Annular modes and apparent eddy feedbacks in the Southern Hemisphere.
Lagged correlation analysis is often used to infer intraseasonal dynamical effects but is known to be affected by nonstationarity. We highlight a pronounced quasi 2 year peak in the anomalous zonal wind and eddy momentum flux convergence power spectra in the Southern Hemisphere, which is prima facie evidence for nonstationarity. We then investigate the consequences of this nonstationarity for the Southern Annular Mode and for eddy momentum flux convergence. We argue that positive lagged correlations previously attributed to the existence of an eddy feedback are more plausibly attributed to nonstationary interannual variability external to any potential feedback process in the midlatitude troposphere. The findings have implications for the diagnosis of feedbacks in both models and reanalysis data as well as for understanding the mechanisms underlying variations in the zonal wind.
Department of Meteorology University of Reading Reading UK.
Nicholas J
NJ
Byrne
Department of Meteorology University of Reading Reading UK.
Theodore G
TG
Shepherd
Department of Physics, Atmospheric Oceanic and Planetary Physics Oxford UK.
Tim
T
Woollings
Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology Cambridge Massachusetts USA.
R Alan
RA
Plumb
annular modes; eddy feedbacks; lagged correlation analysis; nonstationary interannual variability
Science. 2001 Oct 19;294(5542):581-4
11641495
Geophys Res Lett. 2016 Apr 28;43(8):3897-3902
27667877