Abstract
Abstract. The second Sporadic E Experiment over Kyushu (SEEK-2) was carried out on 3 August 2002, during an active sporadic-E event that also showed quasi-periodic (QP) echoes. Two rockets were launched into the event from Kagoshima Space Center in southern Japan 15 min apart. Both carried a suite of instruments, but the second rocket also released a trimethyl aluminum (TMA) trail to measure the neutral winds and turbulence structure. In a number of earlier measurements in similar conditions, large winds and shears that were either unstable or close to instability were observed in the altitude range where the ionization layer occurred. The SEEK-2 wind measurements showed similar vertical structure, but unlike earlier experiments, there was a significant difference between the up-leg and down-leg wind profiles. In addition, wave or billow-like fluctuations were evident in the up-leg portion of the trail, while the lower portion of the down-leg trail was found to have extremely strong turbulence that led to a rapid break-up of the trail. The large east-west gradient in the winds and the strong turbulence have not been observed before. The wind profiles and shears, as well as the qualitative characteristics of the strong turbulence are presented, along with a discussion of the implications of the dynamical features. Keywords. Ionosphere (Mid-latitude ionosphere; Ionospheric irregularities; Electric field and currents)
Highlights
The first Sporadic-E Experiment over Kyushu (SEEK) (Fukao et al, 1998) was carried out in August 1996 and provided the first comprehensive measurements of the electrody-namic parameters in a quasi-periodic (QP) radar echo event
Note that the oscillations are evident throughout that height range, but the largest amplitudes occur in the lowest part of the altitude range, i.e. in the same altitude range where the low Richardson number values are found in the stability analysis of the up-leg wind profile
The maximum wind speeds and shear magnitudes observed in the SEEK-2 experiment are comparable to those observed in past experiments (e.g. Larsen et al, 1998; Larsen, 2002), but the horizontal gradients in the flow were unusual when compared with the larger data set of past observations
Summary
The first Sporadic-E Experiment over Kyushu (SEEK) (Fukao et al, 1998) was carried out in August 1996 and provided the first comprehensive measurements of the electrody-. Whitehead, 1970, and references therein), but the magnitude of the shear was large enough to suggest that Kelvin-Helmholtz billows were likely to be present in the altitude range where the ionization layer was found (Larsen et al, 1998). These results led Larsen (2000) to re-examine the data available from past rocket and radar measurements made in sporadic-E conditions, which consistently showed neutral wind shears in the vicinity of the layers that were either unstable or close to instability in the Richardson number sense.
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