| Title: |
Non-Uniqueness in ITCZ Latitude Due To Radiation-Circulation Coupling in an Idealized GCM |
| Authors: |
Zurita-Gotor, Pablo; Held, Isaac M.; Merlis, Timothy M.; Chang, Chiung Yin; Hill, Spencer A.; MacDonald, Cameron G. |
| Contributors: |
Agencia Estatal de Investigación (España); Zurita-Gotor, Pablo; Held, Isaac M.; Merlis, Timothy M.; Chang, Chiung Yin; Hill, Spencer A.; Consejo Superior de Investigaciones Científicas https://ror.org/02gfc7t72 |
| Publisher Information: |
Wiley-Blackwell |
| Publication Year: |
2023 |
| Collection: |
Digital.CSIC (Consejo Superior de Investigaciones Científicas / Spanish National Research Council) |
| Subject Terms: |
atmospheric dynamics | convection | Hadley cell | idealized models | intertropical convergence zone | radiative transfer | tropical circulation |
| Description: |
An idealized aquaplanet moist global atmospheric model with realistic radiative transfer but no clouds and no convective parameterization is found to possess multiple climate equilibria. When forced symmetrically about the equator, in some cases the Inter Tropical Convergence Zone (ITCZ) migrates to an off-equatorial equilibrium position. Mechanism denial experiments prescribing relative humidity imply that radiation-circulation coupling is essential to this instability. The cross-equatorial asymmetry occurs only when the underlying slab ocean is sufficiently deep and the atmosphere's spectral dynamical core is sufficiently coarse (∼T170 or less with our control parameters). At higher resolutions, initializing with an asymmetric state indicates metastability with very slow (thousands of days) return to hemispheric symmetry. There is some sensitivity to the model timestep, which affects the time required to transition to the asymmetric state, with little effect on the equilibrium climate. The instability is enhanced when the planetary boundary layer scheme favors deeper layers or by a prescribed meridional heat transport away from the equator within the slab. The instability is not present when the model is run with a convective parameterization scheme commonly utilized in idealized moist models. We argue that the instability occurs when the asymmetric heating associated with a spontaneous ITCZ shift drives a circulation that rises poleward of the perturbed ITCZ. These results serve as a warning of the potential for instability and non-uniqueness of climate that may complicate studies with idealized models of the tropical response to perturbations in forcing. ; We thank Zhihong Tan for sharing unpublished results producing the ITCZ instability in a different model, Spencer Clark for useful discussions, and Dargan Frierson, Martin Jucker, and Neil Lewis for their help clarifying the boundary layer treatment in the model formulation. We are also grateful to the editor Tapio Schneider, Ori Adam and two anonymous ... |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| Relation: |
#PLACEHOLDER_PARENT_METADATA_VALUE#; info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020/PID2019-109107GB-I00/ES/FORZAMIENTO DINAMICO Y MECANISMOS DE GENERACION DE LOS CALENTAMIENTOS SUBITOS ESTRATOSFERICOS/; Journal of Advances in Modeling Earth Systems; Sí; https://hdl.handle.net/10261/358838; http://dx.doi.org/10.13039/501100011033; https://api.elsevier.com/content/abstract/scopus_id/85173601853 |
| DOI: |
10.1029/2023MS003736 |
| DOI: |
10.13039/501100011033 |
| Availability: |
https://hdl.handle.net/10261/358838; https://doi.org/10.1029/2023MS003736; https://doi.org/10.13039/501100011033; https://api.elsevier.com/content/abstract/scopus_id/85173601853 |
| Rights: |
info:eu-repo/semantics/openAccess |
| Accession Number: |
edsbas.735DE3A6 |
| Database: |
BASE |