The ionosphere in mid-latitudes during the SUNDIAL campaign

This paper comments on the status of the mid-latitude ionosphere and the development of ionospheric disturbance during the SUNDIAL campaign. We distinguish different spatial scales in the response of the mid-latitudes ionosphere to the disturbance in the atmosphere/magnetosphere system that followed the arrival of the high speed solar wind front. The scales range from ''global'' to ''local''. The 5th of October is considered a typical quiet day and gives the baseline for disturbance assessment. The geomagnetic disturbance was persistent but on a rather moderate level. The mid-latitude ionosphere showed no global storm response but moderate disturbances of various and changing degrees. There were distinct hemispheric differences and, in rather small longitude sectors, stormlike depressions were observed, on different days in different sectors. An unusual morning peak and a nighttime enhancement of ionization over a very narrow latitude range complement the list of the more outstanding ''local'' disturbances of the SUNDIAL campaign. We investigated the status and the behaviour of the ionosphere by means of two types of measured data: a) parameters derived from ionosonde measurements (electron densities and characteristic heights), b) parameters derived from beacon satellite measurements (electron content)