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%.
Highlights
The Fengyun 3 (FY-3) C and D are China’s latest operational meteorological satellites operating from polar orbits (Zhang et al, 2019)
A strategy that has been successfully applied to radiances from the Advanced Microwave Sounding Unit A (AMSU-A) and Microwave Humidity Sounder (MHS) instruments, which are assimilated operationally in all-sky conditions in the Met Office global model
In addition to the potential benefit from a more aggressive use of available observations, insights into the added value of the 118 GHz channels can guide the applications related to future satellite missions such as the Microwave Imager (MWI) onboard MetOp-SG platforms or the Cubesats constellation TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats) supported by the NASA Earth Venture-Instrument (EVI-3) program
Summary
The Fengyun 3 (FY-3) C and D are China’s latest operational meteorological satellites operating from polar orbits (Zhang et al, 2019). CARMINATI AND MIGLIORINI ried out at the European Centre for Medium Range Weather Forecast (ECMWF) and the Met Office by Lu et al (2015), Lawrence et al (2017, 2018), Carminati et al (2018, 2020), and Duncan and Bormann (2020) These evaluations have been conducted using short-range forecasts from NWP models as a reference comparator as well as a transfer medium for inter-satellite comparisons in double differences. The ECMWF system, on the other hand, allows for scattering scenes to be used thanks to a variable observation error that accounts for the presence of cloud in the model background and the observation, as well as an observation operator accounting for atmospheric scattering (Lawrence et al, 2018) This is referred to as all-sky assimilation. The structure of this document is as follows: section 2 documents the current usage of MWTS-2 and MWHS-2 in the Met Office system and details how their observations are processed within the new all-sky framework, section 3 presents the assimilation experiment set up and discusses the results, and section 4 concludes the study
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