Preprints
https://doi.org/10.5194/egusphere-2022-965
https://doi.org/10.5194/egusphere-2022-965
 
30 Sep 2022
30 Sep 2022
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

Vortex streets to the lee of Madeira in a km-resolution regional climate model

Qinggang Gao1,a,b, Christian Zeman1, Jesus Vergara‑Temprado1,c, Daniela Lima3, Peter Molnar2, and Christoph Schär1 Qinggang Gao et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 2Institute of Environmental Engineering, ETH Zürich, Zürich, Switzerland
  • 3Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
  • anow at: Ice Dynamics and Paleoclimate, British Antarctic Survey, Cambridge, United Kingdom
  • bnow at: Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom
  • cnow at: UBS, Zurich, Switzerland

Abstract. Atmospheric vortex streets are a widely studied dynamical effect of isolated mountainous islands. Observational evidence comes from case studies and satellite imagery, but the climatology and annual cycle of vortex shedding are often poorly understood. Using the non-hydrostatic limited-area COSMO model driven by the ERA-Interim reanalysis, we conducted a ten-year-long simulation over a mesoscale domain covering Madeira and Canary Archipelagos at high spatial (grid spacing 1 km) and temporal resolutions. Basic properties of vortex streets were analyzed and validated through a 6-day-long case study in the lee of Madeira Island. The simulation compares well with satellite and aerial observations and with existing literature on idealized simulations. Our results show a strong dependency of vortex shedding on local and synoptic flow conditions, which are to a large extent governed by the location, shape, and strength of the Azores high. As part of the case study, we developed a vortex identification algorithm. The algorithm is based on a set of objective criteria and enabled us to develop a climatology of vortex shedding from Madeira Island for the 10-year simulation period. The analysis shows a pronounced annual cycle with an increasing vortex shedding rate from April to August and a sudden decrease in September. This cycle is consistent with mesoscale wind conditions and local inversion height patterns.

Qinggang Gao et al.

Status: open (extended)

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Qinggang Gao et al.

Qinggang Gao et al.

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Short summary
We developed a vortex identification algorithm for realistic atmospheric simulations. The algorithm enabled us to obtain a climatology of vortex shedding from Madeira Island for a 10-year simulation period. This first objective climatological analysis of vortex streets shows consistency with observed atmospheric conditions. The analysis shows a pronounced annual cycle with an increasing vortex shedding rate from April to August and a sudden decrease in September.