MESACLIP Project

Project Overview:

Climate variations on seasonal-to-decadal (S2D) timescales can have enormous social, economic, and environmental impacts, making skillful predictions on these time scales an invaluable tool for policymakers and stakeholders. Such variations modulate the likelihood and intensity of extreme weather events including, tropical cyclones (TCs), heat waves, winter storms, atmospheric rivers (ARs), and floods, which have all been associated with (1) increases in human morbidity and mortality rates; (2) severe impacts on agriculture, energy use, and industrial activity; and (3) economic costs in the billions of dollars. Changes in prevailing climate patterns are also responsible for prolonged droughts, which can have profoundly negative effects on large segments of the world population. Enhancing our foreknowledge of climate variability on S2D time scales and understanding its influence on extreme weather events could help mitigate negative impacts on human and biological populations, making climate predictions an exceptionally important climate and social science frontier.

Over the past three years, our research team consisting of scientists at Texas A&M University (TAMU) and the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), through collaborations with our international partners, has made major breakthroughs in advancing high-resolution global climate modeling and prediction. Not only have we completed an unprecedented set of TC-permitting (0.25° atmosphere–land resolution) and ocean-mesoscale-eddy-resolving (0.1° ocean–sea-ice resolution) (hereafter simply referred to as high-resolution) historical and future climate simulations (Chang et al. 2020) but we also pioneered the first-ever ensemble of global high-resolution S2D climate prediction simulations. These trailblazing efforts have led to multiple thought-invoking and intriguing discoveries about the potentially important role of mesoscale atmosphere-ocean interactions in climate predictability and prediction at S2D timescales, which are now in need of more in-depth investigation and further scrutiny. Building on these initial efforts, the overall objective of the MESACLIP project is to advance our fundamental knowledge and understanding of the multi-scale dynamical processes underlying S2D predictability by 1) expanding the ensemble size of the existing high-resolution simulations to enable more robust and mechanistic insights into predictable dynamics from meso-to-basin scales, and 2) comparing the high-resolution prediction ensemble directly with the existing low-resolution (∼1° in all components) ensemble to quantify the benefits of increased model resolutions and how such benefits arise.

Model Version: The Community Earth System Model (CESM) code used to generate the high-resolution simulations is based on an earlier version of CESM1.3 described by Meehl et al. (2019) with many additional modifications and improvements, including the usage of the global eddy-resolving ocean model of Small et al. (2014). The most recent tag of the so-called cesm-ihesp-hires CESM branch is available here.

Resolutions:

• CESM-HR: Horizontal resolution of 0.25° (∼25 km) for the atmosphere and land models, and nominal 0.1° (∼10 km at the Equator down to ∼4 km at high latitudes) for the ocean and sea-ice models.
• CESM-LR: Horizontal resolution of ∼1° (∼100 km) in all components.

Years: 1920-2100

Experiments:

• A 500-year pre-industrial control simulation with climate forcings sets to the 1850 conditions and kept constant throughout the entire simulation.
• A 10-member ensemble of Historical and Future Transient (HF-TNST) climate simulations. It uses historical forcings from 1920 to 2005 and the representative concentration pathway 8.5 (RCP 8.5) forcings from 2006 to 2100. RCP 8.5 is a high-emissions scenario and is frequently referred to as the "business as usual" scenario. It refers to the concentration of carbon that delivers global warming at an average of 8.5 W/m² across the planet by 2100. The 10-member set consists of over 1800 simulated model-years of CESM-HR integration.
• A 10-member ensemble of Future Transient climate simulations under the representative concentration pathway 6.0 (RCP6.0) forcings from 2006 to 2100. RCP 6.0 represents a stabilization scenario, where the greenhouse gas emission rate is high initially, but the total radiative forcing is stabilized after 2100 through the use of various technologies and strategies for reducing emissions. In this scenario, the specified amount of carbon concentration results in an average global radiative forcing increase of 6.0 W/m² by 2100. This CESM-HR RCP 6.0 ensemble was completed as part of our National Academy of Sciences (NAS) funded project entitled "Improving Prediction and Projection of Gulf of Mexico Sea-Level Changes Using Eddy-Resolving Earth System Models (iPOGS)". This 10-member RCP 6.0 is complementary to the 10-member RCP 8.5 and will enable the exploration of future projections associated with varying levels of mitigation and future greenhouse gas emissions. The 10-member set consists of 950 simulated model-years of CESM-HR integration.
• The CESM HRDP system is an ensemble forecast set using CESM-HR (Yeager et al. 2023). It is currently comprised of 10-member ensembles initialized on November 1st of even year between 1982 and 2022 and integrated for 62 months. CESM HRDP is being augmented to include every year initialization and add an additional May 1st initialization for each year. Upon completion, the CESM HRDP ensemble set will account for over 2000 simulated model-years of CESM-HR integration. The additional ensemble members will be made available to the community following the CESM Data Management & Distribution Plan.
• The CESM HighResMIP set contains data from the 1950-control simulation forced by perpetual 1950 Greenhouse Gas (GHG) emissions for 130 years and the accompanying transient climate simulations that follow the HighResMIP protocol forced by observed GHG emissions from 1950 to 2005 and then by projected GHG emissions from 2006 to 2050 based on RCP85.

