Uncertainty of temperature, humidity and pressure profiles from the first ROM SAF Climate Data Record.
Presenter:
Johannes K. Nielsen
Danish Meteorological Institute, Lyngbyvej 100, DK 2100 Copenhagen, Denmark
Danish Meteorological Institute, Lyngbyvej 100, DK 2100 Copenhagen, Denmark
Talk
The ROM SAF Climate Data Record version 1 (CDR v1.0) is based on radio occultation (RO) data from the COSMIC, METOP, CHAMP and GRACE missions. These data have been reprocessed from Level 1A (excess phase) to Level 2 (profiles of meteorological parameters) and Level 3 (gridded monthly zonal means). Here we describe the 1D-Var algorithm behind the Level 2B (temperature, specific humidity, and pressure) products and assess their quality by comparison against GCOS Reference Upper-Air Network (GRUAN). The temperature, specific humidity, and surface pressure are retrieved by using (ERA-I) as background fields. Improvement in temperature accuracy is achieved primarily in the altitude interval between 10 and 30 km. Improvement in specific humidity accuracy is primarily obtained in the lower troposphere.
The uncertainties of tropospheric RO specific humidity and stratospheric temperature are validated by comparison to 15000 collocated GRUAN RS92 profiles. The specific humidity stochastic errors, which originate mainly from the RO profiles, are found to be consistent with the latitude-dependent predicted RO product uncertainty in an altitude range between 2 and 6 km. The comparison against GRUAN reveals a night-time negative RO specific humidity bias of 5%. The temperature stochastic errors in the lower stratosphere appear to be 0.2 K larger than the predicted uncertainty. Generally, the ROM SAF CDR v1.0 confirms the known day-night differences in GRUAN, but slightly shifted such that RO is 0-5 % dryer and 0-0.15 K colder than GRUAN.
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