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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  17 Feb 2020

17 Feb 2020

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This preprint is currently under review for the journal WCD.

The sensitivity of atmospheric blocking to changes in upstream latent heating – numerical experiments

Daniel Steinfeld1, Maxi Boettcher1, Richard Forbes2, and Stephan Pfahl3 Daniel Steinfeld et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
  • 2European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom
  • 3Institute of Meteorology, Freie Universität Berlin, Germany

Abstract. Recent climatological studies based on trajectory calculations have pointed to an important role of latent heating during cloud formation for the dynamics of anticyclonic circulation anomalies such as atmospheric blocking. However, the causal relationship between latent heating and blocking formation has not yet been fully elucidated. To explicitly study this causal relationship, we perform sensitivity simulations of five selected blocking events with a global weather prediction model in which we artificially eliminate latent heating in clouds upstream of the blocking anticyclones. This elimination has substantial effects on the upper-tropospheric circulation in all case studies, but there is also significant case-to-case variability: some blocking systems do not develop at all without upstream latent heating, while for others the amplitude of the blocking anticyclones is merely reduced. This strong influence of latent heating on the jet stream is due to the injection of air masses with low potential vorticity (PV) into the upper troposphere in strongly ascending warm conveyor belt airstreams, and the interaction of the associated divergent outflow with the upper-level PV structure. The important influence of diabatic heating demonstrated with these experiments suggests that an accurate parameterization of microphysical processes in weather prediction and climate models is crucial for adequately representing blocking dynamics.

Daniel Steinfeld et al.

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Daniel Steinfeld et al.

Daniel Steinfeld et al.

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Latest update: 09 Aug 2020
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Short summary
The causal effect of latent heating on atmospheric blocking is investigated using numerical sensitivity experiments. The modification of latent heating in the upstream cyclone has substantial effects on the upper-tropospheric circulation, demonstrating that some blocking systems do not develop at all without upstream latent heating. The results highlight the importance of moist-diabatic processes for the dynamics of prolonged anticyclonic circulation anomalies.
The causal effect of latent heating on atmospheric blocking is investigated using numerical...
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