Project leads: Ping Chang (TAMU) and Gokhan Danabasoglu (NSF NCAR)

Project co-leads: Dan Fu (TAMU) and Frederic Castruccio (NSF NCAR)

Project investigators: Steve Yeager (NSF NCAR), Xue Liu (TAMU), Nan Rosenbloom (NSF NCAR), Qiuying Zhang (TAMU), Gaopeng Xu (TAMU), Justin Small (NSF NCAR), Xiaoqi Wang (TAMU), Greta Olson (TAMU), and Teagan King (NSF NCAR).

Data acquisition: The datasets are served to the community through the NSF NCAR Research Data Archive (RDA). Datasets archived on the RDA can be accessed within the CISL computing environment or downloaded over HTTP or Globus transfer for fast, secure, and reliable way to use elsewhere. A copy of the archive is stored in Campaign Storage and so is readily accessible by NCAR HPC system users and by individuals who have a Data Analysis project.

The following datasets are currently available on the RDA:

• 500-year CESM HR pre-industrial control simulation forced with perpetual 1850 conditions.
• 10-member ensemble of CESM HR historical (1920-2005) simulations.
• 10-member ensemble of CESM HR RCP85 (2006-2100) simulations.
• 10-member ensemble of CESM HR RCP60 (2006-2100) simulations.
• Nominal 1-degree CESM (low-resolution) simulations corresponding to high-resolution experiments.

Funding: The initial 3-member ensemble was completed through the International Laboratory for High Resolution Earth System Prediction (iHESP) project–a three-way collaboration between the Qingdao National Laboratory for Marine Science and Technology (QNLM), Texas A&M University (TAMU), and the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR). The ensemble expansion from 3- to 10-member is supported by the National Science Foundation (NSF) Division of Atmospheric and Geospace Sciences (AGS) Climate & Large-Scale Dynamics program under Grant #2231237.

HPC resources: We acknowledge the Texas Advanced Computing Center (TACC ; http://www.tacc.utexas.edu) at The University of Texas at Austin (UT Austin) for providing HPC resources on Frontera. We also acknowledge high-performance computing support from Derecho: HPE Cray EX System (https://doi.org/10.5065/qx9a-pg09) provided by NSF NCAR's Computational and Information Systems Laboratory (CISL), sponsored by the National Science Foundation.

The CVDP package was used to create these diagnostics.

Products:

High-resolution CESM outputs relevant to extreme weather risk

Publications:

