scholarly journals Interhemispheric asymmetry of climate change projections of boreal winter surface winds in CanESM5 large ensemble simulations

2021 ◽  
Author(s):  
Bin Yu ◽  
Xuebin Zhang ◽  
Guilong Li ◽  
Wei Yu
Keyword(s):  
Climate Variability ◽  
Wind Power ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Boreal Winter ◽  
Interhemispheric Asymmetry ◽  
Large Ensemble ◽  
Internal Climate Variability ◽  
Climate Simulations ◽  
Extreme Wind

Abstract A recent study of future changes in global wind power using an ensemble of ten CMIP5 climate simulations indicated an interhemispheric asymmetry of wind power changes over the 21st century, featured by power decreases across the Northern Hemisphere mid-latitudes and increases across the tropics and subtropics of the Southern Hemisphere. Here we analyze future global projections of surface mean and extreme winds by means of a single-model initial-condition 50-member ensemble of climate simulations generated with CanESM5, the Canadian model participated in CMIP6. We analyze the ensemble mean and spread of boreal winter mean and extreme wind trends over the next half-century (2021-2070) and explore the contribution of internal climate variability to these trends. Surface wind speed is projected to mostly decrease in northern mid-low latitudes and southern mid-latitudes and increase in northern high latitudes and southern tropical and subtropical regions, with considerable regional variations. Large ensemble spreads are apparent, especially with remarkable differences over northern parts of South America and northern Russia. The interhemispheric asymmetry of wind projections is found in most ensemble members, and can be related to large-scale changes in surface temperature and atmospheric circulation. The extreme wind has similar structure of future projections, whereas its reductions tend to be more consistent over northern mid-latitudes. The projected mean and extreme wind changes are attributed to changes in both externally anthropogenic forced and internal climate variability generated components. The spread in wind projections is partially due to large-scale atmospheric circulation variability.

Interhemispheric asymmetry of surface mean and extreme wind projections in CanESM5 climate change simulations

2021 ◽  
Author(s):  
Bin Yu ◽  
Xuebin Zhang ◽  
Guilong Li ◽  
Wei Yu
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Large Scale ◽  
Surface Wind ◽  
Boreal Winter ◽  
Interhemispheric Asymmetry ◽  
Half Century ◽  
Internal Climate Variability ◽  
Extreme Wind ◽  
The Mean

<p>The internal climate variability contributes to various aspects of climate change projections. This presentation will report results of the ensemble mean and spread of future projections of globally surface mean and extreme winds in boreal winter, based on single model initial-condition simulations forced by the SSP5-8.5 high-emissions scenario from a 50-member ensemble of CanESM5 models. Over the next half century, surface wind is projected to increase in the Northern Hemisphere mid-latitudes and increase in the Southern Hemisphere low-latitudes, an interhemispheric asymmetry feature relevant to large-scale changes in surface temperature and atmospheric circulation. Decreases in the surface extreme wind are clearer than the mean wind in the northern mid-latitudes. Large ensemble spreads are apparent in the mean and extreme wind changes, including spatial pattern and magnitude of the projected trends over the next half century. The internal climate variability generated components of the mean and extreme wind trends exhibit large-scale spatial coherences, and are comparable to the externally anthropogenic forced components of the trends.</p>

Alternate history: A synthetic ensemble of ocean chlorophyll concentrations

2021 ◽  
Author(s):  
Geneviève Elsworth ◽  
Nicole Lovenduski ◽  
Karen McKinnon
Keyword(s):  
Climate Variability ◽  
Internal Variability ◽  
Ensemble Member ◽  
Global Ocean ◽  
Large Ensemble ◽  
Internal Climate Variability ◽  
Surface Ocean ◽  
Large Ensembles ◽  
Long Term Trends

