Introduction

What is Bedymo?

The Bergen Dynamical Model (Bedymo) is an idealised atmospheric model developed at the Geophysical Institute of the University of Bergen. The primary target application of Bedymo is to study the mid-latitude storm tracks. But applications are not limited to this region. For example, one of the standard setups available simulates the atmospheric response to localised heating in tropical beta-plane.

The most important unique feature of Bedymo is that it combines a quasi-gestrophic (QG) with a hydrostatic primitive equation (PE) model in one modelling framework, with the aim to make comparisons between QG and PE as consistent and easy as possible. Bedymo solves both QG and PE in terrain-following sigma coordinates. While this choice of vertical coordinate is standard for PE, it is unique for QG. Solving QG in sigma-coordinates provides some additional insight over traditional approaches, because sigma-coordinates exposes the consequences of the QG approximations around the lower boundary more explicitly than traditional approaches with for example a fixed isobar as their lower boundary.

In addition to the two atmospheric dynamical cores, Bedymo contains a slab-ocean model with several different options for wind-induced and prescribed currents, and a passive tracer module which can serve as the basis for the parameterisation of moist diabatic effects. Further, Bedymo comes with (this) relatively comprehensive documentation and a Graphical User Interface (GUI) which allows to control the model and watch the simulation “live” as it evolves. This makes Bedymo easy to setup, and accessible for student projects and teaching.

When do you want to use Bedymo?

In conclusion, we see two main applications of Bedymo.

As a testbed for atmospheric dynamics

Here, Bedymo is a more idealised complement to Held-Suarez-type and aquaplanet simulations. In contrast to these, the Bedymo mid-latitude setups do not contain a Hadley-circulation and consequently no subtropical jets, thus isolating the mid-latitude dynamics from tropical influences.

For student projects and teaching

Bedymo can represent many of the idealised representations of the atmosphere as they are discussed in atmosphere/ocean dynamics courses. In particular, Bedymo can represent the shallow water (i.e. barotopic PE), quasi-geostrophic and dry hydrostatic PE systems and allows to easily switch between different approximations.

Limitations

At the moment, there are a number of limitations with Bedymo. Some important limitations are listed in the following. For most of these, we have plans to resolve, but the respective timelines are unknown and will depend on factors beyond our control.

  • No parameterisation of latent heating and moist effects.

  • No ocean model that is able to simulate Western Boundary currents.

  • No sea-ice.

  • No parallel execution.

  • No option to use spherical rather than cartesian geometry.

  • No option for open boundaries.

Components of Bedymo

Bedymo follows a very modular approach, designed such that each of the model components can be replaced without technically affecting the other components. Currently, three components are available:

  • A combined QG and PE model for the atmosphere.

  • A passive tracer module for the atmosphere.

  • A slab-ocean model with different options for representing wind-driven currents.

Scientific documentation and references

The development version of the model code is available at the UiB GitLAB instance. The model code repository also contains the sources of this documentation. Further, the most recent archived and citable versions of the model source code and the user guide can be found here: