Validation of ACE-FTS N2O measurements

[摘要] The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launchedon 12 August 2003, carrying two instruments that measure vertical profiles ofatmospheric constituents using the solar occultation technique. One of theseinstruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volumemixing ratio (VMR) profiles of nitrous oxide (N₂O) from the upper troposphereto the lower mesosphere at a vertical resolution of about 3–4 km. In this study,the quality of the ACE-FTS version 2.2 N₂O data is assessed through comparisonswith coincident measurements made by other satellite, balloon-borne, aircraft,and ground-based instruments. These consist of vertical profile comparisons withthe SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR,and single balloon flights of SPIRALE and FIRS-2, and partial column comparisonswith a network of ground-based Fourier Transform InfraRed spectrometers (FTIRs).Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between −42 ppbv and+17 ppbv, with most within ±20 ppbv. This corresponds to relative deviationsfrom the mean that are within ±15%, except for comparisons with MIPAS near30 km, for which they are as large as 22.5%. Between 18 and 30 km, the meanabsolute differences for the satellite comparisons are generally within ±10 ppbv.From 30 to 60 km, the mean absolute differences arewithin ±4 ppbv, and are mostly between −2 and +1 ppbv. Given the smallN₂O VMR in this region, the relative deviations from the mean are thereforelarge at these altitudes, with most suggesting a negative bias in the ACE-FTSdata between 30 and 50 km. In the comparisons with the FTIRs, the mean relativedifferences between the ACE-FTS and FTIR partial columns (which cover a mean altitude range of 14 to 27 km)are within ±5.6% for eleven of the twelve contributing stations. This mean relative difference isnegative at ten stations, suggesting a small negative bias in the ACE-FTS partialcolumns over the altitude regions compared. Excellent correlation (R=0.964) isobserved between the ACE-FTS and FTIR partial columns, with a slope of 1.01 andan intercept of −0.20 on the line fitted to the data.

[学科分类] 大气科学