Simultaneous Emergence of the X-Pattern of the Equatorial Ionization Anomaly in the American and Asian Sectors During a Geomagnetically Quiet Day

In this work, we report the simultaneous emergence of the X-pattern of equatorial ionization anomaly (EIA) in the American and Asian sectors during a geomagnetically quiet day for the first time through the Global-scale Observations of the Limb and Disk and Global Ionosphere Specification data assimilation products. The Ionospheric Connection Explorer (ICON) flying over the X-pattern shows that vertical ion drift is downward around the cross and upward on both sides, along with the simultaneously observed neutral winds. The morphology of the EIA-X is successfully reproduced by the Whole Atmosphere Community Climate Model-Xtended with the constraint lower atmosphere (SD-WACCMX). The mechanism behind the simultaneous EIA-X is further clarified. We find that the EIA-X cross coincides with the amplitude peaks of zonal neutral winds associated with the diurnal tide, and is primarily driven by downward ion drift resulting from the E-region dynamo modulated by these zonal winds.