SOFIE is currently collecting sunset science observations at northern polar latitudes. Housekeeping and
performance data all indicate a stable and healthy instrument. SOFIE V1.3 data are available online.
An improved SOFIE sunrise signal calibration resulted in meteoric smoke extinction retrievals in the
Northern Hemisphere (NH), for the first time. The SOFIE meteoric smoke record now spans 2007 - present in
both hemispheres, as recently described by Hervig et al., . The new observations are in good
agreement with SOFIE Southern Hemisphere (SH) measurements, and with
Whole Atmosphere Community Climate Model (WACCM) simulations. Comparing SOFIE with WACCM requires knowledge
of smoke composition, to relate the optical and physical smoke properties. Based on SOFIE multi-wavelength
observations combined with recent theoretical and laboratory work, the present study assumes that smoke in
the mesosphere exists purely as Fe-rich olivine (Mg0.8Fe1.2SiO4). With this assumption, SOFIE indicates a
global mean ablated meteoric influx of
7.3 ± 2.2 t d-1 (total influx of 24.7 ± 7.3 t d-1), in good agreement with a recent
and independent study from the University of Leeds that used models and
observations to derive an ablated influx of 8.3 ± 4.7 t d-1 (total influx of 28.0 ± 16 t d-1).
The SOFIE time series of mesospheric smoke shows a hemispheric asymmetry with more smoke in the NH
winter compared to the SH (see Figure). This asymmetry is consistent with stronger transport in the NH
winter vs. the SH, and is also present (although weaker) in WACCM smoke. This hemispheric difference is
confirmed by wintertime mesospheric H2O, with both SOFIE and WACCM showing ~10% hemispheric differences
(SH > NH), again consistent with stronger transport in the NH winter. The open issue is that the asymmetry
in smoke is greater in SOFIE than in WACCM. The SOFIE hemispheric difference is not attributed to
sunrise - sunset observational biases, because the difference persists after 2018 when sunrise switched
from the NH to SH (vice versa for sunset; see Figure). The asymmetry is thus taken to indicate a missing
component in our understanding of meteoric processes. One candidate is incomplete chemistry or microphysics
in the smoke simulations. Another is an asymmetry in meteoric influx that is not represented in the current
model. NASA Wind/WAVES measures meteoric flux near the first Lagrange point, and shows a seasonal variation
that was attributed to interstellar particles. The WIND asymmetry is similar to that indicated by SOFIE,
and current efforts are thus exploring these comparisons further, and the possibility of an interstellar
dust component in Earths mesosphere.
Hervig, M. E., Plane, J. M. C., Siskind, D. E., Feng, W., Bardeen, C. G., & Bailey, S. M. (2021). New global meteoric smoke observations from SOFIE: Insight regarding chemical composition, meteoric influx, and hemispheric asymmetry. Journal of Geophysical Research: Atmospheres, 126, e2021JD035007. https://doi. org/10.1029/2021JD035007.SOFIE
a) Time series of SOFIE measurement latitudes as winter means in the NH
(November - February) and SH (May - August). b) The winter mean smoke volume density (the average for 0.2
to 0.01 hPa) from SOFIE observations compared to WACCM simulations. Error bars indicate the standard
deviation during the winter months. The WACCM results are for 8 t d-1 influx and were scaled slightly to
match SOFIE. Note the hemispheric difference in smoke (NH > SH) that is larger in SOFIE than in WACCM.
Some of the interannual variability is due to changing SOFIE latitudes after 2016, and this is captured in
WACCM because the model was sampled to the SOFIE latitude vs. time.