<p>Internal climate variability plays an important role in the abundance and distribution of phytoplankton in the global ocean. Previous studies using large ensembles of Earth system models (ESMs) have demonstrated their utility in the study of marine phytoplankton variability. These ESM large ensembles simulate the evolution of multiple alternate realities, each with a different phasing of internal climate variability. However, ESMs may not accurately represent real world variability as recorded via satellite and in situ observations of ocean chlorophyll over the past few decades. Observational records of surface ocean chlorophyll equate to a single ensemble member in the large ensemble framework, and this can cloud the interpretation of long-term trends: are they externally forced, caused by the phasing of internal variability, or both? Here, we use a novel statistical emulation technique to place the observational record of surface ocean chlorophyll into the large ensemble framework. Much like a large initial condition ensemble generated with an ESM, the resulting synthetic ensemble represents multiple possible evolutions of ocean chlorophyll concentration, each with a different phasing of internal climate variability. We further demonstrate the validity of our statistical approach by recreating a ESM ensemble of chlorophyll using only a single ESM ensemble member. We use the synthetic ensemble to explore the interpretation of long-term trends in the presence of internal variability. Our results suggest the potential to explore this approach for other ocean biogeochemical variables.</p>

Separating Internal Variability from the Externally Forced Climate Response

2015 ◽  
Vol 28 (20) ◽  
pp. 8184-8202 ◽  
Author(s):  
Leela M. Frankcombe ◽  
Matthew H. England ◽  
Michael E. Mann ◽  
Byron A. Steinman
Keyword(s):  
Time Series ◽  
Climate Variability ◽  
Low Frequency ◽  
Internal Variability ◽  
Atlantic Multidecadal Oscillation ◽  
Ensemble Member ◽  
Internal Climate Variability ◽  
Climate Simulations ◽  
Scaling Methods ◽  
Synthetic Time Series

Abstract Separating low-frequency internal variability of the climate system from the forced signal is essential to better understand anthropogenic climate change as well as internal climate variability. Here both synthetic time series and the historical simulations from phase 5 of CMIP (CMIP5) are used to examine several methods of performing this separation. Linear detrending, as is commonly used in studies of low-frequency climate variability, is found to introduce large biases in both amplitude and phase of the estimated internal variability. Using estimates of the forced signal obtained from ensembles of climate simulations can reduce these biases, particularly when the forced signal is scaled to match the historical time series of each ensemble member. These so-called scaling methods also provide estimates of model sensitivities to different types of external forcing. Applying the methods to observations of the Atlantic multidecadal oscillation leads to different estimates of the phase of this mode of variability in recent decades.

scholarly journals Precipitation, Temperature, and Teleconnection Signals across the Combined North American, Monsoon Asia, and Old World Drought Atlases

2017 ◽  
Vol 30 (18) ◽  
pp. 7141-7155 ◽  
Author(s):  
Seung H. Baek ◽  
Jason E. Smerdon ◽  
Sloan Coats ◽  
A. Park Williams ◽  
Benjamin I. Cook ◽  
...  
Keyword(s):  
Climate Variability ◽  
Tree Ring ◽  
North American ◽  
Large Scale ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Old World ◽  
Monsoon Asia ◽  
Teleconnection Patterns ◽  
Hydroclimate Variability

Abstract The tree-ring-based North American Drought Atlas (NADA), Monsoon Asia Drought Atlas (MADA), and Old World Drought Atlas (OWDA) collectively yield a near-hemispheric gridded reconstruction of hydroclimate variability over the last millennium. To test the robustness of the large-scale representation of hydroclimate variability across the drought atlases, the joint expression of seasonal climate variability and teleconnections in the NADA, MADA, and OWDA are compared against two global, observation-based PDSI products. Predominantly positive (negative) correlations are determined between seasonal precipitation (surface air temperature) and collocated tree-ring-based PDSI, with average Pearson’s correlation coefficients increasing in magnitude from boreal winter to summer. For precipitation, these correlations tend to be stronger in the boreal winter and summer when calculated for the observed PDSI record, while remaining similar for temperature. Notwithstanding these differences, the drought atlases robustly express teleconnection patterns associated with El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO). These expressions exist in the drought atlas estimates of boreal summer PDSI despite the fact that these modes of climate variability are dominant in boreal winter, with the exception of the AMO. ENSO and NAO teleconnection patterns in the drought atlases are particularly consistent with their well-known dominant expressions in boreal winter and over the OWDA domain, respectively. Collectively, the findings herein confirm that the joint Northern Hemisphere drought atlases robustly reflect large-scale patterns of hydroclimate variability on seasonal to multidecadal time scales over the twentieth century and are likely to provide similarly robust estimates of hydroclimate variability prior to the existence of widespread instrumental data.

