Homogeneity and Long-term Trend Analysis on Radiosonde Temperature Time Series in China During Recent 50 Years

In order to study long-term trend of upper air temperature in China, radiosonde temperature time series during 1958-2005 at 116 Chinese stations are examined.Firstly, uncertainties in the time series caused by artificial errors and breakpoints are detected by quality control and homogenization procedure. Original radionsonde temperature time series at 7 levels are adjusted by employing hydrostatic and two-phase-regression (TPR) method.The identification results show significant discontinuities in the studied time series, especially in earlier period (1960s-1970s). Parts of the break points are documented by station' s metadata, which contributes to the changes of instrument model or method.Significant impact on long-term trends of original time series is caused by the adjustments which vary with different periods. The cooling trends in mid-upper troposphere during 1958-1978 are weakened by homogenization; also, cooling trends in lower stratosphere are enhanced and warming trends at 400 hPa and 500 hPa during 1979-2005 are weakened.Missing rate, as an important factor influencing the utilization of radiosonde temperature time series in China, is a reasonable index for sampling stations to assess regional average trend. Sampling by low missing rate (high data requirement) results in reduced number of potential stations. By analysis on averaged trend profile with different minimum data requirements (MDR), it is found that warming trends in low troposphere are enhanced and cooling trends in upper troposphere and low stratosphere are weakened by the decreasing number of stations in accordance with low missing rate or high M DR of stations. Critical maximum missing rate is suggested as 30% (MDR as 70%) for examining reliability of the time series. Averaged temperature time series in China are deduced by 92 radiosonde stations, which are selected by meeting maximum missing rate (or minimum data requirement by MDR).Homogenous radiosonde temperature time series show that trends of upper air temperature in China are generally consistent with that at global scale but with some discrepancies. During 1958-2005, atmospheric temperatures in China tend to decrease in the low stratosphere and upper troposphere, and increase in the middle and low troposphere. The trends of upper air vary with different periods. For 1958-1978, cooling trends in the entire atmosphere are similar to those at global scale. During 1979-2005, obvious warming occurs in the low and mid-troposphere; the amplitude of warming trend weakens with the increase of altitude and shifts to cooling trend above 400 hPa. Analysis on decadal averaged temperatures anomalies shows that cooling in low stratosphere has occurred since 1980s and enhances in 1990s and warming in midlow troposphere below 500 hPa has occurred since 1970s and significantly warming in the layer between 700 hPa and 300 hPa has occurred since 1980s.