Challenges and Prospects for Reducing Coupled Climate Model SST Biases in the Eastern Tropical Atlantic and Pacific Oceans: The U.S. CLIVAR Eastern Tropical Oceans Synthesis Working Group

Abstract Well-known problems trouble coupled general circulation models of the eastern Atlantic and Pacific Ocean basins. Model climates are significantly more symmetric about the equator than is observed. Model sea surface temperatures are biased warm south and southeast of the equator, and the atmosphere is too rainy within a band south of the equator. Near-coastal eastern equatorial SSTs are too warm, producing a zonal SST gradient in the Atlantic opposite in sign to that observed. The U.S. Climate Variability and Predictability Program (CLIVAR) Eastern Tropical Ocean Synthesis Working Group (WG) has pursued an updated assessment of coupled model SST biases, focusing on the surface energy balance components, on regional error sources from clouds, deep convection, winds, and ocean eddies; on the sensitivity to model resolution; and on remote impacts. Motivated by the assessment, the WG makes the following recommendations: 1) encourage identification of the specific parameterizations contributing to the biases in individual models, as these can be model dependent; 2) restrict multimodel intercomparisons to specific processes; 3) encourage development of high-resolution coupled models with a concurrent emphasis on parameterization development of finer-scale ocean and atmosphere features, including low clouds; 4) encourage further availability of all surface flux components from buoys, for longer continuous time periods, in persistently cloudy regions; and 5) focus on the eastern basin coastal oceanic upwelling regions, where further opportunities for observational–modeling synergism exist.

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Simulations of the West African Monsoon with a Superparameterized Climate Model. Part II: African Easterly Waves

Journal of Climate ◽

10.1175/jcli-d-13-00677.1 ◽

2014 ◽

Vol 27 (22) ◽

pp. 8323-8341 ◽

Cited By ~ 18

Author(s):

Rachel R. McCrary ◽

David A. Randall ◽

Cristiana Stan

Keyword(s):

General Circulation ◽

Climate Model ◽

Deep Convection ◽

West African Monsoon ◽

General Circulation Models ◽

African Easterly Waves ◽

Climate System Model ◽

Easterly Waves ◽

Cloud Resolving Model ◽

The Waves

Abstract The relationship between African easterly waves and convection is examined in two coupled general circulation models: the Community Climate System Model (CCSM) and the “superparameterized” CCSM (SP-CCSM). In the CCSM, the easterly waves are much weaker than observed. In the SP-CCSM, a two-dimensional cloud-resolving model replaces the conventional cloud parameterizations of CCSM. Results show that this allows for the simulation of easterly waves with realistic horizontal and vertical structures, although the model exaggerates the intensity of easterly wave activity over West Africa. The simulated waves of SP-CCSM are generated in East Africa and propagate westward at similar (although slightly slower) phase speeds to observations. The vertical structure of the waves resembles the first baroclinic mode. The coupling of the waves with convection is realistic. Evidence is provided herein that the diabatic heating associated with deep convection provides energy to the waves simulated in SP-CCSM. In contrast, horizontal and vertical structures of the weak waves in CCSM are unrealistic, and the simulated convection is decoupled from the circulation.

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The Caribbean Low-Level Jet and Its Relationship with Precipitation in IPCC AR4 Models

Journal of Climate ◽

10.1175/jcli-d-11-00134.1 ◽

2011 ◽

Vol 24 (22) ◽

pp. 5935-5950 ◽

Cited By ~ 36

Author(s):

Elinor R. Martin ◽

Courtney Schumacher

Keyword(s):

