A vertical wind structure that leads to extreme rainfall and major flooding in southeast Australia

Callaghan, Jeff; Power, Scott B.

doi:10.22499/3.6604.002

Cited by 14 publications

(14 citation statements)

References 15 publications

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“…At the latter two stations, upper-only cyclone collectively explain approximately 30% of 99th percentile days. This likely reflects the important role of 500 hPa geostrophic winds in the generation of heavy rainfall on days with prevailing onshore flow in these regions (Callaghan and Power 2017).…”

Section: Association Of Cyclones With East Coast Heavy Rainmentioning

confidence: 96%

Intense east coast lows and associated rainfall in eastern Australia

Pepler

Dowdy

2021

J. South. Hemisph. Earth Syst. Sci.

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East coast lows (ECLs) are low pressure systems that occur near the east coast of Australia. But not all lows cause the same level of impact, and a small proportion of ECLs are responsible for more than half of all days with widespread rainfall above 50mm in this region. In this study, we combine analyses of cyclones at both the surface and 500hPa levels to assess the locations of cyclones responsible for widespread heavy rainfall on the east coast. We found that the majority of days with widespread totals above 100mm on the east coast occur when a low at 500hPa over inland southeast Australia coincides with a surface low located more directly over the east coast. Such events occur on about 15 days per year but are responsible for more than 50% of days with widespread heavy rainfall on the eastern seaboard of Australia. We also found that extreme rainfall was most likely when both the surface and upper cyclones were very strong, when measured using the maximum Laplacian of pressure/height. The seasonal frequency of cyclones at the surface and 500hPa were found to be only weakly correlated with each other and often had opposing relationships (albeit weak in magnitude) with both global climate drivers and indices of local circulation variability. Trends in cyclone frequency were weak over the period 1979–2019, but there was a small decline in the frequency of deep cyclone days, which was statistically significant in some parts of the southeast. Understanding which ECLs are associated with heavy rainfall will help us to better identify how future climate change will influence ECL impacts.

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Section: Association Of Cyclones With East Coast Heavy Rainmentioning

confidence: 96%

Intense east coast lows and associated rainfall in eastern Australia

Pepler

Dowdy

2021

J. South. Hemisph. Earth Syst. Sci.

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“…For the TC Dora (2007) case, Leroux et al (2013) showed that PV injection at mid-levels from a mid-latitude cut-off low or PV coherent structure could help rapid intensification by increasing convection on the downshear side and sustaining the formation of an eyewall replacement cycle (PV budget analysis). They also noticed that the general 850-200 hPa shear was not indicative of rapid intensification and that it would be more appropriate to use the 850-500 hPa shear in some cases, which was confirmed in the recent study of Colomb et al (2019).…”

Section: Introductionmentioning

confidence: 72%

“…The centre of ex-TC Oswald was located just to the north-west of Townsville with radar indicating moderate patchy rain along the coast to the south, where the 700-hPa flow was directed from the warm side of the 850-500-hPa vertical wind shear to the cold side of it (Fig. 7b), implying WAA or moist isentropic ascent and heavy rainfall (Callaghan 2017a(Callaghan , 2017bCallaghan and Power 2016;Callaghan and Tory 2014;Tory 2014). A nice illustration is to look at Brisbane airport at 2300 UTC 26 January when storm force winds are turning anticyclonically with height from 850 to 500 hPa (Fig.…”

Section: Thermodynamic and Kinematic Structures Of Ex-tropical Cyclonmentioning

confidence: 99%

Environmental interactions during the extreme rain event associated with ex-tropical cyclone Oswald (2013)

