| Tropopause is one of research hot spots on earth meteorology and climatology,for its structural variation is closely related to troposphere-stratosphere exchange and atmospheric circulation and thus worth studying.Before the emergence of Global Navigation Satellite System(GNSS)Radio Occultation(RO)technique,tropopause researches mainly depended on direct observation method or model data.However,both two methods have some disadvantages and cannot provide global coverage,high vertical resolution and real-time data.The advent of GNSS RO technique makes up for the deficiency of traditional tropopause observations and becomes a strong method for monitoring and measuring tropopause.China's state-of-art GNSS occultation sounder(GNOS)developed by National Space Science Center(NSSC),Chinese Academy of Sciences(CAS)is firstly compatible for both Bei Dou navigation system(BDS)and Global Position System(GPS)signal.GNOS was first onboard the Feng Yun3C(FY3C)satellite and in operation in 2013.Later,the next generation GNOS onboard the FY3 D was successfully launched in 2017.In the following FY3 E mission,the new generation GNOS will be compatible for BDS,GPS and GALILEO signal and will provide more occultation events.Now,the data accumulation of FY3 GNOS is enough for developing climate products and the quality of GNOS data has been confirmed by authorities such as European Centre for Medium-Range Weather Forecasts(ECMWF)and Wegener Center for Climate and Global Change(WEGC),but few of climate products or meteorology and climatology researches use GNOS data,and thus the value of GNOS data needs to be exploit.In view of this situation,my work mainly discusses developing tropopause products based on FY3 C GNOS data;optimizing the tropopause determination methods;analyzing the bias between different tropopause determination method and improving the accuracy of FY3 C GNOS tropopause products.The content of this article mainly includes:1.To introduce the scientific significance,research value and determination methods of thermal tropopause in detail.To introduce the principle and the observation characteristics of RO technique,and to analyze the advantages of RO technique for observing tropopause.To summarize the RO-data-based tropopause research.2.To analyze the principle of bending angle covariance transform tropopause determination method introduced by Lewis in 2009,and optimize the parameter setting in this method to reduce about 50% computational cost.3.Based on FY3 C GNOS data,to analyze the bias characteristic of two mainstream tropopause determination methods.Results indicate that the tropopause height derived from those two methods has a globally 0.6-1.0 km bias due to the different representation of height,but they both show the same variation trend outside the Antarctic.For the Antarctic results,some possible reasons were discussed.4.Research results indicated that FY3 C GNOS tropopause height shows bias compared with ECMWF result.To improve the accuracy of FY3 C GNOS tropopause products,machine learning methods were used to eliminate the bias.Results show that after machine learning correction,the root mean square error between FY3 C GNOS tropopause height/ temperature and corresponding ECMWF results have reduced 0-0.5km/0-1 K,respectively.5.To first give the FY3 C tropopause products and validate its quality by comparing with COSMIC mission results,radiosonde results and related research results.The absolute mean bias between FY3 C tropopause parameter and COSMIC ones is about globally less than 0-0.2 km for tropopause height and less than 2 K for tropopause temperature.Also,FY3 C tropopause products show agreement with radiosonde results.The correlation coefficient between FY3 C and radiosonde results is holistically larger than 0.9-0.95.Besides,the climate phenomena reflected by FY3 C global seasonal tropopause patterns coincide with results of related research,indicating the availability of FY3 C GNOS tropopause products. |
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