The D region winter anomaly at high and middle latitudes induced by planetary waves

Abstract

An observational study of the D region winter anomaly at high and middle latitudes has been made during the period of a sudden stratospheric warming of the 1967/1968 winter. From isopleth analysis of the absorption index, ƒmin, systematic large‐scale distributions of the absorption are found at even higher latitudes than 60° geomagnetic latitude as well as at middle latitudes. On the basis of evidence that geostrophic winds induced by well‐developed planetary waves extend to the upper D region, it is found that when southward winds are dominant, the absorptions become weaker at high latitude but stronger at middle latitude, indicating that abundant NO could be carried away from high‐latitude source regions to middle‐latitude sink regions. Thus large amplitude planetary waves in the D region could induce the winter anomaly through NO transport not only at middle but also at high latitudes.