Sensitivity of Mountain Wave Drag Estimates on Separation Methods and Proposed Improvements

Zuzana Procházková, Christopher G. Kruse, M. Joan Alexander, Lars Hoffmann, Julio T. Bacmeister, Laura Holt, Corwin Wright, Kaoru Sato, Sonja Gisinger, Manfred Ern, Markus Geldenhuys, Peter Preusse, Petr Šácha

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Abstract

Internal gravity waves (GWs) are ubiquitous in the atmosphere, making significant contributions to the mesoscale motions. Since the majority of their spectrum is unresolved in global circulation models, their effects need to be parameterized. In recent decades GWs have been increasingly studied in high-resolution simulations, which, unlike direct observations, allow us to explore full spatiotemporal variations of the resolved wave field. In our study we analyze and refine a traditional method for GW analysis in a high-resolution simulation on a regional domain around the Drake Passage. We show that GW momentum drag estimates based on the Gaussian high-pass filter method applied to separate GW perturbations from the background are sensitive to the choice of a cutoff parameter. The impact of the cutoff parameter is higher for horizontal fluxes of horizontal momentum, which indicates higher sensitivity for horizontally propagating waves. Two modified methods, which choose the parameter value from spectral information, are proposed. The dynamically determined cutoff is mostly higher than the traditional cutoff values around 500 km, leading to larger GW fluxes and drag, and varies with time and altitude. The differences between the traditional and the modified methods are especially pronounced during events with significant drag contributions from horizontal momentum fluxes.

Original languageEnglish
Pages (from-to)1661-1680
Number of pages20
JournalJournal of the Atmospheric Sciences
Volume80
Issue number7
Early online date26 Jun 2023
DOIs
Publication statusPublished - 1 Jul 2023

Bibliographical note

Funding Information:
Acknowledgments. The authors would like to acknowledge discussions with Inna Politchouk, Annelize van Nie-kerk, and Ryosuke Shibuya within the New Quantitative Constraints on Orographic Gravity Wave Stress and Drag Satisfying Emerging Needs in Seasonal-to-Subseasonal and Climate Prediction international team at the ISSI Bern, which helped to shape and conceptualize the paper. Also, Zuzana Procházková and Petr Sˇácha want to acknowledge discussions with Aurélien Podglajen. Manfred Ern was supported by the German Research Foundation (DFG) Grant ER 474/4-2 and by the German Federal Ministry of Education and Research (BMBF) Grant 01LG1905C (QUBICC, ROMIC). Sonja Gisinger was supported by the German Federal Ministry for Education and Research (01LG1907, WASCLIM, ROMIC program). Corwin Wright acknowledges Royal Society University Research Fellowship URF\R\221023. Zuzana Procházková was supported by GACˇR 21-20293J and GAUK 281021, and Petr Sˇácha and Zuzana Procházková further acknowledge the funding from the Czech Science Foundation under the Junior Star Grant 23-04921M.

Keywords

  • Atmosphere
  • Dynamics
  • Filtering techniques
  • Gravity waves
  • Middle atmosphere
  • Orographic effects

ASJC Scopus subject areas

  • Atmospheric Science

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