Emergent constraints on the large scale atmospheric circulation and regional hydroclimate: do they still work in CMIP6 and how much can they actually constrain the future?

2021 ◽  
pp. 1-62
Author(s):  
Isla R. Simpson ◽  
Karen A. McKinnon ◽  
Frances V. Davenport ◽  
Martin Tingley ◽  
Flavio Lehner ◽  
...  
Keyword(s):  
Large Scale ◽  
Coupled Model ◽  
Internal Variability ◽  
Stationary Wave ◽  
Meridional Wind ◽  
Least Squares Regression ◽  
Enso Teleconnections ◽  
Projected Change ◽  
Out Of Sample ◽  
The Relationship

AbstractAn ‘emergent constraint’ (EC) is a statistical relationship, across a model ensemble, between a measurable aspect of the present day climate (the predictor) and an aspect of future projected climate change (the predictand). If such a relationship is robust and understood, it may provide constrained projections for the real world. Here, Coupled Model Intercomparison Project 6 (CMIP6) models are used to revisit several ECs that were proposed in prior model intercomparisons with two aims: (1) to assess whether these ECs survive the partial out-of-sample test of CMIP6 and (2) to more rigorously quantify the constrained projected change than previous studies. To achieve the latter, methods are proposed whereby uncertainties can be appropriately accounted for, including the influence of internal variability, uncertainty on the linear relationship, and the uncertainty associated with model structural differences, aside from those described by the EC. Both least squares regression and a Bayesian Hierarchical Model are used. Three ECs are assessed: (a) the relationship between Southern Hemisphere jet latitude and projected jet shift, which is found to be a robust and quantitatively useful constraint on future projections; (b) the relationship between stationary wave amplitude in the Pacific-North American sector and meridional wind changes over North America (with extensions to hydroclimate), which is found to be robust but improvements in the predictor in CMIP6 result in it no longer substantially constrains projected change in either circulation or hydroclimate; and (c) the relationship between ENSO teleconnections to California and California precipitation change, which does not appear to be robust when using historical ENSO teleconnections as the predictor.

Do CMIP5 emergent constraints on the large scale atmospheric circulation work to constrain CMIP6 projections?

2020 ◽  
Author(s):  
Isla Simpson ◽  
Fances Davenport ◽  
Abdullah Al Fahad ◽  
Flavio Lehner
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Coupled Model ◽  
Internal Variability ◽  
Stationary Waves ◽  
Projected Change ◽  
Emergent Constraints ◽  
Out Of Sample ◽  
Emergent Constraint ◽  
Large Scale Atmospheric Circulation

<p>Accurate future projections of the climate system are hindered by a number of sources of uncertainty: forcing uncertainty, internal variability and model structural uncertainty. An ``Emergent constraint'' is a technique that has been devised to reduce projection uncertainties arising from the model structural component. It consists of a statistical relationship (across a model ensemble) between a model’s representation of some aspect of the present day climate and its future projected climate change. This relationship can then be used to imply the future projected change, given the observed value of that present-day aspect. However, in order for the emergent constraint to be considered robust it must: (a) be accompanied by a physical mechanism and (b) be robust to out-of-sample testing.</p><p> </p><p>In prior Coupled Model Intercomparison Projects (CMIP), in particular CMIP5, a number of emergent constraints on the large scale atmospheric circulation were proposed, with implications for regional hydroclimate change. These include: (1) a relationship between a model’s climatological jet latitude and its future projected poleward shift in the Southern Hemisphere; (2) a relationship between a model’s future projected wintertime circulation and hydroclimate change over North America and its climatological representation of stationary waves in the North Pacific; and (3) a relationship between a model’s future projected precipitation change over California and its representation of the relationship between ENSO and California precipitation. Constraints (2) and (3) actually imply opposite constraints on California precipitation changes for the real world, which speaks to the need for a deeper understanding of these emergent constraints and a comprehensive assessment of their robustness.</p><p> </p><p>While the CMIP6 archive does not represent a true ``out-of-sample’’ test of CMIP5 emergent constraints, it does provide us with a new dataset composed of new and/or more advanced models in which to assess their robustness. This presentation will review the proposed emergent constraints on the large-scale atmospheric circulation and assess whether or not they are robust across both the CMIP5 and CMIP6 ensembles. Their potential for constraining regional hydroclimate projections will also be discussed.</p><p> </p>

scholarly journals Stability of ENSO and its tropical Pacific teleconnections over the Last Millennium

