| Title: |
Characterizing regimes of atmospheric circulation in terms of their global superrotation |
| Authors: |
Lewis, NT; Colyer, GJ; Read, PL |
| Publisher Information: |
American Meteorological Society |
| Publication Year: |
2021 |
| Collection: |
Oxford University Research Archive (ORA) |
| Description: |
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. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| DOI: |
10.1175/jas-d-20-0326.1 |
| Availability: |
https://doi.org/10.1175/jas-d-20-0326.1; https://ora.ox.ac.uk/objects/uuid:50aaef08-e242-4832-8054-16b91d6023a2 |
| Rights: |
info:eu-repo/semantics/openAccess |
| Accession Number: |
edsbas.65CC2C02 |
| Database: |
BASE |