Closed blocking anticyclones are an important aspect of mid-latitude and subtropical weather and climate. In many cases, blocking anticyclones lead to heat waves and drought, which can be detrimental to the population. Also of interest is the character of the disturbances that travel on the periphery of these blocking anticyclones. These disturbances can often be associated with organized mesoscale convective systems on the poleward side and tropical disturbances on the equatorward side of the anticyclone. Given the importance of these anticyclones to the weather and climate of many tropical and mid-latitude locations, the purpose of this poster presentation is to show the results of a global closed anticyclone climatology for 1951-2001.

Gridded 500 hPa height analyses were obtained from the NCEP/NCAR re-analysis, on a 2.5 x 2.5 degree latitude-longitude grid for 0000 and 1200 UTC. Anticyclones were counted as closed if a grid-point was 30 m higher than all surrounding grid-points and the 500 hPa height at the center grid point was at least 588 dam.

Preliminary results show that closed anticyclones, in both hemispheres, are creatures of the subtropical oceans in all seasons and the subtropical continents during the warm season. It is also shown that closed anticyclones prefer the higher terrain, when over continental regions, as these regions serve as elevated heat sources during the warm season due to the high angle of insolation. Specifically, we will: (1) present the results of the global climatology of 500 hPa closed anticyclones, (2) compare and contrast results from the Northern and Southern Hemispheres, (3) compare and contrast the observed closed anticyclone distribution over continental and oceanic regions, and (4) discuss the contribution of closed anticyclones to the occurrence of organized mesoscale convective systems.