General Circulation ◽

Coupled Model ◽

General Circulation Models ◽

Coupled Models ◽

Intergovernmental Panel ◽

Low Level ◽

The North ◽

Moisture Fluxes ◽

Low Level Jet ◽

The Caribbean

Abstract A census of 19 coupled and 12 uncoupled model runs from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) shows that all models have the ability to simulate the location and height of the Caribbean low-level jet (CLLJ); however, the observed semiannual cycle of the CLLJ magnitude was a challenge for the models to reproduce. In particular, model means failed to capture the strong July CLLJ peak as a result of the lack of westward and southward expansion of the North Atlantic subtropical high (NASH) between May and July. The NASH was also found to be too strong, particularly during the first 6 months of the year in the coupled model runs, which led to increased meridional sea level pressure gradients across the southern Caribbean and, hence, an overly strong CLLJ. The ability of the models to simulate the correlation between the CLLJ and regional precipitation varied based on season and region. During summer months, the negative correlation between the CLLJ and Caribbean precipitation anomalies was reproduced in the majority of models, with uncoupled models outperforming coupled models. The positive correlation between the CLLJ and the central U.S. precipitation during February was more challenging for the models, with the uncoupled models failing to reproduce a significant relationship. This may be a result of overactive convective parameterizations raining out too much moisture in the Caribbean meaning less is available for transport northward, or due to incorrect moisture fluxes over the Gulf of Mexico. The representation of the CLLJ in general circulation models has important consequences for accurate predictions and projections of future climate in the Caribbean and surrounding regions.

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Robust Late 21st Century Shift in the Regional Monsoons in RegCM-CORDEX Simulations

10.5194/egusphere-egu2020-12102 ◽

2020 ◽

Author(s):

Moetasim Ashfaq ◽

Tereza Cavazos ◽

Michelle Reboita ◽

José Abraham Torres-Alavez ◽

Eun-Soon Im ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Regional Climate ◽

Lower Boundary ◽

Coupled Model ◽

General Circulation Models ◽

Monsoon Onset ◽

Historical Period ◽

Monsoon Period

We use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas (GHG) forcing. All regional simulations are conducted using RegCM4 at a 25km horizontal grid spacing using lateral and lower boundary forcing from three General Circulation Models (GCMs), which are part of the fifth phase of the Coupled Model Inter-comparison Project (CMIP5). Each simulation covers the period from 1970 through 2100 under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Regional climate simulations exhibit high fidelity in capturing key characteristics of precipitation and atmospheric dynamics across monsoon regions in the historical period. In the future period, regional monsoons exhibit a spatially robust delay in the monsoon onset, an increase in seasonality, and a reduction in the rainy season length at higher levels of radiative forcing. All regions with substantial delays in the monsoon onset exhibit a decrease in pre-monsoon precipitation, indicating a strong connection between pre-monsoon drying and a shift in the monsoon onset. The weakening of latent heat driven atmospheric warming during the pre-monsoon period delays the overturning of atmospheric subsidence in the monsoon regions, which defers their transitioning into deep convective states. Monsoon changes under the RCP2.6 scenario are mostly within the baseline variability.&#160;

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Investigating Future Changes in Southern China Precipitation Characteristics Based on Dynamically Downscaled CMIP5 Climate Projections

10.21203/rs.3.rs-809474/v1 ◽

2021 ◽

Author(s):

Ying Lung Liu ◽

Chi-yung Tam ◽

Hang Wai Tong ◽

Kevin Cheung ◽

Zhongfeng Xu

Keyword(s):

General Circulation ◽

Climate Model ◽

Hydrological Cycle ◽

Southern China ◽

Coupled Model ◽

General Circulation Models ◽

Horizontal Resolution ◽

Annual Number ◽

Climate Projections ◽

Budget Analysis

Abstract The Regional Climate Model version 4 (RegCM4) has been used to dynamically downscale outputs from four different general circulation models (GCM) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) to the horizontal resolution of 25 km × 25km, in order to study 2050-to-2099 changes in the Southern China hydrological cycle according to Representative Concentration Pathway (RCP) 8.5, relative to the period of 1979 to 2003. The mean summertime precipitation is projected to increase by 0.5 – 1.5 mm/day over coastal Southern China, and with significantly enhanced interannual variability. In boreal spring, similar increase in both the seasonal mean and its year-to-year variation north of 25°N is also found. A novel moisture budget analysis shows that changes in mean background humidity (anomalous wind convergence) dominates the increase in the interannual precipitation variability in spring (summer). Extreme daily precipitation (based on the 95 th percentile) is projected to become more intense, roughly following the Clausius–Clapeyron relation for the aforementioned seasons. On the other hand, autumn mean rainfall rate will be reduced over a broad area in Southern China (although this might be subjected to models’ ability in capturing tropical cyclone activities). The annual number of maximum consecutive dry days (CDD) is found to increase by about 3 to 5 days over locations south of 32°N. Analyses of GCM raw outputs indicate that strengthened northerlies over coastal East Asia , which is likely associated with the so-called tropical expansion, are responsible for the drier autumn.

