Ionizing the Atmosphere

Today we are going to discuss solar flares–well, not so much the flares themselves but their effects closer to home. More specifically, their effect on the ionoshere, a section of the atmosphere that is ionized by the sun’s energy. In case you don’t remember, ionization is adding or removing electrons, usually from an atom or molecule, to give it a net charge.
The ionosphere has its own usual amount of electrons, but with energetic solar flares, this is obviously going to change. Actually, today’s article, Observations of the ionospheric impact of M-class solar flares on local and hemispheric scales, by J. F. Helmboldt, N. E. Kassim, and S. W. Teare discusses the effects of moderate (“M-class”) solar flares. Solar flares are known to create sudden ionospheric disturbances (SIDs). Four such solar flares occurred nearly a year ago, on March 12th, 2015. The article, published in the American Geophysical Union’s journal Earth and Space Science in 2015, focuses on these four flares. Data and observations were gathered by GPS and radio frequency telescopes.
The amount of electrons is measured in TEC, total electron content. One TECU, total electron content unit, is 1016 electrons/square meter. So if you had a square area of one meter (close to a yard) on both side, you would have 1016 electrons in that area. In the half of the Earth lit by sunlight–there was an increase in TECU, by about 0.2 TECU, on the scale of the daylight hemisphere. This was a sudden step-up increase, so on a graph it looks like a stair, jumping from one level to the next. Three of the four studied flares resulted in this step-up. Along with this effect, TEC went up and down in ways that seemed to enhance or diminish existing irregularities in the ionosphere. No link was seen between TEC step and x-ray intensity, but then again, this only looked at four flares; that’s not really enough to draw any substantial conclusion.
A typical solar flare, taken by NASA's TRACE satellite. Image credit: NASA/LMSAL
A typical solar flare, taken by NASA’s TRACE satellite. Image credit: NASA/LMSAL
The authors also note FAIs, or field-aligned irregularities, in the plasmasphere (the area above the ionosphere), which coincide with the TEC fluctuations. FAIs are irregularities that run more or less in line with eastwards magnetic field lines. The TEC fluctuations near them were at two heights. The one at 5600 km (3480 miles) in height increased one to two minutes after the peak of the flare, then quickly vanished. The second, at 2600 km (1616 miles) appears immediately after the flare, then decreases in height over about seven minutes, vanishing around 1450 km (900 miles). These later effects may be due to the angle at which this data was taken.
Additionally, the radio telescopes also saw a drop in power. These are associated with SIDs, and are likely due to changes in the ionization. It lasted for several minutes.
There is still a lot of work to be done here. As previously mentioned, this work only focused on a handful of solar flares; while a start, it leaves much more research to be done. Solar flares have many effects on the Earth–the geomagnetic field (which can effect power grids), aurora, radio signals. Solar flares do not happen every day, but the science that studies them doesn’t take breaks.

 

Bibliography
Helmboldt, J. F., N. E. Kassim, and S. W. Teare (2015), Observations of the ionospheric impact of M-class solar flares on local and hemispheric scales, Earth and Space Science, 2, 387–402, doi:10.1002/2015EA000116.
Today’s main article.
Wanjek, Christopher. Monster Stellar Flare Seen by NASA Scientists Dwarfs All OthersNational Aeronautics and Space Administration. 6 November 2006. Web.
An article discussing a large solar flare, from which I took the image used in this post.
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