Dataset Information

Arctic Clouds and Precipitation in the Community Earth System Model Version 2.

ABSTRACT: The Arctic climate is changing rapidly, warming at about twice the rate of the planet. Global climate models (GCMs) are invaluable tools both for understanding the drivers of these changes and predicting future Arctic climate evolution. While GCMs are continually improving, there remain difficulties in representing cloud processes which occur on scales smaller than GCM resolution. Since clouds influence the Arctic energy and water cycles, their accurate representation in models is critical for robust future projections. In this work, we examine the representation of Arctic clouds and precipitation in the Community Earth System Model (CESM) with the Community Atmosphere Model (CAM), comparing the newly released version (CESM2 with CAM6) with its predecessor (CESM1 with CAM5). To isolate changes in the Arctic mean state, we compare preindustrial control runs. Arctic cloud ice has decreased slightly, while cloud water has increased dramatically in CESM2. Annual mean liquid-containing cloud (LCC) frequency has increased from 19% in CESM1 to 51% in CESM2. Since LCCs strongly modulate downwelling radiation at the surface, their increase has led to an increase in mean downwelling longwave (+22?W?m^-2) and corresponding decrease in downwelling shortwave (-23?W?m^-2) radiation. The mean Arctic surface temperature increased from 257?K in CESM1 to 260?K in CESM2, with the largest seasonal difference in winter (+6?K). Annual average snowfall has decreased slightly (-1?mm?month^-1), while rainfall has increased (+5?mm?month^-1).

SUBMITTER: McIlhattan EA

PROVIDER: S-EPMC7757258 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Arctic Clouds and Precipitation in the Community Earth System Model Version 2.

McIlhattan Elin A EA Kay Jennifer E JE L'Ecuyer Tristan S TS

Journal of geophysical research. Atmospheres : JGR 20201120 22

The Arctic climate is changing rapidly, warming at about twice the rate of the planet. Global climate models (GCMs) are invaluable tools both for understanding the drivers of these changes and predicting future Arctic climate evolution. While GCMs are continually improving, there remain difficulties in representing cloud processes which occur on scales smaller than GCM resolution. Since clouds influence the Arctic energy and water cycles, their accurate representation in models is critical for r ...[more]

PMID: 33381360

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Project description:Abstract We describe the approach taken to develop the United Kingdom's first community Earth system model, UKESM1. This is a joint effort involving the Met Office and the Natural Environment Research Council (NERC), representing the U.K. academic community. We document our model development procedure and the subsequent U.K. submission to CMIP6, based on a traceable hierarchy of coupled physical and Earth system models. UKESM1 builds on the well?established, world?leading HadGEM models of the physical climate system and incorporates cutting?edge new representations of aerosols, atmospheric chemistry, terrestrial carbon, and nitrogen cycles and an advanced model of ocean biogeochemistry. A high?level metric of overall performance shows that both models, HadGEM3?GC3.1 and UKESM1, perform better than most other CMIP6 models so far submitted for a broad range of variables. We point to much more extensive evaluation performed in other papers in this special issue. The merits of not using any forced climate change simulations within our model development process are discussed. First results from HadGEM3?GC3.1 and UKESM1 include the emergent climate sensitivity (5.5 and 5.4?K, respectively) which is high relative to the current range of CMIP5 models. The role of cloud microphysics and cloud?aerosol interactions in driving the climate sensitivity, and the systematic approach taken to understand this role, is highlighted in other papers in this special issue. We place our findings within the broader modeling landscape indicating how our understanding of key processes driving higher sensitivity in the two U.K. models seems to align with results from a number of other CMIP6 models. Key Points The United Kingdom has developed its first community Earth system model and delivered a traceable hierarchy of models to CMIP6 We applied a process?based evaluation strategy in model development but chose not to use historic trends or measures of climate response The U.K. models exhibit higher climate sensitivity than seen in CMIP5 arising in part from more positive cloud feedbacks

Dataset Information

Arctic Clouds and Precipitation in the Community Earth System Model Version 2.

Publications

Arctic Clouds and Precipitation in the Community Earth System Model Version 2.

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