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Natural variability contributes to model–satellite differences in tropical tropospheric warming

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2020962118 ◽

2021 ◽

Vol 118 (13) ◽

pp. e2020962118

Author(s):

Stephen Po-Chedley ◽

Benjamin D. Santer ◽

Stephan Fueglistaler ◽

Mark D. Zelinka ◽

Philip J. Cameron-Smith ◽

...

Keyword(s):

Climate Sensitivity ◽

General Circulation ◽

Climate Model ◽

Coupled Model ◽

General Circulation Models ◽

Satellite Observations ◽

Sea Surface ◽

Eastern Pacific ◽

Surface Warming ◽

The Tropics

A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.

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Intrinsic versus Forced Variation in Coupled Climate Model Simulations over the Arctic during the Twentieth Century*

Journal of Climate ◽

10.1175/jcli4043.1 ◽

2007 ◽

Vol 20 (6) ◽

pp. 1093-1107 ◽

Cited By ~ 45

Author(s):

Muyin Wang ◽

James E. Overland ◽

Vladimir Kattsov ◽

John E. Walsh ◽

Xiangdong Zhang ◽

...

Keyword(s):

Twentieth Century ◽

Land Surface ◽

General Circulation ◽

Climate Model ◽

General Circulation Models ◽

Performance Criteria ◽

The Arctic ◽

Temperature Record ◽

Coupled Models ◽

Intergovernmental Panel

Abstract There were two major multiyear, Arctic-wide (60°–90°N) warm anomalies (>0.7°C) in land surface air temperature (LSAT) during the twentieth century, between 1920 and 1950 and again at the end of the century after 1979. Reproducing this decadal and longer variability in coupled general circulation models (GCMs) is a critical test for understanding processes in the Arctic climate system and increasing the confidence in the Intergovernmental Panel on Climate Change (IPCC) model projections. This study evaluated 63 realizations generated by 20 coupled GCMs made available for the IPCC Fourth Assessment for their twentieth-century climate in coupled models (20C3M) and corresponding control runs (PIcntrl). Warm anomalies in the Arctic during the last two decades are reproduced by all ensemble members, with considerable variability in amplitude among models. In contrast, only eight models generated warm anomaly amplitude of at least two-thirds of the observed midcentury warm event in at least one realization, but not its timing. The durations of the midcentury warm events in all the models are decadal, while that of the observed was interdecadal. The variance of the control runs in nine models was comparable with the variance in the observations. The random timing of midcentury warm anomalies in 20C3M simulations and the similar variance of the control runs in about half of the models suggest that the observed midcentury warm period is consistent with intrinsic climate variability. Five models were considered to compare somewhat favorably to Arctic observations in both matching the variance of the observed temperature record in their control runs and representing the decadal mean temperature anomaly amplitude in their 20C3M simulations. Seven additional models could be given further consideration. Results support selecting a subset of GCMs when making predictions for future climate by using performance criteria based on comparison with retrospective data.

