Abstract
Abstract. During the Sporadic E Experiment over Kyushu 2 (SEEK-2) campaign, field-aligned irregularities (FAIs) associated with midlatitude sporadic-E (Es) layers were observed with two backscatter radars, the Lower Thermosphere Profiler Radar (LTPR) and the Frequency Agile Radar (FAR), which were located 40 km apart in Tanegashima, Japan. We conducted observations of FAI echoes from 31 July to 24 August 2002, and the radar data were used to determine launch timing of two sounding rockets on 3 August 2002. Our comparison of echoes obtained by the LTPR and the FAR revealed that echoes often appeared at the FAR about 10min earlier than they did at the LTPR and were well correlated. This indicates that echoing regions drift with a southward velocity component that maintains the spatial shape. Interferometry observations that were conducted with the LTPR from 3 to 8 August 2002, revealed that the quasi-periodic (QP) striations in the Range-Time-Intensity (RTI) plots were due to the apparent motion of echoing regions across the radar beam including both main and side lobes. In most cases, the echo moved to the east-southeast at an almost constant altitude of 100–110 km, which was along the locus of perpendicularity of the radar line-of-sight to the geomagnetic field line. We found that the QP pattern on the RTI plot reflects the horizontal structure and motion of the (Es layer, and that echoing regions seemed to be in one-dimensionally elongated shapes or in chains of patches. Neutral wind velocities from 75 to 105 km altitude were simultaneously derived with meteor echoes from the LTPR. This is the first time-continuous simultaneous observation FAIs and neutral wind with interferometry measurements. Assuming that the echoing regions were drifting with an ambient neutral wind, we found that the echoing region was aligned east-northeast-west-southwest in eight out of ten QP echo events during the SEEK-2 campaign. A range rate was negative (positive), when a frontal structure of echoing regions elongated east-northeast-west-southwest drifts with southward (northward) neutral wind. Keywords. Ionosphere-atmosphere interactions; Ionospheric irregularities; Plasma waves and instabilities
Highlights
There is a general introduction to this Sporadic E Experiment over Kyushu 2 (SEEK-2) campaign by Yamamoto et al (2005)
The Frequency Agile Radar (FAR) was installed in the Tanegashima Meadow of Nishinoomote City (131.03◦ E, 30.75◦ N), which we call “Tanegashima North site (TNN)”
We did the same analysis for 20 events where the Lower Thermosphere Profiler Radar (LTPR) and the FAR observed field-aligned irregularities (FAIs) echoes simultaneously during the whole observation period
Summary
There is a general introduction to this Sporadic E Experiment over Kyushu 2 (SEEK-2) campaign by Yamamoto et al (2005). Woodman et al (1991) pointed out that atmospheric gravity waves could modulate Es layers to keep the plasma unstable and could explain the quasi-periodicity. Tsunoda et al (1994) proposed a model that Es layers deeply modulated in altitude by atmospheric gravity waves could explain both the striation in the RTI plots and the quasiperiodicity. Hysell et al (2002) found that it was necessary to take into account what effect the refraction of radar waves by dense plasma clouds had in order to explain how QP striations were produced They pointed out that echoes resulted from wide azimuth angles to explain very long striations up to 60 km in range extent. By observing meteor echoes with QP echoes, neutral wind velocity around the Es layers were derived simultaneously
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