Thursday November 7 CSL Meeting

Practice Master's Thesis Defense: The Influence of Local Sea Ice and Remote Northern Hemisphere Teleconnections on Cyclones in Baffin Bay, Davis Strait, and Labrador Sea

Presenter: Bradley Barger
Time: Thursday, 7 November 2019, 3:30 p.m.
Location: 805 O&M

Abstract: Cyclones are a primary mode of energy transport between the mid-latitudes and the polar region in the Northern Hemisphere (NH). Due to the North Atlantic experiencing some of the highest frequencies of cyclones, this region has been extensively researched. However, Baffin Bay (BB), Davis Strait (DS), and the Labrador Sea (LS) are also part of the North Atlantic, yet limited literature exists regarding cyclones and the influences of local and remote drivers on their variability in these subregions. This thesis focuses on determining the influence of local sea ice cover and remote NH teleconnections on cyclone variability in BB, DS, and LS from 1980-2015.

To represent the local sea ice area driver, the NH's monthly sea ice was subsetted for each subregion. To establish the remote atmospheric driver, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Pacific Decadal Oscillation, Pacific North American Pattern, Polar Eurasian Pattern, and East Atlantic/West Russia Pattern's monthly indices were obtained for 1980-2015. Cyclone variability was represented with the annual count, central pressure, cyclogenesis, cyclolysis, local laplacian, latitude, and longitude from NSIDC's NH Cyclone Locations and Characteristics record. Local drivers, remote drivers, and cyclone variables were analyzed using linear least-squares regression trends, compared using correlations (95% confidence interval), and all were seasonally standardized and detrended before each cyclone variable was compared with each local and remote driver at the long-term and individual monthly time scales.

Results indicate that sea ice area in BB, DS, and LS decreased significantly, but at lower rates than the NH. Furthermore, each subregion's sea ice variability is unique from the NH's and from the other subregions, however periods of similar sea ice area deviation occurs across all subregions. The overall study area's (BB-DS-LS) total number of cyclogenesis events had the only significant positive trend out of all cyclone variables. Comparing subregions, cyclone variability was noticeably different (especially between BB and LS). Both local and remote drivers significantly correlate with the longitudinal position of cyclones in all subregions at the long-term time scale. At the individual monthly scale, longitude and cyclolysis correlated most frequently and strongly with sea ice, while atmospheric teleconnections correlated most with cyclones' central pressure. Overall, the NAO and AO had the most frequent and strongest correlations. While local sea ice area was significantly related with certain cyclone variables, these associations were typically weaker. Therefore, overall cyclone variability in BB, DS, and LS is influenced more by remote atmospheric forcing than by local sea ice cover. Comparing BB, DS, and LS, it appears that, although they are geographically connected, each experiences unique cyclone variability. Finally, because each subregion's cyclone variability is significantly related to local sea ice cover and remote teleconnections at different magnitudes and times, these regions should be considered independently from one another and from the North Atlantic, to better capture atmospheric variability and interactions with the local environment.

Correlations between each cyclone variable and each teleconnection pattern (red dots indicate p-value < 0.05).