Synoptic conditions during summertime temperature extremes in Alaska

Abstract

The atmospheric state and synoptic situation associated with widespread summer June, July, and August temperature extremes in southern Alaska is explored. Using ERA‐Interim data and a self‐organizing map framework, the evolution of the atmospheric state leading up to days that are defined as experiencing extreme surface temperature are compared with the evolution for non‐extreme days. The variables evaluated include circulation at the surface and aloft and surface radiative fluxes. For warm extremes, blocking evident in the 500 hPa flow combined with anomalously large surface downward shortwave radiation allowed surface temperatures to become extreme. For cold extremes, an upper level trough and cold air advection aloft coupled with a more minor role of anomalously negative surface downward shortwave radiation were important. The self‐organizing map framework allowed an investigation of these details beyond a composite analysis of all extremes.

Temperature extremes in Alaska: temporal variability and circulation background

“…Some researchers choose to use atmospheric circulation indices such as ENSO, PDO, Pacific/North American pattern (PNA), and Arctic Oscillation (AO) (Papineau 2001;Kenyon and Hegerl 2008;L'Heureux et al 2010). Circulation pattern classifications are also becoming increasingly popular and are available for Alaska in Cassano et al (2006Cassano et al ( , 2016a thanks to the use of a self-organizing map (SOM) framework. Another approach used in the present study consists of circulation or advection-type classifications that may be created in an objective or subjective manner (Kyselý 2008(Kyselý , 2010Ustrnul et al 2010).…”

“…As Cassano et al (2016a, b) and Bieniek and Walsh (2017) have shown, warm (cold) extremes in Alaska are generally associated with synoptic patterns resulting in southerly (northerly) flow. In the case of summer warm spells and winter cold spells, blocking situations are of particular importance or the long-term hovering of high pressure systems, which limits the zonal flux of air masses over a given geographic area (Cattiaux et al 2010, Schneidereit et al 2012, Porębska and Zdunek 2013Cassano et al 2016a). Long-lasting cold spells in the winter are also facilitated by ground-level temperature inversions (Papineau 2001;Shulski et al 2010), which were examined for the case of the city of Fairbanks in Alaska (Hartmann and Wendler 2005b).…”

On the use of self-organizing maps in detecting teleconnections. Part II: temporal aspects

“…Although studies comparing SOMs with other classi cation methods (Fleig et al 2010;Huth 2010;Tveito 2010;Lykoudis et al 2010;Broderick and Fealy 2015;Trigo et al 2016;Palm et al 2017) clearly showed that different methods turn out to be optimum depending on the application, it has been the SOM that sparked a new interest in synoptic climatology owing to its novel point of view on circulation variability (Sheridan and Lee 2011). This interest resulted in a wide range of studies on circulation in outputs of reanalyses and climate models, links between circulation and various atmospheric and environmental phenomena, as well as links between synoptic-scale CTs to large-scale teleconnections, bringing new insights into circulation over Asia (Liu et al 2016;Gao et al 2019;Ohba and Sugimoto 2019), Polar regions (e.g., Schuenemann et al 2009;Bezeau et al 2015;Yu et al 2018), Australia and New Zealand (e.g., Jiang et al 2013;Huva et al 2015;Gibson et al 2016a,b;Harrington et al 2016;Theobald et al 2016Theobald et al ,2018, Europe (e.g., Tymvios et al 2010;Polo et al 2011), North America (e.g., Newton et al 2014;Cassano et al 2016Cassano et al ,2017Swales et al 2016;Sugg and Konrad II 2017;Díaz-Esteban and Raga 2018), South America (Espinoza et al 2012;Rodríguez-Morata et al 2018), and southern Africa (e.g., Lennard and Hegerl 2015;Engelbrecht and Landman 2016;Wolski et al 2018;Quagraine et al 2019).…”