Preprints
https://doi.org/10.5194/wcd-2021-58
https://doi.org/10.5194/wcd-2021-58

  09 Sep 2021

09 Sep 2021

Review status: this preprint is currently under review for the journal WCD.

Stationary Waves and Upward Troposphere-Stratosphere Coupling in S2S Models

Chen Schwartz1,, Chaim I. Garfinkel1,, Priyanka Yadav2, Wen Chen4,5, and Daniela Domeisen2,3 Chen Schwartz et al.
  • 1The Fredy and Nadine Herrmann Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, Israel
  • 2Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 3Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland
  • 4College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
  • 5Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • these authors contributed equally

Abstract. The simulated Northern Hemisphere stationary wave (SW) field is investigated in 11 subseasonal-to-seasonal (S2S) models. It is shown that while most models considered can well-simulate the stationary wavenumbers 1 and 2 during the first two weeks of integration, they diverge from observations following week 3. Those models with a poor resolution in the stratosphere struggle to simulate the waves, both in the troposphere and the stratosphere, even during the first two weeks, and biases extend from the troposphere all the way up to the stratosphere. Focusing on the tropospheric regions where SWs peak in amplitude reveals that the models generally do a better job in simulating the Northwest Pacific stationary trough, while certain models struggle to simulate the stationary ridges both in Western North America and the North Atlantic. In addition, a strong relationship is found between regional biases in the stationary height field and model errors in simulated upward propagation of planetary waves into the stratosphere. In the stratosphere, biases mostly are in wave-2 in those models with high stratospheric resolution, whereas in those models with low resolution in the stratosphere, a wave-1 bias is evident, which leads to a strong bias in the stratospheric mean zonal circulation due to the predominance of wave-1 there. Finally, biases in both amplitude and location of mean tropical convection and the subsequent subtropical downwelling, are identified as possible contributors to biases in the regional SW field in the troposphere.

Chen Schwartz et al.

Status: open (until 23 Oct 2021)

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Chen Schwartz et al.

Chen Schwartz et al.

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Short summary
Eleven operational forecast models that run on subseasonal timescales (up to two months) are examined, to assess the errors in their simulated large-scale stationary waves in the Northern Hemisphere winter. We found that models with finer resolved stratosphere generally do better in simulating the waves both in the stratosphere (10–50 km) and troposphere below. Moreover, a connection exists between errors in simulated time-mean convection in tropical regions and errors in the simulated waves.