1. Ping Chang, Dan Fu, Xue Liu, Frederic S. Castruccio, Andreas F. Prein, Gokhan Danabasoglu, Xiaoqi Wang, Julio Bacmeister, Qiuying Zhang, Nan Rosenbloom, Teagan King, and Susan C. Bates (2025). Amplified Future Extreme Precipitation Risks Projected by High-Resolution Climate Models.. Nature Climate Change, Submitted.
   Abstract
   Extreme precipitation events are increasing and intensifying with climate change, raising risks of severe flooding that can damage infrastructure, disrupt communities, and harm ecosystems. Current climate models struggle to accurately simulate these events due to coarse resolution, limiting their ability to capture the multi-scale atmospheric dynamics driving extreme precipitation. Here, we address this by introducing new ensembles of high-resolution climate simulations that improve the representation and statistics of extreme daily precipitation through a more accurate depiction of atmospheric phenomena, particularly mesoscale convective systems and associated multi-scale interactions. These high-resolution ensemble simulations offer greater confidence, with robust uncertainty quantification, in projections of future changes in extreme precipitation on a global scale. Our analysis shows that the projected increase in daily extreme precipitation rate over global land by the end of this century under the business-as-usual scenario is nearly double in the high-resolution model compared to the low-resolution model, suggesting that current models may significantly underestimate the future threat and highlighting the importance of higher-resolution global models for reliable projections.
2. Qiuying Zhang, Ping Chang, Dan Fu, Stephen G Yeager, Gokhan Danabasoglu, Frederic Castruccio, and Nan Rosenbloom (2024). Enhanced Atlantic Meridional Mode predictability in a high-resolution prediction system. Science Advances, 10, 31. DOI: 10.1126/sciadv.ado6298.
   Abstract
   Accurate prediction of sea surface temperatures (SSTs) in the tropical North Atlantic on multiyear timescales is of paramount importance due to its notable impact on tropical cyclone activity. Recent advances in high-resolution climate predictions have demonstrated substantial improvements in the skill of multiyear SST prediction. This study reveals a notable enhancement in high-resolution tropical North Atlantic SST prediction that stems from a more realistic representation of the Atlantic Meridional Mode and the associated wind-evaporation-SST feedback. The key to this improvement lies in the enhanced surface wind response to changes in cross-equatorial SST gradients, resulting from Intertropical Convergence Zone bias reduction when atmospheric model resolution is increased, which, in turn, amplifies the positive feedback between latent and sensible surface heat fluxes and SST anomalies. These advances in high-resolution climate prediction hold promise for extending tropical cyclone forecasts at multiyear timescales.
3. Hendrik Großelindemann, Frederic S Castruccio, Gokhan Danabasoglu, and Arne Biastoch (2024). Long-term Variability and Trends of Agulhas Leakage and its Impacts on the Global Overturning. EGUsphere, . DOI: 10.5194/egusphere-2024-2288.
   Abstract
   Agulhas Leakage transports warm and salty Indian Ocean waters into the Atlantic Ocean and as such is an important component of the global ocean circulation. These waters are part of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and Agulhas Leakage variability has been linked to AMOC variability. Agulhas Leakage is expected to increase under a warming climate due to a southward shift in the South Hemisphere westerlies, which could further influence the AMOC dynamics. This study uses a set of high-resolution pre-industrial control and historical and transient simulations with the Community Earth System Model (CESM) with a nominal horizontal resolution of 0.1° for the ocean and sea-ice and 0.25° for the atmosphere and land. At these resolutions, the model represents the necessary scales to investigate the Agulhas Leakage transport variability and its relation to the AMOC. The simulated Agulhas Leakage transport of 19.7 ± 3 Sv lies well within the observed range of 21.3 ± 4.7 Sv. A positive correlation between the Agulhas Current and the Agulhas Leakage is shown, meaning that an increase of the Agulhas Current transport leads to an increase in Agulhas Leakage. The Agulhas Leakage impacts the strength of the AMOC through Rossby wave dynamics that alter the cross-basin geostrophic balance with a time-lag of 2–3 years. Furthermore, the salt flux associated with the Agulhas Leakage influences AMOC dynamics through the salt-advection feedback by reducing the AMOC’s freshwater transport at 34° S. The Agulhas Leakage transport indeed increases under a warming climate due to strengthened and southward shifting winds. In contrast, the Agulhas Current transport decreases, both due to a decrease in the Indonesian Throughflow as well as the strength of the wind-driven subtropical gyre. The increase in Agulhas Leakage is accompanied by a higher salt flux into the Atlantic Ocean, which suggests a destabilisation of the AMOC by salt-advection-feedback.
