Ionosphere-atmosphere interaction during solar proton events

• Main Author: Verronen, Pekka
• Other Authors: Aylward, Alan, University of Helsinki, Faculty of Science, Department of Physical Sciences, Finnish Meteorological Institute, Helsingin yliopisto, matemaattis-luonnontieteellinen tiedekunta, fysikaalisten tieteiden laitos, Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, institutionen för fysikaliska vetenskaper, Kyrölä, Erkki, Turunen, Esa
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2010
• Subjects: fysiikka; Sodankylä
• Online Access: http://hdl.handle.net/10138/23151

Among the most striking natural phenomena affecting ozone are solar proton events (SPE), during which high-energy protons precipitate into the middle atmosphere in the polar regions. Ionisation caused by the protons results in changes in the lower ionosphere, and in production of neutral odd nitrogen and odd hydrogen species which then destroy ozone in well-known catalytic chemical reaction chains. Large SPEs are able to decrease the ozone concentration of upper stratosphere and mesosphere, but are not expected to significantly affect the ozone layer at 15--30~km altitude. In this work we have used the Sodankylä Ion and Neutral Chemistry Model (SIC) in studies of the short-term effects caused by SPEs. The model results were found to be in a good agreement with ionospheric observations from incoherent scatter radars, riometers, and VLF radio receivers as well as with measurements from the GOMOS/Envisat satellite instrument. For the first time, GOMOS was able to observe the SPE effects on odd nitrogen and ozone in the winter polar region. Ozone observations from GOMOS were validated against those from MIPAS/Envisat instrument, and a good agreement was found throughout the middle atmosphere. For the case of the SPE of October/November 2003, long-term ozone depletion was observed in the upper stratosphere. The depletion was further enhanced by the descent of odd nitrogen from the mesosphere inside the polar vortex, until the recovery occurred in late December. During the event, substantial diurnal variation of ozone depletion was seen in the mesosphere, caused mainly by the the strong diurnal cycle of the odd hydrogen species. In the lower ionosphere, SPEs increase the electron density which is very low in normal conditions. Therefore, SPEs make radar observations easier. In the case of the SPE of October, 1989, we studied the sunset transition of negative charge from electrons to ions, a long-standing problem. The observed phenomenon, which is controlled by the amount of solar radiation, was successfully explained ...