The Microwave Temperature Sounder(MWTS)-2 has a total of 13 temperature-sounding channels with the capability of observing radiance emissions from near the surface to the stratosphere. Similar to the Advanced Technolo...The Microwave Temperature Sounder(MWTS)-2 has a total of 13 temperature-sounding channels with the capability of observing radiance emissions from near the surface to the stratosphere. Similar to the Advanced Technology Microwave Sounder(ATMS), striping pattern noise, primarily in the cross-track direction, exists in MWTS-2 radiance observations. In this study, an algorithm based on principal component analysis(PCA) combined with ensemble empirical mode decomposition(EEMD) is described and applied to MWTS-2 brightness temperature observations. It is arguably necessary to smooth the first three principal component(PC) coefficients by removing the first four intrinsic mode functions(IMFs) using the EEMD method(denoted as PC3/IMF4). After the PC3/IMF4 noise mitigation, the striping pattern noise is effectively removed from the brightness temperature observations. The noise level in MWTS-2 observations is significantly higher than that detected in ATMS observations. In May 2014, the scanning profile of MWTS-2 was adjusted from varying-speed scanning to constantspeed scanning. The impact on striping noise levels brought on by this scan profile change is also analyzed here. The striping noise in brightness temperature observations worsened after the profile change. Regardless of the scan profile change, the striping noise mitigation method reported in this study can more or less suppress the noise levels in MWTS-2 observations.展开更多
The Microwave Temperature Sounder 2(MWTS-2)is a cross-track radiometer that has 13 channels of sampling radiances emitted from different vertical levels of the atmosphere.Because of the varying scan angles of each fie...The Microwave Temperature Sounder 2(MWTS-2)is a cross-track radiometer that has 13 channels of sampling radiances emitted from different vertical levels of the atmosphere.Because of the varying scan angles of each field of view within a scan line,observations from the MWTS-2 are subject to strong scan-position-dependent features,i.e.,the limb effect.When examining brightness temperatures(TBs),weather signals observed at every temperature-sounding channel are often concealed by scan-dependent patterns.This study,therefore,proposes a limb correction method to remove scan-dependent features so that the underlying weather signals can be uncovered.Limb-corrected TBs can be used to monitor large-scale patterns over the globe as well as extreme weather events such as typhoons.Limb-corrected TBs are also more correlated with atmospheric physical variables such as temperature and liquid water path.展开更多
Microwave radiance data assimilation(DA)enhances initial conditions for numerical weather prediction(NWP)and shows great potential for improving forecasts in tropical regions like East Africa,where observational data ...Microwave radiance data assimilation(DA)enhances initial conditions for numerical weather prediction(NWP)and shows great potential for improving forecasts in tropical regions like East Africa,where observational data scarcity and complex tropical dynamics present significant challenges.Effectiveness of radiance assimilation is a function of variations in channel sensitivity to local atmospheric conditions and region-specific bias characteristics.However,microwave radiance assimilation in Limited-Area Models(LAMs)over East Africa remains largely unexplored.This study investigates the impact of assimilating microwave radiance channels with weighting functions peaking in the troposphere and lower stratosphere on rainfall forecasts over East Africa from a five-satellite constellation:the Microwave Temperature Sounder-2(MWTS-2)onboard Fengyun-3D(FY-3D),the Advanced Technology Microwave Sounder(ATMS)onboard JPSS,and the Advanced Microwave Sounding Unit-A(AMSU-A)onboard NOAA-15/18/19 satellites.The 6-h cycling DA experiments over a convectively active 15-day period show that assimilation of ATMS and AMSU-A radiances enhances representation of initial conditions,thereby reducing analysis and forecast errors.Assimilation of MWTS-2 radiances improves the analysis and forecasts further,especially for the tropospheric thermodynamic fields.The joint multi-microwave assimilation fills critical observation gaps over East Africa,allowing realistic simulations of diurnal precipitation trends,and capturing rainfall intensities exceeding 50 mm in 24 h,especially for T+12-h to T+24-h lead times.These findings are validated by a high-intensity rainfall case over Mandera,where spatio-temporal consistency is observed in instability and convection triggering.Forecast evaluation metrics have confirmed enhanced rainfall forecast skill for deep and rapidly developing convective systems.The study provides valuable insights into the gains of assimilating microwave radiance data over tropical regions,particularly in East Africa.展开更多