4. Christine A Shields, Hui Li, Frederic S Castruccio, Dan Fu, Kyle Nardi, Xue Liu, Colin Zarzycki (2024). Response of the upper ocean to northeast Pacific atmospheric rivers under climate change. Communications Earth & Environment, 5 1. DOI: 10.1038/s43247-024-01774-0.
   Abstract
   Atmospheric rivers are important transport vehicles for Earth’s water cycle. Using a high-resolution, eddy-resolving Earth System Model, atmospheric river impacts on the upper ocean are investigated by analyzing historical and climate change simulations. For atmospheric rivers along the North American coastline, strong winds cause significant dynamic and thermodynamic upper ocean responses. They push ocean water towards the coast, measured by sea surface height, a process that is amplified under climate change. Mixed layers are deeper upstream of atmospheric rivers, and shallower downstream, however for climate change, shoaling downstream is subdued. Air-sea heat fluxes tend to promote ocean cooling upstream and warming downstream, although different regions have different climate change heat flux signals. Southern California heat flux changes due to warming are driven by evaporative processes and strengthen the ocean responses seen in historical simulations. The regions north are primarily dominated by sensible heat flux changes and counter the historical patterns.
5. Kristen Krumhardt, Matthew C. Long, Colleen M. Petrik, Michael Levy, Frederic S Castruccio, Keith Lindsay, Lev Romashkov, Anna-Lena Deppenmeier, RémyDenéchè, Zhuomin Chen, Laura Landrum, Gokhan Danabasoglu, and Ping Chang (2024). From nutrients to fish: Impacts of mesoscale processes in a global CESM-FEISTY eddying ocean model framework. Progress in Oceanography, 227. DOI: 10.1016/j.pocean.2024.103314.
   Abstract
   The ocean sustains ecosystems that are essential for human livelihood and habitability of the planet. The ocean holds an enormous amount of carbon, and serves as a critical source of nutrition for human societies worldwide. Climate variability and change impact marine biogeochemistry and ecosystems. Thus, having state-of-the-art simulations of the ocean, which include marine biogeochemistry and ecosystems, is critical for understanding the role of climate variability and change on the ocean biosphere. Here we present a novel global eddy-resolving (0.1° horizontal resolution) simulation of the ocean and sea ice, including ocean biogeochemistry, performed with the Community Earth System Model (CESM). The simulation is forced by the atmospheric dataset based on the Japanese Reanalysis (JRA-55) product over the 1958-2021 period. We present a novel configuration of the CESM marine ecosystem model in this simulation which includes two zooplankton classes: microzooplankton and mesozooplankton. This novel planktonic food web structure facilitates "offline" coupling with the Fisheries Size and Functional Type (FEISTY) model. FEISTY is a size- and trait-based model of fish functional types contributing to fisheries. We present an evaluation of the ocean biogeochemistry, marine ecosystem (including fish types), and sea ice in this high resolution simulation compared to available observations and a corresponding low resolution (nominal 1°) simulation. Our analysis offers insights into environmental controls on trophodynamics within the ocean. We find that this high resolution simulation provides a realistic reconstruction of nutrients, oxygen, sea ice, plankton and fish distributions over the global ocean. On global and large regional scales the high resolution simulation is comparable to the standard 1° simulation, but on smaller scales, explicitly resolving the mesoscale dynamics is shown to be important for accurately capturing trophodynamic structuring, especially in coastal ecosystems. We show that fine-scale ocean features leave imprints on ocean ecosystems, from plankton to fish, from the tropics to polar regions. This simulation also offers insights on ocean acidification over the past 64 years, as well as how large-scale climate variations may impact upper trophic levels. The data generated by the simulations are publicly available and will be a fruitful community resource for a large variety of oceanographic science questions.
6. Gaopeng Xu, M Cameron Rencurrel, Ping Chang, Xiaoqing Liu, Gokhan Danabasoglu, Stephen G Yeager, Michael Steele, Wilbert Weijer, Yuchen Li, Nan Rosenbloom, Frederic Castruccio, and Qiuying Zhang (2024). High-resolution modelling identifies the Bering Strait's role in amplified Arctic warming. Nature Climate Change, 14. DOI: 10.1038/s41558-024-02008-z.
