Comparison of Temperature and Geopotential Height Records Between 59 Type and L band Radiosonde Systems

The radiosonde records such as upper air temperature, pressure and humidity are the fundamental data for weather forecasting and climate analysis, and especially for the latter, a long term continuity and a good consistency of these records are also required. The radiosonde systems used in China have experienced three generations since 1950s. Improvements and updates of the equipment have significantly increased the sounding data acquisition rate, accuracy and reliability, but inconsistencies of historical data arise simultaneously. In order to analyze system deviation between the records obtained from the upper air sounding records before and after applications of new equipment and method, comparison observations between the L band radiosonde systems with 59 ones at 80 upper air stations are conducted in 2002, and totally 60 records are obtained at each station using 60 normal operational 59 radiosonde systems and 60 L band ones which are used for training. From those stations, the sounding data of 70 stations are selected and analyzed. The records of temperature and geopotential height of mandatory level obtained from two types radiosonde systems are compared, and the average deviations between the records of different systems are adopted to show the difference. Considering the data error, which is related to three manufacturers of 59 radiosonde, different solar altitude and different temperature profile, the records are classified for comparison by manufacturer of 59 type, observation time and launching site, etc. On the whole, below the 100 hPa height, the temperature difference is less than 0.3 ℃ and the geopotential height difference is less than 7 meters. Therefore, before and after changing the sounding systems, the radiosonde records below the 100 hPa height do not exhibit obvious change in terms of the overall average. However, according the records higher than the 70 hPa height, the mandatory level temperature measured by 59 radiosonde is 0.1—0.7 ℃ lower than that measured by L band radiosonde, which results in a continuous cumulation of geopotential height difference with increasing height. For example, at the height of 20 hPa, the difference can reach about 30 meters, which is obvious. In summer, compared with the records of L band radiosonde, those of 59 radiosonde made by Taiyuan factory show a significantly higher temperature in troposphere, and a significantly lower temperature beyond the top of troposphere, which brings on a higher geopotential height in troposphere (as much as 20 meters on average), and a lower geopotential height in stratosphere (as much as 18 meters on average). The records of 59 radiosonde made by Shanghai factory exhibit a little lower temperature and geopotential height in both troposphere and stratosphere (with a maximum difference of 37 meters). In winter, 59 radiosondes made by the two factories exhibit the same behavior as in summer respectively but with obvious small amplitudes.