Seasonal occurrence of thin metallic ion layers at high latitudes

A year-long series of incoherent-scatter radar observations of the high-latitude ionosphere conducted at Sondrestrom in Greenland has revealed an apparent increase in the rate of occurrence of thin metallic ion layers within the E-region during the summer months, consistent with the known seasonal effect existing at middle latitudes. Unlike the situation at temperate latitudes, where shears in the neutral wind drive layer formation, layers at high latitudes are often formed by the action of large-scale electric fields of magnetospheric origin. It is suggested here that a summertime increase in layer occurrence at high latitudes is attributable to a seasonal variation in the structure of the convective electric field, which determines the regions in which the necessary conditions for layer formation are present.