Pre-sunrise uplift and sunrise downward excursion in the F-region vertical plasma drift: Observations from the mid-latitude station Nicosia

The characteristics of mid-latitude vertical plasma drift, with a focus on pre-sunrise hours for Nicosia station, Cyprus, based on digital ionosonde measurements, have been investigated and are reported for the first time. The pre-sunrise vertical plasma drift is defined by an uplift prior to sunrise, followed by a downward drift, which is referred to as sunrise downward excursion (SDE). The pre-sunrise uplift at mid-latitudes seems to be apparent due to 'thinning' of the F- layer bottom side. The observed uplift is followed by a sudden descend which is also 'apparent' and is attributed to the downward movement of the ionisation peak during sunrise. The pre-sunrise uplift is more significant in winter but the downward drift is observed irrespective of the season.