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 o...

This paper presents recent observations of the proton gyroresonance over Jicamarca. In October 2006, a single-polarization double-pulse experiment was set up to measure the first gyroresonance peak in the incoherent scatter (IS) auto-correlation function (ACF). Despite the clutter caused by Spread-F and artificial satellites, it was possible to measure the first proton gyroresonance peak of the ACF in the topside ionosphere. For the first time, least-squares fits of theoretical IS ACFs to gyroresonance measurements are reported. Theoretical ACFs that best fit the measurements were found using the H+ fraction and temperature (assuming Te = Ti) as fitting parameters. Uncertainties for the estimated fraction of H+ were as low as 12%, while uncertainties for estimated temperatures were around 30%. These are the first successful gyroresonance measurements since the early observations of Farle...

A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F (ESF) irregularities made with the system. Colocation with the 50 MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to “image” scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the inst...