National Aeronautics and Space Administration

WMO Tropopause Definition

From A Temperature Lapse Rate Definition of the Tropopause Based on
Ozone, J. M. Roe and W. H. Jasperson, 1981

In the following discussion the lapse rate is defined as -dT/dz.

The main features of the WMO tropopause definition are as follows:
* The first tropopause (i.e., the conventional tropopause) is
defined as the lowest level at which the lapse rate decreases to 2
K/km or less, and the average lapse rate from this level to any
level within the next higher 2 km does not exceed 2 K/km.
* If above the first tropopause the average lapse rate between any
level and all higher levels within 1 km exceed 3 K/km, then a
second tropopause is defined by the same criterion as under the
statement above. This tropopause may be either within or above the
1 km layer.
* A level otherwise satisfying the definition of tropopause, but
occuring at an altitude below that of the 500 mb level will not be
designated a tropopause unless it is the only level satisfying the
definition and the average lapse rate fails to exceed 3 K/km over
at least 1 km in any higher layer.
* (GISS failsafe) Some cases occur when the lapse rate never falls
below 2 K/km. In such cases the failsafe level is that where the
lapse rate first falls below 3 K/km. If this still doesn't work
(ever?), the level is set to the pressure level below 30mb.