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Ann. Geophys., 20, 1203-1212, 2002
www.ann-geophys.net/20/1203/2002/
© European Geosciences Union 2002
Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar
J. L. Chau1,2, R. F. Woodman1, and L. A. Flores2
1Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima, Perú
2Laboratorio de Física, Universidad de Piura, Piura, Perú
Correspondence to: J. L. Chau (chau@geo.igp.gob.pe), Perú
Abstract. We present a summary of
the statistical characteristics of echoes from ionospheric (E- and F-region)
field-aligned 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 ms- 1); (3) there is vertical wavelength of about 20 km in the
Doppler velocity, particularly after midnight; (4) the lower (upper) E-region
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.
Key words. Ionosphere (ionospheric
irregularities; equatorial ionosphere; instruments and techniques)
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