EGU22-6952
https://doi.org/10.5194/egusphere-egu22-6952
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Convection-resolving climate simulation of the tropical-to-subtropical Atlantic

Christoph Heim and Christoph Schär
Christoph Heim and Christoph Schär
  • ETH Zurich, Institute for Atmospheric and Climate Science, Environmental Science, Switzerland (christoph.heim@env.ethz.ch)

Even though the complexity and resolution of global climate models has increased over the last decades, the inter-model spread in equilibrium climate sensitivity has not narrowed. The representation of tropical and subtropical marine clouds remains a major source of uncertainty in climate models. Going to higher model resolution to explicitly resolve a larger fraction of the underlying convective circulations is the most direct way towards reducing the uncertainty associated with these clouds. Convection-resolving models (CRMs) are therefore an attractive complementary tool to study tropical cloud feedbacks. Even though decade-long global CRM simulations are not yet computationally feasible, CRMs can be used in climate applications for selected limited-area domains and periods.

Here we run 3-year-long CRM simulations with the COSMO model over the tropical-to-subtropical Atlantic. We run a control simulation to evaluate the model’s capability of representing the clouds and the radiative balance. We also run a climate change scenario simulation using the pseudo-global warming (PGW) approach to study cloud-radiative feedbacks at convection-resolving resolution.

We find a good agreement between the simulated and observed annual cycle in the top-of-the-atmosphere radiative fluxes, despite a mean bias that should be possible to reduce through model calibration. There are pronounced improvements in the CRM simulation compared to the CMIP6 models over the ITCZ and the trade-wind cumulus region, while the representation of stratocumulus clouds remains challenging also in the CRM simulation. The simulated cloud-radiative feedback is at the upper end of what the CMIP6 models predict due to a pronounced positive longwave feedback at the ITCZ caused by an increase in high clouds. The shortwave cloud-radiative feedback is moderately positive and lies well within the range of the CMIP6 models with a reduction in the low-level cloud fraction over the subtropics and a partly compensating increase in the cloud fraction at the ITCZ.

How to cite: Heim, C. and Schär, C.: Convection-resolving climate simulation of the tropical-to-subtropical Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6952, https://doi.org/10.5194/egusphere-egu22-6952, 2022.

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