scholarly journals An Equatorial Ocean Bottleneck in Global Climate Models

2012 ◽  
Vol 25 (1) ◽  
pp. 343-349 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Gregory C. Johnson ◽  
Raghu Murtugudde
Keyword(s):  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Critical Role ◽  
Tropical Pacific ◽  
Global Climate Models ◽  
Momentum Balance ◽  
Equatorial Ocean ◽  
The Tropical Pacific

Abstract The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.

scholarly journals Modeled Arctic sea ice evolution through 2300 in CMIP5 extended RCPs

2014 ◽  
Vol 8 (1) ◽  
pp. 1383-1406 ◽  
Author(s):  
P. J. Hezel ◽  
T. Fichefet ◽  
F. Massonnet
Keyword(s):  
Sea Ice ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Arctic Sea ◽  
Arctic Sea Ice Extent

Abstract. Almost all global climate models and Earth system models that participated in the Coupled Model Intercomparison Project 5 (CMIP5) show strong declines in Arctic sea ice extent and volume under the highest forcing scenario of the Radiative Concentration Pathways (RCPs) through 2100, including a transition from perennial to seasonal ice cover. Extended RCP simulations through 2300 were completed for a~subset of models, and here we examine the time evolution of Arctic sea ice in these simulations. In RCP2.6, the summer Arctic sea ice extent increases compared to its minimum following the peak radiative forcing in 2044 in all 9 models. RCP4.5 demonstrates continued summer Arctic sea ice decline due to continued warming on longer time scales. These two scenarios imply that summer sea ice extent could begin to recover if and when radiative forcing from greenhouse gas concentrations were to decrease. In RCP8.5 the Arctic Ocean reaches annually ice-free conditions in 7 of 9 models. The ensemble of simulations completed under the extended RCPs provide insight into the global temperature increase at which sea ice disappears in the Arctic and reversibility of declines in seasonal sea ice extent.

scholarly journals Evaluating Climate Model Simulations of the Radiative Forcing and Radiative Response at Earth’s Surface

2019 ◽  
Vol 32 (13) ◽  
pp. 4089-4102 ◽  
Author(s):  
Ryan J. Kramer ◽  
Brian J. Soden ◽  
Angeline G. Pendergrass
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Models ◽  
Lapse Rate ◽  
Radiation Budget ◽  
Model Simulations ◽  
Climate Model Simulations

Abstract We analyze the radiative forcing and radiative response at Earth’s surface, where perturbations in the radiation budget regulate the atmospheric hydrological cycle. By applying a radiative kernel-regression technique to CMIP5 climate model simulations where CO2 is instantaneously quadrupled, we evaluate the intermodel spread in surface instantaneous radiative forcing, radiative adjustments to this forcing, and radiative responses to surface warming. The cloud radiative adjustment to CO2 forcing and the temperature-mediated cloud radiative response exhibit significant intermodel spread. In contrast to its counterpart at the top of the atmosphere, the temperature-mediated cloud radiative response at the surface is found to be positive in some models and negative in others. Also, the compensation between the temperature-mediated lapse rate and water vapor radiative responses found in top-of-atmosphere calculations is not present for surface radiative flux changes. Instantaneous radiative forcing at the surface is rarely reported for model simulations; as a result, intermodel differences have not previously been evaluated in global climate models. We demonstrate that the instantaneous radiative forcing is the largest contributor to intermodel spread in effective radiative forcing at the surface. We also find evidence of differences in radiative parameterizations in current models and argue that this is a significant, but largely overlooked, source of bias in climate change simulations.

scholarly journals General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

2011 ◽  
Vol 11 (6) ◽  
pp. 17941-18160 ◽  
Author(s):  
M. Kulmala ◽  
A. Asmi ◽  
H. K. Lappalainen ◽  
U. Baltensperger ◽  
J.-L. Brenguier ◽  
...  
Keyword(s):  
Air Quality ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Global Scale ◽  
Global Climate Models ◽  
Modeling Tools ◽  
Emissions Inventory ◽  
Airborne Measurements ◽  
Aerosol Cloud

Abstract. In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) the first comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. This work enabled EUCAARI to improve our understanding of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.

scholarly journals Potential for western US seasonal snowpack prediction

2018 ◽  
Vol 115 (6) ◽  
pp. 1180-1185 ◽  
Author(s):  
Sarah B. Kapnick ◽  
Xiaosong Yang ◽  
Gabriel A. Vecchi ◽  
Thomas L. Delworth ◽  
Rich Gudgel ◽  
...  
Keyword(s):  
Sierra Nevada ◽  
Climate Models ◽  
Global Climate ◽  
Critical Role ◽  
Weather Conditions ◽  
Global Climate Models ◽  
Climate Indices ◽  
Climate Projections ◽  
Present System ◽  
Western Us

