scholarly journals A statistical examination of the effects of stratospheric sulfate geoengineering on tropical storm genesis

2018 ◽  
Vol 18 (13) ◽  
pp. 9173-9188 ◽  
Author(s):  
Qin Wang ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Relative Humidity ◽  
Climate Model ◽  
Vertical Wind Shear ◽  
Stratospheric Aerosol ◽  
Cmip5 Models ◽  
Potential Index ◽  
Intercomparison Project ◽  
Climate Model Output ◽  
Thermodynamic Variables ◽  
Earth System Models

Abstract. The thermodynamics of the ocean and atmosphere partly determine variability in tropical cyclone (TC) number and intensity and are readily accessible from climate model output, but an accurate description of TC variability requires much higher spatial and temporal resolution than the models used in the GeoMIP (Geoengineering Model Intercomparison Project) experiments provide. The genesis potential index (GPI) and ventilation index (VI) are combinations of dynamic and thermodynamic variables that provide proxies for TC activity under different climate states. Here we use five CMIP5 models that have run the RCP4.5 experiment and the GeoMIP stratospheric aerosol injection (SAI) G4 experiment to calculate the two TC indices over the 2020 to 2069 period across the six ocean basins that generate TCs. GPI is consistently and significantly lower under G4 than RCP4.5 in five out of six ocean basins, but it increases under G4 in the South Pacific. The models project potential intensity and relative humidity to be the dominant variables affecting GPI. Changes in vertical wind shear are significant, but it is correlated with relative humidity, though with different relations across both models and ocean basins. We find that tropopause temperature is not a useful addition to sea surface temperature (SST) in projecting TC genesis, perhaps because the earth system models (ESMs) vary in their simulation of the various upper-tropospheric changes induced by the aerosol injection.

scholarly journals A statistical examination of the effects of stratospheric sulphate geoengineering on tropical storm genesis

2018 ◽  
Author(s):  
Qin Wang ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Relative Humidity ◽  
Wind Shear ◽  
Climate Models ◽  
Climate Model ◽  
Vertical Wind Shear ◽  
Stratospheric Aerosol ◽  
Vertical Wind ◽  
Radiative Heating ◽  
Cmip5 Models ◽  
The North

Abstract. The thermodynamics of the ocean and atmosphere partly determine variability in tropical cyclone (TC) number and intensity and are readily accessible from climate model output, but a complete description of TC variability requires much more dynamical data than climate models can provide at present. Genesis potential index (GPI) and ventilation index (VI) are combinations of potential intensity, vertical wind shear, relative humidity, midlevel entropy deficit, and absolute vorticity that can quantify both thermodynamic and dynamic forcing of TC activity under different climate states. Here we use six CMIP5 models that have run the RCP4.5 experiment and the Geoengineering Model Intercomparison Project (GeoMIP) stratospheric aerosol injection G4 experiment, to calculate the two TC indices over the 2020 to 2069 period across the 6 ocean basins that generate tropical cyclones. Globally, GPI under G4 is lower than under RCP4.5, though both have a slight increasing trend. Spatial patterns in the effectiveness of geoengineering show reductions in TC in the North Atlantic basin, and Northern Indian Ocean in all models except NorESM1-M. In the North Pacific, most models also show relative reductions under G4. Most models project potential intensity and relative humidity to be the dominant variables affecting genesis potential. Changes in vertical wind shear are significant, but both it and vorticity exhibit relatively small changes with large variation across both models and ocean basins. We find that tropopause temperature is not a useful addition to sea surface temperature in projecting TC genesis, despite radiative heating of the stratosphere due to the aerosol injection, and heating of the upper troposphere affecting static stability and potential intensity. Thus, simplified statistical methods that quantify the thermodynamic state of the major genesis basins may reasonably be used to examine stratospheric aerosol geoengineering impacts on TC activity.

scholarly journals The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): Experimental design and forcing input data

2016 ◽  
Author(s):  
Davide Zanchettin ◽  
Myriam Khodri ◽  
Claudia Timmreck ◽  
Matthew Toohey ◽  
Anja Schmidt ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Climatic Response ◽  
Volcanic Forcing ◽  
Intercomparison Project

Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Climate Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the model intercomparison project on the climate response to volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol dataset for each experiment to eliminate differences in the applied volcanic forcing, and defines a set of initial conditions to determine how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically-forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input datasets to be used.

