Assessment of Himawari-8 AMV data in the ECMWF system

This report evaluates Atmospheric Motion Vectors (AMVs) from Himawari-8 in the ECMWF system and compares the results to findings for its predecessor, Multifunction Transport Satellite - 2 (MTSAT-2). Himawari-8, carries a more advanced imaging instrument and a new method has been developed for the AMV derivation. AMVs from the new satellite were first analysed using first guess departure statistics, followed by assimilation trials.

The quality of Himawari-8 data exceeds that of MTSAT-2 and even prior to any screening it is comparable to MTSAT-2 data that has passed through the strict quality control applied for assimilation. Many more AMVs are available due to changes both in the instrument and algorithm with significant changes found in the geographical and height distribution. A large number are also assigned heights at unusually high pressures, most likely a result of surface contamination of the cloud top radiance, however there were no obvious detrimental effects.

The assimilation of Himawari-8 AMVs gives positive impacts on the forecast vector wind fields exceeding the effects of MTSAT-2, especially at low levels and in the tropics. There are also significant improvements in the fit of conventional wind observations (around 1% reduction in error in the tropics). The final channel selection is similar to the configuration for MTSAT-2 AMVs, and in particular makes use of data from only one of the three available water vapour channels, but still increases the global total number of AMVs assimilated by around 40% compared to MTSAT-2. Further refinements were attempted with the addition of remaining water vapour channels and the removal of the near surface AMVs, but these modifications showed no clear benefits. Himawari-8 AMVs have been assimilated at ECMWF since 15th March 2016.