Abstract
Abstract. PV inversion techniques have been widely used in numerical studies of severe weather cases. These techniques can be applied as a way to study the sensitivity of the responsible meteorological system to changes in the initial conditions of the simulations. Dynamical effects of a collection of atmospheric features involved in the evolution of the system can be isolated. However, aspects, such as the definition of the atmospheric features or the amount of change in the initial conditions, are largely case-dependent and/or subjectively defined. An objective way to calculate the modification of the initial fields is proposed to alleviate this problem. The perturbations are quantified as the mean absolute variations of the total energy between the original and modified fields, and an unique energy variation value is fixed for all the perturbations derived from different PV anomalies. Thus, PV features of different dimensions and characteristics introduce the same net modification of the initial conditions from an energetic point of view. The devised quantification method is applied to study the high impact weather case of 9–11 November 2001 in the Western Mediterranean basin, when a deep and strong cyclone was formed. On the Balearic Islands 4 people died, and sustained winds of 30 ms−1 and precipitation higher than 200 mm/24 h were recorded. Moreover, 700 people died in Algiers during the first phase of the event. The sensitivities to perturbations in the initial conditions of a deep upper level trough, the anticyclonic system related to the North Atlantic high and the surface thermal anomaly related to the baroclinicity of the environment are determined. Results reveal a high influence of the upper level trough and the surface thermal anomaly and a minor role of the North Atlantic high during the genesis of the cyclone.
Highlights
Potential Vorticity (PV) as a conservative quantity for adiabatic and frictionless conditions has been revealed as a good variable to study the structure and evolution of cyclones (Hoskins et al, 1985; Gyakum, 1983b; Huo et al, 1995; Hakim et al, 1996)
The piecewise PV inversion technique (Davis and Emanuel, 1991) can be used as a way to modify the initial conditions of numerical simulations
This approach has been shown as a powerful tool towards the understanding of important atmospheric aspects related to the cyclogenesis, such as baroclinic and barotropic development and convection
Summary
Potential Vorticity (PV) as a conservative quantity for adiabatic and frictionless conditions has been revealed as a good variable to study the structure and evolution of cyclones (Hoskins et al, 1985; Gyakum, 1983b; Huo et al, 1995; Hakim et al, 1996). The piecewise PV inversion technique (Davis and Emanuel, 1991) can be used as a way to modify the initial conditions of numerical simulations. The sensitivity to changes in the initial conditions has been used in several dynamical studies of intense storms (Huo et al, 1999a,b; Romero, 2001a; Homar et al, 2002, 2003). This approach has been shown as a powerful tool towards the understanding of important atmospheric aspects related to the cyclogenesis, such as baroclinic and barotropic development and convection. A fourth section with the results of the November 2001 storm is presented, and a final section of conclusions is given
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