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Emulating atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 – Part 2: Applications

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-1457-2011 ◽

2011 ◽

Vol 11 (4) ◽

pp. 1457-1471 ◽

Cited By ~ 92

Author(s):

M. Meinshausen ◽

T. M. L. Wigley ◽

S. C. B. Raper

Keyword(s):

Carbon Cycle ◽

21St Century ◽

General Circulation ◽

Climate Model ◽

Coupled Model ◽

General Circulation Models ◽

Rcp Scenarios ◽

Carbon Cycle Model ◽

Uncertainty Range ◽

Ipcc Ar4

Abstract. Intercomparisons of coupled atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models are important for galvanizing our current scientific knowledge to project future climate. Interpreting such intercomparisons faces major challenges, not least because different models have been forced with different sets of forcing agents. Here, we show how an emulation approach with MAGICC6 can address such problems. In a companion paper (Meinshausen et al., 2011a), we show how the lower complexity carbon cycle-climate model MAGICC6 can be calibrated to emulate, with considerable accuracy, globally aggregated characteristics of these more complex models. Building on that, we examine here the Coupled Model Intercomparison Project's Phase 3 results (CMIP3). If forcing agents missed by individual AOGCMs in CMIP3 are considered, this reduces ensemble average temperature change from pre-industrial times to 2100 under SRES A1B by 0.4 °C. Differences in the results from the 1980 to 1999 base period (as reported in IPCC AR4) to 2100 are negligible, however, although there are some differences in the trajectories over the 21st century. In a second part of this study, we consider the new RCP scenarios that are to be investigated under the forthcoming CMIP5 intercomparison for the IPCC Fifth Assessment Report. For the highest scenario, RCP8.5, relative to pre-industrial levels, we project a median warming of around 4.6 °C by 2100 and more than 7 °C by 2300. For the lowest RCP scenario, RCP3-PD, the corresponding warming is around 1.5 °C by 2100, decreasing to around 1.1 °C by 2300 based on our AOGCM and carbon cycle model emulations. Implied cumulative CO2 emissions over the 21st century for RCP8.5 and RCP3-PD are 1881 GtC (1697 to 2034 GtC, 80% uncertainty range) and 381 GtC (334 to 488 GtC), when prescribing CO2 concentrations and accounting for uncertainty in the carbon cycle. Lastly, we assess the reasons why a previous MAGICC version (4.2) used in IPCC AR4 gave roughly 10% larger warmings over the 21st century compared to the CMIP3 average. We find that forcing differences and the use of slightly too high climate sensitivities inferred from idealized high-forcing runs were the major reasons for this difference.

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Mid-Pliocene climate modelled using the UK Hadley Centre Model: PlioMIP Experiments 1 and 2

Geoscientific Model Development Discussions ◽

10.5194/gmdd-5-837-2012 ◽

2012 ◽

Vol 5 (2) ◽

pp. 837-871 ◽

Cited By ~ 3

Author(s):

F. J. Bragg ◽

D. J. Lunt ◽

A. M. Haywood

Keyword(s):

General Circulation ◽

Atmospheric Carbon Dioxide ◽

Carbon Dioxide Concentration ◽

Coupled Model ◽

General Circulation Models ◽

Coupled Models ◽

Intercomparison Project ◽

Proxy Reconstructions ◽

Hadley Centre ◽

The Uk

Abstract. The Pliocene Model Intercomparison Project (PlioMIP) project is a sub-project of the Paleoclimate Modelling Intercomparison Project (PMIP) whose objective is to compare predictions of the mid-Pliocene climate from the widest possible range of general circulation models. The mid-Pliocene (3.3–3.0 Ma) is the most recent sustained period of greater warmth and atmospheric carbon dioxide concentration than the pre-industrial times and as such has potential to inform predictions of our warming climate in the coming century. This paper describes the UK contribution to PlioMIP using the Hadley Centre Model both in atmosphere-only mode (HadAM3, PlioMIP Experiment 1) and atmosphere-ocean coupled mode (HadCM3, PlioMIP Experiment 2). The coupled model predicts a greater overall warming (3.3 °C) relative to the control than the atmosphere-only (2.5 °C). The Northern Hemisphere latitudinal temperature gradient is greater in the coupled model with a warmer equator and colder Arctic than the atmosphere-only model, which is constrained by sea surface temperatures from Pliocene proxy reconstructions. The atmosphere-only model predicts a reduction in equatorial precipitation and south Asian monsoon intensity whereas the coupled models shows and increase in the intensity of these systems. Sensitivity studies using alternative boundary conditions for both the Pliocene and the control simulations are presented, which indicate the sensitivity of the mid-Pliocene warming to uncertainties in both pre-industrial and mid-Pliocene climate.

