Comparison of Relative Humidity Data Between L-band and 59-701 Sounding System

The importance of consistency of upper-air observation reports in serial of space and time is well recognized by users and upper-air observation operators. It is the most effective way that the systematic differences between observations of pre and post updating radiosondes can be obtained using the method of direct intercomparison. To achieve that, two datasets are used to analyze effects of pre and post radiosondes updating on the relative humidity (RH) observed by 59-701 sounding system and L-band sounding system. The sensor for humidity measurement changes from goldbeaters skin to a carbon hygristor. One-month RH data of these two different sounding systems are compared directly to analyze the consistency of pre and post updating.Average RH biases between 59-701 and L-band sounding system from 1000 hPa to 200 hPa specified isobaric surface are analyzed. Results reveal that without considering the radiosonde errors upon the place, the season of the year, the time of the day, the RH of L-band is obviously lower than that of 59-701 sounding system in China, and differences are increased with altitudes. The RH bias of two sounding systems is less than 5% near the surface, but the value reaches more than 20% at 200 hPa. It shows that the RH bias of two sounding systems in winter is greater than that in summer, but differences with height are not the same in detail. Whether winter or summer, several stations reflect the problem that differences of average RH bias are much larger than the overall average RH bias, which shows that the difference change of average RH bias is not only related with the ambient temperature change, but also related to the change of RH. This phenomenon reflect possible "wet hysteresis loop" effect of humidity sensors. The difference of humidity components performance is not obvious between the type 59 radiosondes from Taiyuan and Shanghai. The effect of solar radiation on humidity components of these two types of radiosondes is also not obvious.Integrating comparison results, it shows that the RH bias between 59-701 and L-band sounding systems isn't affected by the type 59 radiosonde manufacturers, and RH observations are all affected by the ambient temperature, lag and wet hysteresis. But the influence details in different situations should be study further, and these results can be used as reference of correction by related departments.