Seasonal Climatology and Trends of Strong Wind and Lull Events in the Circum-Arctic During the 1980 - 2010 Period Using a Novel Lull/Storm Wind Indicator

Extratropical cyclones (ETCs) generate strong impacts in marine and coastal environments throughout the extended circum-Arctic region. Within a marine context, many impacts are caused by strong winds. For example, hazardous sea states, storm surge, and coastal erosion are common marine/coastal impacts from ETCs. These sea states can greatly affect operations in the North, causing expensive delays in deliveries, particularly in the marine environment. For example, many regions of the circum-Arctic are serviced by tug-and-barge style marine transport that operates during the limited ice-free shipping season. Due to the flat-bottomed construction of most tug-and-barge operations, providers are highly impacted by the marine state. As a result, most shipping via tug-and-barge operations is conducted during periods of lower wind speed (or lulls), which allows for safe transport of materials. Interviews with stakeholders in the marine transport sector have indicated that considering breaks between wind events, termed lull events, as much as the wind events themselves are important for marine operations. If a period of less than 48-hours of safe marine state is present in a forecast period, operations are halted until weather becomes more favorable. For this study, a modified version of a wind event identification algorithm is applied to reanalysis data to determine the spatial and temporal characteristics of strong wind events in the extended circum-Arctic, defined as 45°N to the pole. In addition to wind events, a novel indicator is introduced that characterizes periods of favorable weather between strong wind events that last 48-hours or longer, termed lull events. Lull periods have been found to be an important consideration for northern marine operations – both economic and subsistence. This talk will present the seasonal climatology of wind and lull events and their associated trends over the 1980-2010 period using the ECMWF ERA-Interim, NASA MERRA, and NCEP CFSR reanalyses. Differences between the zonal distribution of both wind and lull events are presented for the Atlantic, Pacific, and Polar regions. Overall, strong wind events are found to often occur in locations and seasons where ETCs are prevalent. One interesting result shows opposing trends between lulls with durations of 48-hour or greater and those with a duration between 6 to 48-hours in the North Atlantic (decreasing/increasing, respectively), which suggests an increasing frequency of wind events in this region. Additionally, combinations of lull and wind event indicators, termed lull/storm winds (LSW), were analyzed. Overall, LSW analysis shows that preferred areas of wind events and lull events are not always spatially coherent.