Climatology and Modeling of Ionospheric Irregularities over Greenland Based on Empirical Orthogonal Function Method

This paper addresses the long-term climatology (over two solar cycles) of total electron content (TEC) irregularities from a polar cap station (Thule) using rate of change of TEC index (ROTI). The climatology reveals various variabilities over different time scales, i.e., solar cycle, seasonal, and diurnal variations. These variations in different time scales can be explained by different drivers/contributors. The solar activity (represented by the solar radiation index F10.7P) dominates the longest time scale variations. The seasonal variations are controlled by the interplay of the energy input into the polar cap ionosphere and the solar illumination that damps the amplitude of ionospheric irregularities. The diurnal variations (with respect to local time) are controlled by the relative location of the station with respect to the auroral oval. We further decompose the climatology of ionospheric irregularities using the empirical orthogonal function (EOF) method. The first four EOFs could reflect the majority (99.49%) of the total data variability. By fitting the EOF coefficients using three geophysical proxies (namely, F10.7P, Bt and Dst), a climatological model of ionospheric irregularities is developed. The data-model comparison shows satisfactory results with high Pearson correlation coefficient and adequate errors. Additionally, we modeled the historical ROTI during the modern grand maximum dating back to 1965 and made the prediction during solar cycle 25. In such a way, we are able to directly compare the climatic variations of the ROTI activity across six solar cycles.