960s that the layers of Na and K atoms, which occur between 80 and 105 km in the Earth's atmosphere as a result of meteoric ablation, exhibit completely different seasonal behavior. In the extratropics Na varies annually, with a pronounced wintertime maximum and summertime minimum. However, K varies semiannually with a small summertime maximum and minima at the equinoxes. This contrasting behavior has never been satisfactorily explained. Here we use a combination of electronic structure and chemical kinetic rate theory to determine two key differences in the chemistries of K and Na. First, the neutralization of K + ions is only favored at low temperatures during summer. Second, cycling between K and its major neutral reservoir KHCO 3 is essentially temperature independent. A whole atmosphere model incorporating this new chemistry, together with a meteor input function, now correctly predicts the seasonal behavior of the K layer. Key Points Surprisingly different behavior of Na and K in the upper mesosphere is explained Development of a new K chemistry model within a 3-D chemistry-climate model ©2014. American Geophysical Union. All Rights Reserved.