Comparisons between ground-based FTIR and MIPAS N2O and HNO3 profiles before and after assimilation in BASCOE

[摘要] Within the framework of the Network for Detection of Atmospheric CompositionChange (NDACC), regular ground-based Fourier transform infrared (FTIR)measurements of many species are performed at several locations. Inversionschemes provide vertical profile information and characterization of theretrieved products which are therefore relevant for contributing to thevalidation of MIPAS profiles in the stratosphere and upper troposphere.We have focused on the species HNO₃ and N₂O at 5NDACC-sites distributed in both hemispheres, i.e., Jungfraujoch(46.5° N) and Kiruna (68° N) for the northern hemisphere, andWollongong (34° S), Lauder (45° S) and Arrival Heights(78° S) for the southern hemisphere. These ground-baseddata have been compared with MIPAS offline profiles (v4.61) for the year2003, collocated within 1000 km around the stations, in the lower to middlestratosphere. To get around the spatial collocation problem, comparisons havealso been made between the same ground-based FTIR data and the correspondingprofiles resulting from the stratospheric 4D-VAR data assimilation systemBASCOE constrained by MIPAS data. This paper discusses the results of the comparisons and theusefullness of using BASCOE profiles as proxies for MIPAS data. It shows goodagreement between MIPAS and FTIR N₂O partial columns: the biases arebelow 5% for all the stations and the standard deviations are below 7% forthe three mid-latitude stations, and below 10% for the high latitude ones.The comparisons with BASCOE partial columns give standard deviations below4% for the mid-latitude stations to less than 8% for the high latitudeones. After making some corrections to take into account the known bias dueto the use of different spectroscopic parameters, the comparisons ofHNO₃ partial columns show biases below 3% and standard deviationsbelow 15% for all the stations except Arrival Heights (bias of 5%, standarddeviation of 21%). The results for this species, which has a larger spatialvariability, highlight the necessity of defining appropriate collocationcriteria and of accounting for the spread of the observed airmasses. BASCOEappears to have more deficiencies in producing proxies of MIPAS HNO₃profiles compared to N₂O, but the obtained standard deviation of lessthan 10% between BASCOE and FTIR is reasonable. Similar results on profilescomparisons are also shown in the paper, in addition to partial column ones.

[学科分类] 大气科学