A historical monthly upper-air humidity dataset for Australia

Monthly humidity (represented as dew point temperature, DWPT) data from 22 land and 5 island Australian upper-air sites were analysed, with trends estimated over the 1965–2017 period at four pressure levels. Humidity data were selected to ensure that data collected under consistent sampling conditions were used (‘modified data’). The quality control process involved examining station metadata and applying an objective statistical test that detected discontinuities in the data series. At each station and pressure level, modified data series were adjusted (homogenised) on a monthly timescale when discontinuities were identified. Analysis of the homogenised (adjusted) modified DWPT data indicates that, over the 1965–2017 period, linear trends are mostly positive and smaller compared to unadjusted modified data. The all-Australian time-series show positive trends at the 850–400-hPa levels. The total increases in DWPT since 1965 at 850-, 700-, 500- and 400-hPa levels are ~0.5, ~1.2, ~1.3 and ~0.8°C respectively. The increase in humidity in the lower and middle troposphere is in accordance with the expectation that, as the troposphere warms, the amount of moisture in it should increase (at a differential rate of ~7% °C–1 at low altitudes globally, following Clausius–Clapeyron scaling) due to increasing surface evaporation and moisture-holding capacity of the air. However, changes in atmospheric dynamics also influence the magnitude and distribution of humidity trends. The homogenised modified Australian radiosonde data for the 850-hPa level show that the amount of moisture at this level increased ~8.8% °C–1 during 1965–2015