2015 ◽  
Vol 11 (3) ◽  
pp. 1579-1613 ◽  
Author(s):  
S. C. Lewis ◽  
A. N. LeGrande
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Last Millennium ◽  
Central Pacific ◽  
Proxy Records ◽  
Enso Teleconnections ◽  
The Pacific

Abstract. Determining past changes in the amplitude, frequency and teleconnections of the El Niño–Southern Oscillation (ENSO) is important for understanding its potential sensitivity to future anthropogenic climate change. Palaeo-reconstructions from proxy records provide long-term information of ENSO interactions with the background climatic state through time. However, it remains unclear how ENSO characteristics have changed through time, and precisely which signals proxies record. Proxy interpretations are underpinned by the assumption of stationarity in relationships between local and remote climates, and often utilise archives from single locations located in the Pacific Ocean to reconstruct ENSO histories. Here, we investigate the stationarity of ENSO teleconnections using the Last Millennium experiment of CMIP5 (Coupled Model Intercomparison Project phase 5) (Taylor et al., 2012). We show that modelled ENSO characteristics vary on decadal- to centennial-scales, resulting from internal variability and external forcings, such as tropical volcanic eruptions. Furthermore, the relationship between ENSO conditions and local climates across the Pacific basin varies throughout the Last Millennium. Results show the stability of teleconnections is regionally dependent and proxies may reveal complex changes in teleconnected patterns, rather than large-scale changes in base ENSO characteristics. As such, proxy insights into ENSO likely require evidence to be synthesised over large spatial areas in order to deconvolve changes occurring in the NINO3.4 region from those pertaining to proxy-relevant local climatic variables. To obtain robust histories of the ENSO and its remote impacts, we recommend interpretations of proxy records should be considered in conjunction with palaeo-reconstructions from within the Central Pacific.

scholarly journals Description and evaluation of NorESM1-F: A fast version of the Norwegian Earth System Model (NorESM)

2018 ◽  
Author(s):  
Chuncheng Guo ◽  
Mats Bentsen ◽  
Ingo Bethke ◽  
Mehmet Ilicak ◽  
Jerry Tjiputra ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Ice ◽  
Large Scale ◽  
Coupled Model ◽  
Coupled System ◽  
Internal Variability ◽  
Earth System Model ◽  
Meridional Overturning Circulation ◽  
System Model ◽  
Earth System

Abstract. A new computationally efficient version of the Norwegian Earth System Model (NorESM) is presented. This new version (here termed NorESM1-F) runs about 2.5 times faster (e.g. 90 model years per day on current hardware) than the version that contributed to the fifth phase of the Coupled Model Intercomparison project (CMIP5), i.e., NorESM1-M, and is therefore particularly suitable for multi-millennial paleoclimate and carbon cycle simulations or large ensemble simulations. The speedup is primarily a result of using a prescribed atmosphere aerosol chemistry and a tripolar ocean-sea ice horizontal grid configuration that allows an increase of the ocean-sea ice component time steps. Ocean biogeochemistry can be activated for fully coupled and semi-coupled carbon cycle applications. This paper describes the model and evaluates its performance using observations and NorESM1-M as benchmarks. The evaluation emphasises model stability, important large-scale features in the ocean and sea ice components, internal variability in the coupled system, and climate sensitivity. Simulation results from NorESM1-F in general agree well with observational estimates, and show evident improvements over NorESM1-M, for example, in the strength of the meridional overturning circulation and sea ice simulation, both important metrics in simulating past and future climates. Whereas NorESM1-M showed a slight global cool bias in the upper oceans, NorESM1-F exhibits a global warm bias. In general, however, NorESM1-F has more similarities than dissimilarities compared to NorESM1-M, and some biases and deficiencies known in NorESM1-M remain.

scholarly journals Description and evaluation of NorESM1-F: a fast version of the Norwegian Earth System Model (NorESM)

