mode is indeed a dynamical mode, rather than a statistical artifact, in the idealized GCM. They further argued that given the similarities between the annular mode in the real atmosphere and the one simulated in the idealized GCM, it is plausible that the annular mode is also the neutral vector and hence a real dynamical mode of the real atmosphere (and atmospheres modeled with more complex GCMs), which can explain the ubiquity of annular-mode-like responses in the forced atmospheric circulations.]{}

For the observational analysis, National Centers for Environmental Prediction reanalysis 2.5$^\circ$ latitude $\times$ 2.5$^\circ$ longitude 6-hourly wind and temperature from 1951 to 2014 are used. Anomalies are calculated by removing the annual average and the first four Fourier harmonics as in LH01. Following @Baldwin2009, spatial weighting is applied to EOF analysis and projections of spatial patterns to compensate for the uneven distribution of grids in both model outputs and reanalysis data. For spectral analyses, input data is divided into 1024-day segments unless otherwise noted.

[Here, we emphasize that 6-hourly data, rather than daily data, is used in the present study in order to capture the medium-scale waves]{} [@Sato2000]. [It has been shown that the medium-scale waves, which have timescales shorter 