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Publication Date
9 April 2022

The Impact of the QBO on the Region of the Tropical Tropopause in QBOi Models: Present‐Day Simulations

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The Quasi-Biennial Oscillation (QBO) is the dominant mode of tropical lower stratospheric variability. Processes occurring in the tropical tropopause layer (TTL) are of great importance for stratosphere-troposphere exchanges, volcanic eruptions, and the variability of the Earth’s climate, including variability of surface precipitation. We examine here QBO impacts on the TTL region, tropopause pressure, and surface precipitation in 13 Atmospheric General Circulation Models (AGCMs) of the Stratosphere–troposphere Processes And their Role in Climate Quasi-Biennial Oscillation initiative (QBOi) for the historical period.


We find that QBOi models exhibit a large spread in TTL variability and that the model biases in water vapor are strongly related to biases in the representation of the temperature in this region. A source of inter-model spread derives from stratospheric aerosols, as the responses to eruptions differ between those models prescribing volcanic aerosol forcing. The QBO influence on the thermal structure is generally realistic in the equatorial region, but the subtropical response is weak compared with the reanalysis. We discuss the QBO impacts on tropopause pressure and precipitation, characterized by large uncertainties due to the small signal in the observational records and sampling uncertainty. Realistic QBO connection with the troposphere in some models suggests that the underlying physical processes can be correctly simulated. Overall, we find that the QBOi models have limited ability to reproduce the observed modulation of the TTL processes, which is consistent with biases in the vertical and latitudinal extent of the simulated QBOs degrading this connection.


In this study, we examine the impact of the QBO on the TTL region, near-tropopause pressure, and surface precipitation using 13 AGCMs that simulated the QBO.  Overall, there is a large spread between models in the representation of TTL processes, which is related to the biases in the representation of the basic state of the QBO. Most models do not reproduce the observed changes between QBO West and QBO East phases.

Point of Contact
Jadwiga Richter
National Center for Atmospheric Research (NCAR)
Funding Program Area(s)