scholarly journals Southern Annular Mode Dynamics in Observations and Models. Part I: The Influence of Climatological Zonal Wind Biases in a Comprehensive GCM

2013 ◽  
Vol 26 (11) ◽  
pp. 3953-3967 ◽  
Author(s):  
Isla R. Simpson ◽  
Peter Hitchcock ◽  
Theodore G. Shepherd ◽  
John F. Scinocca
Keyword(s):  
Zonal Wind ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Global Climate ◽  
Southern Annular Mode ◽  
Global Climate Models ◽  
Annular Mode ◽  
Jet Structure ◽  
Climatological Circulation ◽  
Stratospheric Variability

Abstract A common bias among global climate models (GCMs) is that they exhibit tropospheric southern annular mode (SAM) variability that is much too persistent in the Southern Hemisphere (SH) summertime. This is of concern for the ability to accurately predict future SH circulation changes, so it is important that it be understood and alleviated. In this two-part study, specifically targeted experiments with the Canadian Middle Atmosphere Model (CMAM) are used to improve understanding of the enhanced summertime SAM persistence. Given the ubiquity of this bias among comprehensive GCMs, it is likely that the results will be relevant for other climate models. Here, in Part I, the influence of climatological circulation biases on SAM variability is assessed, with a particular focus on two common biases that could enhance summertime SAM persistence: the too-late breakdown of the Antarctic stratospheric vortex and the equatorward bias in the SH tropospheric midlatitude jet. Four simulations are used to investigate the role of each of these biases in CMAM. Nudging and bias correcting procedures are used to systematically remove zonal-mean stratospheric variability and/or remove climatological zonal wind biases. The SAM time-scale bias is not alleviated by improving either the timing of the stratospheric vortex breakdown or the climatological jet structure. Even in the absence of stratospheric variability and with an improved climatological circulation, the model time scales are biased long. This points toward a bias in internal tropospheric dynamics that is not caused by the tropospheric jet structure bias. The underlying cause of this is examined in more detail in Part II of this study.

scholarly journals Influence of long-term changes in solar irradiance forcing on the Southern Annular Mode

2021 ◽  
Author(s):  
Nicky M. Wright ◽  
Claire E. Krause ◽  
Steven J. Phipps ◽  
Ghyslaine Boschat ◽  
Nerilie J. Abram
Keyword(s):  
Atmospheric Chemistry ◽  
Solar Irradiance ◽  
Climate Models ◽  
Global Climate ◽  
Southern Annular Mode ◽  
Climate Impacts ◽  
Global Climate Models ◽  
Last Millennium ◽  
Solar Forcing ◽  
Annular Mode

Abstract. The Southern Annular Mode (SAM) is the leading mode of climate variability in the extratropical Southern Hemisphere, with major regional climate impacts. Observations, reconstructions, and historical climate simulations all show positive trends in the SAM since the 1960s; however, earlier trends in palaeoclimate SAM reconstructions cannot be reconciled with last millennium simulations. Here we investigate the sensitivity of the SAM to solar irradiance variations using simulations with a range of constant solar forcing values, and last millennium transient simulations with varying amplitude solar forcing scenarios. We find the mean SAM state can be significantly altered by solar irradiance changes, and that transient last millennium simulations using a high-amplitude solar scenario have an improved and significant agreement with proxy-based SAM reconstructions. Our findings suggest that the effects of solar forcing on high-latitude climate may not be adequately incorporated in most last millennium simulations, due to solar irradiance changes that are too small and/or the absence of interactive atmospheric chemistry in global climate models.

Model Uncertainty in Cloud–Circulation Coupling, and Cloud-Radiative Response to Increasing CO2, Linked to Biases in Climatological Circulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10013-10020
Author(s):  
Bernard R. Lipat ◽  
Aiko Voigt ◽  
George Tselioudis ◽  
Lorenzo M. Polvani
Keyword(s):  
Model Uncertainty ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Global Climate Models ◽  
Hadley Cell ◽  
Temperature Structure ◽  
Climatological Circulation

Recent analyses of global climate models suggest that uncertainty in the coupling between midlatitude clouds and the atmospheric circulation contributes to uncertainty in climate sensitivity. However, the reasons behind model differences in the cloud–circulation coupling have remained unclear. Here, we use a global climate model in an idealized aquaplanet setup to show that the Southern Hemisphere climatological circulation, which in many models is biased equatorward, contributes to the model differences in the cloud–circulation coupling. For the same poleward shift of the Hadley cell (HC) edge, models with narrower climatological HCs exhibit stronger midlatitude cloud-induced shortwave warming than models with wider climatological HCs. This cloud-induced radiative warming results predominantly from a subsidence warming that decreases cloud fraction and is stronger for narrower HCs because of a larger meridional gradient in the vertical velocity. A comparison of our aquaplanet results with comprehensive climate models suggests that about half of the model uncertainty in the midlatitude cloud–circulation coupling stems from this impact of the circulation on the large-scale temperature structure of the atmosphere, and thus could be removed by improving the climatological circulation in models. This illustrates how understanding of large-scale dynamics can help reduce uncertainty in clouds and their response to climate change.

