A Climatology of the Tropospheric Thermal Stratification Using Saturation Potential Vorticity
The condition of convective neutrality is assessed in the troposphere by calculating the saturation potential vorticity P* from reanalysis data. Regions of the atmosphere in which saturation entropy is constant along isosurfaces of absolute angular momentum, a state indicative of slantwise-convective neutrality, have values of P* equal to zero. In a global reanalysis dataset spanning the years 1970–2004, tropospheric regions are identified in which P* is near zero, implying that vertical convection or slantwise convection may be important in determining the local thermal stratification. Convectively neutral air masses are common not only in the Tropics but also in higher latitudes, for example, over midlatitude continents in summer and in storm tracks over oceans in winter. Large-scale eddies appear to stabilize parts of the lower troposphere, particularly in winter.
© 2007 American Meteorological Society. (Manuscript received 27 November 2006, in final form 10 April 2007) We thank Kerry Emanuel for sharing numerous insights and beneficial conversations about this topic with us. Anthony Del Genio and two anonymous reviewers provided helpful comments on an earlier draft of this manuscript. We are grateful for support from the Davidow Discovery Fund and the National Science Foundation (Grant ATM-0450059).