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Ann. Geophys., 23, 393-400, 2005
www.ann-geophys.net/23/393/2005/
© European Geosciences Union 2005
Three-dimensional tracking of mid-latitude quasi-periodic E-region echoes observed with the Chung-Li VHF radar
C. L. Chen1, C. J. Pan1, J. Röttger1, and V. K. Anandan*
1Institute of Space Science, National Central University, Chung-Li, 32054, Taiwan
*On leave from National MST Radar Facility, Gadanki, India
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
three-dimensional 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
three-dimensional analysis, which we introduced for tracking individual
striations, shows that LQP echo patches are confined to between 98 and 100km
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.
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