Homogenization of Tianjin Daily Surface Air Temperatures by Software Pack RHtestsV4 during 1951-2012

Based on historical ground-level meteorological data and their metadata in Tianjin, China, produced by the National Meteorological Information Center, China Meteorological Administration, the homogenization of the daily surface air temperature data for Tianjin during the last 60 years, by the software package RHtestV4, is tested. Results indicate that the main cause of the discontinuities in daily mean and minimum temperatures is station relocation, as tested by the penalized maximal t-test; while for daily maximum temperature, it is instrument change. Furthermore, the operation of automatic stations after 2005 does not have a great impact on the homogeneity of temperature at Tianjin. Moreover, some significant discontinuities for unknown reasons are also detected, which we think may be due to reasons such as observer misjudgment or instrument warping. For the adjustment amount, the positive bias corrections are mainly expressed in daily mean and maximum temperature series. Meanwhile, the negative bias corrections are mainly in daily minimum temperature series, in which the largest average quantile-matching (QM) adjustments are for daily maximum temperature (more than 90% are from 0.1 ℃ to 1.0 ℃), and the smallest are for daily mean temperature (more than 90% are from -0.7 ℃ to 0.7 ℃). For daily minimum temperature, the range is -1.5 ℃ to 1.5 ℃. In addition, error analysis reveals that there is much higher consistency between the two datasets of the present paper and those of a previous study, on annual and seasonal scales, by setting the datasets from the previous study as the reference. This can explain why the daily temperature series for the period 1951-2012 in Tianjin, adjusted in this study, show a certain reliability.