The eddy-driven jet and storm-track responses to boundary-layer drag: insights from an idealized dry GCM study

Journal article

Simulations using a dry, idealized general circulation model (GCM) are conducted to systematically investigate the eddy-driven jet’s sensitivity to the location of boundary-layer drag. Perturbations of boundary-layer drag solely within the baroclinic zone reproduce the eddy-driven jet responses to global drag variations. The implications for current theories of eddy-driven jet shifts are discussed. Hemispherically-asymmetric drag simulations in equinoctial and solstitial thermal conditions show that perturbations of surface drag in one hemisphere have negligible effects on the strength and latitude of the eddy-driven jet in the opposite hemisphere. Jet speed exhibits larger sensitivities to surface drag in perpetual winter simulations, while sensitivities in jet latitude are larger in perpetual summer simulations. Near-surface drag simulations with an Earth-like continental profile show how surface drag may facilitate tropical-extratropical teleconnections by modifying waveguides through changes in jet latitude. Longitudinally confined drag simulations demonstrate a novel mechanism for localizing storm tracks. A theoretical analysis is used to show that asymmetries in the Bernoulli function within the baroclinic zone are important for the eddy-driven jet latitude responses because they directly modulate the sensitivity of the zonal-mean zonal wind to drag in the boundarylayer momentum balance. The simulations contained herein provide a rich array of case studies against which to test current theories of eddy-driven jet and storm-track shifts; and the results affirm the importance of correct, well-constrained locations and intensities of boundary-layer drag in order to reduce jet and storm-track biases in climate and forecast models.

Authors: Mbengue, C; Woollings, T

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Meteorological Society
• Journal: Journal of the Atmospheric Sciences
• Volume: 76
• Issue: 4
• Pages: 1055–1076
• Publication date: 2019-02-06
• Acceptance date: 2019-02-01
• DOI: 10.1175/JAS-D-18-0086.1
• EISSN: 1520-0469
• ISSN: 0022-4928
• Keywords: jets; subtropics; extratropics; friction; general circulation models; storm tracks