scholarly journals Does ENSO Regularity Increase in a Warming Climate?

2020 ◽  
Vol 33 (4) ◽  
pp. 1247-1259 ◽  
Author(s):  
Judith Berner ◽  
Hannah M. Christensen ◽  
Prashant D. Sardeshmukh
Keyword(s):  
Time Scale ◽  
Southern Oscillation ◽  
System Model ◽  
The Past ◽  
Ensemble Simulations ◽  
Warming Climate ◽  
Inverse Models ◽  
Community Earth System Model ◽  
Autocorrelation Time ◽  
The Impact

AbstractThe impact of a warming climate on El Niño–Southern Oscillation (ENSO) is investigated in large-ensemble simulations of the Community Earth System Model (CESM1). These simulations are forced by historical emissions for the past and the RCP8.5-scenario emissions for future projections. The simulated variance of the Niño-3.4 ENSO index increases from 1.4°C2 in 1921–80 to 1.9°C2 in 1981–2040 and 2.2°C2 in 2041–2100. The autocorrelation time scale of the index also increases, consistent with a narrowing of its spectral peak in the 3–7-yr ENSO band, raising the possibility of greater seasonal to interannual predictability in the future. Low-order linear inverse models (LIMs) fitted separately to the three 60-yr periods capture the CESM1 increase in ENSO variance and regularity. Remarkably, most of the increase can be attributed to the increase in the 23-month damping time scale of a single damped oscillatory ENSO eigenmode of these LIMs by 5 months in 1981–2040 and 6 months in 2041–2100. These apparently robust projected increases may, however, be compromised by CESM1 biases in ENSO amplitude and damping time scale. An LIM fitted to the 1921–80 observations has an ENSO eigenmode with a much shorter 8-month damping time scale, similar to that of several other eigenmodes. When the mode’s damping time scale is increased by 5 and 6 months in this observational LIM, a much smaller increase of ENSO variance is obtained than in the CESM1 projections. This may be because ENSO is not as dominated by a single ENSO eigenmode in reality as it is in the CESM1.

scholarly journals Atmospheric dynamics drive most interannual U.S. droughts over the last millennium

2020 ◽  
Vol 6 (32) ◽  
pp. eaay7268
Author(s):  
M. P. Erb ◽  
J. Emile-Geay ◽  
G. J. Hakim ◽  
N. Steiger ◽  
E. J. Steig
Keyword(s):  
American West ◽  
Large Scale ◽  
Sea Surface ◽  
System Model ◽  
Drought Risk ◽  
Last Millennium ◽  
Atmospheric Variability ◽  
The Past ◽  
Small Influence ◽  
Community Earth System Model

The American West exemplifies drought-sensitive regions with growing populations. Paleoclimate investigations have documented severe droughts in this region before European settling, with major implications for water management and planning. Here, we leverage paleoclimate data assimilation to reconstruct past climate states, enabling a large-scale multivariate investigation of U.S. drought dynamics over the last millennium. These results confirm that La Niña conditions significantly influence southwest U.S. drought over the past millennium but only account for, by one metric, ~13% of interannual drought variability in that region. Atlantic sea surface temperatures may also contribute a small influence, but unexplained variability suggests a substantial role for internal atmospheric variability. This conclusion is buttressed by analysis of simulations from the Community Earth System Model Last Millennium Ensemble. While greenhouse gases will increase future drought risk, as shown in other work, interannual U.S. drought variations will also be widely influenced by processes internal to the atmosphere.

scholarly journals Progress towards a probabilistic Earth system model: examining the impact of stochasticity in the atmosphere and land component of EC-Earth v3.2

2019 ◽  
Vol 12 (7) ◽  
pp. 3099-3118 ◽  
Author(s):  
Kristian Strommen ◽  
Hannah M. Christensen ◽  
Dave MacLeod ◽  
Stephan Juricke ◽  
Tim N. Palmer
Keyword(s):  
Climate Model ◽  
Weather Forecasting ◽  
Southern Oscillation ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Beneficial Impact ◽  
The Impact ◽  
Mean State

Abstract. We introduce and study the impact of three stochastic schemes in the EC-Earth climate model: two atmospheric schemes and one stochastic land scheme. These form the basis for a probabilistic Earth system model in atmosphere-only mode. Stochastic parametrization have become standard in several operational weather-forecasting models, in particular due to their beneficial impact on model spread. In recent years, stochastic schemes in the atmospheric component of a model have been shown to improve aspects important for the models long-term climate, such as El Niño–Southern Oscillation (ENSO), North Atlantic weather regimes, and the Indian monsoon. Stochasticity in the land component has been shown to improve the variability of soil processes and improve the representation of heatwaves over Europe. However, the raw impact of such schemes on the model mean is less well studied. It is shown that the inclusion of all three schemes notably changes the model mean state. While many of the impacts are beneficial, some are too large in amplitude, leading to significant changes in the model's energy budget and atmospheric circulation. This implies that in order to maintain the benefits of stochastic physics without shifting the mean state too far from observations, a full re-tuning of the model will typically be required.

