Saharan warm air intrusions in the Western Mediterranean: identification, impacts on temperature extremes and large-scale mechanisms

Abstract. Saharan warm intrusions are air masses that develop over the Saharan region and that get advected into surrounding regions, creating anomalous atmospheric situations in other regions. This paper focuses on the characteristics of these intrusions into the Western Mediterranean region (WMed) and their relationship with extreme temperatures in the neighbouring areas during the recent past (1959–2022). We describe and evaluate a methodology to identify Saharan air masses throughout the year and, consequently, a historical catalogue of intrusion events that reach the WMed is built. To identify which large-scale phenomena might be relevant for the formation of the intrusions, we first identify different intrusion types (IT) through a clustering procedure. Four different ITs are found, which discriminate the intrusions according to their longitudinal position over the Mediterranean region. Upper-tropospheric anomalies are linked to the onset of these events, in particular, an anomalous geopotential high over the intrusions region that slows down the upper-tropospheric circulation over northern Africa. These events are very relevant as they impact extreme temperatures throughout the year and account for a high percentage of the extreme temperature events recorded in the WMed and neighbouring regions in summer.