ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-20-1203-2002 Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar Chau J. L. 2 1 3 Woodman R. F. 1 Flores L. A. 2 Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima, Perú Laboratorio de Física, Universidad de Piura, Piura, Perú Correspondence to: J. L. Chau (chau@geo.igp.gob.pe), Perú 31 08 2002 20 8 1203 1212 Copyright: © 2002 J. L. Chau et al. 2002 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/20/1203/2002/angeo-20-1203-2002.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/20/1203/2002/angeo-20-1203-2002.pdf

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 <i>F </i>(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 (&gt; 100 ms<sup>- 1</sup>); (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.<br><br><b>Key words. </b>Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)