Atmospheric circulation features in the ACCESS model simulations for CMIP5: historical simulation and future projections

2013 ◽  
Vol 63 (1) ◽  
pp. 145-160 ◽  
Author(s):  
H Rashid ◽  
A Hirst ◽  
M Dix
Keyword(s):  
Atmospheric Circulation ◽  
Future Projections ◽  
Model Simulations ◽  
Historical Simulation ◽  
Access Model

scholarly journals ATMOSPHERIC CIRCULATION OF HOT JUPITERS: COUPLED RADIATIVE-DYNAMICAL GENERAL CIRCULATION MODEL SIMULATIONS OF HD 189733b and HD 209458b

2009 ◽  
Vol 699 (1) ◽  
pp. 564-584 ◽  
Author(s):  
Adam P. Showman ◽  
Jonathan J. Fortney ◽  
Yuan Lian ◽  
Mark S. Marley ◽  
Richard S. Freedman ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Model Simulations ◽  
Hot Jupiters

scholarly journals The influence of atmospheric circulation on the mid-Holocene climate of Europe: a data–model comparison

2014 ◽  
Vol 10 (5) ◽  
pp. 1925-1938 ◽  
Author(s):  
A. Mauri ◽  
B. A. S. Davis ◽  
P. M. Collins ◽  
J. O. Kaplan
Keyword(s):  
Climate Change ◽  
Atmospheric Circulation ◽  
Data Model ◽  
Atmospheric Dynamics ◽  
Future Climate Change ◽  
Seasonal Temperature ◽  
Holocene Climate ◽  
Model Simulations ◽  
Recent Climate

Abstract. The atmospheric circulation is a key area of uncertainty in climate model simulations of future climate change, especially in mid-latitude regions such as Europe where atmospheric dynamics have a significant role in climate variability. It has been proposed that the mid-Holocene was characterized in Europe by a stronger westerly circulation in winter comparable with a more positive AO/NAO, and a weaker westerly circulation in summer caused by anti-cyclonic blocking near Scandinavia. Model simulations indicate at best only a weakly positive AO/NAO, whilst changes in summer atmospheric circulation have not been widely investigated. Here we use a new pollen-based reconstruction of European mid-Holocene climate to investigate the role of atmospheric circulation in explaining the spatial pattern of seasonal temperature and precipitation anomalies. We find that the footprint of the anomalies is entirely consistent with those from modern analogue atmospheric circulation patterns associated with a strong westerly circulation in winter (positive AO/NAO) and a weak westerly circulation in summer associated with anti-cyclonic blocking (positive SCAND). We find little agreement between the reconstructed anomalies and those from 14 GCMs that performed mid-Holocene experiments as part of the PMIP3/CMIP5 project, which show a much greater sensitivity to top-of-the-atmosphere changes in solar insolation. Our findings are consistent with data–model comparisons on contemporary timescales that indicate that models underestimate the role of atmospheric circulation in recent climate change, whilst also highlighting the importance of atmospheric dynamics in explaining interglacial warming.

Recent atmospheric circulation trends: two major flaws in reanalyses and in climate models

2020 ◽  
Author(s):  
Rei Chemke ◽  
Lorenzo Polvani
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Heat Fluxes ◽  
Hadley Cell ◽  
Polar Regions ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Eddy Heat Flux

<p>The weakening of the Hadley cell and of the midlatitude eddy heat fluxes are two of the most robust responses of the atmospheric circulation to increasing concentrations of greenhouse gases.  These changes have important global climatic impacts, as the large-scale circulation acts to transfer heat and moisture from the tropics to polar regions.  Here, we examine Hadley cell and eddy heat flux trends in recent decades: contrasting model simulations with reanalyses, we uncover two important flaws -- one in the reanalyses and other in the model simulations -- that have, to date, gone largely unnoticed.<br><br>First, we find that while climate models simulate a weakening of the Hadley cell over the past four decades, most atmospheric reanalyses indicate a considerable strengthening.  Interestingly, that discrepancy does not stem from biases in climate models, but appears to be related to artifacts in the representation of latent heating in the reanalyses.  This suggests that when dealing with the divergent part of the large-scale circulation, reanalyses may be fundamentally unreliable for the calculation of trends, even for trends spanning several decades.<br><br>Second, we examine recent trends in eddy heat fluxes at midlatitudes, which are directly linked the equator-to-pole temperature gradient.  In the Northern Hemisphere models and reanalyses are in good agreement. In the Southern Hemisphere, however, models show a weakening while reanalyses indicate a robust strengthening.  In this case, the flaw is found to be with the climate models, which are unable to simulate the observed multidecadal cooling of the Southern Ocean at high-latitudes, and the accompanying increase in sea-ice.  While the biases in modeled Antarctic sea ice trends have been widely reported, our results demonstrates that such biases have important implications well beyond the high Southern latitudes, as they impact the equator-to-pole temperature and, as a consequence, the midlatitude atmospheric circulation.</p>

