School of Earth Sciences - Research Publications

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    Sub-synoptic scale features associated with extreme surface gusts during the South Australia Storm of September 2016-Part I: characteristics of the event
    Earl, N ; Simmonds, I ; Rudeva, I (WILEY, 2019-08)
    Abstract Winds are one of the major meteorological contributors to deaths, damage and insured losses in Australia. A ‘freak storm’ hit the state of South Australia on 28 September 2016, causing state‐wide blackouts and leaving 1.7 million people without power. In the first part of this two‐part study, we analyse this event and find that it was indeed extreme, deepening more explosively than all but two Adelaide‐affecting extratropical cyclones over the past 37 years and exhibiting the lowest central pressure. This generated hurricane force winds, with the central South Australia site of Neptune Island recording a gust of over 120kmh−1. We show that this storm potentially contained a sting jet. Such jets are well known as a cause of major damage across Europe, and this is the first study which investigates whether a sting jet can be produced over Australia. The main deepening of the system occurred over the Great Australian Bight, so if a sting jet did form and make it to the surface, it was not the cause of the state‐wide damage. However, the cyclone did contain numerous extreme gust‐producing mesoscale features, as explored in part II of this paper (Earl and Simmons, 2018).
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    Sub synoptic scale features of the South Australia Storm of September 2016-Part II: analysis of mechanisms driving the gusts
    Earl, N ; Simmonds, I (WILEY, 2019-09)
    Abstract An extreme extratropical cyclone (ETC) struck South Australia on 28 September 2016, causing state‐wide blackouts and damage. In the second part of this two‐part study, we examine the extreme surface wind producing mechanisms within the ETC. ETCs have been extensively studied in the Northern Hemisphere (particularly in western Europe), highlighting the gust‐producing mesoscale features within. Before now, no Southern Hemisphere ETC has been examined in this way. There were a number of extreme gust‐producing features within the ETC, comparable to those observed in storms over western Europe. One such feature was a convective line, which caused many of the most extreme gusts and knocked out the state power grid. However, dry slot convection also contributed to the extremes, and this feature rarely causes extreme gusts in ETCs over the UK. Thus, further analysis is warranted to examine whether this is a common extreme‐gust‐producing ETC feature over Southern Australia. The strongest winds recorded throughout the event occurred on 29 September, and these were associated with the cold conveyor belt which spiralled around the low‐pressure centre.
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    Spatial and Temporal Variability and Trends in 2001-2016 Global Fire Activity
    Earl, N ; Simmonds, I (AMER GEOPHYSICAL UNION, 2018-03-16)
    Abstract Fire regimes across the globe have great spatial and temporal variability, and these are influence by many factors including anthropogenic management, climate, and vegetation types. Here we utilize the satellite‐based “active fire” product, from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, to statistically analyze variability and trends in fire activity from the global to regional scales. We split up the regions by economic development, region/geographical land use, clusters of fire‐abundant areas, or by religious/cultural influence. Weekly cycle tests are conducted to highlight and quantify part of the anthropogenic influence on fire regime across the world. We find that there is a strong statistically significant decline in 2001–2016 active fires globally linked to an increase in net primary productivity observed in northern Africa, along with global agricultural expansion and intensification, which generally reduces fire activity. There are high levels of variability, however. The large‐scale regions exhibit either little change or decreasing in fire activity except for strong increasing trends in India and China, where rapid population increase is occurring, leading to agricultural intensification and increased crop residue burning. Variability in Canada has been linked to a warming global climate leading to a longer growing season and higher fuel loads. Areas with a strong weekly cycle give a good indication of where fire management is being applied most extensively, for example, the United States, where few areas retain a natural fire regime.
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    A high-resolution climatological study on the comparison between surface explosive and ordinary cyclones in the Mediterranean
    Kouroutzoglou, J ; Flocas, HA ; Hatzaki, M ; Keay, K ; Simmonds, I (SPRINGER HEIDELBERG, 2014-10)
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    Large scale features and energetics of the hybrid subtropical low 'Duck' over the Tasman Sea
    Pezza, AB ; Garde, LA ; Paixao Veiga, JA ; Simmonds, I (SPRINGER, 2014-01)
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    Sensitivity of the distribution of thunderstorms to sea surface temperatures in four Australian east coast lows
    Chambers, CRS ; Brassington, GB ; Walsh, K ; Simmonds, I (SPRINGER WIEN, 2015-10)
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    Vertical characteristics of cyclonic tracks over the eastern Mediterranean during the cold period of the year
    Flocas, HA ; Kountouris, P ; Kouroutzoglou, J ; Hatzaki, M ; Keay, K ; Simmonds, I (SPRINGER WIEN, 2013-05)
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    Antarctic skin temperature warming related to enhanced downward longwave radiation associated with increased atmospheric advection of moisture and temperature
    Sato, K ; Simmonds, I (IOP PUBLISHING LTD, 2021-06)
    Abstract We investigate linear trends in Antarctic skin temperatures (temperatures from about the top millimeter of the surface) over the four seasons using ERA5 ensemble mean reanalysis data. During 1950–2020, statistically significant warming occurred over East and West Antarctica in spring, autumn and winter, and over the Antarctic Peninsula in autumn and winter. A surface energy budget analysis revealed that increases in downward longwave radiation related to increases in air temperature and total column integrated cloud had a key role in Antarctic surface warming. There were negative sea level pressure trends around the periphery of Antarctica throughout the year, and the associated circulation contributed to warm advection from the middle latitudes to West Antarctica and the Antarctic Peninsula. Over the interior of East Antarctica, increase in moisture advection from lower latitudes enhanced the low-level cloud cover. A two-dimensional parameter diagram showed that skin temperature trends for time segments longer than 30 years starting before 1960 exhibited statistically significant warming in autumn and winter in East and West Antarctica and the Antarctic Peninsula. In spring, West Antarctica also showed statistically significant warming for long segments. In summer, the Antarctic Peninsula had statistically significant warming trends for long segments and cooling trends for segments less than 30 years. For all the studied time intervals, when skin temperatures had statistically significant positive trends, increases in downward longwave radiation contributed more than 70% of the warming and vice versa. This result demonstrates that on all time and space scales, changes in downward longwave radiation associated with variations in air temperature and atmospheric moisture loading play a dominant role controlling skin temperatures.
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