Abstract
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)
Highlights
At low latitudes, but outside the equatorial electrojet (EEJ) region, i.e. ±3◦ off the dip equator (e.g. Forbush and Casaverde, 1961), the characteristics of the ionospheric irregularities are not well known, mainly because there have been only few observational and theoretical studies at these latitudes
The few radar observations at low latitudes have been made with the Indian VHF radar in Gadanki (13.5◦ N, 79.2◦ E; dip latitude 12.5◦ N) (e.g. Choudhary et al, 1996; Krishna Murthy et al, 1998; Choudhary and Mahajan, 1999; Patra et al, 1997; Rao et al, 1997), the Piura VHF radar in Peru (5.2◦ S, 80.63◦ W; dip latitude 13.9◦ N) (Woodman et al, 1999; Chau and Woodman, 1999) and with a forwardscatter radar system installed in South America during the International Geophysical Year (IGY) (Cohen and Bowles, 1963)
The main characteristics of the E-region echoes at these low latitudes are very similar to those observed at midlatitudes, i.e. they occur mainly at night, are produced by gradient drift instabilities, where the lower echoes are of a continuous type and the upper E-region echoes are of QP type
Summary
But outside the equatorial electrojet (EEJ) region, i.e. ±3◦ off the dip equator (e.g. Forbush and Casaverde, 1961), the characteristics of the ionospheric irregularities are not well known, mainly because there have been only few observational and theoretical studies at these latitudes. But outside the equatorial electrojet (EEJ) region, i.e. Forbush and Casaverde, 1961), the characteristics of the ionospheric irregularities are not well known, mainly because there have been only few observational and theoretical studies at these latitudes. Ionospheric field-aligned irregularities (FAI) have been intensively studied in the equatorial and auroral regions with radars and in situ measurements The few radar observations at low latitudes have been made with the Indian VHF radar in Gadanki (13.5◦ N, 79.2◦ E; dip latitude 12.5◦ N) The main characteristics of the E-region echoes at these low latitudes are very similar to those observed at midlatitudes, i.e. they occur mainly at night, are produced by gradient drift instabilities, where the lower echoes are of a continuous type and the upper E-region echoes are of QP type. The few F-region observations present very similar characteristics to the equatorial F-region irreg-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
