Results from the SPARC Reanalysis Intercomparison Project (S-RIP) during 2013-2017

• Reanalysis is particularly challenging in the tropical stratosphere because:•(i) Very limited in situ wind data•(ii) The Coriolis parameter is small–Satellite temperature observations do not constrain the winds as strongly as higher latitudes•(iii) Large vertical shears (~ 30 m/s over~ 3 km)•(iv) Most forecast models used for reanalysis do not simulate a spontaneous QBO–Persistent model bias damp the QBO signals as introduced by data assimilation