   Abstract
   The Arctic region has warmed nearly four times faster than the global average since 1979, with far-reaching global implications. However, model projections of Arctic warming rates are uncertain and one key component is the ocean heat transport (OHT) into the Arctic Ocean. Here we use high-resolution historical and future climate simulations to show that the OHT through the Bering Strait exerts a more substantial influence on Arctic warming than previously recognized. The high-resolution ensemble exhibits a 20% larger warming rate for 2006-2100 compared with standard low-resolution model simulations. The enhanced Arctic warming in the high-resolution simulations is primarily attributable to an increased OHT through the narrow and shallow Bering Strait that is nearly four times larger than in the low-resolution simulations. Consequently, the projected rate of Arctic warming by low-resolution climate simulations is likely to be underestimated due to the model resolution being insufficient to capture future changes in Bering Strait OHT.
7. Justin Small, Jaison Kurian, Ping Chang, Gaopeng Xu, Hiroyuki Tsujino, Stephen G Yeager, Gokhan Danabasoglu, Who Kim, Alper Altuntas, and Frederic Castruccio (2024). Eastern Boundary Upwelling Systems in Ocean–Sea Ice Simulations Forced by CORE and JRA55-do: Mean State and Variability at the Surface. Journal of Climate, 37, 9. DOI: 10.1175/JCLI-D-23-0511.1.
   Abstract
   In this paper we summarize improvements in climate model simulation of eastern boundary upwelling systems (EBUS) when changing the forcing dataset from the Coordinated Ocean-Ice Reference Experiments (CORE; ∼2° winds) to the higher-resolution Japanese 55-year Atmospheric Reanalysis for driving ocean–sea ice models (JRA55-do, ∼0.5°) and also due to refining ocean grid spacing from 1° to 0.1°. The focus is on sea surface temperature (SST), a key variable for climate studies, and which is typically too warm in climate model representation of EBUS. The change in forcing leads to a better-defined atmospheric low-level coastal jet, leading to more equatorward ocean flow and coastal upwelling, both in turn acting to reduce SST over the upwelling regions off the west coast of North America, Peru, and Chile. The refinement of ocean resolution then leads to narrower and stronger alongshore ocean flow and coastal upwelling, and the emergence of strong across-shore temperature gradients not seen with the coarse ocean model. Off northwest Africa the SST bias mainly improves with ocean resolution but not with forcing, while in the Benguela, JRA55-do with high-resolution ocean leads to lower SST but a substantial bias relative to observations remains. Reasons for the Benguela bias are discussed in the context of companion regional ocean model simulations. Finally, we address to what extent improvements in mean state lead to changes to the monthly to interannual variability. It is found that large-scale SST variability in EBUS on monthly and longer time scales is largely governed by teleconnections from climate modes and less sensitive to model resolution and forcing than the mean state.
8. Gaopeng Xu, Ping Chang, Justin Small, Gokhan Danabasoglu, Stephen Yeager, Sanjiv Ramachandran, and Qiuying Zhang (2023). Enhanced upper ocean warming projected by the eddy-resolving Community Earth System Model. Geophysical Research Letters, 50. DOI: 10.1029/2023GL106100.
   Abstract
   Ocean warming is a key factor impacting future changes in climate. Here we investigate vertical structure changes in globally averaged ocean heat content (OHC) in high- (HR) and low-resolution (LR) future climate simulations with the Community Earth System Model (CESM). Compared with observation-based estimates, the simulated OHC anomalies in the upper 700 and 2,000 m during 1960–2020 are more realistic in CESM-HR than -LR. Under RCP8.5 scenario, the net surface heat into the ocean is very similar in CESM-HR and -LR. However, CESM-HR has a larger increase in OHC in the upper 250 m compared to CESM-LR, but a smaller increase below 250 m. This difference can be traced to differences in eddy-induced vertical heat transport between CESM-HR and -LR in the historical period. Moreover, our results suggest that with the same heat input, upper-ocean warming is likely to be underestimated by most non-eddy-resolving climate models.
9. Ping Chang, Gaopeng Xu, Jaison Kurian, Justin Small, Gokhan Danabasoglu, Stephen Yeager, Frederic S. Castruccio, Qiuying Zhang, Nan Rosenbloom, and Piers Chapman (2023). Uncertain future of sustainable fisheries environment in eastern boundary upwelling zones under climate change. Communications Earth & Environment, 4, 19. DOI: 10.1038/s43247-023-00681-0.
