Validation of the Atmospheric Chemistry Experiment by noncoincident MkIV balloon profiles

We have compared volume mixing ratio profiles of atmospheric trace gases measured by the Atmospheric Chemistry Experiment (ACE) version 2.2 and the MkIV solar occultation Fourier transform infrared spectrometers. These gases are H2O, O3, N2O, CO, CH4, HNO3, HF, HCl, OCS, ClONO2, HCN, CH3Cl, CF4, CCl2F2, CCl3F, COF2, CHF2Cl, and SF6. Due to the complete lack of close spatiotemporal coincidences between the ACE occultations and the MkIV balloon flights, we used potential temperatures and equivalent latitudes from analyzed meteorological fields to find comparable ACE and MkIV profiles. The results show excellent agreement for CH4, N2O, and other long‐lived gases but slightly poorer agreement for shorter‐lived species like CO, O3, and HCN. For example, in the upper troposphere (∼400–650 K), maximum differences between MkIV and ACE are 2.4% for CH4, 1.7% for N2O, −12.4% for CO, −15.9% for O3, and −5.6% for HCN. In the lower stratosphere (∼650–900 K), maximum MkIV‐ACE differences are 7.6% for CH4, 14.1% for N2O, 7.3% for CO, −9.2% for O3, and 31.5% for HCN. Apart from a small vertical misregistration problem, the overall agreement between MkIV and ACE is very good. Key Points First use of a noncoincident validation method for MkIV and ACE profiles Equivalent latitudes and theta coordinates allow better validation Very good agreement between ACE and MkIV profiles of long‐lived gases