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

Abstract

Abstract. This study quantifies differences among four widely used atmospheric reanalysis datasets (ERA5, JRA-55, MERRA-2, and CFSR) in their representation of the dynamical changes induced by springtime polar stratospheric ozone depletion in the Southern Hemisphere from 1980 to 2001. The intercomparison is undertaken as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The reanalyses are generally in good agreement in their representation of the strengthening of the lower stratospheric polar vortex during the austral spring–summer season, associated with reduced radiative heating due to ozone loss, as well as the descent of anomalously strong westerly winds into the troposphere during summer and the subsequent poleward displacement and intensification of the polar front jet. Differences in the trends in zonal wind between the reanalyses are generally small compared to the mean trends. The exception is CFSR, which exhibits 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. The dynamical changes associated with the ozone hole are examined by investigating the momentum budget and then the eddy heat and momentum fluxes in terms of planetary- and synoptic-scale Rossby wave contributions. The dynamical changes are consistently represented across the reanalyses and support our dynamical understanding of the response of the coupled stratosphere–troposphere system to the ozone hole. Although our results suggest a high degree of consistency across the four reanalysis datasets in the representation of these dynamical changes, there are larger differences in the wave forcing, residual circulation, and eddy propagation changes compared to the zonal wind trends. In particular, there is a noticeable disparity in these trends in CFSR compared to the other three reanalyses, while the best agreement is found between ERA5 and JRA-55. Greater uncertainty in the components of the momentum budget, as opposed to mean circulation, suggests that the zonal wind is better constrained by the assimilation of observations compared to the wave forcing, residual circulation, and eddy momentum and heat fluxes, which are more dependent on the model-based forecasts that can differ between reanalyses. Looking forward, however, these findings give us confidence that reanalysis datasets can be used to assess changes associated with the ongoing recovery of stratospheric ozone.

Seasonally dependent increases in subweekly temperature variability over Southern Hemisphere landmasses detected in multiple reanalyses

“…They are, however, less consistent with the intensification and poleward shift of the summertime (DJF) polar-front jet. This is observed since the beginning of the satellite era as a result of the stratospheric ozone P. Martineau et al: Increases in SH temperature variability depletion (Orr et al, 2021), although pausing since 2000 due to a hint of its recovery (Banerjee et al, 2020). From these changes, one would expect a weakening of temperature variability over South America.…”

The Variation Characteristics of Stratospheric Circulation under the Interdecadal Variability of Antarctic Total Column Ozone in Early Austral Spring

“…The propagation of planetary waves can change EMF by adjusting the wave-driving rate of the polar vortex [39]. In the southern hemisphere, a negative EHF reflects upward wave propagation, while a positive EMF reflects the enhanced poleward motion [45]. Table 1 shows the abbreviations and full names of terms used in the text.…”

“…Eddy heat flux and eddy momentum flux can reflect the direction of planetary waves [40,45]. Figure 9 shows the difference in the linear trends of EHF and EMF calculated by waves 1-3 as a function of altitude and latitude between the two periods.…”

“…The weaker poleward movements are in favor of the transport of ozone from the polar to the equator, thus being consistent with the depletion of the TCO in the polar regions. Eddy heat flux and eddy momentum flux can reflect the direction of planetary waves [40,45]. Figure 9 shows the difference in the linear trends of EHF and EMF calculated by waves 1-3 as a function of altitude and latitude between the two periods.…”