scholarly journals Constraints on Southern Australian Rainfall Change Based on Atmospheric Circulation in CMIP5 Simulations

2017 ◽  
Vol 30 (1) ◽  
pp. 225-242 ◽  
Author(s):  
Michael R. Grose ◽  
James S. Risbey ◽  
Aurel F. Moise ◽  
Stacey Osbrough ◽  
Craig Heady ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Storm Track ◽  
Polar Front ◽  
Rainfall Trends ◽  
Circulation Change ◽  
Eastern Australia ◽  
Projected Change ◽  
Rainfall Reduction ◽  
Rainfall Projection ◽  
Australian Rainfall

Atmospheric circulation change is likely to be the dominant driver of multidecadal rainfall trends in the midlatitudes with climate change this century. This study examines circulation features relevant to southern Australian rainfall in January and July and explores emergent constraints suggested by the intermodel spread and their impact on the resulting rainfall projection in the CMIP5 ensemble. The authors find relationships between models’ bias and projected change for four features in July, each with suggestions for constraining forced change. The features are the strength of the subtropical jet over Australia, the frequency of blocked days in eastern Australia, the longitude of the peak blocking frequency east of Australia, and the latitude of the storm track within the polar front branch of the split jet. Rejecting models where the bias suggests either the direction or magnitude of change in the features is implausible produces a constraint on the projected rainfall reduction for southern Australia. For RCP8.5 by the end of the century the constrained projections are for a reduction of at least 5% in July (with models showing increase or little change being rejected). Rejecting these models in the January projections, with the assumption the bias affects the entire simulation, leads to a rejection of wet and dry outliers.

Alpine Evidence for Atmospheric Circulation Patterns in Europe during the Last Glacial Maximum

2000 ◽  
Vol 54 (3) ◽  
pp. 295-308 ◽  
Author(s):  
Duri Florineth ◽  
Christian Schlüchter
Keyword(s):  
Atmospheric Circulation ◽  
Last Glacial Maximum ◽  
Storm Track ◽  
Polar Front ◽  
Glacial Maximum ◽  
Geological Mapping ◽  
Last Glacial ◽  
The Alps ◽  
The Last Glacial Maximum ◽  
The Last Glacial

The configuration of Alpine accumulation areas during the last glacial maximum (LGM) has been reconstructed using glacial–geological mapping. The results indicate that the LGM ice surface consisted of at least three major ice domes, all located south of the principal weather divide of the Alps. This implies that the buildup of the main Alpine ice cover during oxygen isotope stage (OIS) 2 was related to precipitation by dominant southerly atmospheric circulation, in contrast to today's prevalent westerly airflow. Such a reorganization of the atmospheric circulation is consistent with a southward displacement of the Oceanic Polar Front in the North Atlantic and of the associated storm track to the south of the Alps. These results, combined with additional paleoclimate records from western and southern Europe, allow an interpretation of the asynchronous evolution of the different European ice caps during the last glaciation. δ18O stages (OIS) 4 and 3 were characterized by location of the Polar Front north of 46°N (Gulf of Biscay). This affected prevailing westerly circulation and thus, ice buildup in western Scandinavia, the Pyrénées, Vosges, and northern Alps. At the LGM, however, the Polar Front lay at ∼44°N, causing dominating southerly circulation and reduced precipitation in central and northern Europe.

scholarly journals Observed Storm Track Dynamics in Drake Passage

2019 ◽  
Vol 49 (3) ◽  
pp. 867-884 ◽  
Author(s):  
Annie Foppert
Keyword(s):  
Mean Field ◽  
Storm Track ◽  
Drake Passage ◽  
Polar Front ◽  
Mean Flow ◽  
Track Dynamics ◽  
Flow Interactions ◽  
Circumpolar Current ◽  
Eddy Potential Energy ◽  
Shackleton Fracture Zone

AbstractThe dynamics of an oceanic storm track—where energy and enstrophy transfer between the mean flow and eddies—are investigated using observations from an eddy-rich region of the Antarctic Circumpolar Current downstream of the Shackleton Fracture Zone (SFZ) in Drake Passage. Four years of measurements by an array of current- and pressure-recording inverted echo sounders deployed between November 2007 and November 2011 are used to diagnose eddy–mean flow interactions and provide insight into physical mechanisms for these transfers. Averaged within the upper to mid-water column (400–1000-m depth) and over the 4-yr-record mean field, eddy potential energy is highest in the western part of the storm track and maximum eddy kinetic energy occurs farther away from the SFZ, shifting the proportion of eddy energies from to about 1 along the storm track. There are enhanced mean 3D wave activity fluxes immediately downstream of SFZ with strong horizontal flux vectors emanating northeast from this region. Similar patterns across composites of Polar Front and Subantarctic Front meander intrusions suggest the dynamics are set more so by the presence of the SFZ than by the eddy’s sign. A case study showing the evolution of a single eddy event, from 15 to 23 July 2010, highlights the storm-track dynamics in a series of snapshots. Consistently, explaining the eddy energetics pattern requires both horizontal and vertical components of W, implying the importance of barotropic and baroclinic processes and instabilities in controlling storm-track dynamics in Drake Passage.

