Trends and projections of Southern Hemisphere baroclinicity: the role of external forcing and impact on Australian rainfall

Frederiksen, Carsten S.; Frederiksen, Jørgen S.; Sisson, Janice M.; Osbrough, Stacey Lee

doi:10.1007/s00382-016-3263-8

Cited by 15 publications

(22 citation statements)

References 42 publications

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“…The dynamical indices that we have used for this study are based on the NCEP-NCAR reanalysis (NNR) data (Kalnay et al, 1996). There is generally close correspondence between the major global atmospheric circulation data sets that, like the NNR data, use full data assimilation throughout the atmosphere (Frederiksen and Frederiksen, 2007;Frederiksen et al, 2017a;Rikus, 2018). We have confirmed this by recalculating our dynamical indices and main correlations with C mlo−cgo based on the NASA Modern Era Retrospectiveanalysis for Research and Applications (MERRA) data (Rienecker et al, 2011).…”

Section: The Role Of the Hadley Circulation In Mean Ih Co 2 Transportmentioning

confidence: 58%

“…6; Frederiksen and Webster, 1988), resulting in intermittent changes in the mixing of trace gases. This effect may not be adequately represented in the parameterizations (Frederiksen et al, 2017b) used in atmospheric circulation and transport models. Model determinations of short-term variations in the Hadley circulation exchange are also susceptible to uncertainties in representations of the equatorial convective dynamics (Lintner et al, 2004).…”

Section: Discussionmentioning

confidence: 99%

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Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

Frederiksen

Francey

2018

Atmos. Chem. Phys.

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Abstract. The extreme El Niño of 2015 and 2016 coincided with record global warming and unprecedented strength of the Hadley circulation with significant impact on mean interhemispheric (IH) transport of CO2. The relative roles of eddy transport and mean advective transport on interannual differences in CO2 concentration between Mauna Loa and Cape Grim (Cmlo−cgo), from 1992 through to 2016, are explored. Eddy transport processes occur mainly in boreal winter–spring when Cmlo−cgo is large; an important component is due to Rossby wave generation by the Himalayas and propagation through the equatorial Pacific westerly duct generating and transmitting turbulent kinetic energy. Mean transport occurs mainly in boreal summer–autumn and varies with the strength of the Hadley circulation. The timing of annual changes in Cmlo−cgo is found to coincide well with dynamical indices that we introduce to characterize the transport. During the unrivalled 2009–2010 step in Cmlo−cgo, the effects of the eddy and mean transport were reinforced. In contrast, for the 2015 to 2016 change in Cmlo−cgo, the mean transport counteracts the eddy transport and the record strength of the Hadley circulation determines the annual IH CO2 difference. The interaction of increasing global warming and extreme El Niños may have important implications for altering the balance between eddy and mean IH CO2 transfer. The effects of interannual changes in mean and eddy transport on interhemispheric gradients in other trace gases are also examined.

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Section: The Role Of the Hadley Circulation In Mean Ih Co 2 Transportmentioning

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

Frederiksen

Francey

2018

Atmos. Chem. Phys.

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“…Variability in synoptic-scale processes and associated precipitation in the midlatitudes have implications for water security over southern Australia. For example, both the declining trend in precipitation over southwestern Australia since the late 1970s (Hope et al 2006;Frederiksen 2007) andthe Millennium Drought (1997 to ;2010) in southeast Australia (Murphy and Timbal 2008;Verdon-Kidd and Kiem 2009;Kiem and Verdon-Kidd 2010;Verdon-Kidd et al 2014) have been linked to decreased baroclinicity in the midlatitudes (Frederiksen et al 2017). This has been associated with a southward shift in the midlatitude storm tracks and subtropical ridge (Frederiksen and Frederiksen 2007;Rudeva et al 2019) and poleward expansion of the SH Hadley cell (Nguyen et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Links between Large-Scale Modes of Climate Variability and Synoptic Weather Patterns in the Southern Indian Ocean

