TIME-SERIES ANALYSIS OF NATURAL VARIABILITY IN BAROTROPIC ENERGY OF THE ATMOSPHERE WITH ECMWF GLOBAL ANALYSIS

In this study, we conducted time series analyses of barotropic energy of the atmosphere using a ten-year period of ECMWF global analysis. Th e spectral features are compared with the idealized model simulation s pectrum of Tanaka et al. (1996). We find a regime transition over the frequency domain from fed to white noise in eddy barotropic energy. Th e red noise spectral slope at high-frequency is approximately -3. The red noise spectrum changes to white noise at low-frequency as predicte d by the model simulation. The transition from red to white noise occu rs, however, at the frequency 1/20 (day(-1)) in the observed atmospher e, compared with 1/50 (day(-1)) in the model atmosphere. The differenc e results from the higher energy level of white noise in the model atm osphere.