Energetic Particle Precipitation Indirect Effect:
ODIN/SMR Observations Compared to Models
Pérot, Kristell; Urban, Joachim; Murtagh, Donal
Chalmers University of Technology, Department of Earth and Space Sciences, SWEDEN
The Sub-Millimeter Radiometer (SMR) on board the Odin platform, launched in 2001, is a limb emission sounder measuring trace gases in the stratosphere, mesosphere, and lower thermosphere. Odin is a Swedish-led satellite project funded jointly by Sweden (SNSB), Canada (CSA), Finland (TEKES), and France (CNES), with support by the 3rd party mission programme of the European Space Agency (ESA).
Energetic Particle Precipitation (EPP) represents an important solar-terrestrial coupling mechanism because of its important implications for atmospheric chemistry. These effects can be direct (formation of NOx and HOx radicals) or indirect. Magnetospheric electron precipitation into the polar atmosphere during geomagnetic perturbations leads to nitric oxide formation in the polar mesosphere and lower thermosphere. In the winter hemisphere, generated NOx can be transported downward into the stratosphere by the meridional circulation. This mechanism is called EPP indirect effect. SMR supplies the scientific community with rich data set for studying this effect on middle atmosphere composition.
Inter-comparisons of SMR measurements of several species with results from different models will be presented, focusing on the 2008/2009 northern hemisphere polar winter. This period is very interesting because it is characterized by peculiar dynamic conditions. A major sudden stratospheric warming (SSW) indeed occurred, followed by the reformation of a strong upper stratospheric vortex. This dynamic phenomenon was associated to a descent particularly efficient in the following weeks. This work is part of HEPPA-MMI (High Energy Particle Precipitation in the Atmosphere – Model-Measurement Intercomparison), an international working group whose goal is to get a better understanding of EPP-induced middle atmospheric changes, and to assess the ability of current models to reproduce those phenomena. Several instruments and models are involved.