A PV VIEW OF THE ZONAL MEAN DISTRIBUTION OF TEMPERATURE AND WIND IN THE EXTRATROPICAL TROPOSPHERE

The dependence of the temperature and wind distribution of the zonal m ean flow in the extratropical troposphere on the gradient of potential vorticity along isentropes is examined. The extratropics here refer t o the region outside the Hadley circulation. Of particular interest is whether the distribution of temperature and wind corresponding to a c onstant PV along isentropes resembles the observed, and the implicatio ns of PV homogenization along isentropes for the role of the tropics. With the assumption that PV is homogenized along isentropes, it is fou nd that the temperature distribution in the extratropical troposphere may be determined by a linear, first-order partial differential equati on. When the observed surface temperature distribution and tropical la pse rate are used as the boundary conditions, the solution of the equa tion is close to the observed temperature distribution except in the u pper troposphere adjacent to the Hadley circulation, where the troposp here with no PV gradient is considerably colder. Consequently, the jet is also stronger. It is also found that the meridional distribution o f the balanced zonal wind is very sensitive to the meridional distribu tion of the tropopause temperature. The result may suggest that the re quirement of the global momentum balance has no practical role in dete rmining the extratropical temperature distribution. The authors furthe r investigated the sensitivity of the extratropical troposphere with c onstant PV along isentropes to changes in conditions at the tropical b oundary (the edge of the Hadley circulation). It is found that the tem perature and wind distributions in the extratropical troposphere are s ensitive to the vertical distribution of PV at the tropical boundary. With a surface distribution of temperature that decreases linearly wit h latitude, the jet maximum occurs at the tropical boundary and moves with it. The overall pattern of wind distribution is not sensitive to the change of the position of the tropical boundary. Finally, the temp erature and wind distributions of an extratropical troposphere with a finite PV gradient are calculated. It is found that the larger the ise ntropic PV gradient, the warmer the troposphere and the weaker the jet .