Comparison of E‐region electric fields observed with a sounding rocket and a Doppler radar in the Seek Campaign

Yamamoto, M.; Itsuki, Tetsuya; Kishimoto, Takeshi; Tsunoda, Roland T.; Pfaff, R. F.; Fukao, S.

doi:10.1029/98gl01055

Cited by 24 publications

(16 citation statements)

References 12 publications

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“…As far as the neutral wind shear driven KHI is concerned, Larsen [2000], based on the simulation studies of KHI made by Fritts et al [1996], showed that the timescale for the build up and restabilization of the shear flow is ∼30 min, which means that if the shear instability is the seed for the gradient drift instability, QP event should be observed for about 30 min at a time and this could repeat as long as the shear flow repeats. Some of the midlatitude QP events occurring in a condition of large wind shear have been found to occur in patches with temporal spacings of 40–60 min [ Yamamoto et al , 1998; Larsen et al , 1998], which are quite consistent with that expected from KHI. The QP echoes that we observed, however, continued to occur for 2–8 h. Thus it is not clear as to how the QP striations should occur continuously for such a long period if they were to be associated with KHI.…”

Section: Discussionsupporting

confidence: 61%

Morphology and seasonal characteristics of low latitude E‐region quasiperiodic echoes studied using large database of Gadanki radar observations

et al. 2008

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[1] In this paper we study the morphology, seasonal features, and statistics of low latitude quasiperiodic (QP) echoes using an unprecedented data set of 147 nights of observations spanning over all seasons made using the Gadanki radar. The QP echoes have periods 2-20 min and occur on more than 50% nights. They are often found embedded in descending echoing layers whose characteristics resemble to those of tidal winds. Their occurrence shows strong seasonal dependence with 48% of the time in summer, 26-32% in equinox, and 14% in winter. The QP echoes have a tendency to appear first during 21-00 LT, which could last for 2-8 h, leading to their maximum occurrence rate during postmidnight hours. Height-time occurrences of radar echoes and QP structures both show common descending behavior, which agree extremely well with the observed descending behavior of the Es layers. We also find that the seasonal variations of QP echo occurrence are in very close agreement with that of the Es activity, tidal activity in the same height region, and also gravity wave activity in the mesosphere. Interestingly, the occurrence statistics are much more than their midlatitude counterpart; and time of first appearance, time of maximum occurrence, and duration of QP echoes all strongly contrast the midlatitude features. These observations have been discussed in detail in the light of current understanding of QP echoes.Citation: Venkateswara Rao, N., A. K. Patra, T. K. Pant, and S. V. B. Rao (2008), Morphology and seasonal characteristics of low latitude E-region quasiperiodic echoes studied using large database of Gadanki radar observations,

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Section: Discussionsupporting

confidence: 61%

Morphology and seasonal characteristics of low latitude E‐region quasiperiodic echoes studied using large database of Gadanki radar observations

et al. 2008

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“…From the rocket observations it was found that the E s layers were horizontally stratified rather than modulated in altitude as proposed by Woodman et al [1991]. On the other hand, they found very large electric fields of more than 10 mV m −1 and very large wind shear in the lower E ‐region associated with the QP echoes [ M. Yamamoto et al , 1998; M.‐Y. Yamamoto et al , 1998; Nakamura et al , 1998; Pfaff et al , 1998; Larsen et al , 1998].…”

Section: Introductionmentioning

confidence: 83%

Computer simulation of polarization electric fields as a source of midlatitude field‐aligned irregularities

2003

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[1] The generation of quasi-periodic (QP) echoes and the associated polarization electric fields in the midlatitude E-region are considered by using a computer simulation. It is shown that the horizontal structure of a sporadic-E (E s ) layer plays an important role in the generation of polarization electric fields. Where rod-like enhancements of plasma density exist in an E s layer, a large polarization electric field can be generated by an ambient zonal electric field or meridional neutral wind. The generated polarization electric fields map along the geomagnetic field up to the higher E-region and form a field-aligned plasma density structure. The growth rate of the gradient-drift instability becomes positive up to an altitude of 120 km. Meridional neutral winds can also produce striated QP echoes as a trace of the field-aligned structure. Even if the E s layer is uniform, a polarization electric field is generated by atmospheric gravity waves, especially those propagating northward, which support the resemblance of a period and a wavelength between the gravity waves and the QP echoes. The large polarization electric fields associated with the E s layer are thought to be a common phenomenon in the midlatitude and play a key role in the generation of the QP echoes.

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“…The instability characteristics are consistent with the morphology of QP echoes, which are coherent radar echoes associated with E s layers that occur in the midlatitude region during summer nights [ Yamamoto et al , 1991, 1992], when the field‐line‐integrated Hall conductivity would be most likely to dominate. The mean Doppler velocities associated with QP echoes imply electric fields of 3–5 mV/m [ Yamamoto et al , 1998]. Furthermore, the Doppler spectrum often has a very broad spread, exceeding ±200 m/s, which may indicate that small scale electric fields can approach 10 mV/m.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the nonlinear evolution of the sporadic‐E layer instability in the nighttime midlatitude ionosphere

Cosgrove

Tsunoda

2003

J. Geophys. Res.

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[1] Recently, it has been shown that the configuration of a midlatitude sporadic-E (E s ) layer at a zonal wind-shear node is unstable at night. The instability is the result of a windshear driven polarization process that occurs when a plane-wave perturbation in altitude is imposed on the E s layer. The growth rate of the instability depends on the azimuthal alignment of the plane wave distortion, a feature that is reminiscent of the Perkins instability. The plane wave nature of the growing modes, combined with the azimuthal dependance of the growth rate, suggests that the instability may provide an explanation for frontal structures observed in E s layers, which are found to consistently adopt the same azimuthal alignment preferred by the instability. In this paper the nonlinear evolution of the instability is simulated using a flux-corrected transport finite difference method for the orientation of maximum linear growth rate. It is found that the instability generates significant polarization electric fields that structure the layer; yet the structuring saturates without destroying the layer completely. Decreasing the wind shear decreases the polarization electric field and increases the evolution time scale but otherwise does not profoundly affect the structures that form in the layer. Increasing the F layer conductivity, which is assumed to map perfectly to the E s layer, damps the instability. The results suggest the instability as a possible source of the so-called quasi-periodic (QP) echoes, which are coherent radar echoes found in the nighttime midlatitude ionosphere. Citation: Cosgrove, R. B., and R. T. Tsunoda, Simulation of the nonlinear evolution of the sporadic-E layer instability in the nighttime midlatitude ionosphere,

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Comparison of E‐region electric fields observed with a sounding rocket and a Doppler radar in the Seek Campaign

Cited by 24 publications

References 12 publications

Morphology and seasonal characteristics of low latitude E‐region quasiperiodic echoes studied using large database of Gadanki radar observations

Morphology and seasonal characteristics of low latitude E‐region quasiperiodic echoes studied using large database of Gadanki radar observations

Computer simulation of polarization electric fields as a source of midlatitude field‐aligned irregularities

Simulation of the nonlinear evolution of the sporadic‐E layer instability in the nighttime midlatitude ionosphere

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