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.

Highlights

  • Potential vorticity (PV) has been well established as a highly useful and important parameter within dynamical meteorology (Hoskins et al 1985)

  • Numerical experiments using potential vorticity (PV) inversion diagnostics reveal that stratospheric depth is crucial in the amount of cyclogenesis at the surface

  • The results show that stratospheric intrusions with a -1.5PVU stratospheric tropopause associated with 250hPa cut-off lows that extend to 300hPa or below, are more likely to result in surface cyclogenesis

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Summary

Introduction

Potential vorticity (PV) has been well established as a highly useful and important parameter within dynamical meteorology (Hoskins et al 1985). The first is the fact PV is conserved for adiabatic and frictionless flow (Hoskins 25 et al 1985; Holton and Hakim 2013). The second of these characteristics is the invertibility of PV (Røsting and Kristjánsson 2012). PV inversion, under suitable balance and boundary conditions, allows for the calculation of other meteorological parameters such as pressure and wind velocity as a result of a distribution of PV (Davis 1992; Lackmann 2011). Kleinschmidt (1950) introduced the initial ideas of PV invertibility for specific cases, attributing circulation patterns in the low-levels to an upper-level PV anomaly and introducing the idea of deducing wind, pressure and temperature fields from PV distributions.

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