Solar proton events may affect cloud formation in mesosphere

NLCs are very sensitive to thermal conditions and water abundance in the upper boundary of the mesosphere and are considered to be possible early indicators of global climate change. Von Savigny et al. observe that little is known about space environment interactions with NLCs. They seek to determine how solar energetic particles, which precipitate into the Earth's polar cap areas, leading to ionization and subsequent chemical reactions, affect NLCs and their formation environment. Using satellite data on NLC occurrence and mesospheric temperature, the authors found that immediately after the onset of enhanced solar particle precipitation on 16 January 2005, a severe decrease in NLC occurrence rate was detected. Further, the decrease in the NLC occurrence rate was matched by temperature enhancements at NLC formation latitudes. The authors provide several mechanisms to explain this pattern, but suggest that detailed model simulations are needed to better understand causal mechanisms of temperature increase.- American Geophysical Union