Sources of longitudinal variations in the high-middle latitude ionosphere over Eurasia

Abstract

In the present study we analyze the relation of longitudinal effects in the mid-latitude and subauroral ionosphere with neutral atmosphere dynamics during quiet and disturbed geomagnetic conditions. Particularly, we analyze the large scale ionospheric effects that are initiated by large scale processes both in strato-mesosphere and in geomagnetic field. Comparing to our previous studies, we focus on processes in winter strato-mesosphere in quiet geomagnetic conditions and on lower thermosphere disturbances generated during the disturbed magnetosphere conditions. The disturbances under consideration are caused by different sources. The first source is active during quiet geomagnetic conditions in winter Northern Hemisphere, it is generated by a jet stream in strato-mesosphere. The difference between critical frequencies for the ionosondes spaced longitudinally by only 15–20 degrees could reach about 1.5–2 MHz, depending on the observation point location as related to the jet stream which usually has the specific zones of upward and downward fluxes. Second process that highly depends on neutral gas dynamics was previously analyzed on the basis of the ionosphere response to the March 2015 severe geomagnetic storm. It was shown that some unexpected longitudinal dynamics of the middle latitude ionosphere arose, while the storm-associated [O]/[N 2 ] disturbances have been moving westward during a few days. The third source of longitudinal irregularities of the ionosphere is determined by the characteristics of geomagnetic field variations. It was shown that during the storm, the three active zones with specific longitudinal structure were formed. One is shifted from the geographic pole toward the magnetic pole at ∼ 270° longitude. Two other zones were formed symmetrically opposite to the geomagnetic pole at ∼ 40°E and ∼ 130°E longitudes, and major electron density depletions were observed in the high-middle latitude ionosphere at these longitudes. On the contrary, the ∼ 80–110°E longitudinal sector showed electron density maximum in quiet conditions and fast ionosphere restoration after the storm decay. It is interesting, that the ionospheric disturbances in quiet and disturbed periods tend to be localized in the same longitudinal sectors, so that we can suggest some common mechanism responsible for the global ionosphere dynamics. Specific longitudinal structure of the middle latitude and subauroral ionosphere is analyzed. The stratosphere dynamics, geomagnetic disturbances and background geomagnetic field structure are considered as main drivers of the observed ionosphere variations.