The maps found on these pages are derived from the Ertel potential vorticity (PV), and are useful for understanding atmospheric dynamics. Because the PV usually jumps in value by approximately an order of magnitude over a short vertical distance near the tropopause, one may define the tropopause as a PV surface. This 'dynamical' definition of the tropopause is adopted here; specifically, we use the 1.5 PVU surface.

Tropopause maps are derived by a two step process. The first step involves computing the PV from gridded data fields on the sphere from 1000 hPa to 10 hPa. The second step involves searching for the tropopause surface in the 3D PV space. Here we search for the tropopause at each grid point by starting at 10 hPa (PV >> 1.5) and working down until 1.5 PVU is crossed. Any field [e.g., potential temperature ("theta")] may then be interpolated to this surface.

Isentropic maps are determined in a similar manner, by searching for the appropriate potential-temperature surface, and interpolating quantities to that surface.

An example of tropopause maps in research problems, along with references to other papers, can be found in:

Hakim, G. J., L. F. Bosart, and D. Keyser, 1995: The Ohio Valley wave-merger cyclogenesis event of 25-26 January 1978. Part I: Multiscale case study. Mon. Wea. Rev, 123, 2663--2692.

A more general discussion of tropopause maps can be found in:

Morgan, M.C. and J.W. Nielsen-Gammon, 1998: Using tropopause maps to diagnose midlatitude weather systems, Mon. Wea. Rev, 126, 2555--2579.