The Response of the Es Layer to the January 2013 Sudden Stratospheric Warming and Its Physical Mechanisms

Abstract

The sporadic E (Es) layer is a thin metallic‐ion layer in the lower ionosphere whose formation is strongly influenced by neutral‐wind shear. Regional observations have revealed multiday variations in Es‐layer parameters during sudden stratospheric warming (SSW) events, but their large‐scale zonal structure remains unclear. Using near‐global Formosa Satellite‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT‐3/COSMIC) radio‐occultation observations, we examine the Es‐layer‐related occurrence rate (EsOR) during the January 2013 SSW. Neutral winds from the specified‐dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD‐WACCM‐X) are used to diagnose vertical ion convergence efficiency (VICE). Northern Hemisphere midlatitude EsOR exhibits a pronounced 10–16‐day variation dominated by a westward‐propagating zonal‐wavenumber‐1 (W1) structure. A corresponding period, propagation direction, and zonal structure are resolved in VICE. Latitude–height diagnostics further show that the 10–16‐day W1 zonal‐wind amplitude increased during the SSW; mode separation indicates that the quasi‐10‐day W1 component provides the principal event‐related enhancement within the broader band. The agreement among EsOR, VICE, and modeled winds supports planetary‐wave‐scale modulation of the E‐region wind‐shear and ion‐convergence environment. This event‐specific association does not imply that W1 alone determines individual Es‐layer formation.