Abstract-

A major sudden stratospheric warming (SSW) occurred in January 2013 during moderate‐to‐high solar activity conditions. Observations during the winter of 2012/2013 reveal strong ionospheric disturbances associated with this event. Anomalous variations in vertical ion drift measured at the geomagnetic equator at Jicamarca (12°S, 77°W) are observed for over 40 days. We report strong perturbations in the total electron content (TEC) that maximize in the crests of equatorial ionization anomaly, reach 100% of the background value, exhibit significant longitudinal and hemispheric asymmetry, and last for over 40 days. The magnitude of ionospheric anomalies in both vertical drifts and TEC is comparable to the anomalies observed during the record‐strong SSW of January 2009 that coincided with the extreme solar minimum. This observation contrasts with results of numerical simulations that predict weaker ionospheric response to the tidal forcing during high solar activity.

Solar radio emission, especially at metre-wavelengths, is well known to vary over small spectral ( 100 kHz) and temporal (< 1 s) spans. It is comparatively recently, with the advent of a new generation of instruments, that it has become possible to capture data with sufficient resolution (temporal, spectral and angular) that one can begin to characterize the solar morphology simultaneously along the axes of time and frequency. This ability is naturally accompanied by an enormous increase in data volumes and computational burden, a problem which will only become more acute with the next generation of instruments such as the Square Kilometre Array (SKA). The usual approach, which requires manual guidance of the calibration process, is impractical. Here we present the "Automated Imaging Routine for Compact Arrays for the Radio Sun (AIRCARS)", an end-to-end imaging pipeline optimized for solar imaging with arrays with a compact core. We have used AIRCARS so far on data from the Murchison Widefield Array (MWA) Phase-I. The dynamic range of the images is routinely from a few hundred to a few thousand. In the few cases, where we have pushed AIRCARS to its limits, the dynamic range can go as high as ∼75000. The images made represent a substantial improvement in the state-of-the-art in terms of imaging fidelity and dynamic range. This has the potential to transform the multi-petabyte MWA solar archive from raw visibilities into science-ready images. AIRCARS can also be tuned to upcoming telescopes like the SKA, making it a very useful tool for the heliophysics community.

Long‐term data (1996–2001) for a number of Super Dual Auroral Radar Network (SuperDARN) HF radars in both the Northern and Southern Hemispheres are used to study the midnight F region echo occurrence. We confirm the previously reported increase of echo occurrence toward the solar cycle maximum for all radars considered and a clear winter maximum for some of them. The echo occurrence rate experiences clear equinoctial maxima for many radar locations, especially at higher latitudes and in Antarctica. We attribute the solar cycle echo increase in the midnight sector to the more frequent occurrence of enhanced electric fields and strong plasma density gradients. The equinoctial maxima are believed to be controlled entirely by the electric field increase due both to the Russell‐McPherron effect and to differences in conjugate ionospheric conductances controlled by the tilt of the Earth's axis. For the low geographic latitude portion of the Saskatoon radar observations, the echo statistics differ from the other radars; there is a clear summer maximum in echo occurrence and no definite signature of equinoctial maxima. A summer maximum in low‐latitude echo occurrence also is observed by the Hankasalmi radar during the solar cycle minima. The effect is attributed to improved propagation conditions for HF radio waves during summer periods for the latitudes where, for other seasons, there is a deficiency in the electron density.