Delayed response of the ionosphere to solar EUV variability (DRIVAR)

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The ionospheric plasma reacts on solar EUV and UV variations in the course of the solar rotation with a time delay of 1-2 days. This delay is assumed to be owing to transport processes from the lower ionosphere to the F region, but only limited modeling has been performed so far to prove this hypothesis.Within DRIVAR, the processes responsible for the ionospheric delay will be investigated through comprehensive data analyses and modeling. Different kinds of solar proxies as well as spectral EUV and UV fluxes from satellite observations will be used and analyzed together with ionospheric parameters from GPS radio occultations and ionosondes, and, providing both global and high-resolution coverage, GPS total electron content maps. In particular, the ionospheric delay will be analyzed at different time scales (short-term, solar rotation, seasonal time scale), and the regional dependence of the delay will be analyzed.Due to the complex character of numerous interacting processes in the thermosphere and ionosphere numerical modeling is required to physically understand the basic processes contributing to the delay. We shall use the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model to simulate the delay and, through sensitivity experiments, investigate and analyze in detail the processes that lead to the observed delay. Additional model experiments will be performed using the Upper Atmosphere Model (UAM) for comparison.The DRIVAR results will provide more insight into ionospheric processes in general, and will be most valuable for ionospheric applications in forecasting ionospheric weather, e.g. for the use in GNSS error analyses and predictions.