2019 ◽  
Vol 12 (1) ◽  
pp. 343-362 ◽  
Author(s):  
Chuncheng Guo ◽  
Mats Bentsen ◽  
Ingo Bethke ◽  
Mehmet Ilicak ◽  
Jerry Tjiputra ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Ice ◽  
Large Scale ◽  
Coupled Model ◽  
Coupled System ◽  
Internal Variability ◽  
Earth System Model ◽  
Meridional Overturning Circulation ◽  
System Model ◽  
Earth System

Abstract. A new computationally efficient version of the Norwegian Earth System Model (NorESM) is presented. This new version (here termed NorESM1-F) runs about 2.5 times faster (e.g., 90 model years per day on current hardware) than the version that contributed to the fifth phase of the Coupled Model Intercomparison project (CMIP5), i.e., NorESM1-M, and is therefore particularly suitable for multimillennial paleoclimate and carbon cycle simulations or large ensemble simulations. The speed-up is primarily a result of using a prescribed atmosphere aerosol chemistry and a tripolar ocean–sea ice horizontal grid configuration that allows an increase of the ocean–sea ice component time steps. Ocean biogeochemistry can be activated for fully coupled and semi-coupled carbon cycle applications. This paper describes the model and evaluates its performance using observations and NorESM1-M as benchmarks. The evaluation emphasizes model stability, important large-scale features in the ocean and sea ice components, internal variability in the coupled system, and climate sensitivity. Simulation results from NorESM1-F in general agree well with observational estimates and show evident improvements over NorESM1-M, for example, in the strength of the meridional overturning circulation and sea ice simulation, both important metrics in simulating past and future climates. Whereas NorESM1-M showed a slight global cool bias in the upper oceans, NorESM1-F exhibits a global warm bias. In general, however, NorESM1-F has more similarities than dissimilarities compared to NorESM1-M, and some biases and deficiencies known in NorESM1-M remain.

scholarly journals Effect of Tropical Nonconvective Condensation on Uncertainty in Modeled Projections of Rainfall

2019 ◽  
Vol 32 (19) ◽  
pp. 6571-6588 ◽  
Author(s):  
Benjamin A. Stephens ◽  
Charles S. Jackson ◽  
Benjamin M. Wagman
Keyword(s):  
Large Scale ◽  
Coupled Model ◽  
Hadley Circulation ◽  
Strong Correlations ◽  
Community Atmosphere Model ◽  
Precipitation Response ◽  
Intercomparison Project ◽  
Model Ensembles ◽  
The Relationship ◽  
Co2 Forcing

Abstract We find that part of the uncertainty in the amplitude and pattern of the modeled precipitation response to CO2 forcing traces to tropical condensation not directly involved with parameterized convection. The fraction of tropical rainfall associated with large-scale condensation can vary from a few percent to well over half depending on model details and parameter settings. In turn, because of the coupling between condensation and tropical circulation, the different ways model assumptions affect the large-scale rainfall fraction also affect the patterns of the response within individual models. In two single-model ensembles based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), versions 3.1 and 5.3, we find strong correlations between the fraction of tropical large-scale rain and both climatological rainfall and circulation and the response to CO2 forcing. While the effects of an increasing tropical large-scale rain fraction are opposite in some ways in the two ensembles—for example, the Hadley circulation weakens with the large-scale rainfall fraction in the CAM3.1 ensemble while strengthening in the CAM5.3 ensemble—we can nonetheless understand these different effects in terms of the relationship between latent heating and circulation, and we propose explanations for each ensemble. We compare these results with data from phase 5 of the Coupled Model Intercomparison Project (CMIP5), for which some of the same patterns hold. Given the importance of this partitioning, there is a need for constraining this source of uncertainty using observations. However, since a “large-scale rainfall fraction” is a modeling construct, it is not clear how observations may be used to test various modeling assumptions determining this fraction.

scholarly journals Projections of northern hemisphere extratropical climate underestimate internal variability and associated uncertainty

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Christopher H. O’Reilly ◽  
Daniel J. Befort ◽  
Antje Weisheimer ◽  
Tim Woollings ◽  
Andrew Ballinger ◽  
...  
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Coupled Model ◽  
Internal Variability ◽  
Uncertainty Range ◽  
Coupled Climate Models ◽  
Large Scale Atmospheric Circulation

