The sun is only a year or so from the minimum of its 11-year sunspot cycle. This means few solar storms and not many solar charged particles hitting Earth's upper atmosphere triggering auroras. However, the sun has shown an unusual amount of activity the past 2 years, and last night both hemispheres were again treated to spectacular aurora displays (see the great aurora borealis and aurora australialis photos below!)
In a recent discovery
published in March 2005 in Geophysical Research Letters
, scientists reported that the high-energy particles that trigger auroras can also cause significant destruction of our protective ozone layer. Normally, ozone destruction
is associated with human-emitted Chlorofluorocarbons (CFCs) in the lower stratosphere. However, the new discovery shows that natural processes can cause significant ozone destruction in the upper stratosphere.
"The 2003-2004 Arctic winter was unique," said Dr. Gloria Manney, a JPL atmospheric scientist and one of the paper's co-authors. "First, the stratospheric polar vortex, a massive low-pressure system that confines air over the Arctic, broke down in a major stratospheric warming that lasted from January to February 2004. Such midwinter warmings typically last only a few days to a week. Then, in February and March 2004, winds in the upper stratospheric polar vortex sped up to their strongest levels on record. The vortex allowed the nitrogen gases, which are believed to have formed at least 10 kilometers (6 miles) above the stratosphere as a result of chemical reactions triggered by energetic solar particles, to descend more easily than normal into the stratosphere."
What does all this mean in terms of the amount of skin-damaging UV radiation hitting the surface? Should you put on extra sunscreen the day after seeing an aurora? No, the time to put on extra sunscreen is when the polar vortex breaks up in the Spring, when ozone-poor air that was created by CFCs and the energetic solar particles bombarding the upper stratosphere finally gets mixed down to the mid-latitudes where most of us live. This has already happened this year, back in March and April. In another blog entry later this week, I will discuss the record ozone loss--up to 30%--that was seen in the Northern Hemisphere this Spring when the polar vortex broke down. I'll answer the question, "why are we seeing record ozone losses when we've already phased out CFCs?"