Stratospheric intrusion depth and its effect on surface cyclogenetic forcing: an idealized potential vorticity (PV) inversion experiment

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 surface cyclogenetic forcing. Numerical experiments using PV inversion diagnostics reveal that stratospheric depth is crucial in the intensity of cyclonic circulation induced at the surface. In an idealized setting, shallow, high-PV intrusions (above 300 hPa) resulted in a marginal effect on the surface, whilst growing stratospheric depth resulted in enhanced surface pressure anomalies and surface cyclonic circulation. It is shown that the height above the surface that intrusions reach is more critical than the vertical size of the intrusion when inducing cyclonic flow at the surface. This factor is however constrained by the height of the dynamical tropopause above the surface. The width of the stratospheric intrusion is an additional factor, with broader intrusions resulting in enhanced surface cyclogenetic forcing.