Evolution of the monsoon system over the past 250 million years

2021 ◽  
Author(s):  
Yongyun Hu ◽  
Jiaqi Guo ◽  
Xiang Li ◽  
Jiaenjing Lan ◽  
Qifan Lin ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Land Surface ◽  
System Model ◽  
Earth System ◽  
Global Monsoon ◽  
The Past ◽  
Climate Simulations ◽  
Monsoon System ◽  
Community Earth System Model ◽  
Carbon Dioxide Co2

<p>The evolution of continents over the past 250 million year is remarked by the breakup of the Pangea supercontinent. The changes of continents must have important influences on regional and global monsoon systems because monsoons are primarily a result of land-sea thermal contrast.</p><p>To study how the monsoon system had been evolved with continent changes over the past 250 million years, we carried out a series of climate simulations, using the Community Earth System Model (CESM). Changes in continents, mountain building, solar radiation, and carbon dioxide (CO2) are all considered in the simulations. In the present talk, we will present our preliminary simulation results of how the mega-monsoon associated with the supercontinent Pangea evolved into the six regional monsoons at the present over the past 250 million years. We will also demonstrate ocean circulation changes with different continent distributions, such as ENSO, and its influences on regional monsoons. Monsoon impacts on land-surface processes and the associated carbon-cycle will be also presented.</p>

Snow on Arctic sea ice in a warming climate as simulated in CESM

2021 ◽  
Author(s):  
Melinda Webster ◽  
Alice DuVivier ◽  
Marika Holland ◽  
David Bailey
Keyword(s):  
Sea Ice ◽  
Snow Cover ◽  
Arctic Sea Ice ◽  
System Model ◽  
Ice Melt ◽  
Warming Climate ◽  
Arctic Sea ◽  
Community Earth System Model ◽  
Snow Distribution ◽  
Snow Conditions

<p>Snow on Arctic sea ice is important for several reasons: it creates a habitat for microorganisms and mammals, it changes sea-ice growth and melt, and it affects the speed at which ships and people can travel through sea ice. Therefore, investigating how snow on Arctic sea ice may change in a warming climate is useful for anticipating its potential effects on ecosystems, sea ice, and socioeconomic activities. Here, we use experiments from two versions of the Community Earth System Model (CESM) to study how snow conditions change over time. Comparison with observations indicates that CESM2 produces an overly-thin, overly-uniform snow distribution, while CESM1-LE produces a variable, excessively-thick snow cover. The 1950-2050 snow depth trend in CESM2 is 75% smaller than in CESM1-LE due to CESM2 having less snow. In CESM1-LE, long-lasting, thick sea ice, cool summers, and excessive summer snowfall facilitate a thicker, longer-lasting snow cover. In a warming climate, CESM2 shows that snow on Arctic sea ice will: (1) have greater, earlier spring melt, (2) accumulate less in summer-autumn, (3) sublimate more, and (4) cause marginally more snow-ice formation. CESM2 reveals that snow-free summers can occur ~30-60 years before an ice-free central Arctic, which may promote faster sea-ice melt.</p>

scholarly journals Streamflow Reconstruction and Variation Characteristic Analysis of the Ganjiang River in China for the Past 515 Years

2020 ◽  
Vol 12 (3) ◽  
pp. 1168 ◽  
Author(s):  
Zhiwei Wan ◽  
Xi Chen ◽  
Min Ju ◽  
Chaohao Ling ◽  
Guangxu Liu ◽  
...  
Keyword(s):  
Sustainable Development ◽  
Southern Oscillation ◽  
Characteristic Analysis ◽  
The Sustainable Development ◽  
The Past ◽  
Drought And Flood ◽  
Flood Disasters ◽  
The Future ◽  
High Flows ◽  
The Impact