   Abstract
   Upwelling along ocean eastern boundaries is expected to intensify due to coastal wind strengthening driven by increasing land-sea contrast according to the Bakun hypothesis. Here, the latest high-resolution climate simulations that exhibit drastic improvements of upwelling processes reveal far more complex future upwelling changes. The Southern Hemisphere upwelling systems show a future strengthening in coastal winds with a rapid coastal warming, whereas the Northern Hemisphere coastal winds show a decrease with a comparable warming trend. The Bakun mechanism cannot explain these changes. Heat budget analysis indicates that temperature change in the upwelling region is not simply controlled by vertical Ekman upwelling, but also influenced by horizontal heat advection driven by strong near-coast wind stress curl that is neglected in the Bakun hypothesis and poorly represented by the low-resolution models in the Coupled Model Intercomparison Project. The high-resolution climate simulations also reveal a strong spatial variation in future upwelling changes, which is missing in the low-resolution simulations.
10. Stephen G. Yeager, Ping Chang, Gokhan Danabasoglu, Nan Rosenbloom, Qiuying Zhang, Frederic S. Castruccio, Abishek Gopal, M. Cameron Rencurrel, and Isla R. Simpson (2023). Reduced Southern Ocean warming enhances global skill and signal-to-noise in an eddy-resolving decadal prediction system. npj Climate and Atmospheric Science, 6, 107. DOI: 10.1038/s41612-023-00434-y. Abstract
    The impact of increased model horizontal resolution on climate prediction performance is examined by comparing results from low-resolution (LR) and high-resolution (HR) decadal prediction simulations conducted with the Community Earth System Model (CESM). There is general improvement in global skill and signal-to-noise characteristics, with particularly noteworthy improvements in the eastern tropical Pacific, when resolution is increased from order 1° in all components to order 0.1°/0.25° in the ocean/atmosphere. A key advance in the ocean eddy-resolving HR system is the reduction of unrealistic warming in the Southern Ocean (SO) which we hypothesize has global ramifications through its impacts on tropical Pacific multidecadal variability. The results suggest that accurate representation of SO processes is critical for improving decadal climate predictions globally and for addressing longstanding issues with coupled climate model simulations of recent Earth system change.
11. Ping Chang, Shaoqing Zhang, Gokhan Danabasoglu, Stephen G. Yeager, Haohuan Fu, Hong Wang, Frederic S. Castruccio, Yuhu Chen, James Edwards, Dan Fu, Yinglai Jia, Lucas C. Laurindo, Xue Liu, Nan Rosenbloom, Justin Small, Gaopeng Xu, Yunhui Zeng, Qiuying Zhang, Julio Bacmeister, David A. Bailey, Xiaohui Duan, Alice K. DuVivier, Dapeng Li, Yuxuan Li, Richard Neale, Achim Stössel, Li Wang, Yuan Zhuang, Allison Baker, Susan Bates, John Dennis, Xiliang Diao, Bolan Gan, Abishek Gopal, Dongning Jia, Zhao Jing, Xiaohui Ma, R. Saravanan, Warren G. Strand, Jian Tao, Haiyuan Yang, Xiaoqi Wang, Zhiqiang Wei, and Lixin Wu (2020). An unprecedented set of high-resolution earth system simulations for understanding multiscale interactions in climate variability and change. Journal of Advances in Modeling Earth Systems, 12, e2020MS002298. DOI: 10.1029/2020MS002298.
    Abstract
    We present an unprecedented set of high-resolution climate simulations, consisting of a 500-year pre-industrial control simulation and a 250-year historical and future climate simulation from 1850 to 2100. A high-resolution configuration of the Community Earth System Model version 1.3 (CESM1.3) is used for the simulations with a nominal horizontal resolution of 0.25° for the atmosphere and land models and 0.1° for the ocean and sea-ice models. At these resolutions, the model permits tropical cyclones and ocean mesoscale eddies, allowing interactions between these synoptic and mesoscale phenomena with large-scale circulations. An overview of the results from these simulations is provided with a focus on model drift, mean climate, internal modes of variability, representation of the historical and future climates, and extreme events. Comparisons are made to solutions from an identical set of simulations using the standard resolution (nominal 1°) CESM1.3 and to available observations for the historical period to address some key scientific questions concerning the impact and benefit of increasing model horizontal resolution in climate simulations. An emerging prominent feature of the high-resolution pre-industrial simulation is the intermittent occurrence of polynyas in the Weddell Sea and its interaction with an Interdecadal Pacific Oscillation. Overall, high-resolution simulations show significant improvements in representing global mean temperature changes, seasonal cycle of sea-surface temperature and mixed layer depth, extreme events and in relationships between extreme events and climate modes.