Investigation of the Surface and Circulation Impacts of Cloud-Brightening Geoengineering

2012 ◽  
Vol 25 (21) ◽  
pp. 7527-7543 ◽  
Author(s):  
E. Baughman ◽  
A. Gnanadesikan ◽  
A. Degaetano ◽  
A. Adcroft
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Cloud Condensation Nuclei ◽  
Vertical Wind Shear ◽  
Coupled Model ◽  
Walker Circulation ◽  
Cloud Albedo ◽  
Potential Index ◽  
Marine Stratus ◽  
The Impact

Projected increases in greenhouse gases have prompted serious discussion on geoengineering the climate system to counteract global climate change. Cloud albedo enhancement has been proposed as a feasible geoengineering approach, but previous research suggests undesirable consequences of globally uniform cloud brightening. The present study uses GFDL’s Climate Model version 2G (CM2G) global coupled model to simulate cloud albedo enhancement via increases in cloud condensation nuclei (CCN) to 1000 cm−3 targeted at the marine stratus deck of the Pacific Ocean, where persistent low clouds suggest a regional approach to cloud brightening. The impact of this regional geoengineering on global circulation and climate in the presence of a 1% annual increase of CO2 was investigated. Surface temperatures returned to near preindustrial levels over much of the globe with cloud modifications in place. In the first 40 years and over the 140-yr mean, significant cooling over the equatorial Pacific, continued Arctic warming, large precipitation changes over the western Pacific, and a westward compression and intensification of the Walker circulation were observed in response to cloud brightening. The cloud brightening caused a persistent La Niña condition associated with an increase in hurricane maximum potential intensity and genesis potential index, and decreased vertical wind shear between July and November in the tropical Atlantic, South China Sea, and to the east of Japan. Responses were similar with CCN = 500 cm−3.

scholarly journals Use of a Genesis Potential Index to Diagnose ENSO Effects on Tropical Cyclone Genesis

2007 ◽  
Vol 20 (19) ◽  
pp. 4819-4834 ◽  
Author(s):  
Suzana J. Camargo ◽  
Kerry A. Emanuel ◽  
Adam H. Sobel
Keyword(s):  
Tropical Cyclone ◽  
Relative Humidity ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Vertical Wind Shear ◽  
Vertical Shear ◽  
Interannual Variations ◽  
Genesis Potential Index ◽  
Potential Index

Abstract ENSO (El Niño–Southern Oscillation) has a large influence on tropical cyclone activity. The authors examine how different environmental factors contribute to this influence, using a genesis potential index developed by Emanuel and Nolan. Four factors contribute to the genesis potential index: low-level vorticity (850 hPa), relative humidity at 600 hPa, the magnitude of vertical wind shear from 850 to 200 hPa, and potential intensity (PI). Using monthly NCEP Reanalysis data in the period of 1950–2005, the genesis potential index is calculated on a latitude strip from 60°S to 60°N. Composite anomalies of the genesis potential index are produced for El Niño and La Niña years separately. These composites qualitatively replicate the observed interannual variations of the observed frequency and location of genesis in several different basins. This justifies producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology, to determine which among the factors are most important in causing interannual variations in genesis frequency. Specific factors that have more influence than others in different regions can be identified. For example, in El Niño years, relative humidity and vertical shear are important for the reduction in genesis seen in the Atlantic basin, and relative humidity and vorticity are important for the eastward shift in the mean genesis location in the western North Pacific.

scholarly journals Exploring precipitation pattern scaling methodologies and robustness among CMIP5 models

2017 ◽  
Vol 10 (5) ◽  
pp. 1889-1902 ◽  
Author(s):  
Ben Kravitz ◽  
Cary Lynch ◽  
Corinne Hartin ◽  
Ben Bond-Lamberty
Keyword(s):  
Climate Model ◽  
Cmip5 Models ◽  
Future Climate Change ◽  
Precipitation Pattern ◽  
Established Method ◽  
Global Mean Temperature ◽  
Precipitation Response ◽  
Climate Model Output ◽  
Time Invariant ◽  
Global Mean

Abstract. Pattern scaling is a well-established method for approximating modeled spatial distributions of changes in temperature by assuming a time-invariant pattern that scales with changes in global mean temperature. We compare two methods of pattern scaling for annual mean precipitation (regression and epoch difference) and evaluate which method is better in particular circumstances by quantifying their robustness to interpolation/extrapolation in time, inter-model variations, and inter-scenario variations. Both the regression and epoch-difference methods (the two most commonly used methods of pattern scaling) have good absolute performance in reconstructing the climate model output, measured as an area-weighted root mean square error. We decompose the precipitation response in the RCP8.5 scenario into a CO2 portion and a non-CO2 portion. Extrapolating RCP8.5 patterns to reconstruct precipitation change in the RCP2.6 scenario results in large errors due to violations of pattern scaling assumptions when this CO2-/non-CO2-forcing decomposition is applied. The methodologies discussed in this paper can help provide precipitation fields to be utilized in other models (including integrated assessment models or impacts assessment models) for a wide variety of scenarios of future climate change.

