Articles | Volume 10, issue 2
Model description paper
21 Feb 2017
Model description paper |  | 21 Feb 2017

OZO v.1.0: software for solving a generalised omega equation and the Zwack–Okossi height tendency equation using WRF model output

Mika Rantanen, Jouni Räisänen, Juha Lento, Oleg Stepanyuk, Olle Räty, Victoria A. Sinclair, and Heikki Järvinen

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.

Short summary
This paper describes new software OZO, which is a meteorological tool for both studying and research purposes. OZO can be used for investigating physical mechanisms affecting the development of extratropical cyclones. The software is an open-source tool and the distribution is supported by the authors. OZO will be used as a part of the author's PhD, in which the changes in cyclone dynamics due to warmer climate are studied.