12. Gerald A. Meehl, Dongxia Yang, Julie M. Arblaster, Susan C. Bates, Nan Rosenbloom, Richard Neale, Julio Bacmeister, Peter H. Lauritzen, Frank Bryan, Justin Small, John Truesdale, Cecile Hannay, Christine Shields, Warren G. Strand, John Dennis, and Gokhan Danabasoglu (2019). Effects of model resolution, physics, and coupling on Southern Hemisphere storm tracks in CESM1.3. Geophysical Research Letters, 46, 12408-12416. DOI: 10.1029/2019GL08405.
    Abstract
    Two high-resolution versions of a Coupled Earth System Model (CESM1.3: 0.25° atmosphere, 1° ocean; CESM1.1: .25° atmosphere, 0.1° ocean) are compared to the standard resolution CESM1.1 and CESM1.3 (1° atmosphere, 1° ocean). The CESM1.3 versions are documented, and the consequences of model resolution, air-sea coupling, and physics in the atmospheric models are studied with regard to storm tracks in the Southern Hemisphere as represented by 850-hPa eddy kinetic energy. Increasing the resolution from 1° to 0.25° in the atmosphere (same physics) coupled to the 1° ocean intensifies the strength of the storm tracks closer to observations. The 0.25° atmosphere with the older CESM1.1 physics coupled to the 0.1° ocean has fewer low clouds, warmer Southern Ocean sea surface temperatures, a weaker meridional temperature gradient, and a degraded storm track simulation compared to the 0.25° atmosphere with CESM1.3 physics coupled to the 1° ocean. Therefore, deficient physics in the atmospheric model can negate the gains attained by higher resolution in atmosphere and ocean.
13. Justin Small, Julio Bacmeister, David Bailey, Allison Baker, Stuart Bishop, Frank Bryan, Julie Caron, John Dennis, Peter Gent, Hsiao-ming Hsu, Markus Jochum, David Lawrence, Ernesto Muñoz, Pedro diNezio, Tim Scheitlin, Robert Tomas, Joseph Tribbia, Yu-heng Tseng,and Mariana Vertenstein (2014). A new synoptic scale resolving global climate simulation using the Community Earth System Model. Journal of Advances in Modeling Earth Systems, 6, 1065-1094, DOI: 10.1002/2014MS000363.
    Abstract
    High-resolution global climate modeling holds the promise of capturing planetary-scale climate modes and small-scale (regional and sometimes extreme) features simultaneously, including their mutual interaction. This paper discusses a new state-of-the-art high-resolution Community Earth System Model (CESM) simulation that was performed with these goals in mind. The atmospheric component was at 0.25° grid spacing, and ocean component at 0.1°. One hundred years "present-day" simulation were completed. Major results were that annual mean sea surface temperature (SST) in the equatorial Pacific and El-Niño Southern Oscillation variability were well simulated compared to standard resolution models. Tropical and southern Atlantic SST also had much reduced bias compared to previous versions of the model. In addition, the high resolution of the model enabled small-scale features of the climate system to be represented, such as air-sea interaction over ocean frontal zones, mesoscale systems generated by the Rockies, and Tropical Cyclones. Associated single component runs and standard resolution coupled runs are used to help attribute the strengths and weaknesses of the fully coupled run. The high-resolution run employed 23,404 cores, costing 250 thousand processor-hours per simulated year and made about two simulated years per day on the NCAR-Wyoming supercomputer "Yellowstone".

Visualization Credit: Matt Rehme, Visualization Services and Research Group, Computational and Information Systems Laboratory (CISL) at NSF NCAR.

Animation showing the Specific humidity (in kg/kg), Sea Surface Temperature (in °C), and precipitation over land (in m/s) simulated by CESM-HR during year 2100. Multiple atmospheric rivers (ARs) can be seen along with strong precipitation associated with landfalling ARs over the West Coast of the United States. Later in the animation, during the fall season, tropical cyclone (TC) induced surface cooling signatures (TC cold wakes) are clearly visible in the Tropical Western Pacific. Cyclonic precipitation can be seen over land after the TCs have made landfalls.

Figure: Sea surface temperature field from September 21, 2018, as represented in (top) CESM-HR and (bottom) CESM-LR simulations submitted to HighResMIP. Right panels show a blow-up of the Western North Atlantic region. The cold wake generated by a tropical cyclone is clearly visible east of the Bahamas in the HR panel (top right). Units are in degrees Celsus.