scholarly journals US daily temperature records past, present, and future

2016 ◽  
Vol 113 (49) ◽  
pp. 13977-13982 ◽  
Author(s):  
Gerald A. Meehl ◽  
Claudia Tebaldi ◽  
Dennis Adams-Smith
Keyword(s):  
Climate Model ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Coupled Climate Model ◽  
Future Projections ◽  
A Value ◽  
Daily Record ◽  
Intercomparison Project ◽  
Temperature Records ◽  
Specific Scenario

Observed temperature extremes over the continental United States can be represented by the ratio of daily record high temperatures to daily record low minimum temperatures, and this ratio has increased to a value of about 2 to 1, averaged over the first decade of the 21st century, albeit with large interannual variability. Two different versions of a global coupled climate model (CCSM4), as well as 23 other coupled model intercomparison project phase 5 (CMIP5) models, show larger values of this ratio than observations, mainly as a result of greater numbers of record highs since the 1980s compared with observations. This is partly because of the “warm 1930s” in the observations, which made it more difficult to set record highs later in the century, and partly because of a trend toward less rainfall and reduced evapotranspiration in the model versions compared with observations. We compute future projections of this ratio on the basis of its estimated dependence on mean temperature increase, which we find robustly at play in both observations and simulations. The use of this relation also has the advantage of removing dependence of a projection on a specific scenario. An empirical projection of the ratio of record highs to record lows is obtained from the nonlinear relationship in observations from 1930 to 2015, thus correcting downward the likely biased future projections of the model. For example, for a 3 °C warming in US temperatures, the ratio of record highs to lows is projected to be ∼15 ± 8 compared to the present average ratio of just over 2.

scholarly journals Defining Sudden Stratospheric Warming in Climate Models: Accounting for Biases in Model Climatologies

2017 ◽  
Vol 30 (14) ◽  
pp. 5529-5546 ◽  
Author(s):  
Junsu Kim ◽  
Seok-Woo Son ◽  
Edwin P. Gerber ◽  
Hyo-Seok Park
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Coupled Model ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Cmip5 Models ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Intercomparison Project ◽  
Wave Flux

A sudden stratospheric warming (SSW) is often defined as zonal-mean zonal wind reversal at 10 hPa and 60°N. This simple definition has been applied not only to the reanalysis data but also to climate model output. In the present study, it is shown that the application of this definition to models can be significantly influenced by model mean biases (i.e., more frequent SSWs appear to occur in models with a weaker climatological polar vortex). To overcome this deficiency, a tendency-based definition is proposed and applied to the multimodel datasets archived for phase 5 of the Coupled Model Intercomparison Project (CMIP5). In this definition, SSW-like events are defined by sufficiently strong vortex deceleration. This approach removes a linear relationship between SSW frequency and intensity of the climatological polar vortex in the CMIP5 models. The models’ SSW frequency instead becomes significantly correlated with the climatological upward wave flux at 100 hPa, a measure of interaction between the troposphere and stratosphere. Lower stratospheric wave activity and downward propagation of stratospheric anomalies to the troposphere are also reasonably well captured. However, in both definitions, the high-top models generally exhibit more frequent SSWs than the low-top models. Moreover, a hint of more frequent SSWs in a warm climate is found in both definitions.

scholarly journals The representation of Northern Hemisphere blocking in current global climate models

2020 ◽  
Author(s):  
Reinhard Schiemann ◽  
Panos Athanasiadis ◽  
David Barriopedro ◽  
Francisco Doblas-Reyes ◽  
Katja Lohmann ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Model Development ◽  
Reanalysis Data ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
The Pacific ◽  
Intercomparison Project ◽  
Blocking Index

Abstract. Global Climate Models (GCMs) are known to suffer from biases in the simulation of atmospheric blocking, and this study provides an assessment of how blocking is represented by the latest generation of GCMs. It is evaluated (i) how historical CMIP6 (Climate Model Intercomparison Project Phase 6) simulations perform compared to CMIP5 simulations, and (ii) how horizontal model resolution affects the simulation of blocking in the CMIP6-HighResMIP (PRIMAVERA) model ensemble, which is designed to address this type of question. Two blocking indices are used to evaluate the simulated mean blocking frequency and blocking persistence for the Euro-Atlantic and Pacific regions in winter and summer against the corresponding estimates from atmospheric reanalysis data. There is robust evidence that CMIP6 models simulate blocking frequency and persistence better than CMIP5 models in the Atlantic and Pacific and in winter and summer. This improvement is sizeable so that, for example, winter blocking frequency in the median CMIP5 model in a large Euro-Atlantic domain is underestimated by 32 % using the absolute geopotential height (AGP) blocking index, whereas the same number is 19 % for the median CMIP6 model. As for the sensitivity of simulated blocking to resolution, it is found that the resolution increase, from typically 100 km to 20 km grid spacing, in the PRIMAVERA models, which are not re-tuned at the higher resolutions, benefits the mean blocking frequency in the Atlantic in winter and summer, and in the Pacific in summer. Simulated blocking persistence, however, is not seen to improve with resolution. Our results are consistent with previous studies suggesting that resolution is one of a number of interacting factors necessary for an adequate simulation of blocking in GCMs. The improvements reported in this study hold promise for further reductions in blocking biases as model development continues.

