Characteristics of Sporadic E Layer Occurrence in a Global Chemistry-Climate Model: A Comparison With COSMIC-Derived Data

Abstract

This study presents an analysis of sporadic-E (Es) structures within WACCM-X (the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension), including electrodynamical transport of metallic ions. A set of selection criteria have been developed to identify Es layers in WACCM-X output based on the total metal ion density in each model grid box. These criteria are used to create a climatology of Es, which is compared to Es occurrence rates derived from FORMOSAT/COSMIC-1 (Constellation Observing System for Meteorology, Ionosphere, and Climate) radio-occultation measurements. The novel identification algorithm analyses 2-week time slices between altitudes of 90–150 km, with Es layer events identified where the three selection criteria are met. Distinct seasonal distributions in Es occurrence were observed that are consistent with previous studies, with peaks during summer and reduced frequencies during winter, alignment of Es with geomagnetic contours, and layers descending in altitude as a function of local time. While discrepancies exist between WACCM-X and COSMIC data (WACCM-X occurrence rates are a factor of ∼2 lower than COSMIC-derived occurrence rates at mid-latitudes), highlighting the ongoing challenges in modeling Es layers, this study enhances the modeling capabilities of sporadic Es and deepens our understanding of their formation; it establishes a basis for their enhanced integration into global climate models and facilitates further investigation of Es behavior under different atmospheric conditions, paving the way to improved prediction of the occurrence of Es.