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COSMIC反演精度和有关特性的检验
Evaluation for Retrieving Precision and Some Merits of COSMIC Data
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摘要: COSMIC是一个由6颗低轨卫星组成的用于天气、气候和电离层观测的空基GPS星座观测系统, 从2006年9月开始每天可提供覆盖全球的约2000~3000个掩星点, 掩星过程可提供从40 km高空到近地面的大气温、压、湿的廓线资料。为了有效利用这些资料, 以探空资料为基准, 对2007年1-10月我国及邻近区域的COSMIC掩星资料进行精度、可用性和全天候性的检验。结果表明: COSMIC反演的温度和折射率的精度很高, 水汽压的精度相对较差。与NCEP/NCAR再分析资料相比, 折射率和湿度廓线有更高精度。Abstract: The COSMIC (Constellation Observing System for Meteorology Ionosphere and Climate) consists of six Low Earth Orbit (LEO) satellites. Based on the GPS signals observed by LEO in the occultation condition of the GPS satellites, the profiles of atmospheric temperature, pressure, humidity and ionosphere are retrieved. COSMIC provides these to about 2000 to 3000 GPS soundings globally every day since September 2006, and it can be the effective supplementary of regular radiosonde. COSMIC data is collected in the area of China and Northwest Pacific during the period of January to October in 2007.And the precision, applicability and characteristics of fitting all weather condition are evaluated by the error statistics based on radiosonde data. The results show that the accuracy of temperature profiles retrieved from COSMIC is excellent. The root-mean-square error (RMS) is less than 2 K and the relative error is less than 1%. The retrieved refractivity above 500 hPa level is very accurate, with the RM S less than 1, while under 500 hPa level the RMS increases from 1 to 10 near the ground. The precision of water vapor is high above 500 hPa level, but the RMS increases linearly from 0.2 hPa or less to 2 hPa near the ground under 500 hPa level. Meanwhile the error comparison between COSMIC data and NCEP (National Center of Environment Precipitation) reanalysis data shows that COSMIC data have higher accuracy than NC EP in vapor pressure and refractivity, for instance, the relative error of vapor pressure of COSMIC is 2%-5% less than NCEP data. Additionally two COSMIC occultation events in the clouds are studied to compare COSMIC data with the nearby radiosonde and airborne dropsonde observations. It' s validated that the profiles of the temperature, vapor pressure and refractivity of COSMIC data coincide well with the corresponding radiosonde profiles, so the COSMIC data are appropriate under all weather condition.
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图 1 COSMIC掩星资料反演与无线电探空仪在各个气压层的探测结果比较
(a)相对误差, (b)均方根误差, (c)相对偏差, (d)平均误差
Fig. 1 Comparison of COSMIC inversion with radiosonde in all the pressure layers
(a) relative error, (b) root-mean-square error, (c) bias, (d) mean error
图 2 NCEP/ NCAR再分析资料与无线电探空仪探测结果比较
(a) 相对误差, (b) 均方根误差
Fig. 2 Comparison of NCEP/ NCAR reanalysis with radiosonde
(a) relative error, (b) root-mean-square error
图 3 COSMIC掩星反演资料误差与NCEP/ NCAR再分析资料误差的差别
(a)相对误差之差, (b)均方根误差之差
Fig. 3 Difference of COSMIC inversion error and NCEP/ NCAR reanalysis error
(a)difference of relative error, (b)difference of root-mean-square error
图 4 发生在密蔽云区内的COSMIC掩星点与临近的探空点
(a) 南海对流云团内掩星点A和临近常规探空站B, (b) 0713号韦帕台风螺旋云带内的掩星点C和下投探空点D
Fig. 4 COSMIC occultation and sounding points occurred in dense cloud covered region
(a) occultation point A close to radiosonde Station B in convective cloud clusters over the South China Sea, (b) occultation point C and dropsonde point D in spiral cloud band of typhoon Wipha (0713)
图 5 对流云团内COSMIC掩星点和临近探空站探测廓线比较
(a)温度和露点, (b)折射率指数, (c)温度差和露点差, (d)水汽压
Fig. 5 Comparison of profiles from COSMIC inversion and radiosonde in convective cloud clusters
(a) temperature and dewpoint, (b) refractive index, (c) temperature difference and dewpoint difference, (d) vapor pressure
图 6 2007年13号台风韦帕螺旋云带内COSMIC掩星探测与下投探空仪观测廓线比较
(a)温度和露点, (b)折射率指数, (c)气压, (d)水汽压
Fig. 6 Comparison of profiles from COSMIC inversion and radiosonde in convective cloud clusters
(a) temperature and dewpoint, (b) refractive index, (c) pressure, (d) vapor pressure
表 1 空基COSMIC部分探空资料列表
Table 1 List of part data for COSMIC profiles
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