# Comparative terrestrial atmospheric circulation regimes in simplified global circulation models: I. from cyclostrophic super-rotation to geostrophic turbulence

## TL;DR

This study uses a simplified global circulation model to explore how planetary rotation rate and temperature gradients influence atmospheric circulation regimes, revealing transitions from super-rotation to turbulence and similarities to planetary phenomena.

## Contribution

It systematically maps circulation regimes in a simplified GCM across parameter space, linking them to laboratory experiments and planetary observations.

## Key findings

- Different circulation regimes are mapped as functions of planetary rotation and thermal parameters.
- Multiple jets form at high rotation rates, resembling gas giant atmospheres.
- Baroclinic waves resemble Martian storms under certain conditions.

## Abstract

The regimes of possible global atmospheric circulation patterns in an Earth-like atmosphere are explored using a simplified GCM based on the University of Hamburg's Portable University Model for the Atmosphere with simplified (linear) boundary layer friction, a Newtonian cooling scheme and dry convective adjustment. A series of controlled experiments are conducted by varying planetary rotation rate and imposed equator-to-pole temperature difference. These defining parameters are cast into dimensionless forms to establish a parameter space, in which different circulation regimes are mapped and classified. Clear trends are found when varying planetary rotation rate and frictional and thermal relaxation timescales. The sequence of circulation regimes as a function of planetary rotation rate strongly resembles that obtained in laboratory experiments on rotating, stratified flows, especially if a topographic $\beta$-effect is included in those experiments to emulate the planetary vorticity gradients induced by the spherical curvature of the planet. A regular baroclinic wave regime is also obtained at intermediate values of thermal Rossby number and its characteristics and dominant zonal wavenumber depend strongly on the strength of radiative and frictional damping. These regular waves exhibit some strong similarities to baroclinic storms observed on Mars under some conditions. Multiple jets are found at the highest rotation rates, when the Rossby deformation radius and other eddy-related length scales are much smaller than the radius of the planet. These exhibit some similarity to the multiple zonal jets observed on gas giant planets. Jets form on a scale comparable to the most energetic eddies and the Rhines scale poleward of the supercritical latitude. The balance of heat transport varies strongly with {\Omega}* between eddies and zonally symmetric flows, becoming weak with fast rotation.