scholarly journals Northern Hemisphere blocking simulation in current climate models: evaluating progress from the Climate Model Intercomparison Project Phase 5 to 6 and sensitivity to resolution

2020 ◽  
Vol 1 (1) ◽  
pp. 277-292 ◽  
Author(s):  
Reinhard Schiemann ◽  
Panos Athanasiadis ◽  
David Barriopedro ◽  
Francisco Doblas-Reyes ◽  
Katja Lohmann ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Model Development ◽  
Global Climate Models ◽  
Assessment Model ◽  
Climate Simulation ◽  
Cmip5 Models ◽  
Model Intercomparison ◽  
Intercomparison Project

Abstract. Global climate models (GCMs) are known to suffer from biases in the simulation of atmospheric blocking, and this study provides an assessment of how blocking is represented by the latest generation of GCMs. It is evaluated (i) how historical CMIP6 (Climate Model Intercomparison Project Phase 6) simulations perform compared to CMIP5 simulations and (ii) how horizontal model resolution affects the simulation of blocking in the CMIP6-HighResMIP (PRIMAVERA – PRocess-based climate sIMulation: AdVances in high-resolution modelling and European climate Risk Assessment) model ensemble, which is designed to address this type of question. Two blocking indices are used to evaluate the simulated mean blocking frequency and blocking persistence for the Euro-Atlantic and Pacific regions in winter and summer against the corresponding estimates from atmospheric reanalysis data. There is robust evidence that CMIP6 models simulate blocking frequency and persistence better than CMIP5 models in the Atlantic and Pacific and during winter and summer. This improvement is sizeable so that, for example, winter blocking frequency in the median CMIP5 model in a large Euro-Atlantic domain is underestimated by 33 % using the absolute geopotential height (AGP) blocking index, whereas the same number is 18 % for the median CMIP6 model. As for the sensitivity of simulated blocking to resolution, it is found that the resolution increase, from typically 100 to 20 km grid spacing, in most of the PRIMAVERA models, which are not re-tuned at the higher resolutions, benefits the mean blocking frequency in the Atlantic in winter and summer and in the Pacific in summer. Simulated blocking persistence, however, is not seen to improve with resolution. Our results are consistent with previous studies suggesting that resolution is one of a number of interacting factors necessary for an adequate simulation of blocking in GCMs. The improvements reported in this study hold promise for further reductions in blocking biases as model development continues.

scholarly journals The impact of stratospheric aerosol intervention on the North Atlantic and Quasi-Biennial Oscillations in the Geoengineering Model Intercomparison Project (GeoMIP) G6sulfur experiment

2021 ◽  
Author(s):  
Andy Jones ◽  
Jim M. Haywood ◽  
Adam A. Scaife ◽  
Olivier Boucher ◽  
Matthew Henry ◽  
...  
Keyword(s):  
North Atlantic ◽  
Stratospheric Aerosol ◽  
Injection Rate ◽  
Model Intercomparison ◽  
Quasi Biennial Oscillation ◽  
The North ◽  
Global Mean Temperature ◽  
Intercomparison Project ◽  
The Impact ◽  
Earth System Models

Abstract. As part of the Geoengineering Model Intercomparison Project a numerical experiment known as G6sulfur has been designed in which temperatures under a high-forcing future scenario (SSP5-8.5) are reduced to those under a medium-forcing scenario (SSP2-4.5) using the proposed geoengineering technique of stratospheric aerosol intervention (SAI). G6sulfur involves introducing sulphate aerosol into the tropical stratosphere where it reflects incoming sunlight back to space, thus cooling the planet. Here we compare the results from six Earth-system models which have performed the G6sulfur experiment and examine how SAI affects two important modes of natural variability, the northern wintertime North Atlantic Oscillation (NAO) and the Quasi-Biennial Oscillation (QBO). Although all models show that SAI is successful in reducing global-mean temperature as designed, they are also consistent in showing that it forces an increasingly positive phase of the NAO as the injection rate increases over the course of the 21st century, exacerbating precipitation reductions over parts of southern Europe compared with SSP5-8.5. In contrast to the robust result for the NAO there is less consistency for the impact on the QBO, but the results nevertheless indicate a risk that equatorial SAI could cause the QBO to stall and become locked in a phase with permanent westerly winds in the lower stratosphere.

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