River flow reconstruction under the background of long-term climate change is of great significance for understanding the regional response to future drought and flood disasters, and the sustainable development of water resources. Investigating the basic characteristics and changing trends of the streamflow of the Ganjiang River is scientifically important to mitigate drought and flood disasters in the future. This study reconstructed drought and flood grade series of five regional stations of the Ganjiang River based on spatially explicit and well-dated local chronicle materials and used a linear regression model of modern drought/flood grades and precipitation to reconstruct historical precipitation for the past 515 years. The relationships between the modern precipitation of five regional stations and streamflow of Waizhou Station, which is the last hydrological station of the Ganjiang River were analyzed through principal component regression. The adjusted R2 is 0.909, with a low relative bias of −1.82%. The variation of streamflow from AD 1500 to AD 2014 was reconstructed using the proposed model. Result shows that high flows occur in nine periods and low flows occur in 11 periods. Extremely low stream flow in 515 years appears during the middle and late 17th century. Cumulative anomaly and Mann-Kendall mutation test results reveal that a transition point from predominantly low to high flows occur in AD 1720. Redfit power spectrum analysis result shows that the variation periods of streamflow are 2–5, 7–8 years, and approximately 32 years, where the most significant period is 2–3 years. Continuous wavelet transform indicates that the corresponding relation occurs between streamflow and El Niño/Southern Oscillation for eight years. Streamflow is affected by temperature and East Asian monsoon that is controlled by solar activities. The flood may be related to strong solar activity, monsoon failure, and vice versa. Hydrological frequency curve analysis shows that the streamflow of the Ganjiang River once in a hundred years may reach up to 1031 × 108 m3 for flood or 485 × 108 m3 for drought and the standard of once in a millennium runoff may reach up to 1188 × 108 m3 for flood or 450 × 108 m3 for drought. These results may provide basic hydrological data for the sustainable development of society and serve as a reference for mitigating the impact of drought and flood disasters in the future.

scholarly journals Dynamics of the Mediterranean droughts from 850 to 2099 AD in the Community Earth System Model

2020 ◽  
Author(s):  
Woon Mi Kim ◽  
Christoph C. Raible
Keyword(s):  
Mediterranean Region ◽  
Southern Oscillation ◽  
Earth System Model ◽  
System Model ◽  
Drought Indices ◽  
Positive Temperature ◽  
Earth System ◽  
Modes Of Variability ◽  
Community Earth System Model ◽  
The Mediterranean

Abstract. In this study, we analyze the dynamics of multi-year long droughts over the western and central Mediterranean region for the period of 850–2099 AD using the Community Earth System model version 1.0.1. Our study indicates that Mediterranean droughts during the period of 850–1849 AD are mainly driven by the internal variability of the climate system. A barotropic high pressure system together with a positive temperature anomaly over central Europe and the Mediterranean is the prominent pattern that occurs in all seasons with droughts. Modes of variability, i.e. the North Atlantic Oscillation and El Niño Southern-Oscillation, play an important role at the initial stage of droughts. However, the persistence of multi-year droughts is determined by the interaction between the regional atmospheric and soil moisture variables. This interaction becomes stronger during the 1850–2099 AD period, reducing the importance of modes of variability and inducing a constant dryness over the Mediterranean region. Additionally, the discrepancy among diverse drought metrics in representing past droughts is shown, re-affirming the necessity of assessing a variety of drought indices even in the paleoclimate context.

scholarly journals Introducing the new Regional Community Earth System Model, R-CESM

2021 ◽  
pp. 1-53
Author(s):  
Dan Fu ◽  
Justin Small ◽  
Jaison Kurian ◽  
Yun Liu ◽  
Brian Kauffman ◽  
...  
Keyword(s):  
High Resolution ◽  
Earth System Model ◽  
Model Systems ◽  
System Model ◽  
Earth System ◽  
Regional Ocean Modeling System ◽  
Ocean Atmosphere ◽  
Community Earth System Model ◽  
Regional Community ◽  
The Impact

AbstractThe development of high-resolution, fully-coupled, regional Earth system model systems is important for improving our understanding of climate variability, future projections, and extreme events at regional scales. Here we introduce and present an overview of the newly-developed Regional Community Earth System Model (R-CESM). Different from other existing regional climate models, R-CESM is based on the Community Earth System Model version 2 (CESM2) framework. We have incorporated the Weather Research and Forecasting (WRF) model and Regional Ocean Modeling System (ROMS) into CESM2 as additional components. As such, R-CESM can be conveniently used as a regional dynamical downscaling tool for the global CESM solutions or/and as a standalone high-resolution regional coupled model. The user interface of R-CESM follows that of CESM, making it readily accessible to the broader community. Among countless potential applications of R-CESM, we showcase here a few preliminary studies that illustrate its novel aspects and value. These include: 1) assessing the skill of R-CESM in a multi-year, high-resolution, regional coupled simulation of the Gulf of Mexico; 2) examining the impact of WRF and CESM ocean-atmosphere coupling physics on tropical cyclone simulations; and 3) a convection-permitting simulation of submesoscale ocean-atmosphere interactions. We also discuss capabilities under development such as i) regional refinement using a high-resolution ROMS nested within global CESM; and ii) “online” coupled data assimilation. Our open-source framework (publicly available at https://github.com/ihesp/rcesm1) can be easily adapted to a broad range of applications that are of interest to the users of CESM, WRF, and ROMS.

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