scholarly journals Summer Season Squall-Line Simulations: Sensitivity of Gravity Waves to Physics Parameterization and Implications for Their Parameterization in Global Climate Models

2014 ◽  
Vol 71 (9) ◽  
pp. 3376-3391 ◽  
Author(s):  
Claudia Stephan ◽  
M. Joan Alexander
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Global Climate ◽  
Global Climate Models ◽  
Squall Line ◽  
The Impact

Abstract Gravity waves have important effects on the middle atmosphere circulation, and those generated by convection are prevalent in the tropics and summer midlatitudes. Numerous case studies have been carried out to investigate their characteristics in high-resolution simulations. Here, the impact of the choice of physics parameterizations on the generation and spectral properties of these waves in models is investigated. Using the Weather Research and Forecasting Model (WRF) a summertime squall line over the Great Plains is simulated in a three-dimensional, nonlinear, and nonhydrostatic mesoscale framework. The distributions of precipitation strength and echo tops in the simulations are compared with radar data. Unsurprisingly, those storm features are most sensitive to the microphysics scheme. However, it is found that these variations in storm morphology have little influence on the simulated stratospheric momentum flux spectra. These results support the fundamental idea behind climate model parameterizations: that the large-scale storm conditions can be used to predict the spectrum of gravity wave momentum flux above the storm irrespective of the convective details that coarse-resolution models cannot capture. The simulated spectra are then contrasted with those obtained from a parameterization used in global climate models. The parameterization reproduces the shape of the spectra reasonably well but their magnitudes remain highly sensitive to the peak heating rate within the convective cells.

scholarly journals Evaluation of the Quasi-Biennial Oscillation in global climate models for the SPARC QBO-initiative

2020 ◽  
Author(s):  
Andrew Bushell ◽  
Francois Lott ◽  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Global Climate ◽  
Coupled Model ◽  
Global Climate Models ◽  
Multimodel Ensemble ◽  
Quasi Biennial Oscillation ◽  
Modelling Uncertainties ◽  
Biennial Oscillation

<p>The Stratosphere-troposphere Processes And their Role in Climate (SPARC) Quasi-Biennial Oscillation initiative (QBOi) seeks to improve confidence in general circulation and earth system model (GCM and ESM) simulations of the QBO, a prominent feature of middle atmosphere tropical variability first identified nearly sixty years ago. Although only five out of 47 models contributing to the Coupled Model Intercomparison Project Phase 5 (CMIP5) had spontaneous QBOs, simulated QBOs are anticipated to be more common among CMIP6 models as more atmospheric GCMs are able to reproduce the phenomenon, both by ensuring adequate vertical resolution in the stratosphere and by parametrizing accelerations due to subgrid nonorographic gravity waves (NOGWs). The complexity of CMIP6 models and their forcing scenarios, however, is an obstacle to using the CMIP6 multimodel ensemble for analysis of modelling uncertainties that are specific to the QBO and its impacts. The QBOi multimodel ensemble represents an alternative approach in which modelling uncertainties related to the QBO are assessed by performing coordinated experiments with atmospheric GCMs that have simplified external forcings and boundary conditions, designed to characterize QBO representation and its response to idealised future climate scenarios. </p><p>Results are presented from an analysis of QBOs in thirteen atmospheric GCMs forced with both observed and annually repeating sea surface temperatures (SSTs). Mean QBO periods in most of these models are close to, though shorter than, the period of 28 months observed in ERA-Interim. Amplitudes are within ±20% of the observed QBO amplitude at 10hPa, but typically about half of that observed at lower altitudes (50 and 70hPa). For almost all models the oscillation's amplitude profile shows an overall upward shift compared to reanalysis and its meridional extent is too narrow. Asymmetry in the duration of eastward and westward phases is reasonably well captured though not all models replicate the observed slowing as the westward shear descends. Westward phases are generally too weak, and most models have an eastward time mean wind bias throughout the depth of the QBO. Intercycle period variability is realistic and in some models is enhanced in the experiment with observed SSTs compared to the experiment with repeated annual cycle SSTs. Mean periods are also sensitive to this difference between SSTs but only when parametrized NOGW sources are coupled to tropospheric parameters and not prescribed with a fixed value. But, overall, modelled QBOs are very similar whether or not the prescribed SSTs vary interannually. A portrait of the overall ensemble performance is provided by a normalised grading of QBO metrics. To simulate a QBO all but one model used parametrized NOGWs, which provided the majority of the total wave forcing at altitudes above 70hPa in most models. Thus the representation of NOGWs either explicitly or through parametrization is still a major uncertainty underlying QBO simulation in these present-day experiments.</p><p> </p>

scholarly journals Dependence of Precipitation Scaling Patterns on Emission Scenarios for Representative Concentration Pathways

2013 ◽  
Vol 26 (22) ◽  
pp. 8868-8879 ◽  
Author(s):  
Yasuhiro Ishizaki ◽  
Hideo Shiogama ◽  
Seita Emori ◽  
Tokuta Yokohata ◽  
Toru Nozawa ◽  
...  
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Regional Climate ◽  
Longwave Radiation ◽  
Regional Climate Change ◽  
Southern Annular Mode ◽  
Global Climate Models ◽  
Shortwave Radiation ◽  
Emission Scenarios ◽  
Sensitivity Experiments

