An unusual spread-F-like event over Arecibo

Abstract

We describe an apparent mid-latitude spread-F-like event identified with the Arecibo Observatory (AO) incoherent scatter radar (ISR) but also observed using a newly introduced software-defined HF radar and via analysis of Global Positioning System-Total Electron Content (GPS-TEC) data. We show that this event was in fact nonlocal and appeared, as seen in delta-vTEC Keogram results to be propagating from west-to-east and back to the west crossing over AO twice. We suggest that this event, while indistinguishable from similar long ISR -observed events, has strong non-local properties. The combination of observations, from multiple instruments of this unique event helps tie its development and progression. The Penn State Ionospheric Radar Imager (PIRI), essentially a single frequency ionosonde, was deployed near AO (18.36° N, 66.75° W, 46.5° dip-angle, and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> = 4.42 MHz), Puerto Rico. The apparent PIRI-observed range spread of the event exceeds 400 km - a likely indication of spread-F viewed with an ionosonde. We also compare PIRI results with ISR and GPS-TEC results. ISR range-time intensity plots show rather a calm ionosphere, with exception of a major upwelling, that seems to include kilometer-scale layered structures, in the F-region. In contrast, the HF radar observations reveal that the ionosphere is disturbed by Perkins-like large scale instability structures. The data set is exceptional, consisting of simultaneous fixed frequency, wide-beam high frequency (HF) radar observations, ISR power intensity maps, and delta-vTEC measurements. These joint data sets characterized the nighttime ionosphere F-region and offer new insights into the ionospheric processes leading to what is observed by the very narrow-beam ISR.