scholarly journals Twentieth Century Winter Changes in Southern Hemisphere Synoptic Weather Modes

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Jorgen S. Frederiksen ◽  
Carsten S. Frederiksen
Keyword(s):  
Growth Rate ◽  
Southern Hemisphere ◽  
Western Australia ◽  
Three Dimensional ◽  
Storm Track ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Winter Rainfall ◽  
Cloud Band ◽  
Eastern Australia

During the last sixty years, there have been large changes in the southern hemisphere winter circulation and reductions in rainfall particularly in the southern Australian region. Here we examine the corresponding changes in dynamical modes of variability ranging from storm tracks, onset-of-blocking modes, northwest cloud-band disturbances, Antarctic low-frequency modes, intraseasonal oscillations, and African easterly waves. Our study is performed using a global two-level primitive equation instability-model with reanalyzed observed July three-dimensional basic states for the periods 1949–1968, 1975–1994, and 1997–2006. We relate the reduction in the winter rainfall in the southwest of Western Australia since the mid-1970s and in south-eastern Australia since the mid-1990s to changes in growth rate and structures of leading storm track and blocking modes. We find that cyclogenesis and onset-of-blocking modes growing on the subtropical jet have significantly reduced growth rates in the latter periods. On the other hand there is a significant increase in the growth rate of northwest cloud-band modes and intraseasonal oscillation disturbances that cross Australia and are shown to be related to recent positive trends in winter rainfall over northwest Western Australia and central Australia, in general. The implications of our findings are discussed.

scholarly journals Anomalous mid-twentieth century atmospheric circulation change over the South Atlantic compared to the last 6000 years

2016 ◽  
Vol 11 (6) ◽  
pp. 064009 ◽  
Author(s):  
Chris S M Turney ◽  
Richard T Jones ◽  
David Lister ◽  
Phil Jones ◽  
Alan N Williams ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Atmospheric Circulation ◽  
South Atlantic ◽  
The South ◽  
Circulation Change ◽  
Atmospheric Circulation Change

scholarly journals Northern Hemispheric Trends of Pressure Indices and Atmospheric Circulation Patterns in Observations, Reconstructions, and Coupled GCM Simulations

2005 ◽  
Vol 18 (19) ◽  
pp. 3968-3982 ◽  
Author(s):  
C. C. Raible ◽  
T. F. Stocker ◽  
M. Yoshimori ◽  
M. Renold ◽  
U. Beyerle ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
General Circulation ◽  
Southern Oscillation ◽  
Storm Track ◽  
General Circulation Models ◽  
Aleutian Low ◽  
Climate Conditions ◽  
Atmospheric Circulation Patterns ◽  
The North ◽  
Decadal Trend

Abstract The decadal trend behavior of the Northern Hemisphere atmospheric circulation is investigated utilizing long-term simulations with different state-of-the-art coupled general circulation models (GCMs) for present-day climate conditions (1990), reconstructions of the past 500 yr, and observations. The multimodel simulations show that strong positive winter North Atlantic Oscillation (NAO) trends are connected with the underlying sea surface temperature (SST) and exhibit an SST tripole trend pattern and a northward shift of the storm-track tail. Strong negative winter trends of the Aleutian low are associated with SST changes in the El Niño–Southern Oscillation (ENSO) region and a westward shift of the storm track in the North Pacific. The observed simultaneous appearance of strong positive NAO and negative Aleutian low trends is very unlikely to occur by chance in the unforced simulations and reconstructions. The positive winter NAO trend of the last 50 yr is not statistically different from the level of internal atmosphere–ocean variability. The unforced simulations also show a strong link between positive SST trends in the ENSO region and negative Aleutian low trends. With much larger observed SST trends in the ENSO region, this suggests that the observed negative Aleutian low trend is possibly influenced by external forcing, for example, global warming, volcanism, and/or solar activity change.

scholarly journals Shorter cyclone clusters modulate changes in European wintertime precipitation extremes

