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

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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Evaluation of the tail of the probability distribution of daily and sub-daily precipitation in CMIP6 models

Journal of Climate ◽

10.1175/jcli-d-20-0182.1 ◽

2021 ◽

pp. 1-61

Author(s):

Jesse Norris ◽

Alex Hall ◽

J. David Neelin ◽

Chad W. Thackeray ◽

Di Chen

Keyword(s):

General Circulation ◽

Daily Precipitation ◽

Precipitation Amount ◽

Coupled Model ◽

Lower Troposphere ◽

General Circulation Models ◽

Intercomparison Project ◽

Cloud Tops ◽

The Tropics ◽

Fraction Models

AbstractDaily and sub-daily precipitation extremes in historical Coupled-Model-Intercomparison-Project-Phase-6 (CMIP6) simulations are evaluated against satellite-based observational estimates. Extremes are defined as the precipitation amount exceeded every x years, ranging from 0.01–10, encompassing the rarest events that are detectable in the observational record without noisy results. With increasing temporal resolution there is an increased discrepancy between models and observations: for daily extremes the multi-model median underestimates the highest percentiles by about a third, and for 3-hourly extremes by about 75% in the tropics. The novelty of the current study is that, to understand the model spread, we evaluate the 3-D structure of the atmosphere when extremes occur. In midlatitudes, where extremes are simulated predominantly explicitly, the intuitive relationship exists whereby higher-resolution models produce larger extremes (r=–0.49), via greater vertical velocity. In the tropics, the convective fraction (the fraction of precipitation simulated directly from the convective scheme) is more relevant. For models below 60% convective fraction, precipitation amount decreases with convective fraction (r=–0.63), but above 75% convective fraction, this relationship breaks down. In the lower-convective-fraction models, there is more moisture in the lower troposphere, closer to saturation. In the higher-convective-fraction models, there is deeper convection and higher cloud tops, which appears to be more physical. Thus, the low-convective models are mostly closer to the observations of extreme precipitation in the tropics, but likely for the wrong reasons. These inter-model differences in the environment in which extremes are simulated hold clues into how parameterizations could be modified in general circulation models to produce more credible 21st-Century projections.

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Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-6505-2008 ◽

2008 ◽

Vol 8 (21) ◽

pp. 6505-6525 ◽

Cited By ~ 11

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

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The Transient Circulation Response to Radiative Forcings and Sea Surface Warming*

Journal of Climate ◽

10.1175/jcli-d-14-00035.1 ◽

2014 ◽

Vol 27 (24) ◽

pp. 9323-9336 ◽

Cited By ~ 9

Author(s):

Paul W. Staten ◽

Thomas Reichler ◽

Jian Lu

Keyword(s):

General Circulation ◽

Climate Model ◽

Stratospheric Ozone ◽

Sea Surface ◽

Sea Surface Temperatures ◽

Indirect Response ◽

Radiative Forcings ◽

Surface Warming ◽

Impact Surface ◽

Surface Temperatures

Abstract Tropospheric circulation shifts have strong potential to impact surface climate. However, the magnitude of these shifts in a changing climate and the attending regional hydrological changes are difficult to project. Part of this difficulty arises from the lack of understanding of the physical mechanisms behind the circulation shifts themselves. To better delineate circulation shifts and their respective causes the circulation response is decomposed into 1) the “direct” response to radiative forcings themselves and 2) the “indirect” response to changing sea surface temperatures. Using ensembles of 90-day climate model simulations with immediate switch-on forcings, including perturbed greenhouse gas concentrations, stratospheric ozone concentrations, and sea surface temperatures, this paper documents the direct and indirect transient responses of the zonal-mean general circulation, and investigates the roles of previously proposed mechanisms in shifting the midlatitude jet. It is found that both the direct and indirect wind responses often begin in the lower stratosphere. Changes in midlatitude eddies are ubiquitous and synchronous with the midlatitude zonal wind response. Shifts in the critical latitude of wave absorption on either flank of the jet are not indicted as primary factors for the poleward-shifting jet, although some evidence for increasing equatorward wave reflection over the Southern Hemisphere in response to sea surface warming is seen. Mechanisms for the Northern Hemisphere jet shift are less clear.

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Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-12115-2008 ◽

2008 ◽

Vol 8 (3) ◽

pp. 12115-12162 ◽

Cited By ~ 1

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall on both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affecting mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

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Evaluating parametric sensitivity of climate feedbacks in CNRM-CM6

10.5194/egusphere-egu21-15730 ◽

2021 ◽

Author(s):

Saloua Peatier ◽

Benjamin Sanderson ◽

Laurent Terray

Keyword(s):