scholarly journals Deciphering the spatio-temporal complexity of climate change of the last deglaciation: a model analysis

2011 ◽  
Vol 7 (2) ◽  
pp. 591-602 ◽  
Author(s):  
D. M. Roche ◽  
H. Renssen ◽  
D. Paillard ◽  
G. Levavasseur
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Last Deglaciation ◽  
Regional Variability ◽  
Internal Climate Variability ◽  
The North ◽  
Sequence Of Events ◽  
Transient Simulations ◽  
The Last Deglaciation ◽  
Spatio Temporal

Abstract. Understanding the sequence of events occuring during the last major glacial to interglacial transition (21 ka BP to 9 ka BP) is a challenging task that has the potential to unveil the mechanisms behind large scale climate changes. Though many studies have focused on the understanding of the complex sequence of rapid climatic change that accompanied or interrupted the deglaciation, few have analysed it in a more theoretical framework with simple forcings. In the following, we address when and where the first significant temperature anomalies appeared when using slow varying forcing of the last deglaciation. We used here coupled transient simulations of the last deglaciation, including ocean, atmosphere and vegetation components to analyse the spatial timing of the deglaciation. To keep the analysis in a simple framework, we did not include freshwater forcings that potentially cause rapid climate shifts during that time period. We aimed to disentangle the direct and subsequent response of the climate system to slow forcing and moreover, the location where those changes are more clearly expressed. In a data – modelling comparison perspective, this could help understand the physically plausible phasing between known forcings and recorded climatic changes. Our analysis of climate variability could also help to distinguish deglacial warming signals from internal climate variability. We thus are able to better pinpoint the onset of local deglaciation, as defined by the first significant local warming and further show that there is a large regional variability associated with it, even with the set of slow forcings used here. In our model, the first significant hemispheric warming occurred simultaneously in the North and in the South and is a direct response to the obliquity forcing.

scholarly journals Deciphering the spatio-temporal complexity of climate change of the last deglaciation: a model analysis

2010 ◽  
Vol 6 (6) ◽  
pp. 2593-2623 ◽  
Author(s):  
D. M. Roche ◽  
H. Renssen ◽  
D. Paillard
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Last Deglaciation ◽  
Regional Variability ◽  
Temporal Complexity ◽  
Internal Climate Variability ◽  
Sequence Of Events ◽  
Transient Simulations ◽  
The Last Deglaciation ◽  
Spatio Temporal

Abstract. Understanding the sequence of events occuring during the last major glacial to interglacial transition (21 ka BP to 9 ka BP) is a challenging task that has the potential to unveil the mechanisms behind large scale climate changes. Though many studies have focused at a complex understanding of the sequence of rapid climatic change that accompanied or interrupted the deglaciation, few have analysed it in a more theoretical framework with simple forcings. In the following, we address when and where the first significant temperature anomalies appear when using slow varying forcing of the last deglaciation. We use here coupled transient simulations of the last deglaciation, including ocean, atmosphere and vegetation components to analyse the spatial timing of the deglaciation. To keep the analysis in a simple framework, we do not include rapid freshwater forcings that have led to rapid climate shifts during that time period. We aim to disentangle the direct and subsequent response of the climate system to slow forcing and moreover the location where those changes are more clearly expressed. In a data-modelling comparison perspective this could help understanding the physically plausible phasing between known forcings and recorded climatic changes. Our analysis of climate variability could also help to distinguish deglacial warming signals from internal climate variability. We thus are able to better pinpoint the onset of local deglaciation, as defined by the first significant local warming, and further show that there is a large regional variability associated with it, even with the set of slow forcings used here.

