Ionospheric variability unrelated to solar and geomagnetic activity

Ionospheric variability has become a subject of one of the most intensive studies in the area of ionospheric physics. Regardless of our improved knowledge of the ionosphere dynamics, the day-to-day variability still lies within the framework of statistical estimations and the underlying physical mechanisms are far from being fully understood. Significant deviations from monthly median values are observed from time to time in ionospheric records during completely quiet solar and geophysical conditions and are not fully understood. Recently the important role of the large scale vertical atmospheric electric fields penetrating into the ionosphere was revealed. The origin of such fields can be different, starting from orographic effect up to seismic activity. The recently published physical model of electric field effect on the ionosphere at least in part explains the ionospheric variability and the present paper is a modest attempt to demonstrate the effects of anomalous electric fields on the ionosphere using some examples.