Implications of Tropopause Definitions on sub-Tropical Ozone Distributions Derived from Observations

Various definitions of the tropopause (thermal, dynamical, chemical) are compared with respect to their implications on ozone distributions around the interface level they define. Our work examines ozonesonde measurements from various stations as well as satellite observations to give a latitudinal picture of the distribution of ozone. The thermal (lapse rate) and dynamical (PV) definitions of the tropopause are compared to the definition of a tracer defined interface level, which uses the gradient of the ozone profile. We will focus on the sub-tropics, the region of transition between the tropical tropopause layer (TTL) and the relatively distinctly defined mid-latitude tropopause. The characterisation derived from the sonde data will be compared to ERA- 40. This work forms an observational basis for a process-oriented validation applicable to data from global circulation models (CCMs in particular). First results establishing the process-oriented framework for a model intercomparison are presented in a different paper.