Abstract
Abstract. This study correlates different ionospheric parameters with the integrated solar extreme ultraviolet radiation (EUV) radiation to analyze the delayed ionospheric response, testing and improving upon previous studies on the ionospheric delay. Several time series of correlation coefficients and delays are presented to characterize the trend of the ionospheric delay from January 2011 to December 2013. The impact of the diurnal variations of ionospheric parameters in the analysis at an hourly resolution for fixed locations are discussed and specified with calculations in different timescales and with comparison to solar and geomagnetic activity. An average delay for the total electron content (TEC) of ≈18.7 h and for foF2 of ≈18.6 h is calculated at four European stations. The difference between the Northern and Southern hemispheres is analyzed by comparisons with the Australian region. A seasonal variation of the delay between the Northern and Southern hemispheres is calculated for TEC with ≈5±0.7 h and foF2 with ≈8±0.8 h. The latitudinal and longitudinal variability of the delay is analyzed for the European region, and found to be characterized by a decrease in the delay from ≈21.5 h at 30∘ N to ≈19.0 h at 70∘ N for summer months. For winter months, a roughly constant delay of ≈19.5 h is calculated. The results based on solar and ionospheric data at an hourly resolution and the analysis of the delayed ionospheric response to solar EUV show seasonal and latitudinal variations. Results also indicate a relationship of the ionospheric delay with geomagnetic activity and a possible correlation with the 11-year solar cycle in the analyzed time period.
Highlights
Solar extreme ultraviolet radiation (EUV) is the dominant source of ionization in the ionosphere
Parts of the EUV spectrum has been continuously measured since 2000, with publicly available EUV observations provided by the Solar EUV Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite (Woods et al, 2005), the Geostationary Operational Environmental Satellites (GOES; Machol et al, 2016), and the Solar Auto-Calibrating EUV/UV Spectrophotometers (SolACES; Nikutowski et al, 2011; Schmidtke et al, 2014)
The main challenge of delay calculation at high temporal resolution is the impact of the diurnal variations of ionospheric parameters
Summary
Solar extreme ultraviolet radiation (EUV) is the dominant source of ionization in the ionosphere. The delayed ionospheric response to solar EUV radiation is captured in various ionospheric models (Ren et al, 2018; Vaishnav et al, 2018), and respective simulations can confirm results of previous studies estimating the ionospheric delay with observational data at a daily resolution. The time series of the delays and the correlation coefficients are calculated between solar EUV radiation and two ionospheric parameters: total electron content (TEC) and the critical frequency of the F2 layer (foF2). FoF2 describes only the F2 layer of the ionosphere without complicating contributions from the plasmasphere and lower ionospheric layers Both ionospheric parameters are highly correlated (Kouris et al, 2004), but variations like different peak time of the diurnal variation (Liu et al, 2014) could have a considerable impact on the delayed ionospheric response. The results will show that the ionospheric delay is very similar for TEC and foF2
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