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Discussion papers
https://doi.org/10.5194/acp-2018-585
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-585
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Jun 2018

Research article | 27 Jun 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

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

Edwin P. Gerber1 and Patrick Martineau2 Edwin P. Gerber and Patrick Martineau
  • 1Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York NY 10012, USA
  • 2Research Center for Advanced Science and Technology, University of Tokyo, Japan

Abstract. The annular modes characterize the dominant variability of the extratropical circulation in each hemisphere, quantifying vacillations in the position of the tropospheric jet streams and the strength of the stratospheric polar vortices. Their representation in all available reanalysis products is assessed. Reanalysis uncertainty associated with limitations in the ability to constrain the circulation with available observations, i.e., the inter-reanalysis spread, is contrasted with sampling uncertainty associated with the finite length of the reanalysis records.

It is shown that the annular modes are extremely consistent across all modern reanalyses during the satellite era (1979 onward). Consequently, uncertainty in annular mode variability, e.g., the coupling between the stratosphere and troposphere and the variation in the amplitude and time scale of jet variations throughout the annual cycle, is dominated by sampling uncertainty. Comparison of reanalyses based on conventional or surface observations alone with those using all available observations indicates that there is limited ability to characterize the Southern Annular Mode in the pre-satellite era. For the Northern Annular Mode, however, there is evidence that conventional observations are sufficient, at least from 1958 onward. The addition of two additional decades of records substantially reduces sampling uncertainty in several key measures of annular mode variability, demonstrating the value of more historic reanalyses. Implications for the assessment of atmospheric models and the strength of coupling between the surface and upper atmosphere are discussed.

Edwin P. Gerber and Patrick Martineau
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Edwin P. Gerber and Patrick Martineau
Edwin P. Gerber and Patrick Martineau
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The annular modes characterize the variability of the extratropical circulation. We show that they are extremely consistent across all reanalyses during the satellite era (1979 onward). Consequently, uncertainty in the annual cycle of variability of the tropospheric jet streams and their coupling with the stratospheric polar vortices is dominated by sampling uncertainty. Pre-satellite reanalysis of the boreal hemisphere appears to be of high quality, and can help reduce this uncertainty.
The annular modes characterize the variability of the extratropical circulation. We show that...
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