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Enhanced extended‐range predictability of the 2018 late‐winter Eurasian cold spell due to the stratosphere

Kautz, Lisa-Ann and Polichtchouk, Inna and Birner, Thomas and Garny, Hella and Pinto, Joaquim (2020) Enhanced extended‐range predictability of the 2018 late‐winter Eurasian cold spell due to the stratosphere. Quarterly Journal of the Royal Meteorological Society, 146 (727), pp. 1040-1055. Wiley. doi: 10.1002/qj.3724. ISSN 0035-9009.

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Official URL: https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.3724?af=R


A severe cold spell with surface temperatures reaching 10 K below its climatology hit Eurasia during late February/early March 2018. This cold spell was associated with a Scandinavian blocking pattern followed by an extreme negative North Atlantic Oscillation (NAO) phase. Here we explore the predictability of this cold spell/NAO event using ensemble forecasts from the Subseasonalto-Seasonal (S2S) archive of the European Centre for Medium-Range Weather Forecasts. We find that this event was predicted with the observed strength roughly 10 days in advance. However, the probability of the cold spell occurring doubled up to 25 days in advance, when a sudden stratospheric warming (SSW) occurred. Our results indicate that the amplitude of the cold spell was increased by a regime shift to the negative NAO phase at the end of February, which was likely favoured by the SSW. We quantify the contribution of the SSW to the enhanced extended-range forecast skill for this particular event by running forecast ensembles in which the evolution of the stratosphere is nudged to (a) the observed evolution, and (b) a time-invariant state. In the experiment with nudging to the observed stratospheric evolution, the probability of a strong cold spell occurring is enhanced to 45%, while it is at its climatological value of 5% when the stratosphere is nudged to a time-invariant state. These results showing enhanced predictability of surface extremes following SSWs extend previous observational evidence, which is mostly based on composite analyses, to a single event. Our results suggest that it is the subsequent evolution throughout the lower stratosphere following the SSW, rather than the occurrence of the SSW itself, that is crucial in coupling to large-scale tropospheric flow patterns. However, we caution that probabilistic gain in predictability alone is insufficient to conclude a causal link between the SSW and the cold spell event.

Item URL in elib:https://elib.dlr.de/134943/
Document Type:Article
Title:Enhanced extended‐range predictability of the 2018 late‐winter Eurasian cold spell due to the stratosphere
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Kautz, Lisa-AnnKIT, KarlsruheUNSPECIFIED
Polichtchouk, InnaECMWF, Reading, UKUNSPECIFIED
Birner, ThomasMIM, Univ. MünchenUNSPECIFIED
Pinto, JoaquimKIT, KarlsruheUNSPECIFIED
Date:3 March 2020
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:pp. 1040-1055
Keywords:Stratosperic sudden warmings, Predictability, North Atlantic Oscillation
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Atmospheric and climate research
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Modelling
Deposited By: Garny, Hella
Deposited On:15 May 2020 17:24
Last Modified:19 May 2020 12:34

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