Leroux

Nguyen-Hankinson

Davidson

et al. 2019

JSHESS

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Tropical cyclone (TC) Oswald made landfall over north-east Australia as a minimal or Category 1 TC on the Australian scale on 21 January 2013. As it moved southward, it intensified over land and produced extreme rainfall for nearly 7 days. Tornadoes were reported and confirmed. Tragically, seven people died and insurance estimates were ~$1 billion. It is demonstrated that the event was associated with an interaction between the ex-Oswald circulation and an amplifying Rossby wave, which propagated north-eastward from high latitudes. Diagnoses showed that as the wave amplified and broke, a potential vorticity (PV) anomaly (PVA) extended to mid-levels, moved equatorward, merged with or axisymmetrised the ex-Oswald circulation through mid-levels. Backward trajectories from locations regularly scattered within the mid-level circulation illustrated that the storm transitioned from an isolated vortex into a circulation which was strongly influenced by its environment for at least 5 days. During this interaction, PV was advected from the environment towards the storm through mid-levels. The heavy rain coincided with the commencement and maintenance of this PV injection. The PV injection is quantified and shown to be consistent with PV advection by the mean radial flow. In addition, eddy angular momentum convergence in the mid- to upper levels coincided with an intensification of the circulation through this region. This was first related to outward transport of anticyclonic momentum by the asymmetric outflow at upper levels, followed by inward transport of cyclonic momentum by the asymmetric inflow. It is shown that the environmental interaction had an impact on vortex structure changes, rainfall and tornado development. We propose that the environmental processes influenced the ascent within the storm (1) via differential vorticity advection and baroclinic forcing, as the mid- to upper level PVA approached the circulation and (2) by low- to mid-level warm air advection.

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“…Goff and Hanson (2012) found this to be the case in the middle latitudes of the US. Previous studies (Bonell et al 2005;Bonell and Callaghan 2008;Callaghan and Tory 2014;Tory 2014;Callaghan and Power 2016) examined winds associated with extreme rainfall in both the tropics and the mid-latitudes of Australia. Further studies (Callaghan 2017a(Callaghan , 2019 found this to apply in many cases around the globe.…”

Section: Mechanisms Which Produce Extreme Rainfallmentioning

confidence: 99%

“…In every case (i) atmospheric moisture content was high and (ii) the low-level winds were onshore, and in almost every case (iii) the wind-direction turned anticyclonically with increasing height up to 500 hPa. Further details of this wind structure can be found in Callaghan and Power (2016).…”

Section: Mechanisms Which Produce Extreme Rainfallmentioning

confidence: 99%

Weather systems and extreme rainfall generation in the 2019 north Queensland floods compared with historical north Queensland record floods

Callaghan¹

2021

J. South. Hemisph. Earth Syst. Sci.

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Earlier papers have addressed floods from warm-air advection (WAA) in southeast Australia and around the globe, and extreme rainfall in US hurricanes and Australian tropical cyclones (TCs). This is the first paper to address the WAA phenomena in causing monsoon and TC floods and in TC-like systems which develop over the interior of northern Australia. The inland events help explain Australia’s worst tropical flooding disaster in 1916. A disastrous series of floods during late January and early February 2019 caused widespread damage in tropical north Queensland both in inland regions and along the coast. This occurred when some large-scale climate influences, including the sea surface temperatures suggested conditions would not lead to major flooding. Therefore, it is important to focus on the weather systems to understand the processes that resulted in the extreme rainfall responsible for the flooding. The structure of weather systems in most areas involved a pattern in which the winds turned in an anticyclonic sense as they ascended from the low to middle levels of the atmosphere (often referred to as WAA) which was maintained over large areas for 11 days. HYSPLIT air parcel trajectory observations were employed to confirm these ascent analyses. Examination of a period during which the heaviest rain was reported and compared with climatology showed a much stronger monsoon circulation, widespread WAA through tropical Queensland where normally its descending equivalent of cold-air advection is found, and higher mean sea level pressures along the south Queensland coast. The monsoon low was located between strong deep monsoon westerlies to the north and strong deep easterlies to the south which ensured its slow movement. This non-TC event produced heavy inland rainfall. Extreme inland rainfall is rare in this region. Dare et al. (2012), using data from 1969/70 to 2009/10, showed that over north Queensland non-TC events produced a large percentage of the total rainfall. The vertical structure associated with one of the earlier events that occurred in 2008 had sufficient data to detect strong and widespread WAA overlying an onshore moist tropical airstream. This appears to have played a crucial role in such extreme rainfall extending well inland and perhaps gives insight to the cause of a 1916 flooding disaster at Clermont which claimed around 70 lives. Several other events over the inland Tropics with strong WAA also help explain the 1916 disaster.

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A vertical wind structure that leads to extreme rainfall and major flooding in southeast Australia

Cited by 14 publications

References 15 publications

Intense east coast lows and associated rainfall in eastern Australia

Intense east coast lows and associated rainfall in eastern Australia

Environmental interactions during the extreme rain event associated with ex-tropical cyclone Oswald (2013)

Weather systems and extreme rainfall generation in the 2019 north Queensland floods compared with historical north Queensland record floods

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