Negative and positive near noontime prolonged (≥3 hours) F2-layer Q-disturbances with deviations in NmF2 > 35% occurred at Rome have been analyzed using aeronomic parameters inferred from fp180 (plasma frequency at 180 km height) and foF2 observations. Both types of NmF2 perturbations occur under quiet (daily Ap < 15 nT) geomagnetic conditions. Day-to-day atomic oxygen [O] variations at F2-region heights specify the type (positive or negative) of Q-disturbance. The [O] concentration is larger on positive and is less on negative Q-disturbance days compared to reference days. This difference takes place not only on average but for all individual Q-disturbances in question. An additional contribution to Q-disturbances formation is provided by solar EUV day-to-day variations. Negative Q-disturbance days are characterized by lower hmF2 while positive – by larger hmF2 compared to reference days. This is due to larger average Tex and vertical plasma drift W on positive Q-disturbance days, the inverse situation takes place for negative Q-disturbance days. Day-to-day changes in global thermospheric circulation may be considered as a plausible mechanism. The analyzed type of F2-layer Q-disturbances can be explained in the framework of contemporary understanding of the thermosphere-ionosphere interaction based on solar and geomagnetic activity as the main drivers.

European near-noontime ionosonde observations were considered during the period of deep solar minimum in 2008–2009 to analyze foF2 perturbations not related to solar and geomagnetic activity. Sudden stratospheric warming (SSWs) events in January 2008 and 2009 were analyzed. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F-region. Atomic oxygen was shown to be the main aeronomic parameter responsible both for the observed day-to-day and long-term (during SSWs) foF2 variations. Atomic oxygen rather than neutral temperature mainly controls the decrease of thermospheric neutral gas density in the course of the SSW events. Day-to-day variations of thermospheric circulation and an intensification of eddy diffusion during SSWs are suggested to be the processes changing the atomic oxygen abundance in the upper atmosphere for the periods in question. Recent Global-Scale Observations of the Limb and Disk (GOLD) observations of O/N2 column density confirm the depletion of the atomic oxygen abundance not related to geomagnetic activity during SSWs.

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