Abstract
The regimes of possible global atmospheric circulation patterns in an Earth‐like atmosphere are explored using a simplified Global Circulation Model (GCM) based on the University of Hamburg's Portable University Model for the Atmosphere (PUMA)—with simplified (linear) boundary‐layer friction, a Newtonian cooling scheme, and dry convective adjustment (designated here as PUMA‐S). A series of controlled experiments is conducted by varying planetary rotation rate and imposed equator‐to‐pole temperature difference. These defining parameters are combined further with each other into dimensionless forms to establish a parameter space in which the occurrences of different circulation regimes are mapped and classified. Clear, coherent trends are found when varying planetary rotation rate (thermal Rossby number) and frictional and thermal relaxation time‐scales. The sequence of circulation regimes as a function of parameters, such as the planetary rotation rate, strongly resembles that obtained in laboratory experiments on rotating, stratified flows, especially if a topographic β‐effect is included in those experiments to emulate the planetary vorticity gradients in an atmosphere 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 Ω∗ between eddies and zonally symmetric flows, becoming weak with fast rotation.
Highlights
An understanding of the dominant factors and mechanisms controlling the general circulation of a planetary atmosphere is a prerequisite to our understanding of the climate variability of the Earth, both in the past and in the future
Portable University Model for the Atmosphere (PUMA) represents the dynamical core of a spectral atmospheric general circulation model (AGCM), based on the work of Hoskins and Simmons (1975)
While the representation of atmospheric dynamics is similar to a full state-of-the-art AGCM, the representation of diabatic and subgrid-scale processes in PUMA is very simple and linear
Summary
An understanding of the dominant factors and mechanisms controlling the general circulation of a planetary atmosphere is a prerequisite to our understanding of the climate variability of the Earth, both in the past and in the future. Flow behaviours under various conditions have been thoroughly measured and classified, and their dependence on nondimensional parameters can be shown by mapping the flow patterns within a parameter space (the resulting map is known as a regime diagram: for example, see Read et al, 1998; Read, 2001; Wordsworth et al, 2008; von Larcher and Williams, 2014, and references therein) Another approach, adopted here, is to make use of simplified numerical models of planetary atmospheres to investigate the behaviour of the circulation.
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