In Situ Measurements of Surface Winds, Waves, and Sea State in Polar Lows Over the North Atlantic

Abstract

Polar low (PL) storms are an important feature of the wintertime subsynoptic‐scale atmospheric circulation of middle‐ and higher‐latitude ocean areas. They can generate hazardous conditions impacting coastal and marine activities like fishing, transport, and oil extraction. However, there are few studies available of individual PL systems based on high‐resolution maritime surface data. Accordingly, the meteorological impacts of 29 PLs have been investigated for the 14 winters 1999–2013, using in situ measurements at eight stations in the Norwegian and North Seas. On average, the highest wind speed and significant wave height (SWH) occur following the minimum in sea level pressure of the PL, respectively, 1 and 3 hr after its passage. The strongest wind speed averages 17.1 m/s, and the highest peak SWH is 6.3 m, but these can reach 31 m/s and 11 m, respectively. PL characteristics of system horizontal extent, propagation speed, and the larger‐scale atmospheric circulation environment explain the large intercase differences. Large, multiple, and fast‐moving PLs within a meridional circulation environment appear to generate stronger near‐surface winds and higher waves than do small, single, and slow‐moving PLs within a zonal circulation. Multiple systems may have the largest impacts (e.g., SWH > 8 m), although a larger sample size is required to confirm this possibility. The impacts of PLs on sea surface temperature (SST) are quite small and are difficult to interpret separate from the background SST variation. The observed SST decrease may be mainly caused by the cold air outbreak within which the PL is embedded; indeed, a positive SST minus air temperature anomaly is found during the 24 hr preceding the passage of PL vortices, indicating enhanced low‐level atmospheric instability.

Recent advances in polar low research: current knowledge, challenges and future perspectives

“…At the time when the rogue wave developed, the significant wave height of the sea was nearly 12 m. The Draupner wave reached 25.6 m of height (Cavaleri et al, 2016). Multiple PLs seem to generate larger maximum wind speeds and maximum significant wave heights than single PLs, although more data are needed to confirm these extreme wave features (Rojo et al, 2019).…”

“…This phenomenon is known as 'group velocity quasi-resonance' or 'extended fetch' (Orimolade et al, 2016). Based on conventional observations of 29 PLs that passed over marine stations in the Norwegian and the North Seas, Rojo et al (2019) found that the maximum significant wave height ranged from 3.2 to 11 m and, on average, the maximum significant wave height was 6.3 m. Orimolade et al (2016) used a one-dimensional parametric wave model to determine significant wave height associated with 155 PLs. They found that extended wave development was possible in more than 50% (90%) of the PLs if they had an average translation speed of 10 m s À1 (8 m s À1 ).…”

“…Regarding the weather conditions associated with PLs, Rojo et al (2019) analysed conventional observations of 29 PLs developed over the Norwegian Sea and the North Sea between 1999 and 2013 to obtain their associated maximum wind speeds and associated maximum significant wave heights. They found that the maximum wind speed associated with the PLs ranged from 7 to 31 m s À1 and, on average, the maximum wind speed was 17.1 m s À1 .…”

“…Although upper-air stations are particularly sparse in high latitudes and the observation frequency is much lower than that of surface stations, these type of observations have also been used to study PLs (e.g., Kristj ansson et al, 2011b). Observations from maritime stations provide not only atmospheric variables such as MSLP, wind speed and temperature, but also SST and significant wave height associated with PLs (e.g., Rojo et al, 2019).…”

Satellite-Derived Spatio-Temporal Distribution and Parameters of North Atlantic Polar Lows for 2015–2017

“…Polar lows are characterized by short lifetimes (generally, less than 48 h) and small sizes (generally, less than 600 km), and are often not captured by synoptic charts or atmospheric re-analyses [4][5][6]. Near-surface wind speeds within polar lows may exceed 30 m/s and significant wave height may exceed 10 m [7][8][9]. Polar lows are, thus, certainly dangerous maritime weather events.…”