High quality monthly upper-air temperature and humidity datasets for Australia

2017-02-16T23:40:55Z (GMT) by Jovanovic, Branislava
High-quality monthly upper-air temperature and humidity datasets of 22 stations have been developed for monitoring and assessing long-term trends in temperature and humidity over Australia. In addition, high quality monthly upper-air temperature and humidity time series have been developed for five Australian remote island sites: the subantarctic Macquarie Island, Lord Howe Island in the Tasman Sea, Norfolk Island in the southwest Pacific Ocean, Willis Island in the Coral Sea and Cocos Island in the eastern Indian Ocean. The datasets are based on 23UTC soundings with most records starting in 1958 for temperature and in 1965 for humidity. The quality control process involved the examination of station metadata (historical information about stations and recordings) and an objective statistical test which detected discontinuities in the data series. At each station and each level, data series were adjusted (on a monthly timescale) when discontinuities were identified. Homogenised temperature and humidity (represented by the dew point temperature, DWPT) data were analysed at mandatory levels. Temperature time series were found to be mostly complete since 1958, with higher levels having more missing data than lower levels. For humidity it was found that there were insufficient daily observations to compute monthly means in the period 1965 to 1991 at all levels except 850 hPa. Furthermore, DWPT data contained a number of biases due to changes in technology. To be able to analyse humidity data at least at the two lowest levels (850 and 700 hPa), we explored the possibility of removing part of the daily data, in order to make the record over the period 1965-2011 consistent (i.e. independent of technological changes). The all-Australian mean annual temperature shows statistically significant increases/decreases over the 1958-2011 period at all examined levels except the 150 hPa level. Since 1958 temperatures at the 850 and 700 hPa levels increased about 1.2°C, while at the 500, 400 and 300 hPa levels they increased about 1.6°C. At levels which intercept the tropopause height, temperature over the same period of time increased by 0.9°C at the 200 hPa and a decreased by -0.3°C at the 150 hPa. In the lower stratosphere, at the 100 hPa level, temperature decreased by -1.8°C. A similar vertical structure of changes in temperature is found in remote islands data. The observed patterns of change in the upper-air temperature over Australia are in agreement with physical principles and model simulations under the enhanced greenhouse effect, both of which show general warming in the troposphere and cooling in the lower stratosphere (noting that stratospheric cooling is predominantly due to the decrease in stratospheric ozone and to a smaller extent to the increase of greenhouse gases). Results are also consistent with the expectation that the troposphere should warm at a faster rate than the surface. Analysis of the homogenised humidity data indicates that over the 1965-2011 period, all-Australian DWPT shows statistically significant increases at the 850 and 700 hPa levels. The increase since 1965 at 850 hPa is about 0.9°C (comparable to the temperature tend), while at 700 hPa the increase in DWPT is nearly double in magnitude, about 1.rc (larger than the temperature trend). The increase in humidity in the lower troposphere is in accordance with the expectation that, as the troposphere warms, the amount of moisture in it should increase. It is also consistent with an upward trend in observed Australian near-surface humidity.