MIPAS ozone retrieval version 8: middle-atmosphere measurements

We present a new version of O$_3$ data retrieved
from the three Michelson Interferometer for Passive Atmo-
spheric Sounding (MIPAS) observation modes that we refer
to for simplicity as the modes of the middle atmosphere (mid-
dle atmosphere, MA; upper atmosphere, UA; and noctilucent
cloud, NLC). The O$_3$ profiles cover altitudes from 20 up to
100 km for the daytime and up to 105 km at nighttime, for all
latitudes, and the period 2005 until 2012. The data have been
obtained with the IMK–IAA (Institute of Meteorology and
Climate Research and Instituto de Astrofísica de Andalucía)
MIPAS level-2 data processor and are based on ESA version-
8 re-calibrated radiance spectra with improved temporal sta-
bility. The processing included several improvements with
respect to the previous version, such as the consistency of
the microwindows and spectroscopic data with those used in
the nominal-mode V8R data, the O$_3$ a priori profiles, and
updates of the non-local thermodynamic equilibrium (non-
LTE) parameters and the nighttime atomic oxygen. In par-
ticular, the collisional relaxation of O3(v1,v3) by the atomic
oxygen was reduced by a factor of 2 in order to obtain a
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better agreement of nighttime mesospheric O3 with “non-
LTE-free” measurements. Random errors are dominated by
the measurement noise with 1σ values for single profiles
for the daytime of < 5 % below ∼ 60 km, 5 %–10 % between
60 and 70 km, 10 %–20 % at 70–90 km, and about 30 % at
95 km. For nighttime, they are very similar below 70 km but
smaller above (10 %–20 % at 75–95 km, 20 %–30 % at 95–
100 km and larger than 30 % above 100 km). The systematic
error is ∼ 6 % below ∼ 60 km (dominated by uncertainties
in spectroscopic data) and 8 %–12 % above ∼ 60 km, mainly
caused by non-LTE uncertainties. The systematic errors in
the 80–100 km range are significantly smaller than in the pre-
vious version. The major differences with respect to the pre-
vious version are as follows: (1) the new retrievals provide
O$_3$ abundances in the 20–50 km altitude range that are larger
by about 2 %–5 % (0.2–0.5 ppmv); (2) O$_3$ abundances were
reduced by ∼ 2 %–4 % between 50 and 60 km in the trop-
ics and mid-latitudes; (3) O$_3$ abundances in the nighttime
O$_3$ minimum just below 80 km were reduced, leading to a
more realistic diurnal variation; (4) daytime O$_3$ concentra-
tions in the secondary maximum at the tropical and middle
latitudes (∼ 40 %, 0.2–0.3 ppmv) were larger; and (5) night-
time O$_3$ abundances in the secondary maximum were re-
duced by 10 %–30 %. The O$_3$ profiles retrieved from the
nominal mode (NOM) and the middle-atmosphere modes are
fully consistent in their common altitude range (20–70 km).
Only at 60–70 km does daytime O$_3$ of NOM seem to be
larger than that of MA/UA by 2 %–10 %. Compared to other
satellite instruments, MIPAS seems to have a positive bias of
5 %–8 % below 70 km. Noticeably, the new version of MI-
PAS data agrees much better than before with all instruments
in the upper mesosphere–lower thermosphere, reducing the
differences from ∼ ± 20 % to ∼ ± 10 %. Further, the diur-
nal variation in O$_3$ in the upper mesosphere (near 80 km) has
been significantly improved.