92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Tuesday, 24 January 2012
Seasonal Variability of the Width of the Tropical Belt From GPS Radio Occultations and Reanalyses
Hall E (New Orleans Convention Center )
Jason Keefer, State Univ. of New York/Univ. at Albany, Albany, NY; and T. Birner

Evidence exists that the recent climate change trend is contributing to the widening of the tropical belt. Birner (2010) used tropopause statistical diagnostics to investigate this widening. He concluded that a seasonal cycle based on these diagnostics could be robust. The tropical belt can also be defined as the area between the Northern Hemisphere and Southern Hemisphere subtropical jet streams. A local maximum in the horizontal temperature gradient near 30 latitude is a signal of the subtropical jet. Temperature gradient data was generated from raw data from GPS radio occultations and from four different reanalysis datasets: ECMWF, NCEP, NCEP-2, and JRA25. Data from Jan 2007 to Dec 2010 was used because of the limited time range of the GPS radio occultation dataset. The latitude of the subtropical jet in a certain hemisphere is defined as the latitude that falls at a 20% reduction threshold of the maximum between 60 and 0. The latitude closest to the equator at this threshold is considered to be the subtropical jet. Seasonal variability at 300 mb is shown to be consistent with the tropopause-based methods in Birner (2010). Seasonal variability patterns for the tropical belt width at low- and mid-levels (e.g. 700 mb, 500 mb, respectively.) are shown to be notably different. Most notably, the variability pattern at the southern edge is shown to differ greatly from the pattern at the northern edge.

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