Cross‐tropopause transport in the extratropical northern winter hemisphere, diagnosed from high‐resolution ECMWF data

摘要: The upward and downward mass fluxes of air across the tropopause, defined as 3.5 potential vorticity unit (PVU) surface, are diagnosed for extratropical northern hemisphere, using high spatial temporal resolution (0.5° latitude longitude, 31 levels, 3-hourly) circulation data January 1994 from European Centre Medium-Range Weather Forecasts. The net cross-tropopause transport is 0.35 × 1017 kg (downward) area north 28°N. This smaller than that 2.5 1.5 PVU surfaces, larger ‘downward control’ result. indicates tropopause a combination upper stratosphere to troposphere, lower troposphere. latter existence in which transported subtropical troposphere at middle higher latitudes via without ever reaching stratosphere. The ‘local’ ‘instantaneous’ (i.e. smallest resolved scales) are, on average, about 40 times large their time-mean values. confirms relatively bidirectional exchange extratropics between troposphere. The local instantaneous flux do not notably change if horizontal decreased 1° 6 h. A further decrease 3.75° 12 h, however, generally leads quite different results flux. zonal monthly mean very sensitive decrease, except subpolar latitudes. small sensitivity range concentrated scales, nonetheless irrelevant global budgets stratosphere.