Abstract
Abstract. We present the first coordinated observations of quasi-periodic (QP) radar echoes from sporadic-E (Es) 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-2 campaign. 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 echo regions is consistent with the motions of neutral winds, airglow structures, and FAIs, suggesting that the electrodynamics of Es-layers is fundamentally controlled by the neutral atmospheric dynamics. During the QP echo event, the echo altitudes clearly went up (down) in harmony with an airglow enhancement (subsidence) that also moved to the east. This fact suggests that the eastward-moving enhanced airglow region included an upward (downward) component of neutral winds to raise (lower) the altitude of the wind-shear node responsible for the Es formation. The airglow intensity, echo intensity, and Doppler velocity of FAIs at around 96 km altitude fluctuated with periods from 10 min to 1h, indicating that these parameters were modulated with short-period atmospheric disturbances. Some QP echo regions below 100km altitude contained small-scale QP structures in which very strong neutral winds exceeding 100 m/s existed. The results are compared with recent observations, theories, and simulations of QP echoes. Keywords. Ionosphere (Ionosphere-atmosphere interactions; Ionospheric irregularities; Mid-latitude ionosphere)
Highlights
Detailed behavior of 3.2-m field-aligned irregularities (FAIs) in the nighttime mid-latitude E-region in summer was presented for the first time by Yamamoto et al (1991), who used the powerful middle and upper atmosphere (MU) radar at Shigaraki, Japan (34.9◦ N, 136.1◦ E; 25.0◦ N geomagnetic)
The QP echoes appeared at altitudes of 90–110 km, which were lower by 10 km than usual QP echo altitudes, enabling us to study the relationship among FAIs, short-period atmospheric disturbances, and neutral winds at around 96 km altitude
The QP echo regions moved toward the east, contrary to the southwestward movements that have been often observed by the MU radar and radars at other locations
Summary
Detailed behavior of 3.2-m field-aligned irregularities (FAIs) in the nighttime mid-latitude E-region in summer was presented for the first time by Yamamoto et al (1991), who used the powerful middle and upper atmosphere (MU) radar at Shigaraki, Japan (34.9◦ N, 136.1◦ E; 25.0◦ N geomagnetic). They found spectacular radar echoes, called “quasi-periodic” (QP) echoes, that appear intermittently at altitudes above 100 km with periods of 5–20 min from post-sunset to midnight. Similar low-altitude QP echoes at other locations have been reported
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