Spatial Features of the Delayed Ionospheric Response During Low and High Solar Activity

The ionospheric response to solar 27‐day signatures has complex temporal and spatial variations, which are driven by short‐ and long‐term changes of the solar activity among other processes (e.g., geomagnetic activity). A delay between these solar and ionospheric signatures occurs due to accumulation of plasma, which depends on the rates of photoionization, photodissociation and recombination in the upper atmosphere. The balance of these processes changes significantly at different solar activity levels. Therefore the present study investigates the delayed ionospheric response during low and high solar activity. For that purpose, global as well as latitude‐ and longitude‐dependent total electron content (TEC) is analyzed via superposed epoch analysis (SEA). Different results based on the solar proxy F10.7 and solar extreme ultraviolet (EUV) irradiance measurements are presented to discuss findings of preceding studies and to provide a first wavelength‐dependent analysis of the spatial features. The SEA shows a good correlation between solar activity level and delayed ionospheric response with particular strong enhancements of the delay at mid‐latitudes. Increased delays are also observed for morning and evening hours. Thus, the present study confirms the correlation of delayed ionospheric response and solar activity level as indicated in preceding studies, and also quantifies the temporal and spatial variations with commonly used data sets. This in turn allows a better understanding of the processes that cause the delayed ionospheric response.