%0 Journal Article %1 lewis2021characterizing %A Lewis, Neil T. %A Colyer, Greg J. %A Read, Peter L. %D 2021 %I American Meteorological Society %J Journal of the Atmospheric Sciences %K circulation dynamics exoplanets spin theory %N 4 %P 1245--1258 %R 10.1175/jas-d-20-0326.1 %T Characterizing Regimes of Atmospheric Circulation in Terms of Their Global Superrotation %U https://doi.org/10.1175%2Fjas-d-20-0326.1 %V 78 %X The global superrotation index S compares the integrated axial angular momentum of the atmosphere to that of a state of solid-body corotation with the underlying planet. The index S is similar to a zonal Rossby number, which suggests it may be a useful indicator of the circulation regime occupied by a planetary atmosphere. We investigate the utility of S for characterizing regimes of atmospheric circulation by running idealized Earthlike general circulation model experiments over a wide range of rotation rates Ω, 8ΩE to ΩE/512, where ΩE is Earth’s rotation rate, in both an axisymmetric and three-dimensional configuration. We compute S for each simulated circulation, and study the dependence of S on Ω. For all rotation rates considered, S is on the same order of magnitude in the 3D and axisymmetric experiments. For high rotation rates, S ≪ 1 and S ∝ Ω−2, while at low rotation rates S ≈ 1/2 = constant. By considering the limiting behavior of theoretical models for S, we show how the value of S and its local dependence on Ω can be related to the circulation regime occupied by a planetary atmosphere. Indices of S ≪ 1 and S ∝ Ω−2 define a regime dominated by geostrophic thermal wind balance, and S ≈ 1/2 = constant defines a regime where the dynamics are characterized by conservation of angular momentum within a planetary-scale Hadley circulation. Indices of S ≫ 1 and S ∝ Ω−2 define an additional regime dominated by cyclostrophic balance and strong equatorial superrotation that is not realized in our simulations.

@article{lewis2021characterizing, abstract = {The global superrotation index S compares the integrated axial angular momentum of the atmosphere to that of a state of solid-body corotation with the underlying planet. The index S is similar to a zonal Rossby number, which suggests it may be a useful indicator of the circulation regime occupied by a planetary atmosphere. We investigate the utility of S for characterizing regimes of atmospheric circulation by running idealized Earthlike general circulation model experiments over a wide range of rotation rates Ω, 8ΩE to ΩE/512, where ΩE is Earth’s rotation rate, in both an axisymmetric and three-dimensional configuration. We compute S for each simulated circulation, and study the dependence of S on Ω. For all rotation rates considered, S is on the same order of magnitude in the 3D and axisymmetric experiments. For high rotation rates, S ≪ 1 and S ∝ Ω−2, while at low rotation rates S ≈ 1/2 = constant. By considering the limiting behavior of theoretical models for S, we show how the value of S and its local dependence on Ω can be related to the circulation regime occupied by a planetary atmosphere. Indices of S ≪ 1 and S ∝ Ω−2 define a regime dominated by geostrophic thermal wind balance, and S ≈ 1/2 = constant defines a regime where the dynamics are characterized by conservation of angular momentum within a planetary-scale Hadley circulation. Indices of S ≫ 1 and S ∝ Ω−2 define an additional regime dominated by cyclostrophic balance and strong equatorial superrotation that is not realized in our simulations.}, added-at = {2021-04-06T14:44:37.000+0200}, author = {Lewis, Neil T. and Colyer, Greg J. and Read, Peter L.}, biburl = {https://www.bibsonomy.org/bibtex/2595be5a04f61dd03246c9197f0f8c937/pbett}, doi = {10.1175/jas-d-20-0326.1}, interhash = {ad7fbfbcadc3426f2501ca2704603281}, intrahash = {595be5a04f61dd03246c9197f0f8c937}, journal = {Journal of the Atmospheric Sciences}, keywords = {circulation dynamics exoplanets spin theory}, month = apr, number = 4, pages = {1245--1258}, publisher = {American Meteorological Society}, timestamp = {2021-04-06T14:44:37.000+0200}, title = {Characterizing Regimes of Atmospheric Circulation in Terms of Their Global Superrotation}, url = {https://doi.org/10.1175%2Fjas-d-20-0326.1}, volume = 78, year = 2021 }