Influence of thermospheric effects of solar activity on the middle atmosphere circulation and stationary planetary waves

2020 ◽  
Author(s):  
Andrey Koval ◽  
Nikolai Gavrilov ◽  
Alexander Pogoreltsev ◽  
Nikita Shevchuk
Keyword(s):  
Solar Activity ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Thermal Structure ◽  
Planetary Waves ◽  
Boreal Winter ◽  
Zonal Wavenumber ◽  
The Mean

<p>Atmospheric large-scale disturbances, for instance planetary waves, play a significant role in atmospheric general circulation, influencing its dynamical and thermal conditions. Solar activity may influence the mean temperature at altitudes above 100 km and alter conditions of wave propagation and reflection in the thermosphere. Using numerical simulations of the general atmospheric circulation during boreal winter, statistically confident evidences are obtained for the first time, demonstrating that changes in the solar activity (SA) in the thermosphere at heights above 100 km can influence propagation and reflection conditions for stationary planetary waves (SPWs) and can modify the middle atmosphere circulation below 100 km. A numerical mechanistic model simulating  atmospheric circulation and SPWs at heights 0 – 300 km is used. To achieve sufficient statistical confidence, 80 pairs of 15-day intervals were extracted from an ensemble of 16 pairs of model runs corresponding to low and high SA. Results averaged over these intervals show that impacts of SA above 100 km change the mean zonal wind and temperature up to 10% at altitudes below 100 km. The statistically confident changes in SPW amplitudes due to SA impacts above 100 km reach up to 50% in the thermosphere and 10 – 15% in the middle atmosphere depending on zonal wavenumber. Changes in wave amplitudes correspond to variations of the EP-flux and may alter dynamical and thermal SPW impacts on the mean wind and temperature. Thus, variable conditions of SPW propagation and reflection at thermospheric altitudes may influence the middle atmosphere circulation, thermal structure and planetary waves at different altitudes.</p>

Relative Importance of Internal Climate Variability versus Anthropogenic Climate Change in Global Climate Change

2021 ◽  
Vol 34 (2) ◽  
pp. 465-478
Author(s):  
Jie Chen ◽  
Xiangquan Li ◽  
Jean-Luc Martel ◽  
François P. Brissette ◽  
Xunchang J. Zhang ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Global Climate ◽  
Regional Climate ◽  
Baseline Period ◽  
Anthropogenic Climate Change ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Internal Climate Variability ◽  
Equatorial Band

AbstractTo better understand the role of internal climate variability (ICV) in climate change impact studies, this study quantifies the importance of ICV [defined as the intermember variability of a single model initial-condition large ensemble (SMILE)] in relation to the anthropogenic climate change (ACC; defined as multimodel ensemble mean) in global and regional climate change using a criterion of time of emergence (ToE). The uncertainty of the estimated ToE is specifically investigated by using three SMILEs to estimate the ICV. The results show that using 1921–40 as a baseline period, the annual mean precipitation ACC is expected to emerge within this century over extratropical regions as well as along the equatorial band. However, ToEs are unlikely to occur, even by the end of this century, over intratropical regions outside of the equatorial band. In contrast, annual mean temperature ACC has already emerged from the temperature ICV for most of the globe. Similar spatial patterns are observed at the seasonal scale, while a weaker ACC for boreal summer (June–August) precipitation and additional ICV for boreal winter (December–February) temperature translate to later ToEs for some regions. In addition, the uncertainty of ToE related to the choice of a SMILE is mostly less than 20 years for annual mean precipitation and temperature. However, it can be as large as 90 years for annual mean precipitation over some regions. Overall, results indicate that the choice of a SMILE is a significant source of uncertainty in the estimation of ToE and results based on only one SMILE should be interpreted with caution.

scholarly journals Role of the Gulf Stream and Kuroshio–Oyashio Systems in Large-Scale Atmosphere–Ocean Interaction: A Review

2010 ◽  
Vol 23 (12) ◽  
pp. 3249-3281 ◽  
Author(s):  
Young-Oh Kwon ◽  
Michael A. Alexander ◽  
Nicholas A. Bond ◽  
Claude Frankignoul ◽  
Hisashi Nakamura ◽  
...  
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Gulf Stream ◽  
Large Scale ◽  
Climate Model ◽  
Low Frequency ◽  
Heat Fluxes ◽  
Western Boundary ◽  
Basin Scale ◽  
Sst Anomalies

