Daytime Observations of Mid-latitude Sporadic-E and QP Radar Echoes

Although sporadic-E layers and quasi-periodic (QP) radars are typically detected during nighttime conditions at mid-latitudes, they also may exist in the daytime lower ionosphere as well. We present observations of ionosonde observations of daytime sporadic-E layers gathered at the Wallops Flight Facility, Virginia, in the late morning to noon local times. The data reveal sporadic-E characteristics similar to nighttime observations including considerable variations in frequency and altitude. For one event, observed on 23 July 1999 near 14 U.T. (10 L.T.), we present coincident strong Wallops ionosonde sporadic-E observations and 50MHz backscatter radar observations of quasi-periodic echoes gathered with the University of Illinois radar situated at Ft. Macon, N.C., whose beam was perpendicular to the magnetic field in the lower E-region over Wallops. The radar data show daytime QP structuring that is very similar to the nighttime observations, suggesting a similar driving mechanism. A statistical survey of the daytime ionogram data at Wallops shows a preponderance of daytime sporadic-E events occurring during the local summer months, a seasonal dependence that is well-established for nighttime sporadic-E conditions in the northern hemisphere. No clear correlation is observed between the daytime sporadic-E events and magnetic storms, suggesting that the daytime sporadic-E events are not necessarily driven by the disturbance dynamo. Rather, we speculate that the same large wind shears that are believed to be the main engine for the nighttime sporadic-E and QP echoes, may also be at work during the daytime. The existence of enhanced plasma density layers during the daytime and their role in generating QP- echoes during the day remain open questions.