Development of an Oceanic Storminess Index to Identify Fishing Fleet Impacts in the Northwest Atlantic

Presenting Author(s): Gabe Larouche

Title: Development of an Oceanic Storminess Index to Identify Fishing Fleet Impacts in the Northwest Atlantic

Conference: American Meteorological Society, 104th AMS Annual Meeting, 28th Conference on Applied Climatology

Session: Development of Indices for Applied Climatology Research in Large Datasets

Abstract:

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, the oceanic storminess index was developed in two phases. Phase one qualitatively compared National Weather Service issued gale warnings within the NES LME to the spatial and temporal behavior of wind speed, waves, and mean sea-level pressure. The Iowa State mesonet provided gale warning time series data for the NES LME. Identifying specific hours of a previously issued gale warning allowed for the plotting of ERA5 reanalysis data to classify various storm modes resulting in the issuance of gale warnings. The maps of wind speed, waves and mean sea-level pressure rendered qualitative information regarding the spatial distribution and temporal evolution of gale warning events. Phase two converted qualitative properties regarding the spatial and temporal characteristics of ocean storms into quantitative thresholds applicable to gridded ERA5 data. The objective of phase two was to use thresholds to count distinct ‘storminess events’ within five NES LME subregions and compare event trends through time. 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 then tested against duration and intervening period thresholds to temporally capture both mesoscale events bringing gale force winds such as squall lines and synoptic scale events such as mid-latitude cyclones. Storminess events’ that passed threshold tests were grouped into both annual and seasonal time series for the NES LME subregions. Phase two was initially completed using ERA5 hourly data on single levels from 1950 to the present, however time series from Blended Sea Surface Wind Product from NOAA CoastWatch provided an affirmative comparison of ERA5 storminess trends. Composite maps of 500 mb geopotential height and mean sea-level pressure additionally confirmed that the oceanic storminess index detected real storm events. Seasonal analyses indicated winter and spring drove annual trends, and areas further north and east have typically experienced the greatest annual statistically significant increases in ocean storm frequency. These results could guide adaptations to economic and recreational fishery strategies through time.