Daily to decadal modulation of jet variability

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2018): 1297-1314, doi:10.1175/JCLI-D-17-0286.1.The variance of a jet’s position in latitude is found to be related to its average speed: when a jet becomes stronger, its variability in latitude decreases. This relationship is shown to hold for observed midlatitude jets around the world and also across a hierarchy of numerical models. North Atlantic jet variability is shown to be modulated on decadal time scales, with decades of a strong, steady jet being interspersed with decades of a weak, variable jet. These modulations are also related to variations in the basinwide occurrence of high-impact blocking events. A picture emerges of complex multidecadal jet variability in which recent decades do not appear unusual. An underlying barotropic mechanism is proposed to explain this behavior, related to the change in refractive properties of a jet as it strengthens, and the subsequent effect on the distribution of Rossby wave breaking.We would like to acknowledge funding from NERC and the Research Council of Norway project jetSTREAM under Grants NE/ L01047X/1 (IMPETUS) and 231716, respectively, for a contribution to the work presented here. EAB is supported in part by the NSF Climate and Large-Scale Dynamics Program under Grant 1545675. Y-OK was supported by the NSF Climate and Large-Scale Dynamics Program under Grant 1355339. KW was supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101). RL was supported by the Met Office and the National Centre for Atmospheric Science.2018-07-2