Sixteen years (2002-2018) of SABER measurements and the MSIS model were
used to study the average SAO (semiannual oscillation) and AO (annual
oscillation) variations of k$_{zz}$ (eddy diffusion coefficient) in
the mesosphere (80-96 km).
Abstract
The climatology of atomic oxygen (O) in the MLT (mesosphere and lower
thermosphere) is balanced by O production via photodissociation in the
lower thermosphere and recombination in the upper mesosphere. The
motivation here is to establish the intra-annual variation in the eddy
diffusion coefficients and eddy velocity in the MLT based on the
constituent climatology of the region. The analysis method, originally
developed in the 60’s (Colegrove et al. 1965), was refined for a study
of MLT global inter-annual variations in global mean values (Swenson et
al. 2018, 2019, respectively) ,(S19). In the this 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 degrees ),
southern hemisphere (SH, -15 to -55 degrees ), and the equatorial region
(EQ, 15 to -15 degrees ). Sixteen years of SABER O density measurements
(2002-2018) and MSIS 2.0 model N , O and T profiles (80-96 km) were
determined for each of the periods and zones for determination of O eddy
diffusion velocities and fluxes. Atomic oxygen diffusive fluxes
([O]*v, 80-96 km) are balanced by the continuity of chemical loss,
but the intra-annual variation of k$_{zz}$ (determined from v ) and
[O] are determined separately. The major findings include: 1) A
dominant AO below 87 km in the NH and SH zones, with the largest
variation in amplitude between winter and summer at 83 km. 2) A dominant
SAO at all altitudes (80-96 km) in the EQ zone. 3) Intra-annual
variability in the global average [O] and k$_{zz}$ contribute
to variability of O eddy transport in the MLT.