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Uncertainty of climate change and its impact on reference evapotranspiration in Rasht City, Iran

Journal of Water and Climate Change ◽

10.2166/wcc.2011.055 ◽

2011 ◽

Vol 2 (1) ◽

pp. 72-83 ◽

Cited By ~ 4

Author(s):

Heerbod Jahanbani ◽

Lee Teang Shui ◽

Alireza Massah Bavani ◽

Abdul Halim Ghazali

Keyword(s):

Climate Change ◽

General Circulation ◽

Climate Model ◽

Reference Evapotranspiration ◽

Global Climate ◽

Global Climate Model ◽

Coupled Model ◽

General Circulation Models ◽

Model Version ◽

The Impact

There are many factors of uncertainty regarding the impact of climate change on reference evapotranspiration (ETo). The accuracy of the results is strictly related to these factors and ignoring any one of them reduces the precision of the results, and reduces their applicability for decision makers. In this study, the uncertainty related to two ETo models, the Hargreaves-Samani (HGS) and Artificial Neural Network (ANN), and two Atmosphere-Ocean General Circulation Models (AOGCMs), Hadley Centre Coupled Model, version 3 (HadCM3) climatic model and the Canadian Global Climate Model, version 3 (CGCM3) climatic model under climate change, was evaluated. The models predicted average temperature increases by 2010 to 2039 of 0.95 °C by the HadCM3 model and 1.13°C by the CGCM3 model under the A2 scenario relative to observed temperature. Accordingly, the models predicted average ETo would increase of 0.48, 0.60, 0.50 and 0.60 (mm/day) by 2010 to 2039 projected by four methods (by introducing the temperature of the HadCM3-A2 model and the CGCM3-A2 to ANN and HGS) relative to ETo of the observed period. The results showed that uncertainty of the AOGCMs is more than that of the ETo models applied in this study.

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Assessment of precipitation extremes in CMIP6 decadal hindcasts over India

10.5194/egusphere-egu21-14766 ◽

2021 ◽

Author(s):

Jayshri Patel ◽

Gnanaseelan Chellappan ◽

Anant Parekh ◽

jasti Chowdhary

Keyword(s):

General Circulation ◽

Coupled Model ◽

General Circulation Models ◽

Precipitation Extreme ◽

Coupled Models ◽

Precipitation Prediction ◽

Straight Line ◽

Coarse Spatial Resolution ◽

Extreme Precipitation Index ◽

Intercomparison Project

A skillful decadal precipitation prediction (DPP) is valuable for sustainable development, which currently face many challenges.Deriving reliable information from DPP is still a challenge because of the difficulties linked with precipitation predictions and coarse spatial resolution by General Circulation Models (GCMs) not able to be in a straight line appropriate for impact assessment.This study examines the decadal hindcast simulations of precipitation extreme over seven sub regions of India from different ocean-atmosphere coupled models from the Coupled Model Intercomparison Project(CMIP6) by applying quantile mapping approach.Each decadal hindcast consists of predictions for a 10-year period from the initial climate states of 1961 to 2014/2018 and the assessment of skill is carried out lead-wise from 1 to 10 for different season and different regions over India (both raw and bias corrected). The potential skill of precipitation extreme is examined in terms of&#160; extreme precipitation index (EPIs) i.e.cumulative wet days (CWD), cumulative dry days (CDD), precipitation events between P1020(10 and 20 mm),P20P40(20 and 40 mm), PG40(>40 mm) and &#160;annual maximum 1 & 5 day precipitation (Rx1day and Rx5day). The promising results revealed that the skills of DPPs are enhanced after the bias adjustment and the data product can be used as a key input for impacts assessments in the region.&#160;

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