基于流体动力学的探空仪GTS1湿度测量误差修正研究

准确的湿度垂直廓线对短期数值天气预报和中长期气候研究分析均具有重要参考价值,但太阳辐射与高空云雨等因素导致探空湿度测量精度较低.针对探空仪GTS1白天进行湿度测量时存在明显偏干误差的现象,本文建立了GTS1湿度测量结构模型,采用计算流体动力学方法重点研究了太阳辐射对GTS1湿度测量的影响,同时探讨了其防雨/防辐射罩的防雨效果.结合改进的太阳辐射计算模型,利用Fluent模拟分析了防雨/防辐射罩云雨滴轨迹和内部温度场分布,数值仿真结果表明:在垂直气流下防雨/防辐射罩基本保护湿度传感器免受高空云雨的影响,对太阳辐射也起到一定防护作用.但太阳辐射对GTS1湿度测量的偏干影响仍较显著,海拔30km左右相对误差甚至高达70%.通过与RS92及GTS1探空湿度测量中的太阳辐射偏干误差相对比,发现基于流体动力学数值计算的湿度相对误差随海拔高度的变化趋势与之基本吻合.本文也给出了理论计算与实验测量存在一定差异的原因,进而以南京探空站2014年不同季节的温度、气压、气球的上升速度等探空数据为计算参数,获取了太阳辐射误差与海拔及环境温度的关系,并对四组探空湿度廓线进行太阳辐射误差修正,提升了GTS1探空仪高空湿度测量的精度.本文研究结果为探空湿度测量太阳辐射偏干误差的有效修正提供了一定的参考.

Research on corrections of humidity measurement errors from GTS1 radiosonde based on fluid dynamics analysis

An accurate humidity profile has important reference values for short-term numerical weather prediction and long-term climate research. However, the solar radiation, high-altitude clouds and rains as well as other factors lead to the low accuracy of radiosonde humidity measurement. In order to solve the problem that the GTS1 radiosonde has a strong solar radiation dry bias during daytime humidity measurement, the structure model of GTS1 humidity sensor was established in this paper. The influence of solar radiation on humidity measurement was carefully studied by computational fluid dynamics (CFD) method and the rainproof effect of the rain/radiation shield was also discussed at the same time.Combining with the improved solar radiation calculation model, both the trajectories of clouds and raindrops and internal temperature distribution of the rain/radiation shield were specifically simulated and analyzed by using Fluent. The numerical simulation results show that the rain/radiation shield basically protects the humidity sensor from the effects of high-altitude clouds and rains in the vertical airflow and it also plays a certain protective role against the solar radiation. However, the solar radiation dry bias of humidity measurements from GTS1 radiosonde is still significant, and the relative error at altitude of 30 km is even up to 70%.Compared to the solar radiation dry biases of humidity measurements from RS92 and GTS1 radiosondes, it is found that the change trend of humidity relative error with the altitude based on fluid dynamics numerical calculation is basically consistent with them. The reason of the difference between theoretical calculation and experiment measurement is also given. Furthermore, the measurement datum of Nanjing sounding station such as temperature, air pressure and balloon rising speed in different seasons of 2014 were taken as the CFD calculation parameters and the relationships between the solar radiation error and altitude as well as ambient temperature were obtained, and finally the solar radiation error corrections were carried out for four sets of sounding humidity profiles, which enhances the accuracy of humidity measurement from the GTS1 radiosonde. The research results in this paper provide some reference for the effective correction of the solar radiation dry bias of the humidity measurements.