Sixteen years (2002-2018) of SABER measurements and the MSIS model were used to study the average SAO (semi-annual oscillation) and AO (annual oscillation) variations of kzz (eddy diffusion coefficient) in the mesosphere (80-96 km).

Abstract:

The climatology of atomic oxygen in the MLT (mesosphere and lower thermosphere) is balanced by O production via photodissociation of O₂ in the lower thermosphere and recombination in the upper mesosphere. This work serves to establish a climatology of eddy diffusion and eddy diffusive velocity, including its intra-annual variations in the MLT based on the climatology of the region as a function of latitude and altitude. Atomic oxygen k_zz velocity profiles and fluxes (80-96 km) are balanced by the continuity of chemical loss, a method originally developed in the 1960’s, was refined in 2019, in order to determine global mean k_zz profiles. In the current study, the intra-annual cycle was divided into twenty six (two-week periods) for each of three zones, the northern hemisphere (NH, 15 to 55^o), southern hemisphere (SH, -15 to -55^o), and the equatorial region (EQ, 15 to -15^o). Sixteen years of TIMED SABER O density measurements (2002-2018) and the most recent MSIS model N₂, O₂, H, and temperature profiles were used to calculate the chemical loss rates and determine the eddy diffusive velocities and fluxes of atomic oxygen. Our primary findings include a dominant SAO (semiannual oscillation) at all altitudes between 80-96 km at the equator, and a dominant AO (annual oscillation) below 87 km in the NH and SH, with a factor of 3-4 k_zz increase from winter to summer at 83 km. Although k_zz variability in the NH and SH is minimal at 96 km, an important height for thermospheric and ionospheric global circulation models, the O density increases by a factor of 1.5 between winter and summer.