This version not peer reviewed
Higher Ocean Surface Wind Speeds During Marine Cold Air Outbreaks
: Received: 5 April 2017 / Approved: 6 April 2017 / Online: 6 April 2017 (16:26:35 CEST)
: Received: 2 May 2017 / Approved: 2 May 2017 / Online: 2 May 2017 (17:45:56 CEST)
A peer-reviewed article of this Preprint also exists.
Journal reference: Q. J. R. Meteorol. Soc. 2017
Marine cold air outbreaks (MCAOs) are large-scale phenomena 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 the behaviour of ocean surface wind speeds during MCAOs in three atmospheric reanalysis products with different horizontal grid spacings, along with 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. The main findings are: 1) Wind speeds during the most extreme MCAO events are stronger than normal and higher than wind speeds during less severe events; 2) The peak times of MCAO usually occur when baroclinic waves pass over the regions; and 3) Reanalyses with grid spacings of more than 50 km appear to underestimate winds driven by the large ocean–atmosphere energy fluxes during MCAOs. It is also shown that while the strong wind episodes during MCAOs generally last for just a few days, MCAOs can persist for up to 50 days. These findings demonstrate that it would be worthwhile to forecast MCAOs, and that it might be possible to do this beyond the standard weather forecasting range of up to 10 days.
polar lows; meteorology; cold air outbreaks; mesoscale; air–sea interaction; numerical modelling
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