Vertical diffusion transport of atomic oxygen in the mesopause region consistent with chemical losses and continuity: Global mean and inter-annual variability

This study describes the vertical diffusion velocity and eddy transport coefficient means derived from the climatological measurements of mesospheric [O] by SABER. Fifty years ago, Colegrove et al. (1967) described a process to transition between the two regions of the atmosphere using transport and continuity equations along with a 1-D composition profile. The two parts of this study are calculations of the downward O diffusion velocities and eddy diffusion coefficients using O densities derived from SABER for: 1) the global mean (±55°) and 2) the inter-annual variation of global and equatorial annual mean O densities. The derived transport diffusion velocities range from ∼1 to 4 cm s−1 at 95-83 km, and kzz varies between ∼9.0-5.0 × 105 cm2 s−1 over the same altitude range. The values of kzz derived here in the 80-100 km region are larger at 98 km than those calculated by Salinas et al. (2016) using SABER CO2 measurements and ∼0.5 times less than Qian et al. (2009, 2013 and TIEGCM model) which were derived from studies of thermospheric O/N2 measurements. Consideration of the kzz altitude profiles in the mesosphere, the mean values for both Salinas et al. (2016) and this study is ∼7. E+05 cm2s-1. The standard deviation of the inter-annual variability in kzz (and downward transport velocities) from globally averaged O profiles is <5%. The deviation is slightly larger (7.4%) at the equator, where a QBO trend is noted at 88 km, although not sufficiently large to be detected in the time history of the mesospheric O column density. The global average column density of O in the mesosphere (80-100 km) had a 0.30% change per sunspot. We suggest that model studies may need to consider higher turbulence (and kzz) in the 100-110 km region in order to satisfy both mesospheric and thermospheric composition.