This dataset contains water budget and Lagrangian analysis of the tropical tropopause from climate model simulations and Lagrangian trajectory calculations. This study was conducted to understand better the role of convection as water vapour enters the tropical stratosphere (above about 17.4km), in particular in future scenarios.

The atmosphere component of HadGEM3, Global Atmosphere (GA) 7.0, was run for three different scenarios. Based on the SPARC Quasi-Biennial Oscillation initiative (QBOi) experiments 2,3,4, these force the atmosphere model with year 2002 conditions (e.g. of solar radiation and sea surface temperatures) every year for 21 years, so that each year experiences identical boundary conditions. The first scenario has no modifications (as a control), the second has doubled CO2 concentrations and sea surface temperatures (SSTs) are increased by 2K, andthe third has quadrupled CO2 concentrations and SSTs are increased by 4K. Simulations were allowed 10 years to stabilise to their modified forcing conditions and the final 11 years were analysed further. These simulations were chosen because they give a simplified indication of how the atmosphere might change in the 21st century.

A second component to this dataset is estimates of water vapour entering the stratosphere with the available output. For this, climate model output was used for Lagrangian calculations which were conducted with the OFFLINE trajectory model.

Records includes:
-increments of all model processes that affect water vapour and ice (to get a full water budget) at grid points around the tropical tropopause (altitude of 17.4km and 18.0km, 40degS - 40degN and 180W - 180E) as monthly means of 6 hourly instantaneous values across the first two years after stabilisation.
- locations and timing of model grid points above the minimum saturation mixing ratio in the vertical profile (the dry point) that exhibit convective ice injection (fast transport of ice by strong cloud processes)
- monthly mean values of estimates of water vapour concentration above the tropical tropopause. These values include the HadGEM3 calculation, and proxies based on the dry point or on Lagrangian (trajectory-following) calculations of water vapour passing through the tropical tropopause.

These records are analysed in:
Smith, J. W., Bushell, A. C., Butchart.,N. , Haynes, P. H., Maycock, A. C., The effect of convective injection of ice on stratospheric water vapor in a changing climate, Geophysical Research Letters, submitted 12/21.

Links for further information:

HadGEM3:
https://www.metoffice.gov.uk/research/approach/modelling-systems/unified-model/climate-models/hadgem3

QBOi experiment:
Butchart, N., Anstey, J. A., Hamilton, K., Osprey, S., McLandress, C., Bushell, A. C., … Yukimoto, S. (2018). Overview of experiment design and comparison of models participating in phase 1 of the SPARC Quasi-Biennial Oscillation initiative (QBOi). Geoscientific Model Development, 11(3), 1009–1032. https://doi.org/10.5194/gmd-11-1009-2018

OFFLINE trajectory model:
http://www.met.reading.ac.uk/~swrmethn/offline/