2021 ◽  
Author(s):  
Emanuele Bevacqua ◽  
Giuseppe Zappa ◽  
Theodore G Shepherd
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Climate Models ◽  
Precipitation Extremes ◽  
Southern Europe ◽  
Circulation Change ◽  
The Future ◽  
The Mean ◽  
Future Direction ◽  
Atmospheric Circulation Change

<p>Wintertime extreme precipitation from cyclone clusters, i.e. consecutive cyclones moving across the same region, can lead to flooding and devastating socio-economic impacts in Europe. Previous studies have suggested that the future direction of the changes in these events are uncertain across climate models. By employing an impact-based metric of accumulated precipitation extremes, we show that projections of cyclone clusters are instead broadly robust, i.e. consistent in sign, across models. A novel physical diagnostic shows that accumulated precipitation extremes are projected to grow by only +1.0 %/K on average across Europe, although the mean precipitation per cyclone increases by +4.7 %/K. This results from a decreased number of clustered cyclones, associated with decreased wintertime storminess, the extent of which varies from northern to southern Europe and depends on the future storyline of atmospheric circulation change. Neglecting the changes in the number of clustered cyclones, i.e. assuming that accumulated precipitation extremes would change as the mean precipitation per cyclone, would lead to overestimating the population affected by increased accumulated wintertime precipitation extremes by 130–490 million across Europe.</p>

scholarly journals The relationship between the subtropical ridge and Australian temperatures

2018 ◽  
Vol 68 (1) ◽  
pp. 201
Author(s):  
Acacia Pepler ◽  
Linden Ashcroft ◽  
Blair Trewin
Keyword(s):  
Strong Influence ◽  
Southeast Australia ◽  
Eastern Australia ◽  
Autumn And Winter ◽  
The Relationship ◽  
Subtropical Ridge ◽  
Australian Rainfall

The intensity and latitude of the subtropical ridge over eastern Australia is strongly associated with southeast Australian rainfall, particularly during the cool months of the year. We show that the subtropical ridge also exerts a strong influence on temperatures across much of Australia, with warmer daytime temperatures and more warm extremes across southern Australia when the subtropical ridge is stronger than average, which is largely independent of the relationship between the subtropical ridge and rainfall. A strong subtropical ridge is also linked to warmer than average minimum temperatures over southern Australia throughout much of the year, except from May to August when a strong ridge is associated with cooler mean minimum temperatures and an increased frequency of cool nights. This relationship, and the observed strengthening of the subtropical ridge during autumn and winter in recent decades, can partially explain the weaker warming trends in minimum temperatures in southeast Australia compared to elsewhere in the country over the period 1960-2016.

scholarly journals Development, Amplification, and Decay of Atlantic/European Summer Weather Patterns Linked to Spring North Atlantic Sea Surface Temperatures

2020 ◽  
Vol 33 (14) ◽  
pp. 5939-5951
Author(s):  
Albert Ossó ◽  
Rowan Sutton ◽  
Len Shaffrey ◽  
Buwen Dong
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
North Atlantic Ocean ◽  
Storm Track ◽  
Early Summer ◽  
Specific Pattern ◽  
Sea Surface ◽  
Ocean Atmosphere ◽  
The Relationship

AbstractA recent study identified a relationship between North Atlantic Ocean sea surface temperature (SST) gradients in spring and a specific pattern of atmospheric circulation in the following summer: the summer east Atlantic (SEA) pattern. It was shown that the SEA pattern is closely associated with meridional shifts in the eddy-driven jet in response to anomalous SST gradients. In this study, the physical mechanisms underlying this relationship are investigated further. It is shown that the predictable SEA pattern anomalies appear in June–July and undergo substantial amplification between July and August before decaying in September. The associated SST anomalies also grow in magnitude and spatial extent from June to August. The question of why the predictable atmospheric anomalies should occur in summer is addressed, and three factors are identified. The first is the climatological position of the storm track, which migrates poleward from spring to summer. The second is that the magnitude of interannual SST variability underlying the storm track peaks in summer, both in absolute terms, and relative to the underlying mean SST gradient. The third factor is the most interesting. We identify a positive coupled ocean–atmosphere feedback, which operates in summer and leads to the amplification of both SST and atmospheric circulation anomalies. The extent to which the identified processes are captured in the HadGEM3-GC2 climate model is also assessed. The model is able to capture the relationship between spring North Atlantic SSTs and subsequent ocean–atmosphere conditions in early summer, but the relationship is too weak. The results suggest that the real world might be more predictable than is inferred from the models.

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