On the Vertical Structure of Seasonal, Interannual and Intraseasonal Flows
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The vertical structure of the height and wind fields associated with the seasonal, interannual, and intraseasonal cycles is documented by making use of global ECMWF operational analyses for seven pressure levels 1000-100 mb and spanning a 10 year period 1980-89. The role of tropical convection is examined for each of these time scales. The seasonal Cycle is described through the structure of the geopotential height field standing waves, the vertical structure of the first seven wavenumbers of the rotational and divergent winds, and latitudetime cross-sections for the vertical structure of the planetary waves. The change in the vertical structure from the internal mode combinations found in the tropics to a dominant external mode of the extratropics occurs rapidly and within10 deg of the convective source regions. Extensive use is made of a primitive equation PE model, as a diagnostic tool, to explore the extent to which tropical heating might influence the extratropical vertical structure. The PE response indicates the possibility that 25-40 of the Northern Hemisphere and 30-55 of the Southern Hemisphere kinematic vertical structure could be the result of tropical heating. Two significant El Nino Southern Oscillation ENSO events occur during this 10 year period and their vertical structures are examined. The cold phase is found to be dominated by higher internal modes than the warm phase. This may be linked to different air-sea interactive processes during cold and warm ENSO phases.