Preprints
https://doi.org/10.5194/egusphere-2023-2676
https://doi.org/10.5194/egusphere-2023-2676
14 Dec 2023
 | 14 Dec 2023

Improving seasonal predictions of German Bight storm activity

Daniel Krieger, Sebastian Brune, Johanna Baehr, and Ralf Weisse

Abstract. Extratropical storms are one of the major coastal hazards along the coastline of the German Bight, the southeastern part of the North Sea, and a major driver of coastal protection efforts. However, the predictability of these regional extreme events on a seasonal scale is still limited. We therefore improve the seasonal prediction skill of the Max-Planck-Institute Earth System Model (MPI-ESM) large-ensemble decadal hindcast system for German Bight storm activity (GBSA) in winter. We define GBSA as the 95th percentiles of three-hourly geostrophic wind speeds in winter, which we derive from mean sea-level pressure (MSLP) data. The hindcast system consists of an ensemble of 64 members, which are initialized annually in November and cover the winters of 1960/61–2017/18. We consider both deterministic and probabilistic predictions of GBSA, for both of which the full ensemble produces poor predictions in the first winter. To improve the skill, we observe the state of two physical predictors of GBSA, namely 70 hPa temperature anomalies in September, as well as 500 hPa geopotential height anomalies in November, in areas where these two predictors are correlated with winter GBSA. We translate the state of these predictors into a first guess of GBSA and remove ensemble members with a GBSA prediction too far away from this first guess. The resulting subselected ensemble exhibits a significantly improved skill in both deterministic and probabilistic predictions of winter GBSA. We also show how this skill increase is associated with better predictability of large-scale atmospheric patterns.

Daniel Krieger, Sebastian Brune, Johanna Baehr, and Ralf Weisse

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2676', Anonymous Referee #1, 10 Jan 2024
  • RC2: 'Comment on egusphere-2023-2676', Lisa Degenhardt, 23 Jan 2024
  • RC3: 'Comment on egusphere-2023-2676', Anonymous Referee #3, 24 Jan 2024
Daniel Krieger, Sebastian Brune, Johanna Baehr, and Ralf Weisse
Daniel Krieger, Sebastian Brune, Johanna Baehr, and Ralf Weisse

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Short summary
Previous studies found that climate models can predict storm activity in the German Bight well for averages of 5–10 years, but struggle in predicting the next winter season. Here, we improve winter storm activity predictions by linking them to physical phenomena that occur before the winter. We guess the winter storm activity from these phenomena and discard model solutions that stray too far from the guess. The remaining solutions then show much higher prediction skill for storm activity.