The Study of Tropospheric Ozone Column Enhancements over North America using a Regional Model and th

1
The Study of Tropospheric Ozone Column
Enhancements over North America using a Regional
Model and the Current Versions of the Aura
Satellite Data 1Qing Yang (qingy_at_eas.gatech.edu),
2Derek M. Cunnold, 3Yunsoo choi, 4Yuhang Wang et
al. 1,2,4School of Earth and Atmospheric
Sciences, Georgia Institute of Technology,
Atlanta, Georgia 3Jet Propulsion Laboratory,
Pasadena, California
4.2 Wave breaking diagnostics
1. Introduction
In case 1, there is steepening of the wave crest
in PV a couple of days before the enhancement. On
May 08 at 12 UTC a high PV cutoff area with PV
values as high as 6 PV units appears beside the
wave crest. At 18hr, March 08, a relatively weak
cutoff high shows up over the West Coast of
California. These PV cut off areas correspond to
the locations of high TCOs in OMI/MLS and
GEOS-CHEM. Similar wave breaking features are
also presented in case 2 (pictures not shown)
with PV cutoffs corresponding to TCO highs over
Baja and the northwest corner of California on
the OMI/MLS TCO maps.
Monthly mean TES tropospheric ozone columns over
North America for spring and summer 2005 and
2006. Only those months with sufficient data are
presented. A Barnes smoothing routine (Ping et
al., 2006) with the influencing distance of 250
km has been used.
A new set of tropospheric ozone columns (TCOs) is
being computed from the difference between the
Aura Ozone Monitoring Instrument (OMI) total
ozone retrieved using TOMS algorithm (level 2
version 3) and the Aura Microwave Limb Sounding
(MLS) measurements of stratospheric ozone
(version 2.2). The derivation of three different
types of OMI/MLS TCOs was described in Yang et
al. (2007), and briefly they are OMI/MLS PV
mapped (Mapped), OMI/MLS 2-D interpolated
(2D-intp), and OMI/MLS coincident (Coinc.)
tropospheric columns. In the derivation of the
first two types of TCOs, PV-ozone mapping and 2-D
spatial interpolation, respectively, have been
performed on MLS data to improve the MLS data
spatial resolution.
2. Comparisons with data from INTEX Ozonesonde
Network Study (IONS)
Comparisons have been made using the new version
of OMI/MLS TCOs and ozonesonde measurements from
the Intercontinental Chemical Transport
Experiment (INTEX) IONS campaign in spring and
summer, 2006. These ozonesonde measurements
possess the advantage that some of these
measurements were close in times and locations to
the MLS measurements. GEOS-CHEM data and OMI-MLS
TCOs derived by Mark Schoeberl using trajectory
mapping (Schoeberl et al., 2007) were also
included in the comparison. Trajectory mapped
(Traj.) and PV mapped products have relatively
high correlation coefficients (0.6) with the
IONS TCOs. PV mapped TCOs possess the smallest
standard deviation of the differences ( 9DU)
among OMI/MLS TCOs. The mean differences of
-7DU between OMI-MLS mapped/interpolated TCOs and
ozonesonde are 2-3 DU less those obtained from
previous comparisons using the earlier OMI and
MLS versions (Yang et al., 2007). The Trajectory
mapped TCOs shown in this comparison used TOMS
version 2 products taking this into
consideration, the mean differences corresponding
to OMI/MLS PV mapped and trajectory mapped TCOs
are consistent with each other. The time series
on the right show reasonable agreement between
OMI/MLS, GEOS-CHEM, and sonde TCOs at the Houston
IONS site.
PV contours on the 350 K isentropic surface. PV
data are calculated using the six-hourly NCEP
reanalysis data.
Despite a relatively high bias (close to 10DU)
compared to OMI/MLS TCOs, TES data also show
patchy high values around the TCO enhancement
regions indicated by the GEOS-CHEM (corr0.5-0.8)
and OMI/MLS (corr0.5-0.7). The TCO enhancements
indicated by the TES data also increase from
March to May in 2006. The monthly means from TES
also show similar month to month TCO enhancements
decreasing only slightly from July to August, in
contrast to GEOS-CHEM results.
