Abstract
A new bicentennial series of the Australian monsoon strength based on historical wind observations has allowed for the assessment of the variability of this system since the early 19th century. Our series covers a period in which the scarcity of meteorological observations in the area had precluded the evaluation of long-term climatic trends. Results indicate that the increase in precipitation over Northern Australia reported for the last 60 years is just a manifestation of a much longer lasting trend related to the strengthening of the Australian monsoon that has been occurring since at least 1816.
Highlights
The Australian monsoon is the strongest monsoon in the Southern Hemisphere
Meteorological observations found in these logbooks contain first-hand and well-dated daily evidence of the weather that ships encountered along their route as an estimate of the state of the sea, information about precipitation and descriptors relative to the observed wind force and direction[8,9]
As the wind is directly related to the atmospheric dynamics, it has been possible to include these early meteorological observations into multiproxy reconstructions of the Sea Level Pressure in heavily navigated areas such as the North Atlantic[10,11,12] and more recently to develop instrumental indices for the North Atlantic Oscillation[13], the strength of northern Hemisphere monsoons[14,15] or the El Niño Southern Oscillation[16,17]
Summary
The inherent spatial variability of the wind inside the area selected to compute the AMDI and the finite number of available measurements in a given month is translated as dispersion or ‘uncertainty’ in a particular realization of the index. To estimate this uncertainty we considered the 1971– 2010 period (in order to have a large enough pool of observations). It must be pointed out that this dispersion measure is purely empirical It should only be interpreted as the estimated standard deviation of an AMDI value computed from a number N of wind direction measurements and not as a confidence interval in a statistical sense. All data used in this paper are freely available at http://www.esrl.noaa.gov/psd/ (NCEP, GPCC, 20CR-V2), http://apps.ecmwf.int/datasets/data/era20c-daily/ (ERA-20c), https://rda.ucar.edu/datasets/ ds548.0/ (ICOADS), and http://www.bom.gov.au/climate/data/stations/ (Darwin precipitation)
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