The Eddy-Driven Jet and Storm-Track Responses to Boundary Layer Drag: Insights from an Idealized Dry GCM Study

Abstract

AbstractSimulations 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 Earthlike 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 boundary layer 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.