Daytime F2-layer negative storm effect: what is the difference between storm-induced and Q-disturbance events?

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 in-phase 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 Q-disturbance 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.