AbstractInternal climate variability will play a major role in determining change on regional scales under global warming. In the extratropics, large-scale atmospheric circulation is responsible for much of observed regional climate variability, from seasonal to multidecadal timescales. However, the extratropical circulation variability on multidecadal timescales is systematically weaker in coupled climate models. Here we show that projections of future extratropical climate from coupled model simulations significantly underestimate the projected uncertainty range originating from large-scale atmospheric circulation variability. Using observational datasets and large ensembles of coupled climate models, we produce synthetic ensemble projections constrained to have variability consistent with the large-scale atmospheric circulation in observations. Compared to the raw model projections, the synthetic observationally-constrained projections exhibit an increased uncertainty in projected 21st century temperature and precipitation changes across much of the Northern extratropics. This increased uncertainty is also associated with an increase of the projected occurrence of future extreme seasons.

scholarly journals Investigating Possible Arctic–Midlatitude Teleconnections in a Linear Framework

2016 ◽  
Vol 29 (20) ◽  
pp. 7329-7343 ◽  
Author(s):  
Raymond Sellevold ◽  
Stefan Sobolowski ◽  
Camille Li
Keyword(s):  
Large Scale ◽  
Lower Troposphere ◽  
Internal Variability ◽  
Stationary Wave ◽  
The Arctic ◽  
Stationary Waves ◽  
Arctic Amplification ◽  
Weather Patterns ◽  
Linear Framework ◽  
Circulation Changes

Abstract There is an ongoing debate over whether accelerated Arctic warming [Arctic amplification (AA)] is altering the large-scale circulation responsible for the anomalous weather experienced by midlatitude regions in recent years. Among the proposed mechanisms is the idea that local processes associated with sea ice loss heat the lower troposphere at high latitudes, thus weakening the equator-to-pole temperature gradient and driving changes in quasi-stationary waves, the midlatitude jets, and storm tracks. It is further hypothesized that these circulation changes are conducive to persistent weather patterns. Because of the short observational record and large atmospheric internal variability, it is difficult to identify robust relationships and infer causality. Here, a simplified, linear, steady-state model is used to investigate the direct response of the midlatitude atmospheric circulation to thermal forcing in the Arctic. The results suggest that there is a weak midlatitude circulation response to an idealized, but representative, Arctic heating perturbation. Further, the stationary wave responses are shown to be well within the bounds of internal variability. A midlatitude response is excited if the idealized heating penetrates up to the tropopause. Such deep, persistent heating is not observed on average during the AA period but does suggest a pathway for Arctic–midlatitude linkages under specific conditions. This study adds to the growing body of work suggesting that warming in the lower troposphere associated with Arctic amplification is not currently a direct driver of anomalous midlatitude circulation changes.

scholarly journals Thermodynamic and Dynamic Mechanisms for Large-Scale Changes in the Hydrological Cycle in Response to Global Warming*

2010 ◽  
Vol 23 (17) ◽  
pp. 4651-4668 ◽  
Author(s):  
Richard Seager ◽  
Naomi Naik ◽  
Gabriel A. Vecchi
Keyword(s):  
Large Scale ◽  
Hydrological Cycle ◽  
Coupled Model ◽  
Hadley Cell ◽  
Specific Humidity ◽  
Intergovernmental Panel ◽  
Projected Change ◽  
Intercomparison Project ◽  
Mean Circulation ◽  
Hadley Cells

Abstract The mechanisms of changes in the large-scale hydrological cycle projected by 15 models participating in the Coupled Model Intercomparison Project phase 3 and used for the Intergovernmental Panel on Climate Change’s Fourth Assessment Report are analyzed by computing differences between 2046 and 2065 and 1961 and 2000. The contributions to changes in precipitation minus evaporation, P − E, caused thermodynamically by changes in specific humidity, dynamically by changes in circulation, and by changes in moisture transports by transient eddies are evaluated. The thermodynamic and dynamic contributions are further separated into advective and divergent components. The nonthermodynamic contributions are then related to changes in the mean and transient circulation. The projected change in P − E involves an intensification of the existing pattern of P − E with wet areas [the intertropical convergence zone (ITCZ) and mid- to high latitudes] getting wetter and arid and semiarid regions of the subtropics getting drier. In addition, the subtropical dry zones expand poleward. The accentuation of the twentieth-century pattern of P − E is in part explained by increases in specific humidity via both advection and divergence terms. Weakening of the tropical divergent circulation partially opposes the thermodynamic contribution by creating a tendency to decreased P − E in the ITCZ and to increased P − E in the descending branches of the Walker and Hadley cells. The changing mean circulation also causes decreased P − E on the poleward flanks of the subtropics because the descending branch of the Hadley Cell expands and the midlatitude meridional circulation cell shifts poleward. Subtropical drying and poleward moistening are also contributed to by an increase in poleward moisture transport by transient eddies. The thermodynamic contribution to changing P − E, arising from increased specific humidity, is almost entirely accounted for by atmospheric warming under fixed relative humidity.

