We explore the causes and predictability of extreme low minimum temperatures (Tmin) that occurred across northern and eastern Australia in September 2019. Historically, reduced Tmin is related to the occurrence of a positive Indian Ocean Dipole (IOD) and central Pacific El Niño. Positive IOD events tend to locate an anomalous anticyclone over the Great Australian Bight, therefore inducing cold advection across eastern Australia. Positive IOD and central Pacific El Niño also reduce cloud cover over northern and eastern Australia, thus enhancing radiative cooling at night-time. During September 2019, the IOD and central Pacific El Niño were strongly positive, and so the observed Tmin anomalies are well reconstructed based on their historical relationships with the IOD and central Pacific El Niño. This implies that September 2019 Tmin anomalies should have been predictable at least 1–2 months in advance. However, even at zero lead time the Bureau of Metereorolgy ACCESS-S1 seasonal prediction model failed to predict the anomalous anticyclone in the Bight and the cold anomalies in the east. Analysis of hindcasts for 1990–2012 indicates that the model's teleconnections from the IOD are systematically weaker than the observed, which likely stems from mean state biases in sea surface temperature and rainfall in the tropical Indian and western Pacific Oceans. Together with this weak IOD teleconnection, forecasts for earlier-than-observed onset of the negative Southern Annular Mode following the strong polar stratospheric warming that occurred in late August 2019 may have contributed to the Tmin forecast bust over Australia for September 2019.
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排序方式： 共有5条查询结果，搜索用时 15 毫秒
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Lim Eun-Pa Hendon Harry H. Shi Li de Burgh-Day Catherine Hudson Debra King Andrew Trewin Blair Griffiths Morwenna Marshall Andrew 《Climate Dynamics》2021,56(11):3625-3641
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Effect of tropospheric temperature change on the zonal mean circulation and SH winter extratropical cyclones 总被引：1，自引：1，他引：0
This study aims to understand the mechanisms which cause an overall reduction of SH extratropical cyclone activity with a
slight increase in the high latitudes in a warmer climate simulated in general circulation models (GCMs) with increasing CO2. For this purpose, we conducted idealized model experiments by forcing warm temperature anomalies to the areas where climate
change models exhibit local maximum warming—the tropics in the upper troposphere and the polar regions in the lower troposphere—simultaneously
and separately. The Melbourne University atmospheric GCM (R21) coupled with prescribed SST was utilized for the experiments.
Our results demonstrate that the reduction of SH extratropical cyclone frequency and depth in the midlatitudes but the slight
increase in the high latitudes suggested in climate change models result essentially from the tropical upper tropospheric
warming. With this tropical warming, the enhanced static stability which decreases baroclinicity in the low and midlatitudes
turns out to be a major contributor to the decrease of cyclone activity equatorward of 45°S whereas the increased meridional
temperature gradient in the high latitudes seems an important mechanism for the increase of cyclone activity over 50°–60°S. 相似文献
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Harry H. Hendon Eun-Pa Lim Julie M. Arblaster David L. T. Anderson 《Climate Dynamics》2014,42(5-6):1155-1174
In 2010 eastern Australia received its highest springtime (September–November) rainfall since 1900. Based on historical relationships with sea surface temperatures (SST) and other climate indices, this record rainfall in 2010 was shown to be largely commensurate with the occurrence of a very strong La Niña event and an extreme positive excursion of the SAM. The pattern and magnitude of the tropical SST anomalies in austral spring 2010 were diagnosed to be nearly perfect to produce high rainfall across eastern Australia. Key aspects of this SST pattern were the strong cold anomaly in the central equatorial Pacific, and the strong warm anomalies in the eastern Indian Ocean and the far western Pacific to the north of Australia. Although the recent upward trend in SSTs in the western Pacific/eastern Indian Ocean warm pool accounted for about 50 % of the SST anomaly surrounding northern Australia in 2010, the contribution by the warming trend in these SSTs to the Australian rainfall anomaly in 2010 was assessed to be relatively modest. The strong positive swing in SAM was estimated to have accounted for upwards of 40 % of the regional anomaly along the central east coastal region and about 10 % of the area mean anomaly across eastern Australia. This contribution by the SAM suggests that a significant portion of the rainfall in 2010 may not have been seasonally predictable. However, predictability arising from the promotion of high SAM by the extreme La Nina event can not be ruled out. 相似文献
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