21 Feb 2023
 | 21 Feb 2023
Status: this preprint is currently under review for the journal WCD.

Strengthening gradients in the tropical west Pacific connect to European summer temperatures on sub-seasonal timescales

Chiem van Straaten, Dim Coumou, Kirien Whan, Bart van den Hurk, and Maurice Schmeits

Abstract. Recent work has shown that (sub-)seasonal variability in tropical Pacific convection, closely linked to ENSO, relates to summertime circulation over the Euro-Atlantic. The teleconnection is non-stationary, probably due to long-term changes in both the tropical Pacific and extra-tropical Atlantic. It also appears imperfectly captured by numerical models. In a previous study we found that the best predictor of errors in sub-seasonal forecasts of European temperature, is a dipole in tropical west Pacific sea surface temperatures (SSTs). In this diagnostic study we use reanalysis data to further investigate the teleconnection pathway and the processes behind its non-stationarity. We show that SST gradients associated with the dipole represent a combination of ENSO variability and west Pacific warming, and have become stronger since 1980. Associated patterns of suppressed and enhanced tropical heating are followed by quasi-stationary waves that linger for multiple weeks. Situations with La Niña-like gradients are followed by high pressure centers over eastern Europe and Russia, three to six weeks later. Inverted situations are followed by high pressure over western Europe, three to six weeks later. The latter situation is however also conditional on a strong meridional tripole in north Atlantic SST and a co-located jet stream. Overall, the sub-seasonal pathway diagnosed in this study connects to patterns detected at seasonal scales, and confirms earlier findings that the summertime connectivity between the Pacific and Europe has shifted in recent decades. It also partly explains the increased occurrence of high sea level pressures and summer temperatures over the European continent.

Chiem van Straaten et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2023-6', Anonymous Referee #1, 21 Mar 2023
  • RC2: 'Comment on wcd-2023-6', Anonymous Referee #2, 05 Apr 2023
  • RC3: 'Comment on wcd-2023-6', Anonymous Referee #3, 11 Apr 2023
  • AC1: 'Author response to comments on wcd-2023-6', Chiem van Straaten, 09 May 2023

Chiem van Straaten et al.

Chiem van Straaten et al.


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Short summary
Variability in the tropics can influence weather over Europe. This study evaluates a summertime connection between the two. It shows that strong deviations in the west Pacific occur more frequently since 1980, likely due to a combination of long-term warming in the west Pacific and the El Niño Southern Oscillation. Three to six weeks later, the distribution of hot and cold airmasses over Europe is affected.