Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 1 2007 10.5194/acpd-7-65-2007 http://www.atmos-chem-phys-discuss.net/7/65/2007/ http://www.atmos-chem-phys-discuss.net/7/65/2007/acpd-7-65-2007.html http://www.atmos-chem-phys-discuss.net/7/65/2007/acpd-7-65-2007.pdf 65 91 2007-01-05 Interannual variability of the stratospheric wave driving during northern winter A. J. Haklander haklande@knmi.nl P. C. Siegmund H. M. Kelder Eindhoven University of Technology (TUE), Department of Applied Physics, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Royal Netherlands Meteorological Institute (KNMI), Climate and Seismology Department, Climate Observation Division, P.O. Box 201, 3730 AE De Bilt, The Netherlands Royal Netherlands Meteorological Institute (KNMI), Climate and Seismology Department, Climate and Chemistry Division, P.O. Box 201, 3730 AE De Bilt, The Netherlands The strength of the stratospheric wave driving during northern winter is often quantified by the January–February mean poleward eddy heat flux at 100 hPa, averaged over 40°–80° N (or a similar area and period). Despite the dynamical and chemical relevance of the wave driving, the causes for its variability are still not well understood. In this study, 45 years of ERA-40 reanalysis data are used to examine several factors that significantly affect the interannual variability of the wave driving. The total poleward heat flux at 100 hPa is poorly correlated with that in the troposphere, suggesting a decoupling between 100 hPa and the troposphere. However, the individual zonal wave-1 and wave-2 contributions to the wave driving at 100 hPa do exhibit a significant coupling with the troposphere, predominantly due to their stationary components. The stationary wave-1 contribution to the total wave driving significantly depends on the latitude of the stationary wave-1 source in the troposphere. The results suggest that this dependence is associated with the varying ability of stationary wave-1 activity to enter the tropospheric waveguide at mid- to subpolar latitudes. If composites of strong and weak wave-driving years are compared, we find significantly higher refractive index values in the midlatitude stratosphere for the strong composite than for the weak composite. Since wave activity tends to propagate towards higher refractive index values, this could explain part of the interannual variability of the wave driving. 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