Abstract Ocean–atmosphere interaction over the Northern Hemisphere western boundary current (WBC) regions (i.e., the Gulf Stream, Kuroshio, Oyashio, and their extensions) is reviewed with an emphasis on their role in basin-scale climate variability. SST anomalies exhibit considerable variance on interannual to decadal time scales in these regions. Low-frequency SST variability is primarily driven by basin-scale wind stress curl variability via the oceanic Rossby wave adjustment of the gyre-scale circulation that modulates the latitude and strength of the WBC-related oceanic fronts. Rectification of the variability by mesoscale eddies, reemergence of the anomalies from the preceding winter, and tropical remote forcing also play important roles in driving and maintaining the low-frequency variability in these regions. In the Gulf Stream region, interaction with the deep western boundary current also likely influences the low-frequency variability. Surface heat fluxes damp the low-frequency SST anomalies over the WBC regions; thus, heat fluxes originate with heat anomalies in the ocean and have the potential to drive the overlying atmospheric circulation. While recent observational studies demonstrate a local atmospheric boundary layer response to WBC changes, the latter’s influence on the large-scale atmospheric circulation is still unclear. Nevertheless, heat and moisture fluxes from the WBCs into the atmosphere influence the mean state of the atmospheric circulation, including anchoring the latitude of the storm tracks to the WBCs. Furthermore, many climate models suggest that the large-scale atmospheric response to SST anomalies driven by ocean dynamics in WBC regions can be important in generating decadal climate variability. As a step toward bridging climate model results and observations, the degree of realism of the WBC in current climate model simulations is assessed. Finally, outstanding issues concerning ocean–atmosphere interaction in WBC regions and its impact on climate variability are discussed.

scholarly journals Large-Scale Pattern of the Diurnal Temperature Range Changes over East Asia and Australia in Boreal Winter: A Perspective of Atmospheric Circulation

2018 ◽  
Vol 31 (7) ◽  
pp. 2715-2728 ◽  
Author(s):  
Lin Liu ◽  
Jianping Guo ◽  
Wen Chen ◽  
Renguang Wu ◽  
Lin Wang ◽  
...  
Keyword(s):  
East Asia ◽  
Atmospheric Circulation ◽  
Diurnal Temperature Range ◽  
Large Scale ◽  
Walker Circulation ◽  
Boreal Winter ◽  
Diurnal Temperature ◽  
Temperature Range ◽  
Enso Events ◽  
Second Mode

The present study applies the empirical orthogonal function (EOF) method to investigate the large-scale pattern and the plausible dynamic processes of the boreal winter diurnal temperature range (DTR) changes in the East Asia (EA)–Australia (AUS) region based on the CRU Time Series version 4.00 (TS4.00) and NCEP–NCAR reanalysis datasets. Results show that the DTR changes during 1948–2015 are dominated by two distinct modes. The first mode, characterized by a same-sign variation over most regions of EA–AUS, represents a declining trend of DTR. The second mode, featuring an opposite-sign variation, represents the interannual variations in DTR. The two modes are both closely associated with the changes in cloud cover (CLT) caused by atmospheric circulation anomalies in EA–AUS. For the trend mode, anomalous southerly and northerly winds over EA and AUS, respectively, bring warm and wet air from low latitudes to EA–AUS, inducing an increase in CLT and thereby reducing DTR in most areas of EA–AUS. The changes of circulation are mainly due to the thermodynamic responses of atmosphere to the nonuniform warming in EA–AUS. In addition, the second mode of DTR is largely forced by the ENSO variability. The weakened Walker circulation associated with warm ENSO events triggers a pair of anomalous low-level anticyclones (south and north of the equator) over the western Pacific. The AUS region is under control of the southern anticyclone, thereby reducing the CLT and increasing the DTR in AUS as a result of anomalous descending motion. In contrast, the EA region is controlled by anomalous southerlies to the west of the northern anticyclone. The northward transports of moistures from the warm ocean increase the CLT, reducing DTR in EA.

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