Decrease in rainfall in the autumn, which is 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 researchers from the State Association of Scientific and Industrial Research (CSIRO) in a paper 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 1997-2009 came scale "drought Goals." Previous studies have suggested that the reason for the decline is the change in precipitation meteosistem and trajectory of storms in the late 20th century.
Marcus Thatcher (Marcus Thatcher) and colleagues tested how reduction of regional rainfall may be associated with the expansion of the so-called Hadley cells — a major element of the atmospheric circulation that brings warm air from the tropics to the subtropical zone.
"The southern boundary of the Hadley cell has grown significantly over the last 30 years, and most of all, to 200-400 kilometers to the pole edge moves in the mid to late fall," — said co-author Tim Cohen (Tim Cowan), whose words are CSIRO.
Researchers have shown that up to 85% overall reduction in rainfall in the south-eastern Australia can be explained by simply replace the measure this region on the data collected at 400 kilometers north.
However, this hardly explains the changing patterns of rainfall in the south of Chile and the African continent. As noted by the authors, the subtropical zone drought consists of several independent segments, so its extension to the south have different impact on the amount of precipitation in areas semi-desert in the southern hemisphere.
In addition, it is not clear why the area hardest drought extends to the 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 specify.