Interannual Variability in the Northern Hemisphere

The goal of this study is to investigate the properties of storm tracks and baro-clinic waves propagation in the Northern Hemisphere. The general characteristics and low-frequency (interannual) variability are the central work of this thesis, which are examined in both observational analysis and theoretical interpretation. We use NCEP/NCAR reanalysis data of 12-hourly wind and geopotential height at 300 hpa, isentropic potential vorticity (IPV) at 330K (potential temperature), monthly mean zonal wind and temperature at 700 and 850 hpa in 23 winters (DJF, 1973-1996) and 16 summers(JJA, 1980-1995). First, complex demodulation technique is applied to meridional wind (v', seasonal mean removed) data to get 12-hourly wave amplitude packets (ve). Based on the data of v ' and ve, we compute the timelag correlation (for lags of-2 and +2 days). After this, the wave coherence index (WCI) and packet coherence index (PCI) are constructed to indicate the coherence of waves and wave packets propagation. Con-trary to previous study by Wallace et al. (1988), baroclinic wave guides revealed i