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A tropospheric signature of upper stratospheric flow regimes: An evaluation of CMIP6

Authors

Collingwood,  Elizabeth
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Lu,  Hua
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Sinha,  Bablu
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Scaife,  Adam
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Marsh,  Robert
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

King,  John
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Collingwood, E., Lu, H., Sinha, B., Scaife, A., Marsh, R., King, J. (2023): A tropospheric signature of upper stratospheric flow regimes: An evaluation of CMIP6, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-3969


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5019864
Abstract
The North Atlantic Oscillation (NAO) plays a crucial role in the development of winter conditions and associated extreme weather in the North Atlantic basin. Although seasonal prediction skill for the NAO has seen recent improvement, the influence of the upper stratosphere, a region that has received relatively little attention, is yet to be clarified.Lu et al. (2021) proposed a flow regime index using early winter upper stratospheric information. It was found that the index characterises the seasonal development of the northern stratospheric polar vortex, the signal of which then projects onto the NAO in middle to late winter. In this study, we examine this stratospheric regime behaviour and subsequent response in the troposphere using ERA5 reanalysis data and will assess the associated bias of the CMIP6 model simulations. Zonal mean winds in the subtropical upper stratosphere are used as a proxy for the flow regime index. Our results based on ERA5 confirm a significant relationship between the strength of this proxy index and the late winter mean sea level pressure and near surface temperature. Stronger winds in the early winter subtropical upper stratosphere are associated with a stronger positive NAO phase in late winter. To test the hypothesis that this connection exists due to planetary wave-breaking feedback processes, we examine the behaviour of the stratospheric surf zone in which the strongest quasi-horizontal mixing occurs. Tropospheric precursors preceding the regime development are also investigated. Implications for improved process understanding of stratosphere-troposphere coupling and its role in seasonal weather forecasting are discussed.