Equivalent potential vorticity
equivalent potential vorticity (EPV)
EPV = −(∇ × u)∙∇θe,
where ∇ is the three-dimensional gradient operator, u is the three-dimensional velocity vector relative to the rotating earth, and θe is equivalent potential temperature. When used as a diagnostic tool for symmetric instability, u is set to the geostrophic wind.
McCann, D. W., 1995: Three-dimensional computations of equivalent potential vorticity. Wea. Forecasting, 10, 798–802, doi:10.1175/1520-0434(1995)010<0798:TDCOEP>2.0.CO;2.
Moore, J. T., and T. E. Lambert, 1993: The use of equivalent potential vorticity to diagnose regions of conditional symmetric instability. Wea. Forecasting, 8, 301–308, doi:10.1175/1520-0434(1993)008<0301:TUOEPV>2.0.CO;2.
(Term added 5/23/2014)