Radio and optical observations of storm induced ionospheric responses over Italy

On 9 November 2012, the Sun released a slow moving CME which reached the Earth at about 23 UT on November 13th, causing a moderately strong geomagnetic storm (Kp=6) which lasted until 16 November. Ionospheric storm effects at mid-latitudes were observed and analysed by means of different ground-based instruments distributed in the Italian peninsula. These included (1) an all sky camera (ASC) deployed in Asiago (45.8oN, 11.5oE) observing at 630 nm, (2) a network of L-band dual-frequencies GNSS receivers (RING network, www.ring.gm.ingv.it), and (3) an HF ionosonde installed in Rome (41.8°N, 12.5°E). Maps derived from GNSS measurements showed an unusual enhancement of the TEC in the southern part of Italy, mainly during the nights of 14 and 15 November. The ASC observed co-located enhancements of 630 nm emission occurring at the same time, as did variations in foF2 measured by the ionosonde. A fine spectral analysis technique (called Ensemble Empirical Mode Decomposition) applied to the vertical TEC values recorded by GNSS stations revealed the simultaneous presence of Travelling Ionospheric Disturbances (TID) propagating from NE to SW in the early morning of 15 November. These TIDs were characterized by very faint oscillations (about ±0.2 TEC unit) and a time period (about 45 minutes) typical of Medium Scale TIDs. Optical images, processed by means of a time-differential technique to extract faint waves, confirmed the presence of MSTIDs.