基金supported by the National Key R&D Program (Grant No. 2018YFC1506702)
文摘The Microwave Temperature Sounder(MWTS)-2 has a total of 13 temperature-sounding channels with the capability of observing radiance emissions from near the surface to the stratosphere. Similar to the Advanced Technology Microwave Sounder(ATMS), striping pattern noise, primarily in the cross-track direction, exists in MWTS-2 radiance observations. In this study, an algorithm based on principal component analysis(PCA) combined with ensemble empirical mode decomposition(EEMD) is described and applied to MWTS-2 brightness temperature observations. It is arguably necessary to smooth the first three principal component(PC) coefficients by removing the first four intrinsic mode functions(IMFs) using the EEMD method(denoted as PC3/IMF4). After the PC3/IMF4 noise mitigation, the striping pattern noise is effectively removed from the brightness temperature observations. The noise level in MWTS-2 observations is significantly higher than that detected in ATMS observations. In May 2014, the scanning profile of MWTS-2 was adjusted from varying-speed scanning to constantspeed scanning. The impact on striping noise levels brought on by this scan profile change is also analyzed here. The striping noise in brightness temperature observations worsened after the profile change. Regardless of the scan profile change, the striping noise mitigation method reported in this study can more or less suppress the noise levels in MWTS-2 observations.
基金supported by the National Natural Science Foundation of China (Grant No.91337218)
文摘The Microwave Temperature Sounder 2(MWTS-2)is a cross-track radiometer that has 13 channels of sampling radiances emitted from different vertical levels of the atmosphere.Because of the varying scan angles of each field of view within a scan line,observations from the MWTS-2 are subject to strong scan-position-dependent features,i.e.,the limb effect.When examining brightness temperatures(TBs),weather signals observed at every temperature-sounding channel are often concealed by scan-dependent patterns.This study,therefore,proposes a limb correction method to remove scan-dependent features so that the underlying weather signals can be uncovered.Limb-corrected TBs can be used to monitor large-scale patterns over the globe as well as extreme weather events such as typhoons.Limb-corrected TBs are also more correlated with atmospheric physical variables such as temperature and liquid water path.
基金Supported by the National Natural Science Foundation of China(U2442218 and U2442601)。
文摘Microwave radiance data assimilation(DA)enhances initial conditions for numerical weather prediction(NWP)and shows great potential for improving forecasts in tropical regions like East Africa,where observational data scarcity and complex tropical dynamics present significant challenges.Effectiveness of radiance assimilation is a function of variations in channel sensitivity to local atmospheric conditions and region-specific bias characteristics.However,microwave radiance assimilation in Limited-Area Models(LAMs)over East Africa remains largely unexplored.This study investigates the impact of assimilating microwave radiance channels with weighting functions peaking in the troposphere and lower stratosphere on rainfall forecasts over East Africa from a five-satellite constellation:the Microwave Temperature Sounder-2(MWTS-2)onboard Fengyun-3D(FY-3D),the Advanced Technology Microwave Sounder(ATMS)onboard JPSS,and the Advanced Microwave Sounding Unit-A(AMSU-A)onboard NOAA-15/18/19 satellites.The 6-h cycling DA experiments over a convectively active 15-day period show that assimilation of ATMS and AMSU-A radiances enhances representation of initial conditions,thereby reducing analysis and forecast errors.Assimilation of MWTS-2 radiances improves the analysis and forecasts further,especially for the tropospheric thermodynamic fields.The joint multi-microwave assimilation fills critical observation gaps over East Africa,allowing realistic simulations of diurnal precipitation trends,and capturing rainfall intensities exceeding 50 mm in 24 h,especially for T+12-h to T+24-h lead times.These findings are validated by a high-intensity rainfall case over Mandera,where spatio-temporal consistency is observed in instability and convection triggering.Forecast evaluation metrics have confirmed enhanced rainfall forecast skill for deep and rapidly developing convective systems.The study provides valuable insights into the gains of assimilating microwave radiance data over tropical regions,particularly in East Africa.
