In Press OPEN JOURNAL OF ATMOSPHERIC AND CLIMATE CHANGE The relationship between the Arctic Oscillation and North Atlantic Blocking Frequency ∗

The Relationship between variability in the Arctic Oscillation (AO) and north Atlantic blocking frequency is studied using the 64-year (1950-2013) daily 500 geopotential height data from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and the Arctic oscillation data from National Weather Service (NWS).The study area is from 0 to 90◦N and 40◦W to 70◦E. First, Blocking events were detected using an automated method for block identification. Then their frequency and variability in study period was derived. After this, the AO variability in study period was studied and relationship between AO variability with north Atlantic blocking variability in study area was analyzed. There were also 4181 days with blocking conditions that were detected over the study region; As a consequence, about 65.3 days in any given year were blocked on average over the region of study area. The results show that based on time series chart there are six regimes of the Arctic Oscillation and North Atlantic blocking frequency in study area. There is a direct relationship between these regimes, so that there is a correlation between the ascending and descending phases of the Arctic Oscillation, North Atlantic blocking frequency experiences increasing and decreasing in study area. Keywords