Climate model biases in jet streams, blocking and storm tracks resulting from missing orographic drag. Issue 13 (8th July 2016)

• Record Type: Journal Article
• Authors: Pithan, Felix; Shepherd, Theodore G.; Zappa, Giuseppe; Sandu, Irina
• Is Part Of: Geophysical research letters. Volume 43:Issue 13(2016)
• Page Start: 7231
• Page End: 7240
• Publication Date: 2016-07-08
• Subjects: orographic drag -- model biases -- extratropical circulation; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL069551
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: State‐of‐the art climate models generally struggle to represent important features of the large‐scale circulation. Common model deficiencies include an equatorward bias in the location of the midlatitude westerlies and an overly zonal orientation of the North Atlantic storm track. Orography is known to strongly affect the atmospheric circulation and is notoriously difficult to represent in coarse‐resolution climate models. Yet how the representation of orography affects circulation biases in current climate models is not understood. Here we show that the effects of switching off the parameterization of drag from low‐level orographic blocking in one climate model resemble the biases of the Coupled Model Intercomparison Project Phase 5 ensemble: An overly zonal wintertime North Atlantic storm track and less European blocking events, and an equatorward shift in the Southern Hemispheric jet and increase in the Southern Annular Mode time scale. This suggests that typical circulation biases in coarse‐resolution climate models may be alleviated by improved parameterizations of low‐level drag. Key Points: CMIP5 circulation biases are consistent with the effect of missing orographic drag Parameterized drag reduces the Southern Annular Mode time scale