Influence of the BrewerDobson Circulation on the MiddleUpper Tropospheric O3

1
Influence of the Brewer-Dobson Circulation on the
Middle/Upper Tropospheric O3
Middle and upper tropospheric ozone is affected
by the downwelling transport of air from the
stratosphere, where most of ozone is produced. We
use the data obtained by Earth Observing System
(EOS) Tropospheric Emission Spectrometer (TES)
and Microwave Limb Sounder (MLS) to study the
ozone distribution from the middle troposphere to
the lower stratosphere. Comparisons with model
results are made. An off-line chemical transport
model (MOZART-2) driven by the NCEP1 and MACCM3
circulations and the on-line model CAM-CHEM, a
newly developed model at NCAR, are used to
simulate the distribution of ozone from the
surface to 5 mbar. We find that the phase of the
seasonal cycle of the modeled O3 in the
mid-troposphere is off by 1-2 months compared
with that of the observed O3, while the phase
between models and observations is good in the
lower stratosphere. This suggests a gap of our
understanding of the cross tropopause transport
in the current model. The TES total column ozone
agrees well with the MOD (TOMS/SBUV Merged Ozone
Data) to be within 5, but the retrieved
vertical profiles of ozone can be differed by as
much as 20 from ozone sondes (Worden et al.,
2007). The MOZART-2 model driven by NCEP tends to
overestimate the abundance of mid-tropospheric
ozone at mid-high latitudes compared with TES
ozone, suggesting that the STE is too strong in
the NCEP.
TES
MLS
MOZART-2-NCEP
MOZART-2-MACCM3
CAM
Latitude
MOZART-2 using reanalysis data of NCEP
TES maximum
MOZART-2-NCEP without surface emission and
lightning
Latitude
x 100
Percentage difference of the above results
(contribution from surface emissions and
lightning)
Latitude
Jan.
Apr.
Figure 4
O3 ppbv
MLS _at_ 68 hPa MOZART-2-MACCM3 _at_ 66
hPa MOZART2-NCEP _at_ 68 hPa CAM-CHEM _at_ 70 hPa

• MOZART-2-NCEP without surface emissions of NOx
  and mechanism of lightning is simulated (center
  picture).
• Lightning is an important source of NOx or O3 at
  low latitudes.
• In MOZART-2-NCEP, the total contribution of
  lightning is 5 Tg/yr.

Figure 1
Jul.
Oct.
O3 ppbv
Figure 1

• MLS data is used to validate the models in the
  stratosphere.
• The upper boundary of models is set at 1hPa.
• The agreement between models and data is good.

• TES and MLS data are used to study tropospheric
  ozone from the middle troposphere to the lower
  stratosphere.
• In both hemispheres, MOZART-2-NCEP overestimates
  the tropospheric ozone at mid-high latitudes
  during winter and spring seasons. The over
  predicted ozone is likely the consequence of the
  STE that is too strong in the NCEP1
  meteorological winds.
• At 450hPa, a time lag of a few months between
  the model and observation is observed, further
  verifying that the STE across the tropopause is
  too strong.

Jan.
Apr.
O3 ppbv
TES _at_ 450 hPa MOZART-2-MACCM3 _at_ 433
hPa MOZART2-NCEP _at_ 435 hPa CAM-CHEM _at_ 433 hPa
Figure 3

• The phase of seasonal cycle between models and
  observations is good in the lower stratosphere.
• A few-month lag is observed at mid-troposphere
  in the spring/summer seasons.

Jul.
Oct.
Figure 2
O3 ppbv
Figure 2

• TES is used in the mid-upper troposphere to
  compare with models.
• Anomalous enrichments are simulated in the
  MOZART-2-NCEP during winter/spring seasons at
  mid-high latitudes.
• Between models, STE ozone fluxes vary by a
  factor of four (340-1440 Tg/yr Wild O., 2007).

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