October 4. Scientists from the CSIRO undertook a study of the issue concerning the reduction of autumn precipitation in the south-eastern Australia. Such a trend researchers discovered in the 1970s of the last century. It is noteworthy that in April and May also reduced the amount of rainfall, which is associated with the approach of the dry subtropics called Hadley cell to the south-east of Australia.
In addition, both the autumn and spring rainfall affected by the shift tracks storms and other weather systems in the more southern regions of the continent in the late 20th century. Great importance has also had devastating "superzasuha" 1997-2009 years. Hadley cell is closer to the south of Australia in the 200-400 km at different points, causing a lack of rainfall in the middle and late autumn and spring.
Except the south-west of Australia from similar problems, but to a lesser extent, affected South Africa and South Indian Ocean. There is lack of autumn rains, and on the southern edge of Chile. As shown by simulation almost 85% of the precipitation, which should fall in the area shown roam and fall in a region that is 400 kilometers north.
To the south-eastern Australia Autumn is a crucial period because during this period the soil gets the right amount of moisture, wet autumn and winter as directly related to the quality of future crops.
The area of drought in Australia for 30 years, "advanced" for 400 km to the south
October 4. Decrease in rainfall in autumn observed in the south-eastern Australia in the past 30 years, was the result of the expansion to the south subtropical zone of drought, according to scientists from the National Commonwealth Scientific and Industrial Research (CSIRO) in an article published in the journal Scientific Reports.
Reducing the amount of rainfall during the period from April to May in the region began in the 1970s, in particular, for the years 1997-2009 came ambitious "Millennium drought." Previous studies have suggested that the reason for the decline is the change in precipitation meteosistem and trajectory of the storm at the end of the 20th century.
Marcus Thatcher (Marcus Thatcher), and his colleagues tested whether reduction of regional rainfall may be associated with the expansion of the so-called Hadley cells — a major element of the atmospheric circulation that transports warm air from the tropics to the subtropical zone.
"The southern boundary of the Hadley cell has expanded significantly over the past 30 years, with the most, up to 200-400 kilometers to the pole, the boundary moves in the middle and late fall," — said co-author Tim Cohen (Tim Cowan), whose words led CSIRO.
Researchers have shown that up to 85% overall reduction in rainfall in south-eastern Australia can be explained if we simply replace in the calculation of indices in the region on data collected at 400 kilometers to the north.
However, it is practically not explain changes in the levels of precipitation in the south of Chile and the African continent. As the authors note, the subtropical zone drought consists of several independent segments, so its extension to the south of the different impact on the amount of rainfall in semi-arid areas in the Southern Hemisphere.
In addition, it is not clear why the drought area is expanding most strongly to a pole in the autumn, and the role played in this process is played by external factors such as the impact of greenhouse gases, the researchers clarify.