Studying the winter anomaly with altimeter-derived TEC data

Abstract

The ionospheric Winter Anomaly (WA) is a phenomenon discovered almost 100 years ago. It can be defined as the situations in which over a given location the winter ionization level is larger than the summer ionization level, for approximately the same solar activity conditions. Along the decades, a lot of studies have been carried out and relevant theories have been formulated to explain this phenomenon, but some aspects of the nature and physical principles of the WA are still a matter of discussion. The first objective of this work was to introduce a new technique for studying the WA, at any given location over the Oceans, based on the 27-year series of altimeter (TOPEX, Jason1, Jason 2 and Jason3 satellites)-derived Total Electron Content (TEC) data. The second objective of this work was to validate the new technique by presenting a comparative analysis between the results obtained with the new technique and those already published. This goal has been accomplished by studying the WA events over the 50°N and 50°S geographic parallels using the 27-year long altimeter data series. The results have indicated clear and systematic WA occurrences over the Northern Hemisphere and a more complex situation over the Southern Hemisphere, with two regions having different behaviors. These results are in full agreement with the findings published in relevant previous works. The last objective of this work was to present some original findings related to WA events. Taking advantage of the new technique, it has been shown that the WA might be interpreted as a high solar activity period consequence of a yearly periodic phenomenon. This phenomenon is always present, also during low solar activity years, even when WA effects are not visible. During winters over the Southern Hemisphere, it systematically produces (at any solar activity level) low maximum TEC values in the (180°E?360°E) longitudinal region and high maximum TEC values in the (0°E?180°E) longitudinal sector. Precisely, this last sector matches with the well-known region over which WA events are observed for high solar activity.