Empirical model of nitric oxide in the lower thermosphere

Abstract

The Student Nitric Oxide Explorer (SNOE) satellite made near‐continuous measurements of nitric oxide in the lower thermosphere (97.5 km to 150 km) between March 1998 and September 2000. Using eigenanalysis, this daily nitric oxide data set is represented as a time mean plus the sum of orthogonal functions of space multiplied by time‐varying coefficients. The functions, typically called empirical orthogonal functions (EOFs), are ordered by the amount of variance they capture from the original data set. While this analysis in no way guarantees that the modes of variability identified by the EOFs are associated with physical processes, we show that it is clearly so for the first three EOFs of the SNOE data set. The dominant mode of variability is associated with auroral activity, followed by a seasonal effect, and then a response to varying solar EUV flux. As a result, it is possible to construct a compact, three‐dimensional nitric oxide empirical model (NOEM) in the lower thermosphere that takes as input a planetary magnetic index, day of year, and 10.7 cm solar radio flux. Since it is possible that changes in lower thermospheric nitric oxide could lead to changes in stratospheric ozone, the model presented here can be utilized in climate simulations without the need to incorporate many thermospheric processes.