HF radar observations of quasiperiodic E layer echoes over North America

Self Cite

Abstract. Large-scale (λ ∼ 1 km) waves in the daytime and nighttime equatorial electrojet are studied using coherent scatter radar data from Jicamarca. Images of plasma irregularities within the main beam of the radar are formed using interferometry with multiple baselines. These images are analyzed according to nonlocal gradient drift instability theory and are also compared to nonlinear computer simulations carried out recently by Ronchi et al. (1991) and Hu and Bhattacharjee (1999). In the daytime, the large-scale waves assume a non-steady dynamical equilibrium state characterized by the straining and destruction of the waves by shear and diffusion followed by spontaneous regeneration as predicted by Ronchi et al. (1991). At night, when steep plasma density gradients emerge, slowly propagating large-scale vertically extended waves predominate. Eikonal analysis suggests that these waves are trapped (absolutely unstable) or are nearly trapped (convectively unstable) and are able to tunnel between altitude regions which are locally unstable. Intermediate-scale waves are mainly transient (convectively stable) but can become absolutely unstable in narrow altitude bands determined by the background density profile. These characteristics are mainly consistent with the simulations presented by Hu and Bhattacharjee (1999). A new class of large-scale primary waves is found to occur along bands that sweep westward and downward from high altitudes through the E-region at twilight.

Section: Imaging Radar Observationssupporting

confidence: 68%

Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet

Hysell

Chau

2002

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“…The QP echoes at mid-latitudes were first observed with the middle and upper atmosphere (MU) radar in Japan and later at other latitudes, as well (Kelley et al, 1995;Pan and Tsunoda, 1998;Hysell and Burcham, 1999;Choudhary and Mahajan, 1999;Chau and Woodman, 1999;Pan and Rao, 2002). The morphology of these echoes was also described by Pan and Rao (2003), who showed that these echoes have different appearances at lower latitudes.…”

Section: Introductionmentioning

confidence: 76%

Three-dimensional tracking of mid-latitude quasi-periodic E-region echoes observed with the Chung-Li VHF radar

Chen

Röttger

et al. 2005

Abstract. This paper presents observations of low-altitude mid-latitude E-region irregularities obtained with the 52-MHz Chung-Li VHF radar. These are carried out in the interferometer mode to investigate the behavior of these irregularities over time and space. The observations presented here show the characteristics of type-II echoes noted by a negative slope, i.e. they are approaching the radar as a function of time. The range-time-intensity (RTI) plots obtained through power spectrum analysis reveal the quasi-periodic striations, which are known as LQP (Low-altitude QP) echoes. Our interferometer analysis allows one to investigate the motion (i.e. "tracking") of the LQP echo patches in three dimensions. This method is superior to just evaluating the variations of the echo power as a function of range and time in the standard RTI-plots. By applying this method, we show that the echo patches in different striations remain at almost the same altitude when we trace the isolated echoing regions until they disappear from the radar view. We further compare the rate of change of the range (range rate dR/dt) by two techniques: one by simply measuring the varying slope of the LQP echoes from RTI plot, the other by tracking the threedimensional locations of the LQP scatterers by using the interferometer technique. We finally prove that the changes in range as a function of time, deduced from the interferometer technique, are significantly correlated with those of the standard range rate analysis. However, the standard range rate analysis does not provide information about the correct location and the variation of the LQP irregularities. The threedimensional analysis, which we introduced for tracking individual striations, shows that LQP echo patches are confined to between 98 and 100 km altitude. This suggests that the irregularities which cause the LQP echoes drifted through the radar beam at approximately constant altitude, which we tend to attribute to a region of large-scale vertical shear of the horizontal wind.

“…At mid-latitudes using the Clemson HF radar, Hysell and Burcham (1999) also observed a correlation between the strength of the echoes and the direction of the Doppler velocities, namely the strongest echoes seemed generally to turn on and intensify when the Doppler velocities were away from (upward/northward) the radar and to diminish when the Doppler velocities were towards (downward/southward) the radar. Recently, Schlegel and Gurevich (1997) proposed a possible dependence of the backscatter echo intensity on neutral turbulence (as well as ionospheric parameters), particularly for lower E-region irregularities.…”

Section: E-region: Mean Doppler Velocitiesmentioning

confidence: 96%

Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar

Chau

Woodman²,

Flores³

2002

Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E-and F-region) fieldaligned irregularities obtained with the Piura VHF radar. This radar is located at ∼7.0 • dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 m s −1 ); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) Eregion Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.