Search

In order to understand the regional impacts of variations in the extent of the Hadley circulation in the Southern Hemisphere, regional Hadley circulations are defined in three sectors centered on the main tropical heat sources over Africa, Asia-Pacific (Maritime Continent) and the Americas. These regional circulations are defined by computing a streamfunction from the divergent component of the meridional wind. A major finding from this study is that year-to-year variability in the extent of the hemispheric Hadley circulation in the Southern Hemisphere is primarily governed by variations of the extent of the Hadley circulation in the Asia-Pacific sector, especially during austral spring and summer when there is little co-variability with the African sector, and the American sector exhibits an out of phase behavior. An expanded Hadley circulation in the Southern Hemisphere (both hemispherically and in the Asia-Pacific sector) is associated with La Niña conditions and a poleward expansion of the tropical wet zone in the Asia-Pacific sector. While La Niña also promotes expansion in the American and African sectors during austral winter, these tropical conditions tend to promote contraction in the two sectors during austral summer as a result of compensating convergence over the Americas and Africa sectors: a process driven by variations in the Walker circulation and Rossby wave trains emanating from the tropical Indian Ocean. [ABSTRACT FROM AUTHOR]

South-Eastern Australia and, in particular the state of Victoria, has experienced record deficits of rainfall over the last 20 years, in which the cool part of the year from April to October has been most affected. This situation has created difficulties for water managers, farmers and fire services, with the need to provide more certainty about future climate trends becoming clear. The latest climate projections for South-Eastern Australia project an overall drying in the cool part of the year with little change in the rest of the year. Although this is in line with current trends, very large uncertainties are associated with these projections. In this study, this range of projections has been investigated, first by assessing how the current suite of climate models simulate the regional rainfall as well as the tropical variability, known to be a key driver of south-eastern Australian climate. The models were found to be reasonable overall, although a number overestimate Victorian summer rainfall. Model rainfall projections are found to be related to the models' projected patterns of tropical warming, where 60% of the range in cool season rainfall projections can be explained by the range of pattern of tropical changes. In addition, the projected drying tends to be more intense in the models best able to simulate summer rainfall, thus suggesting that the upper end of the uncertainty range is less likely to be realized as it may reflect inherent model biases, rather than physical changes. [ABSTRACT FROM AUTHOR]

During the 20th century and early 21st century, the subtropical ridge (STR) in the vicinity of eastern Australia has intensified significantly. While the position of the STR has often been the focus of past studies, its influence on rainfall across southern Australia is less pronounced than the influence of the intensity of the ridge. Most of the Australian continent has experienced above average rainfall from 1997 to 2009, but areas of below average rainfall, including southeastern Australia (SEA), exist and tend to match the pattern of the influence of the STR on Australian rainfall. The spatial extent makes the 1997-2009 rainfall deficit in SEA different from previous dry decades such as 1935-1945. It is also noted that the annual cycle of the rainfall deficiency centred on a continuum from March to October overlaps well with the time of the year when the STR intensity has a strong influence on rainfall. Using simple linear statistics, a rainfall decline for the period 1997-2009 equivalent to nearly two thirds of that observed can be inferred from the intensification of the ridge. The apparent southward shift of the ridge in certain seasons does not appear to have had an additional effect on SEA rainfall. During the 1935-1945 drought, almost a third of the rainfall decline can be attributed to the strengthening of the ridge. Finally, it was observed that the intensification of the STR was not monotonic during the 20th century but happened mostly during two extended periods: from 1900 to the 1940s, culminating at the time of the 1935-1945 dry decade, and from 1970 to 2010 culminating with the 1997-2009 rainfall deficit in SEA. That multidecadal behaviour is reminiscent of the global warming of the planet. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Southeastern Australia has been experiencing ongoing rainfall deficits since 1997. The spatial extent of the current drought closely corresponds to those regions where rainfall is influenced by interannual variations in the intensity of the subtropical ridge. An upward trend in the intensity of the subtropical ridge thus provides an explanation for the recent rainfall deficit. The possibility that slow variations in tropical modes of variability that are known to influence rainfall in the region, such as the El Niño-Southern Oscillation, may have contributed to southeastern Australia rainfall deficits is investigated using a tripole sea surface temperature index. This index takes into account key influences on Australian climate from variations in both the Indian and Pacific Oceans. The tripole index correlates well with rainfall variations across southeastern Australia on interannual to decadal time scales in winter and spring but not in autumn when most of the recent rainfall deficits have occurred. The influence of tropical sea surface temperature (SST) variations associated with the tripole on southeastern Australian rainfall is explained in terms of Rossby wave propagation, which helps us to understand why the impact is stronger in the southern half of the Murray-Darling Basin and why there is no relationship in autumn. On the basis of the linear relationship between the tripole SST variation and rainfall across the Murray-Darling Basin, we conclude that tropical SSTs have not contributed to the observed rainfall deficiencies in southeast Australia since 1997 but did contribute to the 1935-1945 rainfall deficits. [ABSTRACT FROM AUTHOR]

The article presents a study of cool-season tornado (CST) environment in Australia. It mentions that CST commonly occurs in positively buoyant, environments, and with high values of low-level shear. It also states that testing the possibility of adapting a diagnostic tool for high-resolution numerical weather prediction (NWP) models and operational forecasting products is the aim of the study.

The article explores the anomalous activities of typhoon in the Northwestern Pacific and the Northern Japan's extreme precipitation in August 2016. Topics mentioned include the formation of typhoons in the northwestern Pacific basin back in August 2016 that made landfalls, the stark contrast when the first six months of the year have suppressed tropical cyclone activity and the association of the active typhoons in August with the lower troposphere's cyclonic circulation anomalies.