The first coordinated observations of mid-latitude iE/i-region quasi-periodic radar echoes and lower thermospheric 557.7-nm airglow

摘要

We present the first coordinated observations of quasi-periodic (QP) radarechoes from sporadic-E (E_s) field-aligned irregularities (FAIs),OI 557.7-nm airglow, and neutral winds in a common volume over Shigaraki,Japan (34.9° N, 136.1° E) on the night of 5 August 2002 during the SEEK-2campaign. QP echo altitudes of 90-110 km were lower than usual by 10 km,enabling us to make a detailed comparison among QP echoes, airglow intensity,and neutral wind at around 96 km altitude. Eastward movement of the QP echoregions is consistent with the motions of neutral winds, airglow structures,and FAIs, suggesting that the electrodynamics of E_s-layers isfundamentally controlled by the neutral atmospheric dynamics. During the QP echoevent, the echo altitudes clearly went up (down) in harmony with an airglowenhancement (subsidence) that also moved to the east. This fact suggests thatthe eastward-moving enhanced airglow region included an upward (downward)component of neutral winds to raise (lower) the altitude of the wind-shear noderesponsible for the E_s formation. The airglow intensity, echo intensity,and Doppler velocity of FAIs at around 96 km altitude fluctuated with periodsfrom 10 min to 1h, indicating that these parameters were modulated withshort-period atmospheric disturbances. Some QP echo regions below 100kmaltitude contained small-scale QP structures in which very strong neutralwinds exceeding 100 m/s existed. The results are compared with recentobservations, theories, and simulations of QP echoes.Keywords. Ionosphere (Ionosphere-atmosphere interactions;Ionospheric irregularities; Mid-latitude ionosphere)