Climate Sensitivity ◽

General Circulation ◽

Temperature Response ◽

Coupled Model ◽

General Circulation Models ◽

Future Climate Change ◽

Climate Feedbacks ◽

Geophysical Research ◽

Physics Ensemble ◽

Earth’S Climate

The global surface temperature response to CO2 doubling (Equilibrium Climate Sensitivity or ECS) is a key uncertain parameter determining the extent of future climate change. Sherwood et al. (2020) estimated the ECS to be within [2.6K - 4.5K], but in the Coupled Model Intercomparison Project phase 6 (CMIP6), 1/3 of the General Circulation Models (GCMs) show ECS exceeding 4.5K (Zelinka et al., 2020). CNRM-CM6-1 is one of these models, with an ECS of 4.9K. In this paper, we sampled 30 atmospheric parameters of CNRM-CM6-1 and produced a Perturbed Physics Ensemble (PPE) of atmospheric-only simulations to explore the feedback parameters diversity and the climatological plausibility of the members. This PPE showed a comparable&#160; range of feedback parameters to the multi-model archive, from 0.8 W.m-2/K to 1.8 W.m-2/K. Emulators of climatological performance and feedback parameters were used together with&#160; observational datasets to search for optimal model configurations conditional on different net climate feedbacks. The climatological constraints considered here did not themselves rule out the higher end ECS values of 5K and above. An optimal subset of parameter configurations were chosen to sample the range of ECS allowing the assessment of feedback constraints in future fully coupled experiments.&#160;References :Sherwood, S. C., Webb, M. J., Annan, J. D., Armour, K. C., Forster, P. M., Hargreaves, J. C., ... & Zelinka, M. D. (2020). An assessment of Earth's climate sensitivity using multiple lines of evidence. Reviews of Geophysics, 58(4), e2019RG000678.Zelinka, M. D., Myers, T. A., McCoy, D. T., Po&#8208;Chedley, S., Caldwell, P. M., Ceppi, P., ... & Taylor, K. E. (2020). Causes of higher climate sensitivity in CMIP6 models. Geophysical Research Letters, 47(1), e2019GL085782.

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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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Mechanism of the Double peaked El Nino

10.5194/egusphere-egu2020-6492 ◽

2020 ◽

Author(s):

Na-Yeon Shin ◽

Jong-Seong Kug ◽

Felicity S. McCormack ◽

Neil J. Holbrook

Keyword(s):

General Circulation ◽

Heat Budget ◽

Coupled Model ◽

General Circulation Models ◽

Warm Pool ◽

Eastern Pacific ◽

Dynamical Analysis ◽

Cold Tongue ◽

Central Pacific ◽

Sst Anomalies

&#160; &#160;In the past decades, our understanding of the ENSO phenomenon increased steadily. Especially, one of the most interesting topics was the El Ni&#241;o type because of the different global impacts. The classic classification is the two types of the El Ni&#241;o and there are various terms to refer this. The conventional El Ni&#241;o is called the Cold tongue El Ni&#241;o or the Eastern pacific El Ni&#241;o. And the other type of the El Ni&#241;o is called the Warm pool El Ni&#241;o, the Central pacific El Ni&#241;o, the El Ni&#241;o Modoki or the dateline El Ni&#241;o. However, in Coupled Model Intercomparison Project version 5 (CMIP5) Coupled General Circulation Models (CGCMs) results, those have been shown the Double peaked El Ni&#241;o events which are the new type of the El Ni&#241;o due to the climatological cold tongue bias. Double peaked El Ni&#241;o events are defined as a positive sea surface temperature anomalies are separated into two centers (in Western and Eastern Pacific) and grow individually and simultaneously, and the peak of SST anomalies exceeds the threshold.&#160;&#160; Double peaked El Ni&#241;o events are found in not only the models, but also the observations. But there are no dynamical analysis of observations. In this study, the mechanism giving rise to Double peaked El Ni&#241;o in observation is examined by analyzing the mixed layer heat budget equation and comparing with the Warm Pool El Ni&#241;o and Cold tongue El Ni&#241;o.&#160;&#160; The warm SST anomalies of the western peak and the eastern peak are caused by different dynamic mechanism. Western peaks of Double peaked El Ni&#241;o are similar to the Warm Pool El Ni&#241;o. Those can be developed by Zonal advection feedback terms and negative anomalous wind speed, whereas eastern peaks of Double peaked El Ni&#241;o are different from Warm pool El Ni&#241;o. Thermocline feedback term considerably contribute to the occurrence of eastern peak. Differences of intensity of the precipitation(4-8N, 195-225E) derive other significant differences of the zonal wind stress(5S-5N, 170-200E), sea level(5S-5N, 230-250E) and zonal current(5S-5N, 230-250E). Thus, the process above can induce the eastern peak of the Double peaked El Ni&#241;o.

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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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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

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-15-00274.1 ◽

2016 ◽

Vol 97 (12) ◽

pp. 2305-2328 ◽

Cited By ~ 60

Author(s):

Paquita Zuidema ◽

Ping Chang ◽

Brian Medeiros ◽

Ben P. Kirtman ◽

Roberto Mechoso ◽

...

Keyword(s):

Working Group ◽

General Circulation ◽

Climate Model ◽

Deep Convection ◽

Coupled Model ◽

Surface Flux ◽

General Circulation Models ◽

Coupled Models ◽

Tropical Ocean ◽

The U.S

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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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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