Articles | Volume 8, issue 3
Research article
26 Sep 2017
Research article |  | 26 Sep 2017

Climatology of Lyapunov exponents: the link between atmospheric rivers and large-scale mixing variability

Daniel Garaboa-Paz, Jorge Eiras-Barca, and Vicente Pérez-Muñuzuri

Abstract. Large-scale tropospheric mixing and Lagrangian transport properties have been analyzed for the long-term period 1979–2014 in terms of the finite-time Lyapunov exponents (FTLEs). Wind field reanalyses from the European Centre for Medium-Range Weather Forecasts were used to calculate the Lagrangian trajectories of large ensembles of particles. Larger values of the interannual and intra-annual mixing variabilities highlight the El Niño Southern Oscillation, the storm track, or the Intertropical Convergence Zone among other large-scale structures. The mean baroclinic instability growth rate and the mean atmospheric river occurrence show large correlation values with the FTLE climatology as an indication of their influence on tropospheric mixing in the midlatitudes. As a case study, the role that land-falling atmospheric rivers have on large-scale tropospheric mixing and the precipitation rates observed in Saharan Morocco and the British Isles has been analyzed. The atmospheric river contribution to tropospheric mixing is found to decrease from 15 % in Saharan Morocco to less than 5 % for the UK and Ireland regions, in agreement with their contribution to precipitation that is 40 % larger in the former than in the latter region.

Short summary
For the first time, a climatology of Lyapunov exponents (FTLE) for the period 1979–2014 has been established. This climatology is able to reproduce the main large-scale structures observed in the troposphere. The mean FTLE has been shown to correlate with the baroclinic Eady growth rate within timescales of a few days. As a case study, the contribution of atmospheric rivers to this climatology and their contribution to rainfalls over the Sahara and UK regions have been studied.
Final-revised paper