The impact of solar flare induced ionospheric disturbances on 27-day signatures in the T/I-system: preliminary results

Changes in solar activity are dominant drivers of long- and short-term variations in the upper atmosphere, which can affect each other through complex processes. Regular signatures in the ionosphere are caused, for example, by the 27-day solar rotation period and may be described with a delay of 1 to 2 days in addition to the respective amplitude. Such signatures and the associated delayed response of the ionosphere are influenced by several long-term variations (e.g., seasonal variations or 11-year solar cycle) as described in preceding studies. Here, we present the influence of solar flares on the ionospheric 27-day signatures providing a first insight into the interactions with short-term perturbations. Therefore, we present the response of different thermospheric and ionospheric parameters during X-class solar flare influenced 27-day signatures. We show in particular how the occurrence of solar flares can change accumulation processes and the resulting delay. The observed changes are especially dependent on the phase of the 27-day period in which the solar flares occur. The longest delays are observed for solar flares occurring during the ascending phase of the 27-day solar rotation period. The results are discussed in respect to preceding studies. Finally, we provide an outlook on a possible extension of the analysis by including M-class solar flares as well as additional space weather data sets and modeling results.