Is our dynamical understanding of the circulation changes associated with the Antarctic ozone hole sensitive to the choice of reanalysis dataset?

• Main Authors: Orr, Andrew, Lu, Hua, Martineau, Patrick, Gerber, Ed P., Marshall, Gareth, Bracegirdle, Tom J.
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; Austral; Merra; Rip; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-2020-1288; https://acp.copernicus.org/preprints/acp-2020-1288/

This study quantifies differences among four widely used atmospheric reanalysis datasets (ERA5, JRA-55, MERRA-2, and CSFR) in their representation of the dynamical changes induced by severe springtime polar stratospheric ozone depletion in the Southern Hemisphere during 1980–2001. The intercomparison is undertaken as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The dynamical changes associated with the ozone hole are examined by investigating the eddy heat and momentum fluxes and wave forcing. The reanalyses are generally in good agreement in their representation of the expected strengthening of the lower stratospheric polar vortex during the austral spring-summer season, as well as the descent of anomalously strong winds to the surface during summer and the subsequent poleward displacement and intensification of the polar front jet. Differences in the trends in zonal wind are generally small compared to the mean trends. The exception is CSFR, which shows greater disagreement compared to the other three reanalysis datasets, with stronger westerly winds in the lower stratosphere in spring and a larger poleward displacement of the tropospheric westerly jet in summer. Although our results suggest a high degree of consistency across the four reanalysis datasets in the representation of the dynamical changes associated with the ozone hole, there are larger differences in the wave forcing and eddy propagation changes compared to the similarities in the circulation trends. There is a large amount of disagreement in CFSR wave forcing/propagation trends compared to the other three reanalyses, while the best agreement is found between ERA5 and JRA-55. The underlying causes of these differences are consistent with the wind response being more constrained by the assimilation of observations compared to the wave forcing, which is more dependent on the model-based forecasts that can differ between reanalyses. Looking forward, these findings give us confidence that reanalysis datasets can be used to assess changes associated with the ongoing recovery of stratospheric ozone.