Observations & Modelling of the Tropical Tropopause Layer

Programme overview

This programme aimed to enable UK participation in exciting and high impact unmanned aerial vehicle enabled science, through collaboration with NASA partners.

The programme studied the chemical and physical properties of the tropical tropopause layer (TTL) and the impacts of the TTL in controlling the composition of the upper troposphere and lower stratosphere.

The research was delivered in partnership with NASA, through collaboration with the NASA Earth Venture Airborne Tropical Tropopause Experiment (ATTREX) mission, deploying the NASA Global Hawk unmanned aerial vehicle (UAV) and the NERC/Met Office FAAM BAe 146 atmospheric research aircraft.

Background & objectives

This programme formed part of the NERC technologies and climate system themes to:

  1. Improve understanding of upper troposphere lower stratosphere processes, including delivering those observations needed to reduce uncertainty in climate models through improved parameterisations, and contributing to wider goals of the NERC climate system theme.

  2. Stimulate technology development to meet the NERC technologies theme challenges associated with next generation platforms, remote sensing instruments, in situ sensors and modelling technology.

The upper troposphere and lower stratosphere are key atmospheric regions for determining global radiation and energy budgets. Small changes in lower stratospheric water vapour and ozone for example have potential climate impacts that are significant when compared to those of decadal increases in greenhouse gases, and changes in stratospheric humidity and ozone as a result of global change are significant climate feedbacks.

Exchange across the tropopause is dominated by physical processes that occur in tropical regions. The energy at the tropics enables air to loft rapidly via deep convection into the tropical tropopause layer (TTL), a distinct intermediate layer between free troposphere and stratosphere (TTL - typically 13-18 km), from where it may then move more slowly into the lower stratosphere, making this region particularly suitable for investigation.

Improved understanding of the TTL can be subsequently translated in to better parameterisations of water and cirrus processes within climate models and increased confidence in the estimation of TTL effects on radiation and energy budget over long timescales.