Comparison of Temperature and Geopotential Height Records Between L-band and RS90/92 Radiosonde Systems Using First-guess Field
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摘要: 对部分高空台站2007—2009年近3年探空记录的统计分析表明:邻近测站同一型号探空仪的温度和位势高度记录与6 h数值预报初估场的平均偏差一致,但不同型号探空仪记录与初估场的平均偏差存在明显差异,因此可以利用初估场进行邻近测站不同型号探空仪之间的间接对比。该文利用初估场与台站探空记录的差值,分析了使用芬兰Vaisala公司RS92型探空仪的中国香港站与邻近的使用L波段探空仪的梧州、汕头、东源、阳江4站2年的温度和位势高度记录的系统差,结果表明:19:00(北京时,下同),L波段探空仪的温度和位势高度记录在平流层分别偏低达1℃和30 gpm;07:00,L波段探空仪的温度记录在对流层偏高0.4℃,导致其位势高度记录也在对流层偏高;两套设备的系统差不仅有显著的日夜差异和季节性差异,也存在一定的年际差异。Abstract: The first-guess field (FG) has been used to assess the quality of sounding observation data in operation work for many years. A long term data analysis shows that the mean differences of temperature and geopotential height records between observations and FG at those neighboring stations using the same type of radiosondes are very small, while the differences for those neighboring stations using different types of radiosondes are significant. It can be inferred that FG can reflect the regional differences of meteorological elements caused by the synoptic situation. So it is feasible to compare neighboring stations records by using FG as a relative reference, which can eliminate the regional synoptic situation differences. Undoubtedly, such comparison should be applied in small region (i.e., between neighboring stations) by using synchronous observation records, and only sufficient (long term) sampling data has statistical representation.Hongkong sounding station has used the RS90/RS92 radiosonde manufactured by Vaisala since 2005. And during 2007—2009, the L-band radiosondes are used at several stations nearby Hongkong, such as Wuzhou, Shantou, Dongyuan and Yangjiang. So 5 stations above are appropriate for indirect comparison of L-band and RS92 radiosondes by using FG. It shows that there exist significant systematic differences between L-band and RS92 radiosonde systems, for both the temperature records and geopotential height records at each standard pressure level, through the two-year statistical comparison.At 19:00, the mean differences of temperature and geopotential height records are very small in the troposphere. In the stratosphere, the temperature measured by L-band radiosonde is lower than that measured by RS92, and the difference increases with height, reaching over 1℃ at 20 hPa height. The increasing temperature difference with height brings on an increasing geopotential height difference, which is over 30 gpm at 20 hPa height.At 07:00, the temperature measured by L-band is higher than that measured by RS92, which leads to a higher geopotential value. The temperature difference reaches 0.4℃ in the middle and upper troposphere, and the geopotential height difference is over 20 gpm at 100 hPa height. In the stratosphere, although the temperature measured by L-band is lower than that measured by RS92, and the difference also increases with the increase of height, the cumulative difference of temperature at 07:00 is less than that at 19:00. So the geopotential height difference between L-band and RS92 records is only about 10 gpm at 20 hPa height at 07:00.The long term direct comparison between different types of radiosondes is difficult to be carried out because of the high cost. Indirect comparison by using FG is not only economical but can reflect the real difference of operational records, so it is well worth to be widely applied.
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Key words:
- L-band;
- RS92;
- radiosonde records;
- first-guess field;
- comparison
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