Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

Abstract

Abstract. In-situ observational data on the relative humidity (RH) in the upper troposphere and lowermost stratosphere (UT/LS), or tropopause region, respectively, collected aboard civil passenger aircraft in the MOZAIC (Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) programme were reanalysed for the period 2000 to 2009. Previous analyses of probability distribution functions (PDF) of upper troposphere humidity (UTH) data from MOZAIC observations from year 2000 and later indicated a bias of UTH data towards higher RH values compared to data of the period 1994 to 1999. As a result, PDF of UTH data show a substantial fraction of observations above 100% relative humidity with respect to liquid water (RHliquid), which is not possible from thermodynamical principles. An in-depth reanalysis of the data set recovered a calibration artefact from year 2000 on, while data of the previous period from 1994 to 1999 were found to be correct. The full data set for 2000–2009 was reanalysed applying the adjusted calibration procedure. Applied correction schemes and a revised error analysis are presented along with the reanalysed PDF of RHliquid and RHice.