Ionospheric Irregularities Observed During the GLEAM Survey

Nearly 200 hr of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extragalactic All-sky MWA (GLEAM) survey was used to assemble images of ionospheric structure. These images cover a nearly 50° wide area on the sky at a cadence of 10 min over many 5-7 hr long observing runs. They are generated by tracking the apparent motions of ∼200-800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the data set was dominated by three distinct signatures. The first is consistent with field-aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data imply that these are preferentially detected when there is a noticeable shear within the subtropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so-called electrobuoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic E (E_S) was present, supporting a proposed connection between these waves and polarization electric fields that may arise within E_S. We discuss the implications for future observations with the Square Kilometer Array.