Abstract. The observed NmF2 and NmE variations were analyzed for the periods of positive and negative quiet-time F2-layer disturbances (Q-disturbances) observed in the midlatitude daytime F2-layer to specify the mechanism of their origin. The noontime δNmF2 and δNmE deviations demonstrate a synchronous type of variation which can be explained by vertical gas motion in the thermosphere. This neutral gas motion should result in atomic abundance variations, the latter being confirmed by the Millstone Hill ISR observations for periods of positive and negative Q-disturbance events. The analysis of the ISR data has shown that atomic oxygen concentration variations are the main cause of the daytime F2-layer Q-disturbances. The auroral heating which controls the poleward thermospheric wind is considered to be the basic mechanism for the Q-disturbances, however, the specific mechanisms of positive and negative Q-disturbances are different. Some morphological features of the Q-disturbances revealed earlier are explained in the scope of the proposed concept.

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Abstract. Negative F2-layer storms related to geomagnetic activity and quiet-time disturbances (Q-disturbances) belong to different classes of events and exhibit different morphology. Mid-latitude daytime Q-disturbances, unlike the usual negative F2-layer storms, demonstrate NmF2 and hmF2 inphase variations. An analysis of Millstone Hill ISR observations for usual and Q-disturbances has shown the difference in the controlling aeronomic parameter variations for the two classes of events. The decrease in atomic oxygen concentration provides the main contribution to the hmF2 decrease below the monthly median level during Q-disturbance events. Unlike the usual negative storms, the negative effect takes place in the whole topside ionosphere under Qdisturbance conditions. The difference is due to different effective plasma scale heights in the two cases. Clustering of the usual negative F2-layer disturbances around equinoxes and Q-disturbances around winter solstice, as well as different latitudinal variations for the occurrence of the two types of disturbances is due to their different formation mechanisms.

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Abstract. Earlier revealed seasonal/latitudinal variations of the occurrence for positive and negative F2-layer Qdisturbances have been interpreted in the framework of the present-day concept of the thermosphere-ionosphere interaction. The basic process is the solar-driven and storminduced thermospheric circulation's interaction which varies with season and latitude. Such morphological features as clustering of negative Q-disturbances around winter solstice and the appearance of an additional occurrence of summer peak at lower latitudes, the equinoctial occurrence peaks for positive Q-disturbances and their merging to one summer peak at lower latitudes can be explained in the framework of this concept. Moreover, seasonal/latitudinal variations of the occurrence for usual storm-induced F2-layer disturbances, which exhibit quite different morphology, are also explained within this concept and this may be considered as its success. Although some types of F2-layer Q-disturbances are obviously related to the impact from below, the analyzed seasonal/latitudinal occurrence variations are shown to have their origin in the thermosphere itself.