The ionosphere is one of the most fascinating parts of Earth’s atmosphere. Formed when solar radiation hits atoms and molecules in the upper atmosphere, stripping their electrons off to produce a plasma, the ionosphere extends from about 64 to 966 kilometers above the surface of Earth.
As a result of the Sun’s influence, the strength or weakness of the ionosphere depends heavily on the time of day as well as the time of year. The ionosphere on the dayside of Earth, for example, is much more heavily ionized than the nightside ionosphere. Similarly, in the wintertime, when solar radiation is significantly weaker due to the tilt of Earth’s axis, there are fewer charged particles in the ionosphere than during the summertime.
In the fall and winter, scientists frequently observe wavelike disturbances in the ionosphere traveling from higher latitudes toward the equator. These waves are characterized by enhancements and depletions in the density of electrons in the ionosphere. Here Frissell et al. investigate what causes these wavelike disturbances. Some previous studies have suggested that they are caused by space weather activity (such as the aurora), whereas others suggest that the source of the waves is internal to Earth’s atmosphere.
Using newly available Super Dual Auroral Radar Network observations, the authors discovered that the entire North American continent concurrently experiences enhancements and depletions of ionospheric wave activity lasting 2 to 4 weeks. No known space weather phenomenon routinely exhibits these multiweek time scales. However, the polar vortex, a huge cyclone of cold air situated above the North Pole, does. This discovery led the authors to focus research efforts on polar atmospheric dynamics.
After careful analysis, the researchers confirmed that no significant correlation between the ionospheric disturbances and space weather activity could be observed. On the other hand, the team found evidence for a statistically significant correlation between the ionospheric disturbances and polar vortex dynamics. This indicates that the dynamics internal to Earth’s atmosphere, rather than influences external to Earth’s atmosphere, are likely to be responsible for these disturbances. (Journal of Geophysics Research: Space Physics, doi:10.1002/2015JA022168, 2016)
—Kalman J. Knizhnik, Freelance Writer
Citation: Knizhnik, K. J. (2016), Ionospheric waves linked to polar atmospheric dynamics, Eos, 97, doi:10.1029/2016EO051167. Published on 25 April 2016.