Multiple scenarios of climate anomalies over Europe in ensemble seasonal forecasts

• DOI: 10.5194/ems2023-31
• Publication Date: 2023-07-06T12:09:06Z
• Authors: Damien Specq; Shan Li; Lauriane Batté; Christian Viel; Frédéric Gayrard
• Keywords: Ensemble forecasting; Seasonality; Ensemble average

Seasonal prediction uses ensemble forecasting to sample the distribution of possible climate outcomes in upcoming term given slowly-varying constraints on atmosphere. However, translating members’ a seasonal forecast into meaningful information is challenge services are often faced with. When large spread makes difficult interpret, highlighting competing signals from which uncertainty arises may bear added value end users. In order do so, we present an approach extract alternative scenarios over Europe (in temperature, precipitation and atmospheric circulation) forecasts. The aim refine analysis beyond usual products (e.g mean, tercile probabilities), provide additional guidance for preparation bulletins routinely issued at Météo-France. determined with hierarchical clustering members, based their temperature 2-m (T2m). dissimilarity between two members defined spatial correlation respective maps T2m anomalies – relative model climatology European domain (29.5°W-40.5°E; 30.5°N-70.5°N, land grid points only). subsequent matrix across feeds algorithm that groups clusters eventually defining scenarios. corresponding these then described through several diagnostics, e.g composites sensible variables (T2m, precipitation), circulation (Z500, V200), modes variability weather regimes. addition, description how diverge course integration identify teleconnections related each scenario. Finally, also assess skill forecasts assuming only subset representing most likely scenario retained. This methodology has been implemented Copernicus Climate Change Services (C3S) real-time past year experimental purposes, it shown be relevant complement Météo-France operational bulletins.