Preprints
https://doi.org/10.5194/wcd-2021-24
https://doi.org/10.5194/wcd-2021-24

  12 May 2021

12 May 2021

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

Stratospheric intrusion depth and its effect on surface cyclogenesis: An idealized PV inversion experiment

Michael A. Barnes1,2, Thando Ndarana2, Michael Sprenger3, and Willem A. Landman2 Michael A. Barnes et al.
  • 1Marine Research Unit, South African Weather Service, Cape Town, South Africa
  • 2Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, South Africa
  • 3Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

Abstract. Stratospheric intrusions of high potential vorticity (PV) air are well-known drivers of cyclonic development throughout the troposphere. PV anomalies have been well studied with respect to their effect on surface cyclogenesis. A gap however exists in the scientific literature describing the effect that stratospheric intrusion depth has on the amount of surface cyclogenetic forcing at the surface. Numerical experiments using PV inversion diagnostics reveal that stratospheric depth is crucial in the amount of cyclogenesis at the surface. In an idealised setting, shallow intrusions (above 300 hPa) resulted in a marginal effect on the surface, whilst growing stratospheric depth resulted in enhanced surface pressure anomalies and surface cyclogenetic forcing. The horizontal extent of the intrusion is shown to be more important in developing deeper surface cyclones than the vertical depth of the stratospheric intrusion. The size of vertical intrusion depths is however an important factor determining the surface relative vorticity, with larger intrusions resulting in stronger cyclonic circulations. Deeper stratospheric intrusions also result in intrusions reaching closer to the surface. The proximity of intrusions to the surface is a crucial factor favouring surface cyclogenetic forcing. This factor is however constrained by the height of the dynamical tropopause above the surface.

Michael A. Barnes et al.

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Michael A. Barnes et al.

Michael A. Barnes et al.

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Short summary
Stratospheric air can at times intrude into the troposphere and is associated with cyclonic development throughout the atmosphere and at the surface. Through a highly idealised, systematic approach, the effect different intrusion characteristics have on surface cyclones are investigated. The proximity of stratospheric intrusions surface is shown to be the main contributing factor to the development of associated surface cyclones, confirming the results of recent cut-off low climatologies.