Weather is a tricky science, particularly at very high altitudes, with the mix of plasma and neutral particles. In sudden stratospheric warmings (SSWs) – large meteorological disturbances related to the polar vortex in which the polar stratosphere temperature increases as it is affected by the winds around the pole – the polar vortex is weakened. SSWs also have profound atmospheric effects at great distances, causing changes in the hemisphere opposite from the location of the original SSW; changes that extend all the way to the upper thermosphere and ionosphere. A study published in Geophysical Research Letters by MIT Haystack Observatory’s Larisa Goncharenko and colleagues examines the effects of a recent major Antarctic SSW on the Northern Hemisphere by studying changes observed in the upper atmosphere over North America and Europe. This important interhemispheric linkage was identified as drastic shifts at altitudes greater than 100 km – for example, in total electron content (TEC) measurements as well as variations in the thermospheric O/N2 ratio. SSWs are more frequent over the Arctic; these cause TEC and other related anomalies in the Southern Hemisphere, and thus more observations have been made on this linkage. In September 2019, an extreme, record-breaking SSW event occurred over Antarctica. Goncharenko and colleagues found significant resulting changes in the upper atmosphere in mid-latitudes over the Northern Hemisphere following this event. The changes were notable not only in severity, but because they are limited to a narrow (20–40 degrees) longitude range, differ between North America and Europe, and persist for a long time. The authors suggest that a change in the thermospheric zonal (east–west) winds are one reason for the variance between regions. Another factor is differences in magnetic declination angles; in areas with greater declination, the zonal winds can more efficiently transport plasma to higher or lower altitudes, leading to the build-up or depletion of plasma density.