Western US snowpack—snow that accumulates on the ground in the mountains—plays a critical role in regional hydroclimate and water supply, with 80% of snowmelt runoff being used for agriculture. While climate projections provide estimates of snowpack loss by the end of the century and weather forecasts provide predictions of weather conditions out to 2 weeks, less progress has been made for snow predictions at seasonal timescales (months to 2 years), crucial for regional agricultural decisions (e.g., plant choice and quantity). Seasonal predictions with climate models first took the form of El Niño predictions 3 decades ago, with hydroclimate predictions emerging more recently. While the field has been focused on single-season predictions (3 months or less), we are now poised to advance our predictions beyond this timeframe. Utilizing observations, climate indices, and a suite of global climate models, we demonstrate the feasibility of seasonal snowpack predictions and quantify the limits of predictive skill 8 months in advance. This physically based dynamic system outperforms observation-based statistical predictions made on July 1 for March snowpack everywhere except the southern Sierra Nevada, a region where prediction skill is nonexistent for every predictor presently tested. Additionally, in the absence of externally forced negative trends in snowpack, narrow maritime mountain ranges with high hydroclimate variability pose a challenge for seasonal prediction in our present system; natural snowpack variability may inherently be unpredictable at this timescale. This work highlights present prediction system successes and gives cause for optimism for developing seasonal predictions for societal needs.

scholarly journals Response of shortwave cloud radiative effect to greenhouse gases and aerosols and its impact on daily maximum temperature

2020 ◽  
Author(s):  
Tao Tang ◽  
Drew Shindell ◽  
Yuqiang Zhang ◽  
Apostolos Voulgarakis ◽  
Jean-Francois Lamarque ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Maximum Temperature ◽  
Boreal Summer ◽  
Daily Maximum Temperature ◽  
Daily Maximum ◽  
Sulfate Aerosols ◽  
Multilinear Regression

Abstract. Shortwave cloud radiative effects (SWCRE), defined as the difference of shortwave radiative flux between all-sky and clear-sky conditions, have been reported to play an important role in influencing the Earth’s energy budget and temperature extremes. In this study, we employed a set of global climate models to examine the SWCRE responses to CO2, black carbon (BC) aerosols and sulfate aerosols in boreal summer over the Northern Hemisphere. We found that CO2 causes positive SWCRE changes over most of the NH, and BC causes similar positive responses over North America, Europe and East China but negative SWCRE over India and tropical Africa. When normalized by effective radiative forcing, the SWCRE from BC is roughly 3–5 times larger than that from CO2. SWCRE change is mainly due to cloud cover changes resulting from the changes in relative humidity (RH) and, to a lesser extent, changes in circulation and stability. The SWCRE response to sulfate aerosols, however, is negligible compared to that for CO2 and BC. Using a multilinear regression model, it is found that mean daily maximum temperature (Tmax) increases by 0.15 K and 0.13 K per W m−2 increase in local SWCRE under the CO2 and BC experiment, respectively. When domain-averaged, the SWCRE change contribution to summer mean Tmax changes was 10–30 % under CO2 forcing and 30–50 % under BC forcing, varying by region, which can have important implications for extreme climatic events and socio-economic activities.

A synthesis of observations of aerosol-cloud interactions over the pristine, biologically active Southern Ocean and their implications for global climate model predictions

2021 ◽  
Author(s):  
Isabel L. McCoy ◽  
Daniel T. McCoy ◽  
Robert Wood ◽  
Christopher S. Bretherton ◽  
Leighton Regayre ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Model ◽  
Global Climate Models ◽  
Biologically Active ◽  
Aerosol Cloud ◽  
Aerosol Cloud Interactions ◽  
Industrial State

