TY - RPRT
AU - Liam Steele
AU - Niels Bormann
AU - David Duncan
AB - Microwave observations sensitive to temperature and water vapour are one of the most important observation types in the four-dimensional variational assimilation scheme used at ECMWF. In this report we assess the forecast benefits of assimilating early-morning data from the Micro-Wave Humidity Sounder-2 (MWHS-2) instrument aboard the Fengyun-3E (FY-3E) satellite, and also investigate the optimal spatial thinning scale for microwave humidity sounder observations. These investigations will help to inform on how to extract the most benefit from both current and future microwave sounder instruments, such as those on the upcoming Metop second generation satellites and the EPS-Sterna constellation. We find that assimilating the FY-3E MWHS-2 data leads to short- and medium-range forecast improvements, particularly in the southern hemisphere, which are statistically-significant out to day 3. While some of the forecast improvement is due to lower noise compared to previous incarnations of the same instrument, dedicated assimilation experiments demonstrate that the early morning orbit of FY-3E, which complements the local times of other assimilated data, also plays a role. Due to the observed forecast improvements, the FY-3E MWHS-2 instrument became operationally active on 22 February 2023. We also find that the current spatial thinning scale for humidity sounding observations of 111 km can be reduced to ∼55 km. This results in less data being discarded and gives an improvement to forecasts out to day 3. Thinning scales smaller than ∼55 km result in degraded forecasts, likely due to neglected spatial observation error correlations.
BT - EUMETSAT/ECMWF Fellowship Programme Research Report
DA - 12/2023
DO - 10.21957/f42a9d9542
M1 - RR62
M3 - EUMETSAT/ECMWF Fellowship Programme Research Report
N2 - Microwave observations sensitive to temperature and water vapour are one of the most important observation types in the four-dimensional variational assimilation scheme used at ECMWF. In this report we assess the forecast benefits of assimilating early-morning data from the Micro-Wave Humidity Sounder-2 (MWHS-2) instrument aboard the Fengyun-3E (FY-3E) satellite, and also investigate the optimal spatial thinning scale for microwave humidity sounder observations. These investigations will help to inform on how to extract the most benefit from both current and future microwave sounder instruments, such as those on the upcoming Metop second generation satellites and the EPS-Sterna constellation. We find that assimilating the FY-3E MWHS-2 data leads to short- and medium-range forecast improvements, particularly in the southern hemisphere, which are statistically-significant out to day 3. While some of the forecast improvement is due to lower noise compared to previous incarnations of the same instrument, dedicated assimilation experiments demonstrate that the early morning orbit of FY-3E, which complements the local times of other assimilated data, also plays a role. Due to the observed forecast improvements, the FY-3E MWHS-2 instrument became operationally active on 22 February 2023. We also find that the current spatial thinning scale for humidity sounding observations of 111 km can be reduced to ∼55 km. This results in less data being discarded and gives an improvement to forecasts out to day 3. Thinning scales smaller than ∼55 km result in degraded forecasts, likely due to neglected spatial observation error correlations.
PB - ECMWF
PY - 2023
T2 - EUMETSAT/ECMWF Fellowship Programme Research Report
TI - Assimilating FY-3E MWHS-2 obs, and assessing all-sky humidity sounder thinning scales
UR -  
SN - RR62
ER -