Relationships between the local dynamical structure of the atmosphere and ionospheric absorption during the Western European Winter Anomaly Campaign 1975/76

Abstract

During the period December 1975-mid-February 1976 of the Western European Winter Anomaly Campaign, the local dynamical and thermal structure of the stratosphere and mesosphere was determined by some 31 rocket launches at El Arenosillo, Spain, while the mesospheric thermal structure in the winter (northern) hemisphere was derived from Nimbus 6 satellite observations. An analysis of these data is presented here. As determined by the A3 technique and the parameter Ld[= L0 (n +1)], ionospheric absorption is significantly correlated with many features of the dynamical and thermal structure of the atmosphere. The strongest correlations are, on this occasion, with local winds, at a level between 85 and 92 km altitude, the sense being that high absorption corresponds to northward and eastward wind tendencies, while low absorption corresponds to southward and westward wind tendencies. Additionally, there is a significant correlation with local temperature above 60 km, high absorption corresponding to high mesospheric temperatures. These local variations are corroborated by data obtained from the PMR 3000 channel of the Nimbus 6 satellite (centred about 80km). A trivariate analysis of absorption (Ld), temperature (40° latitude) and meridional temperature gradient along the 0° longitude meridian, which corresponds to the pressure gradient driving a 'geostrophic' zonal wind, shows extremely high significance. High ionospheric absorption in Spain is associated with disruption of the normally strong winter vortex around a warm winter mesospheric pole. As the polar temperature decreases, temperatures at low- and mid-latitudes increase and, responding to a decrease of meridional temperature gradient, the mid-latitude zonal and meridonal wind regime changes. Disturbances of the winter mesospheric polar vortex are triggered by the upward propagation of earlier perturbations within the troposphere and/or stratosphere. Delays of 2-4 days are indicated between the onset of stratospheric circulation disturbances, perturbation of the mesospheric polar vortex, and the consequent dynamical and thermal effects in the mid-latitude mesosphere which are associated with anomalously high ionospheric absorption. © 1979.