A Comment on Tmin at Goulburn and at Thredbo Top Station

Abstract

Problems with measurement of air temperatures below -10.4°C at the Bureau of Meteorology’s Goulburn and Thredbo Top Station automatic weather stations have been reviewed to evaluate the effect on the data records from those sites. A nine-minute gap in the Tmin record at Goulburn on just one day, 2 July 2017, is assessed to have no effect on that data record, as the likely actual minimum temperature was estimated to be essentially unchanged at -10.4°C +0.0/-0.1°C. To assess the effect on the Thredbo data of six days within the last decade in which Tmin was inadvertently limited to -10.4°C a hypothetical data record was constructed in which any day after May 2007(seventeenin total) with Tmin below -9.9°C had that value replaced by -13°C, heavily overcompensating for the data logger limitation. Three different tests were carried out comparing the original data record with the overcompensated record. All tests pointed to the conclusion that the small number of limitations has had no material impact on the Thredbo record. Another conclusion from the analysis was that the frequency of occurrence of cool days at Thredbo, including days below -10.4°C, has fallen compared with the late 1960s due to the general warming of Australia since then.