<div> <p>The change in planetary albedo due to aerosol-cloud interactions (aci) during the industrial era is the leading source of uncertainty in inferring Earth's climate sensitivity to increased greenhouse gases from the historical record. Examining pristine environments such as the Southern Ocean (SO) helps us to understand the pre-industrial state and constrain the change in cloud brightness over the industrial period associated with aci. This study presents two methods of utilizing observations of pristine environments to examine climate models and our understanding of the pre-industrial state.</p> </div><div> <p>First, cloud droplet number concentration (<em>N<sub>d</sub></em>) is used as an indicator of aci. Global climate models (GCMs) show that the hemispheric contrast in liquid cloud <em>N<sub>d</sub></em> between the pristine SO and the polluted Northern Hemisphere observed in the present-day can be used<strong> </strong>as a proxy for the increase in <em>N<sub>d</sub></em> from the pre-industrial. A hemispheric difference constraint developed from MODIS satellite observations indicates that pre-industrial <em>N<sub>d</sub></em> may have been higher than previously thought and provides an estimate of radiative forcing associated with aci between -1.2 and -0.6 Wm<sup>-2</sup>. Comparisons with MODIS <em>N<sub>d  </sub></em>highlight significant GCM discrepancies in pristine, biologically active regions.</p> </div><div> <p>Second, aerosol and cloud microphysical observations from a recent SO aircraft campaign are used to identify two potentially important mechanisms that are incomplete or missing in GCMs: i) production of new aerosol particles through synoptic uplift, and ii) buffering of <em>N<sub>d</sub></em> against precipitation removal by small, Aitken mode aerosols entrained from the free troposphere. The latter may significantly contribute to the high, summertime SO <em>N<sub>d</sub></em> levels which persist despite precipitation depletion associated with mid-latitude storm systems. Observational comparisons with nudged Community Atmosphere Model version 6 (CAM6) hindcasts show low-biased SO <em>N<sub>d  </sub></em>is linked to under-production of free-tropospheric Aitken aerosol which drives low-biases in cloud condensation nuclei number and likely discrepancies in composition. These results have important implications for the ability of current GCMs to capture aci in pristine environments.</p> </div>

scholarly journals Process-oriented analysis of aircraft soot-cirrus interactions constrains the climate impact of aviation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Bernd Kärcher ◽  
Fabian Mahrt ◽  
Claudia Marcolli
Keyword(s):  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Climate Impact ◽  
Global Climate Models ◽  
Soot Particles ◽  
Cloud Ice ◽  
The Impact

AbstractFully accounting for the climate impact of aviation requires a process-level understanding of the impact of aircraft soot particle emissions on the formation of ice clouds. Assessing this impact with the help of global climate models remains elusive and direct observations are lacking. Here we use a high-resolution cirrus column model to investigate how aircraft-emitted soot particles, released after ice crystals sublimate at the end of the lifetime of contrails and contrail cirrus, perturb the formation of cirrus. By allying cloud simulations with a measurement-based description of soot-induced ice formation, we find that only a small fraction (<1%) of the soot particles succeeds in forming cloud ice alongside homogeneous freezing of liquid aerosol droplets. Thus, soot-perturbed and homogeneously-formed cirrus fundamentally do not differ in optical depth. Our results imply that climate model estimates of global radiative forcing from interactions between aircraft soot and large-scale cirrus may be overestimates. The improved scientific understanding reported here provides a process-based underpinning for improved climate model parametrizations and targeted field observations.

Impact of the stratosphere on El Niño-Southern Oscillation

2020 ◽  
Author(s):  
Mario Rodrigo ◽  
Javier Garcia-Serrano ◽  
Ileana Bladé ◽  
Froila M. Palmeiro ◽  
Bianca Mezzina
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Active Role ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Enso Cycle ◽  
Vertical Resolution ◽  
The Tropical Pacific

&lt;p&gt;The European Consortium EC-EARTH climate model version 3.1 is used to assess the effects of a well-resolved stratosphere on the representation of El Ni&amp;#241;o-Southern Oscillation (ENSO). Three 100-year&amp;#160; long experiments with fixed radiative forcing representative of the present climate are compared: one with the top at 0.01hPa and 91 vertical levels (HIGH-TOP), another with the top at 5hPa and 62 vertical levels (LOW-TOP), and another high-top experiment with the stratosphere nudged to the climatology of HIGH-TOP from 10hPa upwards (NUDG). The differences in vertical resolution between HIGH-TOP and LOW-TOP start at around 100hPa. This study focuses on the canonical ENSO phenomenon, which is the most important source of variability and predictability on seasonal-to-interannual timescales.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Preliminary results indicate that EC-EARTH realistically simulates the ENSO SST pattern in the tropical Pacific regardless of vertical resolution, although HIGH-TOP (LOW-TOP) overestimates (underestimates) the SST variability during boreal summer (winter). In both configurations, the SST tongue is narrower meridionally and slightly shifted towards the central-western Pacific compared to observations, a common bias of climate models. Resolving the stratosphere has a clear effect on the power spectrum of the Ni&amp;#241;o3.4 index: as compared to observations where there is a well-known frequency range of 2-7 years, HIGH-TOP and LOW-TOP have a prominent peak centered at 4-5 years but additionally both simulations display another peak, towards higher (~ 2yrs) and lower (~ 7yrs) frequencies, respectively. Another impact of including a well-resolved stratosphere is to systematically enhance the amplitude of the SST, wind and convective anomalies in the tropical Pacific throughout the entire ENSO cycle. Finally, similar differences are obtained when comparing HIGH-TOP and NUDG, suggesting an active role of the tropical stratospheric variability on ENSO.&lt;/p&gt;

scholarly journals The effect of rapid adjustments to halocarbons and N2O on radiative forcing

