Stratospheric O3, NO2, and NO3 number density profile from SCIAMACHY lunar occultation spectroscopic measurements: Retrieval, validation and interpretation

Abstract

Stratospheric profiles of O3, NO2, and NO3 were retrieved from lunar transmitted spectra measured by SCIAMACHY over high southern latitude (60Ã °S - 90Ã °S), from March to June 2003 and January to June 2004. The global spectral fitting method by the differential optical depth approach was applied to simultaneously fit O3 and NO2 using the spectral range of 430-460 nm and 510-560 nm. Furthermore, NO3 was fitted using the visible spectral range of 615-680 nm containing NO3 intense absorption bands at 623 nm and 662 nm. Validation of the retrieved SCIAMACHY O3 and NO2 profiles were carried out. O3 profiles were compared with HALOE,POAM-III, SAGE-II and -III, and MIPAS. Whereas NO2 profiles were compared with HALOE, MIPAS, and SAGE-III. The validation results show that the quality of SCIAMACHY O3profiles is high, within 10-25% and 10-35% for O3 and NO2 respectively. To test our current understanding of NO3 chemistry, the retrieved NO3 vertical profiles were compared with a full photochemical model and a relatively simple steady state model. The calculations from a full photochemical model constrained by retrieved O3 and analyzed ECMWF temperatures in the altitude range between 24 to 45 km. Below about 35-40 km, observed NO3 is well reproduced by photochemical steady state calculations. Differences between observed and modeled NO3 are within the estimated accuracy of 20-35%, demonstrating that we have a reasonable understanding of the behavior of NO3 in the polar stratosphere.