Evolution of atmospheric extreme events and the associated oceanic response in the North Pacific

• Main Author: Giamalaki, Aikaterini
• Format: Thesis
• Language: English
• Published: University of Southampton 2019
• Subjects: Pacific; aleutian low
• Online Access: https://eprints.soton.ac.uk/436203/; https://eprints.soton.ac.uk/436203/1/Thesis_Giamalaki.pdf

Ocean – atmosphere interactions have significant effects on climate variability, with extremes in atmospheric conditions playing a key role. Atmospheric extreme events have been associated with major marine ecosystem regime shifts and unusual weather patterns. Regime shifts may be defined as abrupt changes in an ecosystem that propagate through multiple trophic levels and have pronounced effects on the biotic and abiotic environment, potentially resulting in ecosystem reorganization. Such major changes were reported in winter 1976-1977 in the physics of the North Pacific with a prominent biological response in the lower trophic levels and subsequent effects on the fisheries and economy of the region. There are multiple mechanisms that can cause such shifts including natural and anthropogenic factors. An extreme sea level pressure event has previously been linked to abrupt changes of oceanic conditions in the late 1970’s, which were maintained by long term alterations in air-sea interaction processes. The evolution of the oceanic response to driving forcings, such as atmospheric extremes, able to cause abrupt shifts in complex systems as the North Pacific, calls for further scrutiny. This thesis begins by investigating the relationship of extreme atmospheric events with sudden oceanic changes by calculating the dynamical proxies of reanalysis data. The results show the occurrence of an extreme atmospheric event, specifically a deepened Aleutian Low during winter 1976–1977, which constitutes a substantial part of the triggering mechanism of the North Pacific shift. Subsequent sudden changes in the net heat flux occurred in the western North Pacific, particularly in the Kuroshio Extension region, which contributed to the maintenance of the new regime. In order to verify the relationship of Aleutian Low extreme events with changes in Kuroshio Extension net heat flux, statistical and dynamical approaches are applied to historical simulations of the large ensemble of the Community Earth System Model (CESM-LENS). The ...