Main Submonthly Timescals of Northern and Southern Hemispheres Annual Modes

Based on the conception of“Annular Belts of Action (ABAs)”, characteristics of the seasonal variation and main submonthly timescales of Northern and Southern hemispheres annular modes (SAM and NAM) are studied in this paper using NCEP/NCAR reanalysis daily data. The results show that NAM is strong in winter and weak in summer while SAM's intensity has semi-annual cycle. Furthermore, power spectrum analysis is applied year by year to detect the main submonthly timescals of anular modes, the result shows that NAM has quasi-week period and quasi-two-week period variability, which are inclined to accompany each other, the quasi-three-week period is the following time scale; and SAM exhibits similarity of the main submonthly timescales to NAM, that is, the quasi-two-week period and the quasi-week period are the main periods and the quasi-three-week period is the second period. Both the spatial characteristics of NAM and SAM with different submonthly timescales and their temporal evolvement are worth further researching.