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. The annular modes characterize the dominant variability of the extratropicalcirculation in each hemisphere, quantifying vacillations in the position ofthe tropospheric jet streams and the strength of the stratospheric polarvortices. Their representation in all available reanalysis products isassessed. Reanalysis uncertainty associated with limitations in theability to constrain the circulation with available observations, i.e., theinter-reanalysis spread, is contrasted with sampling uncertaintyassociated with the finite length of the reanalysis records. It is shown that the annular modes are extremely consistent across all modernreanalyses during the satellite era (ca. 1979 onward). Consequently,uncertainty in annular mode variability, e.g., the coupling between thestratosphere and troposphere and the variation in the amplitude and timescale of jet variations throughout the annual cycle, is dominated by samplinguncertainty. Comparison of reanalyses based on conventional (i.e.,nonsatellite) or surface observations alone with those using all availableobservations indicates that there is limited ability to characterize theSouthern Annular Mode (SAM) in the presatellite era. Notably, prior to 1979,surface-input reanalyses better capture the SAM at near-surface levels thanfull-input reanalyses. For the Northern Annular Mode, however, there isevidence that conventional observations are sufficient, at least from 1958onward. The addition of 2 additional decades of records substantiallyreduces sampling uncertainty in several key measures of annular modevariability, demonstrating the value of more historic reanalyses.Implications for the assessment of atmospheric models and the strength ofcoupling between the surface and upper atmosphere arediscussed.

Quantifying the variability of the annular modes: reanalysis uncertainty vs. sampling uncertainty