The role of coherent air streams in shaping the Gulf stream’s impact on the large-scale extratropical circulation
Final Report Abstract
The variability of large-scale weather conditions in the North Atlantic region is dominated by quasi-stationary, persistent, and recurrent flow patterns. These so-called weather regimes are characterized by the occurrence of low- and high-pressure systems in specific subregions. Successful weather forecasts on time ranges of several days to a season (the sub-seasonal to seasonal – S2S – time range) rely on the correct representation of the life cycle of weather regimes in numerical models. Thereby, the maintenance of favorable conditions for the intensification of low-pressure systems along a confined storm track and the initiation and maintenance of stationary highpressure systems (atmospheric blocking) downstream, are thought to be key elements. There is increasing evidence that air-sea interaction especially along the Gulf Stream oceanic front, latent heat release in cyclones, and the advection of cold air masses from the Arctic play a key role for the variability of the large-scale circulation over the North Atlantic and Europe. Yet, the mechanistic understanding of how the associated air mass transformations over the ocean affect the largescale flow is still limited. Furthermore, the relevance of these processes for the life cycle of weather regimes has not yet been established. In this three-year collaborative project at KIT and ETH Zürich, we have developed an integral view of the mechanistic pathway linking air-sea interactions in the Gulf Stream region to the large-scale atmospheric flow. Based on a large set of trajectories, we were able to quantify that 20% of air masses that contributed to the development of an atmospheric blocking underwent significant heating and moistening over the Gulf Stream. These modified air masses later ascended within subsequent low-pressure systems, reinforcing and sustaining the block. Through numerical sensitivity experiments, we could further show that the identified pathway is sensitive of gradients of the sea surface temperature in the Gulf stream region. Stronger sea surface temperature gradients enhance moisture availability, increase the ascent rate of ascending air masses in low pressure systems and thus amplify the atmospheric block. In contrast, weaker gradients reduce the intensity of low-pressure systems and are linked to a weaker blocking anticyclone. Overall, these findings reinforce the importance of ocean-atmosphere coupling in shaping extratropical cyclone dynamics and large-scale circulation patterns. Improved representations of SST gradients and air-sea interactions in numerical weather prediction models is essential for better forecasting of blocking events in the North Atlantic- European region on the sub-seasonal to seasonal time range.
Publications
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Air-sea interactions and diabatic processes in the Gulf Stream region and their role in the life-cycle of a blocking anticyclone: a case study of European Blocking in Feb 2019, Stormtrack Workshop 2022, Oléron Island, France, 29 May - 3 June 2022
Wenta, M., Grams C. M., Papritz L. & Federer M.
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Air-sea interactions and diabatic processes in the Gulf Stream region and their role in the life-cycle of a blocking anticyclone: a case study of European Blocking in Feb 2019.. Copernicus GmbH.
Wenta, Marta; Grams, Christian M.; Papritz, Lucas & Federer, Marc
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An Available Potential Energy Perspective on North Atlantic Weather Regimes. Copernicus GmbH.
Federer, Marc; Papritz, Lukas; Grams, Christian; Sprenger, Michael & Wenta, Marta
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Air-sea interactions and diabatic processes in the Gulf Stream region and their role in the development of a blocking anticyclone, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) 2023, Berlin, Germany, 11-20 Jul 2023
Wenta, M., Grams C. M., Papritz L. & Federer M.
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Air-Sea Interactions and Diabatic Processes in the Gulf Stream Region and Their Role in the Life-Cycle of a Blocking Anticyclone: A Case Study of European Blocking in Feb 2019, AMS Annual Meeting 2023, Denver, US, 7–13 Jan 2023
Wenta, M., Grams C. M., Papritz L. & Federer M.
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Linking Gulf Stream air–sea interactions to the exceptional blocking episode in February 2019: a Lagrangian perspective. Weather and Climate Dynamics, 5(1), 181-209.
Wenta, Marta; Grams, Christian M.; Papritz, Lukas & Federer, Marc
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On the Local Available Potential Energy Perspective of Baroclinic Wave Development. Journal of the Atmospheric Sciences, 81(5), 871-886.
Federer, Marc; Papritz, Lukas; Sprenger, Michael; Grams, Christian M. & Wenta, Marta
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Precursors and pathways: dynamically informed extreme event forecasting demonstrated on the historic Emilia-Romagna 2023 flood. Natural Hazards and Earth System Sciences, 24(9), 2995-3012.
Dorrington, Joshua; Wenta, Marta; Grazzini, Federico; Magnusson, Linus; Vitart, Frederic & Grams, Christian M.
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Research data for Understanding the sea surface temperature impact on an atmospheric blocking event using sensitivity experiments with the ICOsahedral Nonhydrostatic (ICON) model. Karlsruhe Institute of Technology [data set]
Christ, S., Oertel, A., Wenta, M. & Grams, C. M.
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From sea to sky: understanding the sea surface temperature impact on an atmospheric blocking event using sensitivity experiments with the ICOsahedral Nonhydrostatic (ICON) model. Weather and Climate Dynamics, 6(1), 17-42.
Christ, Svenja; Wenta, Marta; Grams, Christian M. & Oertel, Annika
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Synoptic perspective on the conversion and maintenance of local available potential energy in extratropical cyclones. Weather and Climate Dynamics, 6(1), 211-230.
Federer, Marc; Papritz, Lukas; Sprenger, Michael & Grams, Christian M.
