Joint Seminar: The weakening of the tropical circulation is caused by the lifting of the tropopause height

In this study we apply a diagnostic model for the large-scale tropical circulation (vertical motion) based on the moist static energy equation for first baroclinic mode anomalies (MSEB model) to examine the cause of the tropical circulation changes in climate change scenarios. The aim of the MSEB model is to provide a basis for conceptual understanding of the drivers of the large-scale tropical circulation changes. It diagnoses the vertical motion in an air column of the tropical regions based on net radiation and advection of moisture or heat into the air column in relation to the stability of the air column due to the gradients in moist static energy. Based on the CMIP model simulations we find that the tropical circulation weakens by about 10% over the 21st century. The analysis of the MSEB model suggests that the primary cause for this weakening of the tropical circulation is the lifting of the tropopause height. This shifts the first baroclinic mode away from lower levels with unstable air masses into high levels of the troposphere where stable air masses lead to a stabilisation of the large-scale circulation.




13:30–14:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Dietmar Dommenget, Monash University, Melbourne, Australia


Bo Liu

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