et al. 2021

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Weather systems in the southern Indian Ocean (SIO) drive synoptic-scale precipitation variability in East Antarctica and southern Australia. Improved understanding of these dynamical linkages is beneficial to diagnose long-term climate changes from climate proxy records as well as informing regional weather and climate forecasts. Self-organising maps (SOMs) are used to group daily 500hPa geopotential height (z500; ERA-Interim) anomalies into nine regional synoptic types based on their dominant patterns over the SIO (30°-75°S, 40°-180°E) from January 1979-October 2018. The pattern anomalies represented include four meridional, three mixed meridional/zonal, one zonal and one transitional node. The frequency of the meridional nodes shows limited association with the phase of the Southern Annular Mode (SAM), especially during SON. The zonal and mixed patterns were nevertheless strongly and significantly correlated with SAM, although the regional synoptic representation of SAM+ conditions was not zonally symmetric and was represented by three separate nodes. We recommend consideration of how different synoptic conditions vary the atmospheric representation of SAM+ in any given season in the SIO. These different types of SAM+ mean a hemispheric index fails to capture the regional variability in surface weather conditions that is primarily driven by the synoptic variability rather than the absolute polarity of the SAM.

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“…While Southern Australia has undergone noteworthy reductions in rainfall since the 1970s, due largely to a reduction in storminess and, particularly, in the intensity of fast-growing extratropical storms (FF05; FF07; FF11; Hope, 2006;Alexander et al, 2011;Risbey et al, 2013;Frederiksen et al, 2017;OF21), Northern Australia (Fig. 1) has seen increased precipitation (Frederiksen and Grainger, 2015;Dey et al, 2019; Bureau of Meteorology and CSIRO, 2020 and references therein).…”

Section: Northern Australian Rainfall and Rainfall Extremesmentioning

confidence: 99%

Regime transitions of Australian climate and climate extremes

Frederiksen

Osbrough

2021

Preprint

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Abstract. Systematic changes, since the beginning of the 20th century, in average and extreme Australian rainfall and temperatures indicate that Southern Australian climate has undergone regime transitions into a drier and warmer state. South-west Western Australia (SWWA) experienced the most dramatic drying trend with average streamflow into Perth dams, in the last decade, just 20 % of that before the 1960s and extreme, decile 10, rainfall reduced to near zero. In south-eastern Australia (SEA) systematic decreases in average and extreme cool season rainfall became evident in the late 1990s with a halving of the area experiencing average decile 10 rainfall in the early 21st century compared with that for the 20th century. The shift in annual surface temperatures over SWWA and SEA, and indeed for Australia as a whole, has occurred primarily over the last 20 years with the percentage area experiencing extreme maximum temperatures in decile 10 increasing to an average of more than 45 % since the start of the 21st century compared with less than 3 % for the 20th century mean. Average maximum temperatures have also increased by circa 1 °C for SWWA and SEA over the last 20 years. The climate changes are associated with atmospheric circulation shifts and are indicative of second order regime transitions, apart from extreme temperatures for which the dramatic increases are suggestive of first order transitions.

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Trends and projections of Southern Hemisphere baroclinicity: the role of external forcing and impact on Australian rainfall

Cited by 15 publications

References 42 publications

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

Links between Large-Scale Modes of Climate Variability and Synoptic Weather Patterns in the Southern Indian Ocean

Regime transitions of Australian climate and climate extremes

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Trends and projections of Southern Hemisphere baroclinicity: the role of external forcing and impact on Australian rainfall

Cited by 15 publications

References 42 publications

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO&lt;sub&gt;2&lt;/sub&gt; interhemispheric difference

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO&lt;sub&gt;2&lt;/sub&gt; interhemispheric difference

Links between Large-Scale Modes of Climate Variability and Synoptic Weather Patterns in the Southern Indian Ocean

Regime transitions of Australian climate and climate extremes

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Product

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Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference