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 two-week time slices between altitudes
of 90-150km, 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 modelling Es layers, this study enhances the
modelling 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
behaviour under different atmospheric conditions, paving the way to
improved prediction of the occurrence of Es.