Stratospheric influence on North Atlantic marine cold air outbreaks following sudden stratospheric warming events

Abstract

Abstract. Marine cold air outbreaks (MCAOs) in the northeastern North Atlantic occur due to the advection of extremely cold air over an ice-free ocean. MCAOs are associated with a range of severe weather phenomena, such as polar lows, strong surface winds and intense cooling of the ocean surface. Given these extreme impacts, the identification of precursors of MCAOs is crucial for improved long-range prediction of associated impacts on Arctic infrastructure and human lives. MCAO frequency has been linked to the strength of the stratospheric polar vortex, but the study of connections to the occurrence of extreme stratospheric events, known as sudden stratospheric warmings (SSWs), has been limited to cold extremes over land. Here, the influence of SSW events on MCAOs over the North Atlantic ocean is studied using reanalysis datasets. Overall, SSW events are found to be associated with more frequent MCAOs in the Barents Sea and the Norwegian Sea compared to climatology and less frequent MCAOs in the Labrador Sea. In particular, SSW events project onto an anomalous dipole pattern of geopotential height 500 hPa, which consists of a ridge anomaly over Greenland and a trough anomaly over Scandinavia. By affecting the variability of the large-scale circulation patterns in the North Atlantic, SSW events contribute to the strong northerly flow over the Barents and Norwegian seas and thereby increase the likelihood of MCAOs in these regions. In contrast, the positive geopotential height anomaly over Greenland reduces the probability of MCAOs in the Labrador Sea after SSW events. As SSW events tend to have a long-term influence on surface weather, these results are expected to benefit the predictability of MCAOs in the Nordic Seas for winters with SSW events.

Sudden Stratospheric Warmings

“…In the NH, the strongest response to SSW events is observed in the North Atlantic Basin (Figure 8), where the response to SSW events often projects onto the negative phase of the NAO (Charlton‐Perez et al, 2018; Domeisen, 2019). The negative phase of the NAO is associated with cold air outbreaks over Northern Eurasia and the eastern United States (Kolstad et al, 2010; King et al, 2019; Lehtonen & Karpechko, 2016) as well as over the Barents and Norwegian Seas (Afargan‐Gerstman et al, 2020), and wet anomalies over Southern Europe (Ayarzagüena, Barriopedro, et al, 2018) due to the southward shift and persistence of the North Atlantic eddy‐driven jet (Maycock et al, 2020) and the storm track (Afargan‐Gerstman & Domeisen, 2020). Further anomalies include positive temperature anomalies over Greenland and eastern Canada, and subtropical Africa and the Middle East.…”

Stratospheric drivers of extreme events at the Earth’s surface

“…1 and 2), particularly over Northern Europe and Asia [17][18][19][20] , which are linked to human health impacts 21,22 . Cold air outbreaks also occur over the North Atlantic and Arctic oceans, termed "marine cold air outbreaks" (MCAOs) 23 (Fig. 2).…”

Predictors and prediction skill for marine cold‐air outbreaks over the Barents Sea

“…The stratospheric polar vortex variability and associated sudden stratospheric warming (SSW) events (Baldwin et al, 2021) are a key driver of cold spells over northern Europe (e.g., Kolstad et al, 2010;Kretschmer et al, 2018b;King et al, 2019). While, Papritz and Grams (2018) did not confirm that the strength of the polar vortex systematically affected MCAO frequency in the Nordic Seas, Afargan-Gerstman et al (2020) show that more than half of SSW events in the ERA-Interim atmospheric reanalysis are associated with MCAOs in the Barents Sea. In their study, SSW events with an enhanced MCAO response in the Barents Sea are also linked with a ridge over Greenland and a trough over Scandinavia.…”

“…The time lag between the inflow of ocean temperature anomaly through the Barents Sea opening and the associated changes in sea-ice cover downstream was reported to be one month (Lien et al, 2017, and references therein). Additionally, the stratosphere was proposed to drive the Barents Sea MCAOs within one month after SSW events (Afargan-Gerstman et al, 2020). In this section, we first evaluate the relationship between these large-scale conditions and the Barents Sea MCAOs.…”

“…Marine cold-air outbreaks (MCAOs) are surges of cold air escaping from the inner Arctic and becoming exposed to the relatively warm ocean surface (Rasmussen, 1983). MCAOs over the Nordic Seas usually occur within the northerly flow associated with large-scale anomalous anticyclonic circulation over Greenland and anomalous cyclonic circulation over Scandinavia (Kolstad et al, 2009;Mallet et al, 2013;Papritz and Grams, 2018;Afargan-Gerstman et al, 2020). Given the importance of MCAOs for the formation of severe weather events such as polar lows (PLs; Rasmussen, 1983;Kolstad, 2011;Landgren et al, 2019), and for driving the ocean convection in the North Atlantic (Kolstad and Bracegirdle, 2008), we evaluate predictability of MCAOs using a seasonal prediction system and by identifying MCAO precursors.…”