Abstract
Abstract. Correctly capturing the teleconnection between the El Niño–Southern Oscillation (ENSO) and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two-step bias correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias corrections are applied to the troposphere and stratosphere independently and jointly to produce a range of climates. ENSO-type sensitivity experiments are then performed to reveal the impact of differing climatologies on the ENSO–Europe teleconnections. The bias corrections do not affect the response of the tropical atmosphere or the Aleutian low to the strong ENSO anomalies imposed in our experiments. However, in El Niño experiments the anomalous upward wave flux and the response of the Northern Hemisphere polar vortex differ between the climatologies. We attribute this to a reduced sensitivity of the upward wave fluxes to the Aleutian low response in the bias correction experiments, where the reduced biases result in a deepened Aleutian low in the base state. Despite the differing responses of the polar vortex, the North Atlantic Oscillation (NAO) response is similar between the climatologies, implying that for strong ENSO events the stratospheric pathway may not be the dominant pathway for the ENSO–North Atlantic teleconnection.
Highlights
The El Niño–Southern Oscillation (ENSO) has been shown to influence European climate via tropospheric and stratospheric teleconnections
It should be noted that using a regression to generate ENSO patterns results in symmetric El Niño–La Niña magnitudes, whereas from observations El Niño anomalies tend to be larger than La Niña and have a slightly different structure
This simplification, along with a constant ENSO forcing and using climatological sea surface temperatures (SSTs) outside the Pacific Ocean basin, has the advantage of reducing the number of controlling parameters when analysing the results of the bias corrections, which was the main aim of the research
Summary
The El Niño–Southern Oscillation (ENSO) has been shown to influence European climate via tropospheric and stratospheric teleconnections. In addition to the patterns of climatological sea surface temperatures (SSTs), the state of the tropical (e.g. Quasi-Biennial Oscillation (QBO) phase) and extratropical atmosphere can influence the response of the NAO and polar vortex (Garfinkel et al, 2007), and biases in the subtropical jet can affect the propagation of Rossby waves from the tropics to the extratropics (Li et al, 2020). It is possible to use a similar technique on the prognostic atmospheric variables of a model This bias correction technique was used by Kharin and Scinocca (2012), and artificially decreased biases were associated with an increase in predictive skill on seasonal timescales. In this study we have used a similar bias correction technique to probe the impact of climatological biases on the communication of ENSO anomalies from the tropical Pacific to the North Atlantic and European sector.
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