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Test of the night‐time polar stratospheric NO 2 decay using wintertime SAOZ measurements and chemical data assimilation
Author(s) -
Marchand M.,
Bekki S.,
Denis L.,
Pommereau J.P.,
Khattatov B. V.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2003gl017582
Subject(s) - sunrise , sunset , stratosphere , atmospheric sciences , polar , polar night , polar vortex , environmental science , occultation , meteorology , sink (geography) , latitude , physics , astrophysics , astronomy , geography , cartography
Chemistry Transport Models (CTMs) tend to underestimate very severely NO 2 concentrations in the polar lower stratosphere during the winter suggesting that either the NO x sink is overestimated or a source of NO x is missing in models. We study the night‐time decay of polar NO 2 because it is controlled by the reaction between NO 2 and O 3 which is thought to be the main NO x sink at high latitudes winter. The model‐calculated night‐time decay of polar NO 2 is tested using solar occultation measurement of NO 2 and O 3 taken within the Northern polar vortex by the “Système d'Analyse parObservation Zénithal” (SAOZ) instrument on board of a long duration balloon in February 2000. A trajectory analysis is performed in order to find air parcels which have been sampled at sunset and at sunrise by the SAOZ instrument and have stayed in the dark between the measurements. Sunset (or sunrise) SAOZ measurements are then assimilated in a trajectory photochemical model in a variational mode and compared to the corresponding sunrise (or sunset) SAOZ measurements which are called validation measurements. The results are used to assess the ability of the model to reproduce the observed night‐time evolution of NO 2 . Overall, there is a good agreement between analyzed NO 2 and validation measurements indicating that the night‐time chemistry of NO 2 appears to be properly described by the model. The results do not hint at all at the existence of a NO x source, and certainly not a source strong enough to counteract the NO 2 sink (NO 2 + O 3 reaction).