The ROM SAF reanalyses
The ROM SAF has recently completed two low resolution GPS-RO reanalyses for the period 2007-2015. These datasets are available to users via ECMWF's web-api service. The aim has been to quantify the impact of the "anchor measurements" in determining the mean reanalysis state. The first ROM SAF reanalysis assimilates just reprocessed GPS-RO data and AMSU-A channel 14 to constrain the upper stratosphere. The second reanalysis also assimilates conventional data that has not been bias corrected using variational bias correction. Comparisons against ERA5 and ERA-Interim will be presented. These comparisons indicate that the ERA5 temperatures at 200 hPa over North America and the north Atlantic are still warm as a result biased aircraft temperature measurements. In addition, we will show that a realistic quasi-biennial oscillation (QBO) of the zonally averaged zonal winds in the tropical stratosphere can be produced by just assimilating GPS-RO and AMSU-A channel 14. Further, it is also shown that a realistic QBO can be retrieved directly from a ROM SAF monthly mean geopotential climatology using a suitable formulation of geostrophic balance.