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Øivind Hodnebrog ◽  
Gunnar Myhre ◽  
Ryan J. Kramer ◽  
Keith P. Shine ◽  
Timothy Andrews ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Temperature Change ◽  
Radiative Forcing ◽  
Climate Models ◽  
Global Climate ◽  
Initial Perturbation ◽  
Global Climate Models ◽  
Radiative Heating ◽  
Surface Temperature Change ◽  
Precipitation Decrease

AbstractRapid adjustments occur after initial perturbation of an external climate driver (e.g., CO2) and involve changes in, e.g. atmospheric temperature, water vapour and clouds, independent of sea surface temperature changes. Knowledge of such adjustments is necessary to estimate effective radiative forcing (ERF), a useful indicator of surface temperature change, and to understand global precipitation changes due to different drivers. Yet, rapid adjustments have not previously been analysed in any detail for certain compounds, including halocarbons and N2O. Here we use several global climate models combined with radiative kernel calculations to show that individual rapid adjustment terms due to CFC-11, CFC-12 and N2O are substantial, but that the resulting flux changes approximately cancel at the top-of-atmosphere due to compensating effects. Our results further indicate that radiative forcing (which includes stratospheric temperature adjustment) is a reasonable approximation for ERF. These CFCs lead to a larger increase in precipitation per kelvin surface temperature change (2.2 ± 0.3% K−1) compared to other well-mixed greenhouse gases (1.4 ± 0.3% K−1 for CO2). This is largely due to rapid upper tropospheric warming and cloud adjustments, which lead to enhanced atmospheric radiative cooling (and hence a precipitation increase) and partly compensate increased atmospheric radiative heating (i.e. which is associated with a precipitation decrease) from the instantaneous perturbation.

scholarly journals Modeling the global emission, transport and deposition of trace elements associated with mineral dust

2015 ◽  
Vol 12 (19) ◽  
pp. 5771-5792 ◽  
Author(s):  
Y. Zhang ◽  
N. Mahowald ◽  
R. A. Scanza ◽  
E. Journet ◽  
K. Desboeufs ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Mineral Dust ◽  
Chemical Elements ◽  
Global Climate ◽  
Global Climate Models ◽  
Data Set ◽  
Desert Dust ◽  
Mineral Data ◽  
The Impact

Abstract. Trace element deposition from desert dust has important impacts on ocean primary productivity, the quantification of which could be useful in determining the magnitude and sign of the biogeochemical feedback on radiative forcing. However, the impact of elemental deposition to remote ocean regions is not well understood and is not currently included in global climate models. In this study, emission inventories for eight elements primarily of soil origin, Mg, P, Ca, Mn, Fe, K, Al, and Si are determined based on a global mineral data set and a soil data set. The resulting elemental fractions are used to drive the desert dust model in the Community Earth System Model (CESM) in order to simulate the elemental concentrations of atmospheric dust. Spatial variability of mineral dust elemental fractions is evident on a global scale, particularly for Ca. Simulations of global variations in the Ca / Al ratio, which typically range from around 0.1 to 5.0 in soils, are consistent with observations, suggesting that this ratio is a good signature for dust source regions. The simulated variable fractions of chemical elements are sufficiently different; estimates of deposition should include elemental variations, especially for Ca, Al and Fe. The model results have been evaluated with observations of elemental aerosol concentrations from desert regions and dust events in non-dust regions, providing insights into uncertainties in the modeling approach. The ratios between modeled and observed elemental fractions range from 0.7 to 1.6, except for Mg and Mn (3.4 and 3.5, respectively). Using the soil database improves the correspondence of the spatial heterogeneity in the modeling of several elements (Ca, Al and Fe) compared to observations. Total and soluble dust element fluxes to different ocean basins and ice sheet regions have been estimated, based on the model results. The annual inputs of soluble Mg, P, Ca, Mn, Fe and K associated with dust using the mineral data set are 0.30 Tg, 16.89 Gg, 1.32 Tg, 22.84 Gg, 0.068 Tg, and 0.15 Tg to global oceans and ice sheets.

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