85th AMS Annual Meeting

Tuesday, 11 January 2005: 2:30 PM
Quasi-stationary anticyclones in the Northern Hemisphere: An analysis of interannual and interdecadal variability and long-term trends at 1000 hPa and 500 hPa using a geometric definition
Mikhail Bardin, Russian Academy of Science, Moscow, Russia; and G. V. Gruza, A. R. Lupo, I. I. Mokhov, and V. A. Tikhonov
Poster PDF (289.7 kB)
An analysis of the interannual variability and long-term trends of quasi-stationary anticyclone events, or blocking, is carried out using a previously unpublished definition for identification of blocking events. This index is based on a geometric definition which uses integrals to calculate the area and volume enclosed by the outermost contour (So) and a cone defined using the height on the pressure surface and So, respectively. This index also defined intensity of anticyclone events by simply dividing volume by area. Using the National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) re-analyses from 1952 2000 inclusive, this index was applied at both 500 hPa and 1000 hPa. The result was a similar climatology at both levels. This climatology was also similar to previously published climatologies using height gradient techniques. Initial results indicate that the overall trend in block occurrences was negligible for the Northern Hemisphere overall, but there was a long-term trend toward increased (decreased) occurrences over the Pacific (Atlantic) region. The trend toward increasing occurrences in the Pacific Region is consistent with a change in phase of the Pacific Decadal Oscillation (PDO), while the negative tend in the Atlantic region is counter to that of the well-known intensification of the North Atlantic Oscillation (NAO).

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