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 …