Large-scale Horizontal Energy Fluxes into the Arctic Analyzed Using Self-organizing Maps

• Main Author: Mewes, Daniel
• Other Authors: Universität Leipzig
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2020
• Subjects: Arctic; Atmospheric Energy Fluxes; Self-organizing Maps; info:eu-repo/classification/ddc/551; ddc:551; Pacific; North Atlantic; North Atlantic oscillation
• Online Access: https://nbn-resolving.org/urn:nbn:de:bsz:15-qucosa2-751794; https://ul.qucosa.de/id/qucosa%3A75179; https://ul.qucosa.de/api/qucosa%3A75179/attachment/ATT-0/

The meridional temperature gradient between middle and high latitudes is decreasing due to Arctic amplification, which enhances the warming in the Arctic region. This change in temperature is also influencing the circulation and the horizontal energy fluxes between the mid latitudes and the Arctic, which itself might influence the Arctic additionally. The horizontal energy flux, to our best knowledge, has never been analyzed using the up-to-date method called self-organizing map (SOM). The SOM is a simple unsupervised neural network that is used to extract patterns of high-dimensional data and presents the patterns in a two dimensional lattice, where similar (more different) patterns are closer together (farther apart) within the lattice. An advantage of using the SOM is that there are no underlying linear assumptions like in other methods that characterize the circulation, such as the Arctic Oscillation or the North Atlantic Oscillation index. The SOM has been used in this work to extract and analyze horizontal heat flux patterns from reanalysis data and climate model data. Using the SOM method, it was possible to find distinct horizontal heat flux patterns into the Arctic, that have been combined into heat flux pathways. The SOM made it possible to characterize the pathways' change in occurrence frequency throughout the last thirty years and the change between present-day climate model simulations and climate projections with increased greenhouse gas concentrations. Using reanalysis data, three distinct patterns have been extracted, which all show different features. They are named according to the main pathway the horizontal heat flux takes to reach the Arctic: the Atlantic pathway, the Pacific pathway, and the continental pathway. For the reanalysis data, it is shown that the Atlantic pathway, which is connected with positive temperature anomalies in the central Arctic, has become more frequent during the last three decades, while the Pacific pathway, that is connected to negative temperature anomalies ...