Linking Atmospheric Waviness to Extreme Temperatures Across the Northern Hemisphere: Comparison of Different Waviness Metrics

Abstract Large meanders in the atmospheric jet stream (Rossby waves) are strongly related to extreme temperature events. It has been theorized that changes in such waves, or “waviness,” may have played a role in observed changes in the frequency of extreme temperature events. There is, however, no consensus on how atmospheric waviness will change in response to climate change; the existence of different metrics used to quantify waviness may be contributing to this lack of consensus. Here, we perform a waviness metric comparison, focusing on their association with extreme daily temperatures across the Northern Hemisphere midlatitudes. Using a probability ratio, we quantify the association between high waviness and colocated extreme temperatures. We find large differences in association strength across different metrics, highlighting that different metrics are associated with very different aspects of waviness, and are not all equally associated with extremes. A composite analysis highlights some differences. We find that the local wave activity (LWA) metric has the strongest associations with temperature extremes, particularly when separated into its cyclonic and anticyclonic components. We also conduct similar analysis using a neural network model to simulate links between metrics and temperature anomalies. We find that probability ratios can be increased through this method of including nonlinear, and not just colocated, connections, but the result of the LWA metric providing the strongest connection to extremes holds. We also show that a simple geopotential height zonal anomaly method provides overall very high associations and may be sufficient for many studies connecting waviness to extremes.