Global stratospheric HOCl distributions retrieved from infrared limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

Vertical profiles of stratospheric HOCl were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the Envisat research satellite. These are the first HOCl measurements with global coverage. The v₂ transitions between 1215.725 and 1275.550 cm^-1 were used for inference of the vertical profiles. The maximal volume mixing ratios were found in the tropics at altitudes of ∼35 km (daytime) and ∼37 km (nighttime), with values up to 0.22 ppbv and 0.23 ppbv for zonal mean values at 5° latitude binning. The peak altitude of nonpolar nighttime measurements is on average higher by 2.4 ± 0.3 km compared to nonpolar daytime measurements and higher by 2.2 ± 0.3 km at high latitudes poleward of ±45° compared to respective equatorward latitudes. The diurnal variability is largest at 30°S at 46 km altitude, reaching amplitudes of 0.11 ppbv. In the Antarctic a secondary peak at 23-25 km (0.14 ppbv) was found on 19-24 September 2002, which is attributed to heterogeneous chemistry. An estimated single-profile precision of 0.03-0.08 ppbv could be achieved at an altitude resolution of 9 km in an altitude range between 20 and 50 km. Taking the trend into account, these measurements are reasonably consistent with former far-infrared measurements.