Daytime mid-latitude F(2)-layer Q-disturbances: A formation mechanism

Negative and positive near noontime prolonged (≥3 hours) F(2)-layer Q-disturbances with deviations in N(m)F(2) > 35% occurred at Rome have been analyzed using aeronomic parameters inferred from f(p180) (plasma frequency at 180 km height) and f(o)F(2) observations. Both types of N(m)F(2) perturbations occur under quiet (daily Ap < 15 nT) geomagnetic conditions. Day-to-day atomic oxygen [O] variations at F(2)-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 h(m)F(2) while positive – by larger h(m)F(2) 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 F(2)-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.