A Comprehensive Rocket and Radar Study of Midlatitude Spread F

Abstract

An instrumented sounding rocket launched from Wallops Island Virginia has flown through a midlatitude spread F (MSF) event in conjunction with simultaneous ionosonde, HF radar, and 244 MHz scintillation observations from the ground. The in situ measurements include the electric field, horizontal neutral wind, and plasma density within the spread F region. The ground-based HF radar measurements of wave signatures in the bottomside F region ledge reveal the presence of waves propagating to the north and northwest prior to and during the spreading event. The periods of these bottomside waves range from 16 to 60 min, and they are shown to be associated with a strong tropical storm located ∼2000 km southeast of the launch site. Enhancements in the auroral current system occur about an hour before the MSF first appears, but none of the observed waves can be attributed to this source. The new phase-sensitive ionosonde system operated at Wallops Island during the experiment confirms the long-standing hypothesis that this particular spread F event arises from multipath echoes distributed over a wide field of view in the bottomside F region. Evidence of vertically displaced plasma that could produce such multipath echoes is observed in the rocket data at and above the F region peak over spatial scales smaller than the wavelengths observed on the bottomside ledge by the HF radar, but similar to the range separation given by the high resolution ionosonde echoes when the scale lengths of the structures are interpreted in magnetic coordinates. No significant plasma density structures smaller than a few kilometers are observed in the rocket data, and no unusual scintillation is observed along a path coincident with the rocket trajectory.