Interdecadal changes in Southern Hemisphere winter explosive storms and Southern Australian rainfall

Osbrough, Stacey Lee; Frederiksen, Jørgen S.

doi:10.1007/s00382-021-05633-y

Cited by 9 publications

(40 citation statements)

References 112 publications

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“…Large‐scale conditions (e.g., Osbrough & Frederiksen, 2021) and moisture sources (e.g., Holgate et al., 2020) are often used as a proxy for rainfall in the extratropics. Knowledge of the large‐scale prerequisite conditions for extreme rain events can thus be used to develop statistical downscaling methods (e.g., Rau et al., 2020; Timbal et al., 2008) that seek to predict the occurrence of extreme rain at a regional scale in global models without using global model precipitation directly.…”

Section: Introductionmentioning

confidence: 99%

Fundamental Ingredients of Australian Rainfall Extremes

2022

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Satellite observations of Australian rainfall are used with reanalysis fields to identify the fundamental ingredients that distinguish extreme rain days from non‐extreme rain days. We analyze regions from the tropics to the mid‐latitudes, seeking to address whether regions with very different large‐scale circulations have common factors required for extreme rainfall, and if so, what synoptic conditions lead to the development of the extremes. In all regions, extreme rain days occur in locally strong ascent, high moisture, and an atmosphere closer to saturation throughout the depth of the free troposphere than on weaker intensity rain days, although the synoptic processes leading to the development of these local conditions vary regionally. The concentration of moisture over several days preceding an extreme is important to the development of the extreme. We show that the local values of precipitable water and mid‐level ascent can indicate whether a rain day will be extreme. The analysis uses 20 years of satellite‐derived rain estimates covering the period 1998–2017, averaged daily and over 100 × 100 km2 areas centered on the Australian cities of Darwin (tropical), Brisbane (subtropical), and Melbourne (mid‐latitude). The daily mean rainfalls are ranked by intensity, and the top 100 days in each region are selected as extremes. The large‐scale conditions of these extreme rain days are taken from reanalysis and compared against those of the median and low intensity rain days in each region.

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Section: Introductionmentioning

confidence: 99%

Fundamental Ingredients of Australian Rainfall Extremes

2022

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“…In contrast to the observed strengthening of the subtropical ridge, there have been no robust trends identified in the Southern Hemisphere subtropical jet (Maher et al, 2019). However, a weakening of 700 hPa zonal winds between 20-35 • S during July was also identified for southeast and southwest Australia by Osbrough and Frederiksen (2021), which they linked to decreases in July baroclinicity and rainfall in southern Australia. Our analysis also indicates no change in the latitude of the subtropical jet (not shown) but a possible weakening of its intensity on front days in eastern Australia, although the average change in zonal wind speed is smaller at 300 hPa than it is at 700 hPa.…”

Section: Discussionmentioning

confidence: 78%

Anomalous subtropical zonal winds drive decreases in southern Australian frontal rain

Pepler

Rudeva²

2023

Weather Clim. Dynam.

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Abstract. Cold fronts make a significant contribution to cool season rainfall in the extratropics and subtropics. In many regions of the Southern Hemisphere the amount of frontal rainfall has declined in recent decades, but there has been no change in frontal frequency. We show that for southeast Australia this contradiction cannot be explained by changes in frontal intensity or moisture at the latitudes of interest. Rather, declining frontal rainfall in southeast Australia is associated with weakening of the subtropical westerlies in the mid-troposphere, which is part of a hemispheric pattern of wind anomalies that modify the extratropical zonal wave 3. Fronts that generate rainfall are associated with strong westerlies that penetrate well into the subtropics, and the observed decrease in frontal rainfall in southern Australia can be linked to a decrease in the frequency of fronts with strong westerlies at 25∘ S.

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“…In constrast to the observed strengthening of the subtropical ridge, there have been no robust trends 415 identified in the southern hemisphere subtropical jet (Maher et al, 2019). However, a weakening of 700hPa zonal winds between 20-35°S during July was also identified for southeast and southwest Australia by Osbrough & Frederiksen (2021), which they linked to decreases in July baroclinicity and rainfall in southern Australia. Our analysis also indicates no change in the latitude of the subtropical jet (not shown), but a possible weakening in its intensity on front days in eastern Australia, although the average change in zonal wind speed is smaller at 300hPa than it is at 700hPa.…”

Section: Discussion and Conclusion 380mentioning

confidence: 92%

Anomalous subtropical zonal winds drive decreases in southern Australian frontal rain

Pepler

Rudeva

2022

Preprint

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Abstract. Cold fronts make a significant contribution to cool season rainfall in the extratropics and subtropics. In many regions of the Southern Hemisphere the amount of frontal rainfall has declined in recent decades, but there has been no change in frontal frequency. We show that for southeast Australia this contradiction cannot be explained by changes in frontal intensity or moisture at the latitudes of interest. Rather, declining frontal rainfall in southeast Australia is associated with weakening of the subtropical westerlies in the mid troposphere, which is part of a hemispheric pattern of wind anomalies that modifies the extratropical zonal wave 3. Fronts that generate rainfall are associated with strong westerlies that penetrate well into the subtropics, and the observed decrease in frontal rainfall in southern Australia can be linked to a decrease in the frequency of fronts with strong westerlies at 25° S.

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Interdecadal changes in Southern Hemisphere winter explosive storms and Southern Australian rainfall

Cited by 9 publications

References 112 publications

Fundamental Ingredients of Australian Rainfall Extremes

Fundamental Ingredients of Australian Rainfall Extremes

Anomalous subtropical zonal winds drive decreases in southern Australian frontal rain

Anomalous subtropical zonal winds drive decreases in southern Australian frontal rain

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