Model results of OH airglow considering four different wavelength regions to derive night-time atomic oxygen and atomic hydrogen in the mesopause region

Abstract

Abstract. Based on the zero-dimensional box model Module Efficiently Calculating the Chemistry of the Atmosphere/Chemistry As\nA Box model Application (CAABA/MECCA-3.72f), an OH\nairglow model was developed to derive night-time number densities of atomic\noxygen ([ O(3P) ]) and atomic hydrogen ([H]) in the mesopause region\n( ∼75 –100\u2009km). The profiles of [ O(3P) ] and [H] were\ncalculated from OH airglow emissions measured at 2.0\u2009 µ m by the Sounding of the Atmosphere using Broadband Emission Radiography (SABER)\ninstrument on board NASA s Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)\nsatellite.\nThe two target species were used to initialize the OH airglow\nmodel, which was empirically adjusted to fit four different OH airglow\nemissions observed by the satellite/instrument configuration TIMED/SABER at\n2.0\u2009 µ m and at 1.6\u2009 µ m as well as measurements by\nthe Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument on board the Environmental Satellite (ENVISAT)\nof the transitions OH(6-2)\nand OH(3-1). Comparisons between\nthe “best-fit model” obtained here and the satellite measurements suggest\nthat deactivation of vibrationally excited OH( ν ) via OH( ν≥7 ) + O2 might favour relaxation to OH( ν ′ ≤ 5 ) + O2 by\nmulti-quantum quenching. It is further indicated that the deactivation\npathway to OH( ν ′ = ν - 5 ) + O2 dominates. The results also provide\ngeneral support of the recently proposed mechanism OH( ν ) + O(3P) → OH( 0 ≤ ν ′ ≤ ν - 5 ) + O(1D) but suggest slower rates of\nOH( ν = 8 , 7 , 6 , 5 ) + O(3P) , partly disagreeing with laboratory\nexperiments. Additionally, deactivation to OH( ν ′ = ν - 5 ) + O(1D) \nmight be preferred. The profiles of [ O(3P) ] and [H] derived here are\nplausible between 80 and 95\u2009km but should be regarded as an upper limit.\nThe values of [ O(3P) ] obtained in this study agree with the\ncorresponding TIMED/SABER values between 80 and 85\u2009km but are larger from\n85 to 95\u2009km due to different relaxation assumptions of OH( ν ) + O(3P) .\nThe [H] profile found here is generally larger than TIMED/SABER [H] by about\n50\u2009% from 80 to 95\u2009km, which is primarily attributed to our faster OH( ν=8 ) + O2 rate.