Blocking and persistence

Time series of observational data have been used to study persistence of blocking over the Atlantic (northern hemisphere) and over the Australian-New Zealand region. The data used are 500-mb geopotential height data. It is shown that the probability that a blocking episode, which has prevailed for i days, will exist day i + 1 is ca 0.7 for northern hemisphere blocking and ca 0.5 for southern hemisphere blocking. The probability increases somewhat the longer the episode lasts. It is demonstrated that the statistics nevertheless may be modelled as a first order Markov process.