Abstract
Microwave radiances from passive polar-orbiting radiometers have been, until recently, assimilated in the Met Office global numerical weather prediction system after the scenes significantly affected by atmospheric scattering are discarded. Recent system upgrades have seen the introduction of a scattering-permitting observation operator and the development of a variable observation error using both liquid and ice water paths as proxies of scattering-induced bias. Applied to the Fengyun 3 Microwave Temperature Sounder 2 (MWTS-2) and the Microwave Humidity Sounder 2 (MWHS-2), this methodology increases the data usage by up to 8% at 183 GHz. It also allows for the investigation into the assimilation of MWHS-2 118 GHz channels, sensitive to temperature and lower tropospheric humidity, but whose large sensitivity to ice cloud have prevented their use thus far. While the impact on the forecast is mostly neutral with small but significant short-range improvements, 0.3% in terms of root mean square error, for southern winds and low-level temperature, balanced by 0.2% degradations of short-range northern and tropical low-level temperature, benefits are observed in the background fit of independent instruments used in the system. The lower tropospheric temperature sounding Infrared Atmospheric Sounding Interferometer (IASI) channels see a reduction of the standard deviation in the background departure of up to 1.2%. The Advanced Microwave Sounding Unit A (AMSU-A) stratospheric sounding channels improve by up to 0.5% and the Microwave Humidity Sounder (MHS) humidity sounding channels improve by up to 0.4%.
摘要
大气订正后的极轨卫星微波辐射计数据不久前同化进入英国气象局全球数值天气预报系统. 最新的系统升级已经引入一个允许散射的观测算子, 同时使用液态水和冰水路径作为散射诱导的代理, 产生了可变的观测误差. 这种方法应用到风云三号气象卫星微波温度计 2 (MWTS-2) 和微波湿度计 2 (MWHS-2) 后, 将 183GHz 通道数据的可用性提高了最多 8%. 同时这种方法的引入还实现了 MWHS-2 118GHz 通道数据的同化研究, 该通道对温度和对流层低层湿度敏感, 但该通道对冰云的高度敏感影响了对该通道的应用. 通过验证表明, 总体来看对预报的影响是中性的, 南半球风场和低层气温短期预报改善幅度很小但很显著, 均方根误差为 0.3%, 但对北半球和热带地区会下降 0.2%. 对短期预报的详细检查表明, 微波和红外光谱域对背景的观测拟合得到了改进. 对红外大气探测干涉仪 (IASI) 各通道对流层低层大气温度背景偏差的标准差的改进达到 1.2%. 对先进微波探测仪 A (AMSU-A) 平流层探测通道的改进达到 0.5%, 对微波湿度计 (MHS) 湿度探测通道的改进达到 0.4%.
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Acknowledgements
This work was supported by the UK — China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund. We are grateful to Chawn HARLOW for the useful discussions that helped us improve this study.
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Article Highlights
• The all-sky assimilation of MWHS-2 118 GHz and 183 GHz channels can benefit the Met Office NWP global system.
• There is added value in the combined assimilation of the 118 GHz and 183 GHz channels compared to the 183 GHz channels alone.
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Carminati, F., Migliorini, S. All-sky Data Assimilation of MWTS-2 and MWHS-2 in the Met Office Global NWP System. Adv. Atmos. Sci. 38, 1682–1694 (2021). https://doi.org/10.1007/s00376-021-1071-5
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DOI: https://doi.org/10.1007/s00376-021-1071-5