scholarly journals Large-Scale Atlantic Salinity Changes over the Last Half-Century: A Model–Observation Comparison

2008 ◽  
Vol 21 (8) ◽  
pp. 1698-1720 ◽  
Author(s):  
Anne Pardaens ◽  
Michael Vellinga ◽  
Peili Wu ◽  
Bruce Ingleby
Keyword(s):  
Large Scale ◽  
Hydrological Cycle ◽  
Coupled Model ◽  
Internal Variability ◽  
Meridional Overturning Circulation ◽  
Historical Period ◽  
Substantial Part ◽  
Freshwater Transport ◽  
Northern Atlantic ◽  
Hadley Centre

Abstract Large-scale freshening of the northern Atlantic, and concurrent salinity increases in the low-latitude Atlantic upper layers, have been widely reported for the second half of the twentieth century. The role of anthropogenic and/or unforced variability processes in these changes, and the potential for the high-latitude freshening to slow the Atlantic meridional overturning circulation (MOC), have been the subject of debate. These issues are investigated by comparing observed and simulated changes, using the Third Hadley Centre Coupled Model (HadCM3). This analysis suggests that a substantial part of the observed trends could be related to multidecadal variability of the MOC. Using an SST-derived proxy for historical MOC changes, in conjunction with model internal variability relationships, suggests that much of the observed evolution of northern Atlantic freshwater content can be explained as being driven by unforced MOC variability. HadCM3 simulations with “external” historical time-varying forcings show anthropogenically forced increases in the main hydrological cycle over the Atlantic: an increase in net precipitation at high latitudes and in net evaporation in the subtropics. In the northern Atlantic the freshening from additional surface freshwater is counteracted by changes in ocean freshwater transport. A similar ocean compensation is absent at lower latitudes, where there is decreasing freshwater content. It is suggested that in the recent historical period this externally forced trend is likely to have led to anomalies exceeding the unforced variability range.

Relationship between total plasma homocysteine and the risk of aneurysms – a meta-analysis

VASA ◽  
2020 ◽  
pp. 1-6
Author(s):  
Hanji Zhang ◽  
Dexin Yin ◽  
Yue Zhao ◽  
Yezhou Li ◽  
Dejiang Yao ◽  
...  
Keyword(s):  
Large Scale ◽  
Meta Analysis ◽  
Single Species ◽  
Total Plasma ◽  
Control Groups ◽  
Randomized Controlled ◽  
Randomized Controlled Studies ◽  
The Difference ◽  
The Relationship ◽  
Healthy Participants

Summary: Our meta-analysis focused on the relationship between homocysteine (Hcy) level and the incidence of aneurysms and looked at the relationship between smoking, hypertension and aneurysms. A systematic literature search of Pubmed, Web of Science, and Embase databases (up to March 31, 2020) resulted in the identification of 19 studies, including 2,629 aneurysm patients and 6,497 healthy participants. Combined analysis of the included studies showed that number of smoking, hypertension and hyperhomocysteinemia (HHcy) in aneurysm patients was higher than that in the control groups, and the total plasma Hcy level in aneurysm patients was also higher. These findings suggest that smoking, hypertension and HHcy may be risk factors for the development and progression of aneurysms. Although the heterogeneity of meta-analysis was significant, it was found that the heterogeneity might come from the difference between race and disease species through subgroup analysis. Large-scale randomized controlled studies of single species and single disease species are needed in the future to supplement the accuracy of the results.

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