Submonthly traveling long waves in an AMIP simulation

This study analyzes the submonthly retrograde long waves in the Northern Hemisphere in an AMIP-type global atmospheric model simulation forced with observed monthly SST. The daily model output from the simulation for 1979-2006 is band-pass filtered to retain the 8-30 day variability. The amplitudes of the wave-1 and wave-2 components of the 250 hPa geopotential height anomaly along the 60N latitude circle are obtained by Fourier analysis, then compared with their counterparts in reanalysis. Despite not incorporating the information of submonthly SST in the simulation, the annual cycle of the simulated submonthly variances of both wave-1 and wave-2 components agree well with observation. This indicates some degree of dynamical control of the amplitude of submonthly traveling waves by the monthly-mean atmospheric basic state. On the other hand, the model fails to reproduce the observed interannual variability of the variance of either wave-1 or wave-2 component, leaving open some questions concerning the nature of the basic-state control of the submonthly variability.