Seasonal and geographical variation of blocking

An examination of grid point values of daily 500 mb geopotential height over the Northern Hemisphere for the 1963-1977 period has been conducted in order to calculate the seasonal frequency blocking variation and its geographical location, where blocking events require the persistence of a large positive anomaly for seven days or more. The geographical locations of the maximum frequency, characterized by three distinctly different maxima, remain nearly the same for all four seasons. Large persistent negative anomalies during the winter season are mostly associated with local high index flow. An examination of the seasonal variability of persistent characteristics of wave numbers 1-4, for 500 mb geopotential height between 50 and 70 deg N, shows that the large scale planetary waves have preferred phase locations for persistence beyond seven days.