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Tropical free-tropospheric humidity differences and their effect on the clear-sky radiation budget in global strom-resolving models

MPS-Authors

Lang,  Theresa
Meteorological Institute, Center for Earth System Research and Sustainability (CEN), Universität Hamburg;
IMPRS on Earth System Modelling, MPI for Meteorology, Max Planck Society;

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Naumann,  Ann Kristin
Meteorological Institute, Center for Earth System Research and Sustainability (CEN), Universität Hamburg;
Drivers of tropical circulation (CLICCS JWG), The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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Stevens,  Bjorn
Director’s Research Group AES, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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2021MS002514.pdf
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Citation

Lang, T., Naumann, A. K., Stevens, B., & Buehler, S. (2021). Tropical free-tropospheric humidity differences and their effect on the clear-sky radiation budget in global strom-resolving models. Journal of Advances in Modeling Earth Systems, 13: e2021MS002514. doi:10.1029/2021MS002514.


Cite as: http://hdl.handle.net/21.11116/0000-0007-FF14-4
Abstract
Reducing the model spread in free-tropospheric relative humidity (RH) and its response to warming is a crucial step toward reducing the uncertainty in clear-sky climate sensitivity, a step that is hoped to be taken with recently developed global storm-resolving models (GSRMs). In this study we quantify the inter-model differences in tropical present-day RH across GSRMs, making use of DYAMOND, a first 40-day intercomparison. We find that the inter-model spread in tropical mean free-tropospheric RH is reduced compared to conventional atmospheric models, except from the tropopause region and the transition to the boundary layer. We estimate the reduction to ∼50%–70% in the upper troposphere and 25%–50% in the mid troposphere. However, the remaining RH differences still result in a spread of 1.2 urn:x-wiley:19422466:media:jame21474:jame21474-math-0001 in tropical mean clear-sky outgoing longwave radiation (OLR). This spread is mainly caused by RH differences in the lower and mid free troposphere, whereas RH differences in the upper troposphere have a minor impact. By examining model differences in moisture space we identify two regimes with a particularly large contribution to the spread in tropical mean clear-sky OLR: rather moist regimes at the transition from deep convective to subsidence regimes and very dry subsidence regimes. Particularly for these regimes a better understanding of the processes controlling the RH biases is needed.