A climatological morphology of ionospheric disturbances at high and polar latitudes

Abstract

After a historical introduction on the first well-documented observations of ionospheric phenomena and a review of the current, state-of-the art polar ionospheric studies, a climatological morphology of the irregular Fregion plasma structures at high and polar latitudes is presented, following a feature-aided pattern recognition method. Using the available in three solar cycles hourly foF2 data from 18 ionosonde stations, an ionospheric definition of disturbed conditions, independent of any causative mechanism, is being applied and positive/negative disturbances of duration smaller than 24 hours are sorted out. No latitudinal/longitudinal bins or seasons are defined and disturbances are handled separately in each month, station and four local time intervals of storm commencement, according to solar zenith angle. In order to gain statistical significance, a median profile per disturbance is produced and studied only when storms of the respective class (phase and duration) are present for more than 15% of time from year-to-year. Non-systematic features are excluded from this analysis by careful selection of the time window under morphological investigation. First, the median profiles of disturbance patterns are fitted to standard distributions; if they fail, median disturbance patterns of each class are grouped according to their major characteristic features and are described by upper and lower limits of the variability area, along with their distribution in space and time. The present model, while being a non-conditional stand-alone model of ionospheric storms at high and polar latitudes offered to radio users, may complement existing empirical models. Finally, the present model may ultimately reveal causeeffect relationships with geomagnetic field or interplanetary parameters after further correlation studies undertaken in the future.