May 24 - July 30
Examining Relationships between Stability and Composition in the Tropopause Transition Layer
Lexy E. J. Elizalde, Emily N. Tinney, and Cameron R. Homeyer
What is already known:
- The tropopause is a transition layer, separating the upper troposphere from the lower stratosphere
- There are many (10+) definitions that can define the tropopause based on different parameters
- The WMO temperature lapse-rate definition is the most used and conventional for all regions, but can fail based on seasonal, latitudinal and dynamical factors
- Ozone is an ideal tracer for stratospheric air correlating with an initial, large stability increase
What this study adds:
- At 9K/km, a stability threshold is identified in comparison with ozone that clearly separates tropospheric air from stratospheric. This threshold can be used universally, in 100-m averaged profiles, at all regions of the Earth with minimal error to locate a sharper and more-accurate tropopause
- During various seasons across the latitudes when the WMO tropopause definition may fail, the stability threshold can be applied reliably
- The relationship between stability and composition established in this study can be assumed with conventional observations, such as what is received from a typical radiosonde with no ozone measurements required
Abstract:
The interface separating the upper troposphere from the lower stratosphere is called the tropopause, a complex transition layer contributing to many dynamical aspects of the atmosphere. In this study, observational data is obtained from the ESRL Ozonesonde Data Archive with a multidecadal time-span from 1967-2021 and 1982-2021. Locations in the tropical, polar, and midlatitude regions are examined due to their variation in latitude, climate, and season. After analyzing the tropopause from a composition and stability perspective at each of these areas, the World Meteorological Organization (WMO) lapse-rate definition of 2°C km−1 is evaluated in comparison. Upon investigation, using a 9 K km−1 potential temperature gradient threshold as a stability identifier has proven to be ideal in determining the location of the tropopause in all regions and seasons. The WMO definition and stability threshold are applied to individual profiles and compared to vertical profiles of ozone for evaluation. The stability threshold tends to always mark a tropopause layer directly below the WMO definition in instances where the temperature lapse rate is not met, while the altitude difference between the two vary based on time of year, location and potentially dynamical impacts. Although there are many different definitions that can be used to find the tropopause, the purpose of this study is to investigate the accuracy and consistency of using the stability threshold, especially in situations where the WMO tropopause may not perform well.