scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Geomagnetic Activity and Polar Surface Air Temperature Variability
Seppälä Annika 1 , Randall Cora 2 , Clilverd Mark 1 , Rozanov Eugene 3 , Rodger Craig 4
1 British Antarctic Survey, 2 University of Colorado, 3 Physical-Meteorological Observatory/World
Radiation Center, and Institute for Atmospheric and Climate Science, Eidgenoössische Technische
Hochschule, 4 University of Otago
ERA-40 and ECMWF operational surface level air temperature (SAT) data sets from 1957 to
2006 were used to examine polar temperature variations during years with different levels of
geomagnetic activity, as defined by the Ap index. Previous modelling work has suggested that
NOx produced at high latitudes by energetic particle precipitation can eventually lead to
detectable changes in polar SATs. We find that during winter months, ERA-40 and ECMWF
polar SATs in years with high Ap index are different than in years with low Ap index; the
differences are statistically significant at the 2-sigma level and range up to about ±4.5 K,
depending on location. The temperature differences are larger when years with wintertime
Sudden Stratospheric Warmings are excluded. Solar irradiance variations were taken into
account in the analysis.
Although using the re-analysis and operational data sets it was not possible to conclusively
show that the polar SAT patterns are physically linked by geomagnetic activity, we conclude
that geomagnetic activity likely plays a role in modulating polar wintertime surface air
temperature patterns. The SAT results were tested against variation in the Quasi Biennial
Oscillation (QBO), the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode
(SAM). The results suggested that these were not driving the observed polar SAT variability.
However, significant uncertainty is introduced by the Northern Annular Mode (NAM) and we
could not robustly exclude a chance linkage between sea surface temperature (SST)
variability and geomagnetic activity. We have further extended the SAT analysis and will in
this presentation discuss the vertical propagation and extent of the temperature signals as well
as wind anomalies from the ERA-40 and ECMWF data sets.
The physical mechanism linking the SAT variability and geomagnetic activity has recently
been examined using atmospheric models and the results will be discussed in another
presentation during this conference.