Observations of QP radar echo structure consistent with neutral wind shear control of the initiation mechanism

Chen, Pan; Larsen, M. F.

doi:10.1029/1999gl010748

Cited by 15 publications

(7 citation statements)

References 16 publications

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“…The handful of chemical release wind measurements that have actually been made during events when sporadic E layers were present all show vertical shears of the horizontal wind with Richardson numbers that are either close to or below 0.25, which is the critical limit for dynamic instability to set in. Observations of QP radar echo structure consistent with neutral wind shear control of the initiation mechanism have also been reported by Pan and Larsen [2000] by using Chung‐Li VHF radar data. Inspecting our observation, we find that the LQP echoes display features that are consistent with the model proposed by Larsen [2000].…”

Section: Discussion Of Interpretationssupporting

confidence: 66%

Radar investigations of low‐altitude quasi‐periodic echoes in Chung‐Li

Chen

Röttger

Chen

2005

Geophysical Research Letters

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[1] Quasi-periodic (QP) radar echoes from the sporadic E-layers are also found at altitudes below 100 km which we call Low-altitude Quasi-Periodic echoes (LQP). We have used the Chung-Li VHF radar to study correct locations of these echoes creating irregularities, which are confined to the height range between 90 km and 100 km, have a thickness of 2 -4 km and are only slowly descending in altitude. They occur with periods of some tens of seconds to maximum three minutes. Since Chung-Li is close to the equatorial region, we can prove that these LQP occur in this temperate region as well. The particular progress reported here is that interferometry allows us to determine the position of the scattering irregularities in three dimensions, which provides new information about the motion of the scatterers. We concur with the assumption that the LQP echoes are created in a strong wind shear below 100 km altitude.

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Section: Discussion Of Interpretationssupporting

confidence: 66%

Radar investigations of low‐altitude quasi‐periodic echoes in Chung‐Li

Chen

Röttger

Chen

2005

Geophysical Research Letters

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“…The Kelvin‐Helmholtz billows associated with the instability then produce electron density structures which, in turn, may result in gradient drift instability. The characteristics of the QP echoes observed by the Chung‐Li VHF radar were found to be consistent with this mechanism [ Pan and Larsen , 2000]. It is not immediately obvious, however, as to what extent the neutral wind shear initiated instability could act as a source in the case of LQP echoes, which are so distinctly different from the QP echoes.…”

Section: Discussionmentioning

confidence: 86%

Low altitude quasi‐periodic radar echoes observed by the Gadanki VHF radar

Chen

Rao

2002

Geophysical Research Letters

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[1] We report here on the low altitude quasi-periodic (LQP) radar echoes from low latitude sporadic E layer (Es) observed by the Gadanki (13.5°N, 79.2°E; geomagnetic latitude 6.3°N) VHF radar. The LQP echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2 -4 km in the height range of 90 -100 km. The periods are found to range from tens of seconds to less than about 3 minutes. The Doppler velocities vary over a range of À20 to +20 m/s during daytime and 0 to 10 m/s during nighttime and are known to be sensitive to the layer height, being dominated by the effect of zonal electric field above and meridional neutral wind below a height of $97 km for the type 2 irregularities [Krishna Murthy et al., 1998]. The spectral widths are found to be of the order of 50 to 75 m/s during daytime and 30 to 60 m/s during nighttime. The LQP echoes reported here are similar to that observed recently over midlatitudes [Rao et al., 2000;Urbina et al., 2000], but distinctly different from the widely reported quasi-periodic (QP) echoes occurring at higher altitudes (>100 km). The observations are discussed briefly in terms of the potential source mechanisms.

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“…These echoes were first observed by Yamamoto et al (1991) using the Middle and Upper atmosphere (MU) radar at Shigaraki, Japan and subsequently by many others (e.g., Kelley et al, 1995;Hysell and Burcham, 1999;Tsunoda et al, 1999;Haldoupis et al, 2001). A number of studies have also been made from the anomaly crest zone using the Chung-Li VHF radar (e.g., Pan et al, 1994;Huang et al, 1995;Chu and Wang, 1997;Huang and Chu, 1998;Tsunoda, 1998, 1999;Pan and Larsen, 2000).…”

Section: Introductionmentioning

confidence: 96%