Six years of mesospheric CO estimated from ground-based frequency-switched microwave radiometry at 57° N compared with satellite instruments

[摘要] Measurements of mesospheric carbon monoxide, CO, provide importantinformation about the dynamics in the mesosphere region since CO has along lifetime at these altitudes. Ground-based measurements of mesosphericCO made at the Onsala Space Observatory, OSO, (57° N, 12° E)are presented. The dataset covers the period 2002–2008 and is hence uniquely long for ground-based observations. The simple and stable 115 GHzfrequency-switched radiometer, calibration method, retrieval procedure anderror characterization are described. A comparison between our measurementsand co-located CO measurements from the satellite sensors ACE-FTS onScisat (v2.2), MLS on Aura (v3-3), MIPAS on Envisat (V3O_CO_12 + 13 and V4O_CO_200) and SMR on Odin (v225 and v021) is carried out. Ourinstrument, OSO, and the four satellite instruments show the same generalvariation of the vertical distribution of mesospheric CO in both theannual cycle and in shorter time period events, with high CO mixingratios during winter and very low amounts during summer in the observed55–100 km altitude range. During 2004–2008 the agreement of the OSOinstrument and the satellite sensors ACE-FTS, MLS and MIPAS (200) is good inthe altitude range 55–70 km. Above 70 km, OSO shows up to 25%higher CO column values compared to both ACE and MLS. For the timeperiod 2002–2004, CO from MIPAS (12 + 13) is up to 50% lower than OSObetween 55 and 70 km. Mesospheric CO from the two versions ofSMR deviates up to ±65% when compared to OSO, but the analysis is basedon only a few co-locations.

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