Interannual variability of the stratospheric wave driving during northern winter

[摘要] The strength of the stratospheric wave driving during northern winter isoften quantified by the January–February mean poleward eddy heat flux at 100 hPa,averaged over 40°–80° N (or a similar area and period). Despitethe dynamical and chemical relevance of the wave driving, the causes for itsvariability are still not well understood. In this study, ERA-40reanalysis data for the period 1979–2002 are used to examine several factors that significantlyaffect the interannual variability of the wave driving. The total polewardheat flux at 100 hPa is poorly correlated with that in the troposphere,suggesting a decoupling between 100 hPa and the troposphere. However, theindividual zonal wave-1 and wave-2 contributions to the wave driving at 100 hPado exhibit a significant coupling with the troposphere, predominantlytheir stationary components. The stationary wave-1 contribution tothe total wave driving significantly depends on the latitude of thestationary wave-1 source in the troposphere. The results suggest that thisdependence is associated with the varying ability of stationary wave-1activity to enter the tropospheric waveguide at mid-latitudes.The wave driving anomalies areseparated into three parts: one part due to anomalies in the zonalcorrelation coefficient between the eddy temperature and eddy meridional wind, anotherpart due to anomalies in the zonal eddy temperature amplitude, and a thirdpart due to anomalies in the zonal eddy meridional wind amplitude. It isfound that year-to-year variability in the zonal correlation coefficient between theeddy temperature and the eddy meridional wind is the most dominant factor inexplaining the year-to-year variability of the poleward eddy heat flux.

[学科分类] 大气科学