Higher Ocean Wind Speeds During Marine Cold Air Outbreaks

Abstract

Marine cold air outbreaks (MCAOs) are large-scale events in which cold air masses are advected over open ocean. It is well-known that these events are linked to the formation of polar lows and other mesoscale phenomena associated with high wind speeds, and that they therefore in some cases represent a hazard to maritime activities. However, it is still unknown whether MCAOs are generally conducive to higher wind speeds than normal. Here this is investigated by comparing ocean near-surface wind speeds during MCAOs in atmospheric reanalysis products with different horizontal grid spacings, along with two case studies using a convection-permitting numerical weather prediction model. The study regions are the Labrador Sea and the Greenland-Iceland-Norwegian (GIN) Seas, where MCAOs have been shown to be important for air-sea interaction and deep water formation. One of the main findings is that wind speeds during the strongest MCAO events are higher than normal and higher than wind speeds during less severe events. Limited evidence from the case studies suggests that reanalyses with grid spacings of more than 50 km underestimate winds driven by the large ocean-atmosphere energy fluxes during MCAOs. The peak times of MCAO usually occur when baroclinic waves pass over the regions. Therefore, the strong wind episodes during MCAOs generally last for just a few days. However, MCAOs can persist for 50 days or more.

Linking Low‐Frequency Large‐Scale Circulation Patterns to Cold Air Outbreak Formation in the Northeastern North Atlantic

“…Marine cold air outbreaks (CAOs) in the Arctic are often accompanied by severe weather—such as polar lows (e.g., Rasmussen & Turner, ) and high near‐surface wind speeds (Kolstad, )—and they play a fundamental role in the climate system by modulating the spatiotemporal variability of air‐sea heat exchanges (Brümmer, ; Fletcher et al, ; Grossman & Betts, ; Jensen et al, ; Renfrew & Moore, ; Shapiro et al, ). Climatologically CAOs contribute the bulk to the wintertime cooling of high‐latitude oceans by sensible and latent heat fluxes (Harden et al, ; Papritz & Spengler, ; Papritz et al, ).…”

“…From a weather system perspective both anticyclones and cyclones can in principle induce CAOs. For example, episodes of persistent blocking over northern Europe are known to favor CAOs over continental Europe and Scandinavia (Buehler et al, ), while anticyclones over Greenland can induce CAOs over the Nordic Seas (Kolstad, ; Kolstad et al, ) and the Irminger Sea (Papritz, ). Often, however, marine CAOs are also embedded in the equatorward flow on the rearward side of extratropical cyclones (Fletcher et al, ; Vannière et al, ; Zolina & Gulev, ).…”

A model‐based comparison of extreme winds in the Arctic and around Greenland

“…Extreme wind speeds enhanced over the Norwegian and Barents Sea, probably in association with better resolved polar lows and marine polar air outbreaks. The latter were recently identified to intensify in higher resolved models (Kolstad, ). However, our results indicate that polar lows might still be under‐represented, even at 15 km resolution.…”

“…These extreme wind speeds are caused by the above described mesoscale wind systems of tip jets, barrier winds, katabatic winds, and plateau jets. High thresholds (up to 22 m/s) also occur in the Norwegian and Barents Sea, which are known for polar lows and strong marine cold air outbreaks (Kolstad, ; ).…”

“…Based on ASRv1, high RL 10 result only over open ocean off the sea ice edge (not as dominant in ASRv2), but already over sea ice in C15, which seems more realistic compared to CCMPv2. High return levels over the sea ice seem reasonable where marine cold air outbreaks occur frequently (Kolstad, ).…”