Polar jet stream variation induced by planetary warming has the potential to disrupt established economic practices such as commercial and recreational fishing by changing typical ocean storm behavior. The oceanic storminess index identifies climate impacts to inform fishing fleet operations in the Northeast U.S. Continental Shelf Large Marine Ecosystem (NES LME) of changes in storminess frequency and intensity over time. To investigate climate indicators of NES LME storminess trends, we developed a 71-year storminess climatology (1950-2021) known as the Oceanic Storminess Index. We first compared National Weather Service issued gale warnings within the NES LME provided by the Iowa State mesonet to the spatial and temporal behavior of ocean storm related variables such as wind speed. To classify various storm modes resulting in the issuance of gale warnings, gridded hourly ERA5 reanalysis data was plotted during specific hours of a previously issued gale warning. Maps of wind speed, waves and mean sea-level pressure rendered qualitative information regarding the spatial distribution and temporal evolution of gale-warned storm events. We then converted the qualitative information into quantitative thresholds and applied them to ERA5 hourly data on single levels from 1950 to the present. An hour became a spatial candidate for a ‘storminess event’ in a NES LME subregion if a given proportion of grids met a selected wind speed threshold. Spatial candidates were tested against duration and intervening period thresholds to temporally capture both mesoscale events such as squall lines and synoptic scale events such as mid-latitude cyclones.
‘Storminess events’ which passed threshold tests were grouped into both annual and seasonal time series for the NES LME subregions. A storminess time series for each NES LME subregion was initially compiled using hourly ERA5 data, however time series from Blended Sea Surface Wind Product from NOAA CoastWatch provided an affirmative comparison of ERA5 storminess trends. Additionally, composite maps of 500 mb geopotential height and mean sea-level pressure confirmed that we had detected real storm events. Our analysis indicates that areas further north and east have typically experienced greater statistically significant increases in ocean storm occurence, with meteorological winter and spring driving annual trends. These results could inform adaptations to fishery strategies.
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