Identification of the tropical tropopause transition layer using the ozone-water vapor relationship

Coincident ozone (O₃) and water vapor (H₂O) measurements over Alajuela, Costa Rica (~10°N), in July and August 2007 are used to demonstrate the concept. In the tracer-tracer space, the O₃ and H₂O relationship helps to separate the transition layer air mass from the background troposphere and stratosphere.

This tracer relationship-based transition layer is found to span an approximately 40 K potential temperature range between 340 and 380 K and is largely confined between the level of minimum stability (LMS) and the cold point tropopause (CPT). This chemical composition-based transition layer is, therefore, consistent with a definition of the TTL based on the thermal structure, for which the LMS and CPT are the lower and upper boundaries of TTL, respectively.