Transient-eddy feedbacks derived from linear theory and observations

Abstract

Linear baroclinic instability theory is used to investigate the subweekly time scale transient eddies (TEs) and their feedbacks associated with three-dimensional basic flows on the Northern Hemisphere, in terms of a two-layer quasi-geostrophic model. We consisder an eight-winter time-mean flow as well as four composites of North Atlantic large-scale quasi-stationary patterns. The structures of the two fastest-growing normal modes associated with the eight-winter climatology are found to compare very well in many aspects with the leading complex empirical orthogonal functions (CEOFs) of the observed bandpass filtered flow. Composites corresponding to blocking (BL), zonal (ZO), Greenland anticyclone (GA), and Atlantic ridge (AR) weather regimes are next used to define basic states and composite maps of TE feedback. In all four cases the principal displacements of TE activity over the North Atlantic are captured by the fastest-growing Atlantic cyclogenesis modes. -from Authors