The Influences of TOVS Radiance Assimilation on Temperature and Moisture Tendencies in JRA-25 and ERA-40

Since ERA-40 selected 3D VAR (the default in cycle 21r4 was 4DV AR), a scheme named FGAT (the first guess at an appropriate time) was used in which observational innovations are calculated and compared with the first guess at the nearest forecast time.\n Relays of calculation streams inevitably bring unrealistic shifts between them. Preadjusting the TOVS radiances (and other quantities) before assimilation appears to be a viable option before attempting a reanalysis update. 2 Inconsistencies in the forecast model and DA systems also lead to inconsistencies in output reanalyses. [...] using a single stream system with preadjusted forcing parameters such quantities as ozone, SST, and ice cover is important.