Abstract
Abstract. A software package (OZO, Omega–Zwack–Okossi) was developed to diagnose the processes that affect vertical motions and geopotential height tendencies in weather systems simulated by the Weather Research and Forecasting (WRF) model. First, this software solves a generalised omega equation to calculate the vertical motions associated with different physical forcings: vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term between vorticity and temperature tendencies. After this, the corresponding height tendencies are calculated with the Zwack–Okossi tendency equation. The resulting height tendency components thus contain both the direct effect from the forcing itself and the indirect effects (related to the vertical motion induced by the same forcing) of each physical mechanism. This approach has an advantage compared with previous studies with the Zwack–Okossi equation, in which vertical motions were used as an independent forcing but were typically found to compensate the effects of other forcings.The software is currently tailored to use input from WRF simulations with Cartesian geometry. As an illustration, results for an idealised 10-day baroclinic wave simulation are presented. An excellent agreement is found between OZO and the direct WRF output for both the vertical motion and the height tendency fields. The individual vertical motion and height tendency components demonstrate the importance of both adiabatic and diabatic processes for the simulated cyclone. OZO is an open-source tool for both research and education, and the distribution of the software will be supported by the authors.
Highlights
Today, high-resolution atmospheric reanalyses provide a three-dimensional (3-D) view on the evolution of synopticscale weather systems (Dee et al, 2011; Rienecker et al, 2011)
Two variables that are of special interest in the study of synoptic-scale weather systems are the geopotential height tendency and vertical motion (Holton and Hakim, 2012)
We introduce a software package Omega–Zwack– Okossi (OZO) that can be used for diagnosing the contributions of different dynamical and physical processes to atmospheric vertical motions and height tendencies
Summary
High-resolution atmospheric reanalyses provide a three-dimensional (3-D) view on the evolution of synopticscale weather systems (Dee et al, 2011; Rienecker et al, 2011). The complexity of atmospheric dynamics often makes the physical interpretation of reanalysis data and model output far from simple. There is a need for diagnostic methods that help to separate the effects of individual dynamical and physical processes on the structure and evolution of weather systems. Two variables that are of special interest in the study of synoptic-scale weather systems are the geopotential height tendency and vertical motion (Holton and Hakim, 2012). Vertical motions affect atmospheric humidity, cloudiness, and precipitation.
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