Morfological analysis of the winter night ionosphere in the middle latitudes of the Asian region

We present a study of particularities of the winter night f0F2 maximum in the middle latitudes of the Asian region. Data from ionospheric stations located at different longitudes and close latitudes: Novosibirsk (54.8° N, 83.2° E), Irkutsk (52.5° N, 104.0° E) and Khabarovsk (48.5° N, 135.1° E) have been used. It has been found that the night f0F2 maximum can be observed after midnight (~02-04 LT) and is a stable regularity of the quiet ionosphere from the middle of October to the middle of March at the decay and minimum of solar activity (SA) at all the stations. This interval decreases with increasing SA. A difference between maximum and minimum f0F2 values in night hours is the most significant in December-January and slightly depends on SA. Variations in f0F2 are inversely related to those in hmF2. We have studied periods when the difference between daily and night f0F2 values is less than 2 MHz. Observation intervals of such events at different longitudes do not coincide. The dependence of the winter night f0F2 maximum amplitude on magnetic activity has not been revealed.