JULIA radar studies of equatorial spread <i>F</i>

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.

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“…Hysell and Burcham, 1998). In addition, our conclusion is also supported by the Gadanki observations (e.g.…”

Section: E-vs F-region Irregularitiessupporting

confidence: 80%

“…none (if no irregularities were observed), bottom (bottomtype or bottomside), top (plumes), and unknown (no data were available from Jicamarca). For a description on the different types of equatorial F-region irregularities, see Woodman and La Hoz (1976) and Hysell and Burcham (1998).…”

Section: Intermittent F-region Observationsmentioning

confidence: 99%

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

Chau

Woodman²,

Flores³

2002

Ann. Geophys.

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“…2 we show observations from instruments at the Jicamarca Radio Observatory (11.95 • S, 76.87 • W, dip 1 • ) on the night of 1-2 October. The upper panel shows isodensity contours measured by the Jicamarca digisonde, and the lower panel shows coherent backscatter as measured by the JULIA radar (Hysell and Burcham, 1998). A large uplift of over 100 km is observed in the ionosphere.…”

Section: Observational Evidencementioning

confidence: 99%

Observations and modeling of post-midnight uplifts near the magnetic equator

et al. 2006

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Abstract. We report here on post-midnight uplifts near the magnetic equator. We present observational evidence from digital ionosondes in Brazil, a digisonde in Peru, and other measurements at the Jicamarca Radio Observatory that show that these uplifts occur fairly regularly in the post-midnight period, raising the ionosphere by tens of kilometers in the most mild events and by over a hundred kilometers in the most severe events. We show that in general the uplifts are not the result of a zonal electric field reversal, and demonstrate instead that the uplifts occur as the ionospheric response to a decreasing westward electric field in conjunction with sufficient recombination and plasma flux. The decreasing westward electric field may be caused by a change in the wind system related to the midnight pressure bulge, which is associated with the midnight temperature maximum. In order to agree with observations from Jicamarca and Palmas, Brazil, it is shown that there must exist sufficient horizontal plasma flux associated with the pressure bulge. In addition, we show that the uplifts may be correlated with a secondary maximum in the spread-F occurrence rate in the post-midnight period. The uplifts are strongly seasonally dependent, presumably according to the seasonal dependence of the midnight pressure bulge, which leads to the necessary small westward field in the post-midnight period during certain seasons. We also discuss the enhancement of the uplifts associated with increased geomagnetic activity, which may be related to disturbance dynamo winds. Finally, we show that it is possible using simple numerical techniques to estimate the horizontal plasma flux and the vertical drift velocity from electron density measurements in the post-midnight period.

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“…Observations of QP echoes made with the Clemson radar in 1998 exhibited a preponderance of echoes with ranges between 400 and 500 km [Hysell and Burchain, 1998]. Had these echoes come from due magnetic north, …”

Section: Experiments Descriptionmentioning

confidence: 99%