Response time of temperature measurements at automatic weather stations in Australia

Bureau of Meteorology automatic weather stations (AWS) are employed to record 1-min air temperature data in accord with World Meteorological Organization recommendations. These 1-min values are logged as the value measured for the last second in each minute. The Bureau explains that this is appropriate because the inherent measurement system time constant means the 1-s data are not instantaneous, but are an average smoothed over the previous 40–80 s. To test this proposition in the field air temperature data were measured at 1-Hz at two Bureau AWS sites between April and June 2018. The frequency distribution of the differences between each 1-s value and the 60-s average centred on that value provided information on the overall measurement system response time constant. Expressed in terms of an e-folding measurement system response time, the data from the two measurement systems studied yielded response times in the range 50–150 s, largely consistent with the Bureau’s explanation.