Closed 1000-500 hPa thickness highs and lows are an important aspect of the mid-latitude and subtropical weather and climate. They provide an indication of the genesis and lysis region(s) for warm and cold air masses and, if studied on the decadal time scale, they can provide a first-order approximation of climate change. Variations in these thickness features in El Nino versus La Nina years are also of interest. Given the importance of these thickness features to the weather and climate, the results of a global climatology of closed 1000-500 hPa thickness highs and lows for 1951-2001 will be presented.

Gridded 1000-500 hPa thickness 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. Closed thickness highs (lows) were counted if a grid-point was 30 m higher (lower) than all surrounding grid-points and the 1000-500 hPa thickness at the center grid-point was greater than or equal to 576 (less than or equal to 540) dam.

Preliminary results show that closed thickness highs occur preferentially in continental regions in all seasons. Closed thickness lows can occur anywhere in all seasons, but tend to occur further equatorward over continental regions, especially in the cold season. Specifically, we will: (1) present the results of the global climatology of closed 1000-500 hPa thickness highs and lows, (2) compare and contrast the Northern and Southern Hemisphere climatology, (3) compare and contrast the climatology of El Nino versus La Nina years, (4) show the decadal spatial variations of the thickness climatology, and (5) present two representative case studies.