Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review

Abstract

Abstract. The physical understanding and timely prediction of extreme weather events are of enormous importance to society due to their associated impacts. In this article, we highlight several types of weather extremes occurring in Europe in connection with a particular atmospheric flow pattern, known as atmospheric blocking. This flow pattern effectively blocks the prevailing westerly large-scale atmospheric flow, resulting in changing flow anomalies in the vicinity of the blocking system and persistent conditions in the immediate region of its occurrence. Blocking systems are long-lasting, quasi-stationary and self-sustaining systems that occur frequently over certain regions. Their presence and characteristics have an impact on the predictability of weather extremes and can thus be used as potential indicators. The phasing between the surface and the upper-level blocking anomalies is of major importance for the development of the extreme event. In summer, heat waves and droughts form below the blocking anticyclone primarily via large-scale subsidence that leads to cloud-free skies and, thus, persistent shortwave radiative warming of the ground. In winter, cold waves that occur during atmospheric blocking are normally observed downstream or south of these systems. Here, meridional advection of cold air masses from higher latitudes plays a decisive role. Depending on their location, blocking systems also may lead to a shift in the storm track, which influences the occurrence of wind and precipitation anomalies. Due to these multifaceted linkages, compound events are often observed in conjunction with blocking conditions. In addition to the aforementioned relations, the predictability of extreme events associated with blocking and links to climate change are assessed. Finally, current knowledge gaps and pertinent research perspectives for the future are discussed.

Towards a diagnostic framework unifying different perspectives on blocking dynamics: insight into a major blocking in the North Atlantic-European region

“…Low-frequency circulation regimes affect continent-size regions for several days and modulate the location and intensity of synoptic-scale weather systems that determine surface weather (Yiou and Nogaj, 2004). Due to their stationarity, these regimes can regionally lead to extreme weather events (Kautz et al, 2022), such as flooding (Houze et al, 2011;Hong et al, 2011), heat waves and associated droughts (Pfahl and Wernli, 2012;Lavaysse et al, 2018;Alvarez-Castro et al, 2018), cold spells (Sillmann et al, 2011;Buehler et al, 2011;Ferranti et al, 2018), and storms (Donat et al, 2010;Grams et al, 2017). In terms of predictability, weather regimes have an undisputed importance in forecasting, as they shape the sub-seasonal 'predictability desert' between medium-range and seasonal forecasts (Vitart et al, 2012;Cortesi et al, 2021).…”

Assessment of Fusarium-Damaged Kernels in Common Wheat in Romania in the Years 2015 and 2016 with Extreme Weather Events

“…The agricultural years 2015 and 2016 with extreme weather events caused by atmospheric blocking (high air temperatures and extreme pedological drought in May–August in 2015 caused by a dipole block, and extreme precipitation and floods in May–June in 2016 caused by an omega block) were preceded by three agricultural years with other extreme weather events: 2012 with cold waves and heavy snowfall produced by a Siberian anticyclone in January–February, extreme precipitation and floods in May, and extreme air temperature and pedological drought in July–August; furthermore, 2013 and 2014 had extreme precipitation and floods produced by Vb cyclones in May–July [ 10 , 16 , 31 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ]. The Vb cyclones and the dipole and omega blocks were favored by the North Atlantic Oscillations and correlated with the planetary wave resonance; they were more or less caused by climate change [ 6 , 8 , 17 , 79 , 80 , 89 ]. These atmospheric systems produced extreme weather events that influenced the aridity indices of the European regions and the occurrence of Fusarium spp.…”

On the relationship between Scandinavian extreme precipitation days, atmospheric blocking and Red Sea coral oxygen isotopes

“…Atmospheric circulation patterns classified as instantaneous blocking by our index are not restricted to classical blocking patterns, that is, omega block, dipole, or open ridges (e.g. Kautz et al 2022), but include a large family of circulation patterns satisfying the instantaneous blocking criteria. We conclude that a high frequency of such types of atmospheric circulation patterns in a certain winter is associated with both an increased frequency of heavy rainfall in southwestern Scandinavia and colder conditions in the northern Red Sea, which are documented as higher values in the winter coral δ 18 O record from Ras Umm Sidd.…”