Abstract Pattern scaling is an efficient way to generate projections of regional climate change for various emission scenarios. This approach assumes that the spatial pattern of changes per degree of global warming (scaling pattern) is the same among emission scenarios. The hypothesis was tested for the scaling pattern of precipitation by focusing on the scenario dependence of aerosol scaling patterns. The scenario dependence of aerosol scaling patterns induced the scenario dependence of the surface shortwave radiation scaling pattern. The scenario dependence of the surface shortwave radiation scaling pattern over the ocean tended to induce the scenario dependence of evaporation scaling patterns. The scenario dependence of evaporation scaling patterns led to the scenario dependence of precipitation scaling patterns locally and downwind. Contrariwise, when the scenario dependence of aerosol scaling patterns occurred over land, the scenario dependence of surface shortwave radiation scaling patterns induced the scenario dependence of the scaling patterns of evaporation, surface longwave radiation, and sensible heat. Consequently, the scenario dependence of evaporation scaling patterns was smaller over land, and the scenario dependence of precipitation scaling patterns tended to be insignificant. Moreover, the scenario dependence of the southern annular mode and polar amplification caused some of the scenario dependence of precipitation scaling patterns. In this study, only one global climate mode was analyzed. In addition, sensitivity experiments that remove aerosol emissions from some regions or some kinds of aerosols are ideal to separate the impacts of aerosols. Thus, an analysis of the dependencies of precipitation scaling pattern among global climate models and the sensitivity experiments are required in future work.

Extreme Events in High Resolution CMCC Regional and Global Climate Models

2011 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Antonella Sanna ◽  
Edoardo Bucchignani ◽  
Myriam Montesarchio
Keyword(s):  
High Resolution ◽  
Extreme Events ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models

scholarly journals Global climatology and trends in convective environments from ERA5 and rawinsonde data

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateusz Taszarek ◽  
John T. Allen ◽  
Mattia Marchio ◽  
Harold E. Brooks
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Convective Precipitation ◽  
The Past ◽  
The Tropics ◽  
Rawinsonde Data

AbstractGlobally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

scholarly journals Regions of intensification of extreme snowfall under future warming

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Lennart Quante ◽  
Sven N. Willner ◽  
Robin Middelanis ◽  
Anders Levermann
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Observational Data ◽  
Climate Models ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Models ◽  
Average Intensity ◽  
High Latitudes ◽  
Future Warming

AbstractDue to climate change the frequency and character of precipitation are changing as the hydrological cycle intensifies. With regards to snowfall, global warming has two opposing influences; increasing humidity enables intense snowfall, whereas higher temperatures decrease the likelihood of snowfall. Here we show an intensification of extreme snowfall across large areas of the Northern Hemisphere under future warming. This is robust across an ensemble of global climate models when they are bias-corrected with observational data. While mean daily snowfall decreases, both the 99th and the 99.9th percentiles of daily snowfall increase in many regions in the next decades, especially for Northern America and Asia. Additionally, the average intensity of snowfall events exceeding these percentiles as experienced historically increases in many regions. This is likely to pose a challenge to municipalities in mid to high latitudes. Overall, extreme snowfall events are likely to become an increasingly important impact of climate change in the next decades, even if they will become rarer, but not necessarily less intense, in the second half of the century.

scholarly journals Reassessing Existing Reservoir Supply Capacity and Management Resilience under Climate Change and Sediment Deposition

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1819
Author(s):  
Eleni S. Bekri ◽  
Polychronis Economou ◽  
Panayotis C. Yannopoulos ◽  
Alexander C. Demetracopoulos
Keyword(s):  
Climate Change ◽  
Climate Models ◽  
Global Climate ◽  
Vital Role ◽  
Sediment Deposition ◽  
Global Climate Models ◽  
Exceedance Probability ◽  
Climate Change Effects ◽  
Management Scenario ◽  
Supply Capacity

Freshwater resources are limited and seasonally and spatially unevenly distributed. Thus, in water resources management plans, storage reservoirs play a vital role in safeguarding drinking, irrigation, hydropower and livestock water supply. In the last decades, the dams’ negative effects, such as fragmentation of water flow and sediment transport, are considered in decision-making, for achieving an optimal balance between human needs and healthy riverine and coastal ecosystems. Currently, operation of existing reservoirs is challenged by increasing water demand, climate change effects and active storage reduction due to sediment deposition, jeopardizing their supply capacity. This paper proposes a methodological framework to reassess supply capacity and management resilience for an existing reservoir under these challenges. Future projections are derived by plausible climate scenarios and global climate models and by stochastic simulation of historic data. An alternative basic reservoir management scenario with a very low exceedance probability is derived. Excess water volumes are investigated under a probabilistic prism for enabling multiple-purpose water demands. Finally, this method is showcased to the Ladhon Reservoir (Greece). The probable total benefit from water allocated to the various water uses is estimated to assist decision makers in examining the tradeoffs between the probable additional benefit and risk of exceedance.

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