A comparison of Arctic and Antarctic climate change, present and future

2009 ◽  
Vol 21 (3) ◽  
pp. 179-188 ◽  
Author(s):  
John E. Walsh
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Low Frequency ◽  
Southern Annular Mode ◽  
The Arctic ◽  
Polar Regions ◽  
Apparent Paradox ◽  
Late 20Th Century ◽  
Model Simulations ◽  
The Antarctic

AbstractOngoing climate variations in the Arctic and Antarctic pose an apparent paradox. In contrast to the large warming and loss of sea ice in the Arctic in recent decades, Antarctic temperatures and sea ice show little change except for the Antarctic Peninsula. However, model simulations indicate that the Arctic changes have been shaped largely by low-frequency variations of the atmospheric circulation, superimposed on a greenhouse warming that is apparent in model simulations when ensemble averages smooth out the circulation-driven variability of the late 20th century. By contrast, the Antarctic changes of recent decades appear to be shaped by ozone depletion and an associated strengthening of the southern annular mode of the atmospheric circulation. While the signature of greenhouse-driven change is projected to emerge from the natural variability during the present century, the emergence of a statistically significant greenhouse signal may be slower than in other regions. Models suggest that feedbacks from retreating sea ice will make autumn and winter the seasons of the earliest emergence of the greenhouse signal in both Polar Regions. Priorities for enhanced robustness of the Antarctic climate simulations are the inclusion of ozone chemistry and the realistic simulation of water vapour over the Antarctic Ice Sheet.

scholarly journals Brief communication: Impact of the recent atmospheric circulation change in summer on the future surface mass balance of the Greenland ice sheet

2018 ◽  
Author(s):  
Alison Delhasse ◽  
Xavier Fettweis ◽  
Christoph Kittel ◽  
Charles Amory ◽  
Cécile Agosta
Keyword(s):  
Mass Balance ◽  
Atmospheric Circulation ◽  
Temperature Increase ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Future Projections ◽  
Surface Mass ◽  
Circulation Change ◽  
Atmospheric Circulation Change

Abstract. Since the 2000's, a change in the atmospheric circulation over North Atlantic has favored warmer and sunnier weather conditions over the Greenland Ice sheet (GrIS) in summer enhancing the melt increase. This circulation change is not represented by General Circulation Models (GCMs) of the 5th Coupled Model Intercomparison Project (CMIP5) which do not predict any circulation change for the next century over the Atlantic. The goal of this study is to evaluate the impact of an atmospheric circulation change (as currently observed) in a warmer climate on future projections of the GrIS surface mass balance (SMB). We compare GrIS SMB estimates from the regional climate model MAR forced by warmer reanalysis (ERA-Interim with a temperature correction of +1 °C, +1.5 °C and +2 °C at the MAR lateral boundaries) over 1980–2016 to future projections of GrIS SMB from MAR simulations forced with three GCMs over a future period for which a similar temperature increase of +1 °C, +1.5 °C and +2 °C is projected by the GCMs in comparison to 1980–1999. Mean SMB anomalies produced with warmer reanalysis over the climatologically stable period 1980–1999 is similar to those produced with MAR forced with GCMs over future periods characterized by a similar warming over Greenland. However, over the two last decades (2000–2016) when a circulation change has been observed in summer, MAR forced with warmer reanalysis suggests that the SMB decrease could be amplified by a factor of two if such atmospheric conditions will persist compared to future projections forced by GCMs for the same temperature increase but without any circulation change.

scholarly journals Understanding nitrate formation in a world with less sulfate

2018 ◽  
Author(s):  
Petros Vasilakos ◽  
Armistead Russell ◽  
Rodney Weber ◽  
Athanasios Nenes
Keyword(s):  
Model Evaluation ◽  
Positive Trend ◽  
Positive Bias ◽  
So2 Emissions ◽  
So2 Emission ◽  
Future Projections ◽  
Model Simulations ◽  
Southeastern Us ◽  
Fine Mode ◽  
Different Response

Abstract. SO2 emission controls, combined with modestly increasing ammonia, have been thought to generate aerosol of significantly reduced acidity where sulfate is partially substituted by nitrate. However, neither expectation agrees with decadal observations in the Southeastern US, suggesting that a fundamentally different response of aerosol pH to emissions changes is occurring. We postulate this ``nitrate substitution paradox'' arises from a positive bias in aerosol pH in model simulations, exacerbated by reductions in SO2 emissions. This bias can elevate pH to where nitrate partitioning is readily promoted, leading to behavior consistent with ``nitrate substitution''. CMAQ simulations are used to investigate this hypothesis; predictions of PM2.5 pH for 2001 emissions compare favorably with observations; for 2011 emissions however, predicted pH increases by 1 unit, presenting a positive trend not seen in the observations. Non-volatile cations (K+, Na+, Ca+2 and Mg+2) in the fine mode are found responsible for most of this trend. pH biases of 1 unit can induce a nitrate bias of 1–2 μg m-3 which may further increase in future projections, reaffirming an otherwise incorrect expectation of “nitrate substitution”. Evaluation of predicted aerosol pH against thermodynamic analysis of observations is therefore a critically important, but overlooked, aspect of model evaluation for robust emissions policy.

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