Albin Ullmann

Weather Regimes in the Euro-Atlantic and Mediterranean Sector, and Relationship with West African Rainfall over the 1989–2008 Period from a Self-Organizing Maps Approach

AbstractWeather regimes (WRs) have been defined over the Euro-Mediterranean region (15°–70°N, 60°W–60°E) from May to October using the daily sea level pressure, 700-hPa geopotential height, and specific humidity from the European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA)-Interim over the 1989–2008 period. Computations are based on a neural network classification technique referred to as self-organizing maps, and the WRs produced can be used by the scientific community for comparison with other periods, projection onto model outputs, seasonal prediction, or teleconnection studies. The article particularly examines the relationship between WRs and West Africa (WA) rainfall, and the study’s results suggest that changes in particular WR frequencies can account for a part of the WA’s interannual rainfall variability. Thus, during anomalous wet (dry) years in WA rainfall, both more occurrences of WRs related to the negative (positive) summer North Atlantic Oscillation (NAO)–like pattern and fe...

Extreme dry spell detection and climatology over the Mediterranean Basin during the wet season

The E-OBS precipitation gridded data set v.10.0 is used to detect very long dry spell (VLDS) events over the entire Mediterranean Basin for the 1957–2013 period, during the wet season (September to April). The main objective is to characterize these events as climatic objects, in terms of location, spatial extent, duration, and temporal variability. In this study, 76 VLDS events were detected in the Mediterranean Basin and grouped into four spatial patterns: scattered localized (with 25 events), northeast Mediterranean (11 events), West Mediterranean (15 events), and southeast Mediterranean (25 events). Each pattern shows seasonality in events. Most of the scattered localized, northeast, and southeast events begin in September, at the beginning of the wet season. In contrast, most of the West Mediterranean events begin in the middle of the wet season. Over time, there is a slight but not significant increase in the cumulative number of days per season affected by VLDS events.