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- Title
The effect of atmospheric nudging on the stratospheric residual circulation in chemistry-climate models.
- Authors
Chrysanthou, Andreas; Maycock, Amanda C.; Chipperfield, Martyn P.; Dhomse, Sandip; Garny, Hella; Kinnison, Douglas; Hideharu Akiyoshi; Makoto Deushi; Garcia, Rolando R.; Jöckel, Patrick; Kirner, Oliver; Morgenstern, Olaf; Pitari, Giovanni; Plummer, David A.; Revell, Laura; Rozanov, Eugene; Stenke, Andrea; Tanaka, Taichu Y.; Visioni, Daniele; Yousouke Yamashita
- Abstract
We perform the first multi-model comparison of the impact of nudged meteorology on the stratospheric residual circulation using hindcast simulations from the Chemistry Climate Model Initiative (CCMI). We examine simulations over the period 1980–2009 from 5 models in which the meteorological fields are nudged towards reanalysis data and compare with equivalent free-running simulations from 9 models. We show that nudging meteorology does not constrain the mean strength of the stratospheric residual circulation and that the inter-model spread is similar, or even larger, than in the free-running simulations. The nudged simulations also simulate stronger upwelling in the tropical lower stratosphere compared to the residual circulation estimated directly from the reanalyses they are nudged towards. Downward control calculations reveal substantial differences between the mean lower stratospheric tropical upward mass flux (TUMF) computed from the modeled wave forcing and that calculated directly from the residual circulation. Although the mean circulation is poorly constrained, the nudged simulations show a high degree of consistency in the interannual variability of the TUMF in the lower stratosphere, which is related to the contribution to variability from the resolved wave forcing. We apply a multiple linear regression (MLR) model to separate the drivers of interannual and long-term variations in the simulated TUMF. The MLR model explains up to ~ 75 % of the variance in TUMF in the nudged simulations and reveals a statistically significant positive trend for most models in TUMF over the period 1980–2009. Overall, nudging meteorological fields leads to increased inter-model spread for most of the measures of the mean climatological stratospheric residual circulation assessed in this study. Our findings show that while nudged simulations by construction produce accurate temperatures and realistic representations of fast horizontal transport, this is not necessarily the case for the slower zonal mean vertical transport. Consequently, caution is required when using nudged simulations to interpret long-lived stratospheric tracers that are controlled by the residual circulation.
- Subjects
STRATOSPHERIC circulation; CIRCULATION models; METEOROLOGY; STRATOSPHERE; WAVE forces; ATMOSPHERIC models; REGRESSION analysis
- Publication
Atmospheric Chemistry & Physics Discussions, 2019, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2019-260