4.3 Study of Tran-Pacific influence back
trajectories GEOS-CHEM
In order to estimate the influence of
cross-Pacific transport, back trajectories have
been initialized around the West Coast every six
hours for both case periods and their respective
comparison periods using the HY-SPLIT model. The
relatively large number of trajectories
initialized at 2 km originating from the near
surface layer over East Asia compared with the
comparison period suggest that the ozone
enhancement at around 2 km over the West Coast of
California may have been influenced by pollutants
from East Asia lifted from the surface layer and
transported across the Pacific. Similarly, the
ozone enhancement at 6km in the case 2 period
may have been under the influence of transpacific
transport.
4. Two spring TCO enhancement case studies
Purpose identify the mechanisms associated with
the TCO enhancements over the West Coast
area. Periods selection Two six-day periods of
enhancement (case 1 March 8-13, 2005 and case 2
May 5-10, 2006) have been chosen for study. Note
that several days are required to obtain complete
OMI/MLS TCO maps over North America because of
the clear sky constraint. GEOS-CHEM and satellite
data both show TCO enhancements over the West
Coast of California and the Baja peninsula in
these periods.
The comparisons of back trajectories initialized
over the West Coast of California during the case
study periods and their respective 6 day
comparison periods (March 2-7, 2005 and May
11-16, 2005). The comparisons are based on 288
trajectories (initial heights of 2, 4, and 6 km)
for each 6-day period. Statistical results for 2
km trajectories in case 1 and 6 km trajectories
in case 2 are significantly different from those
of the comparison periods (CP), and thus are
listed below
The IONS ozonesonde profiles also show dramatic
enhancement during the case 2 period although
there is a large variability in the individual
profiles. Enhancements are indicated from 1km
up.
A few days before the enhancement event in case
1, there is a TCO maximum which propagates across
the Pacific the corresponding CO maps from
GEOS-CHEM indicate some similar transport
activity. However, the CO high in the model
dissipated before it reached the continental
U.S., though there is a slight elevation of CO at
the end over the West Coast. Similar transport
features are indicated in GEOS-CHEM for case 2
(picture not shown) with more obvious propagating
patterns indicated by CO columns than by O3
columns
Means and standard deviations of the differences
of the tropospheric ozone columns calculated from
OMI/MLS TCOs and GEOS-CHEM simulations versus
similar columns at 22 IONS stations locating
between 20o-55oN. The error bars indicate s of
the mean differences. The numbers above and below
the error bars are correlation coefficients and
total pairs of data included in the comparisons.
Time series of tropospheric ozone columns from
IONS ozonesonde, REAM, and three types of OMI/MLS
at Houston for spring and summer 2006. The
numbers on the lower left corner are the
correlation coefficients of sonde TCOs with
mapped OMI/MLS, 2D-interpolated OMI/MLS,
coincident OMI/MLS, and REAM TCOs, respectively.
IONS ozonesonde profiles during the CASE 2 period
(May, 5, 6, 8, and 10, 2006, in red) and one
profile after the enhancement period (May 15,
2006, in black) at Trinidad Head (41N, 124W)
Tropospheric ozone columns during case 1 period
and case 2 periods using GEOS-CHEM, OMI-MLS 2-D
interpolated, OMI-MLS mapped, and TES TCOs (left
to right).
GEOS-CHEM daily mean ozone and CO columns for
March 4 - 7, 2005. The CO columns can be
converted from Dobson units to molecules/cm2 by
multiplying by a constant (2.687E16).
3. Monthly mean distributions in spring and
summer 2005 and 2006 based on GEOS-CHEM and
OMI/MLS mapped TCOs.
4.1 Vertical cross-sections of ozone based on
GEOS-CHEM
5. Summary

• PV mapping and trajectory mapping procedures for
  interpolating MLS data produce TCOs that more
  closely match the variability of tropospheric
  ozone columns from sondes than simpler methods.
  On average the columns as well as GEOS-CHEM
  columns are 7DU less than IONS ozonesonde
  measurements.
• Monthly mean TCOs from GEOS-CHEM, OMI/MLS, and
  TES show an area of high ozone columns in spring,
  extending along the Eastern Pacific from the Baja
  peninsula to northern California. The TCO
  enhancements increase from March to May. A better
  agreement in the monthly change tendency between
  GEOS-CHEM and satellite data is found in spring
  months than in summer months.
• Spring enhancements are concluded to be
  associated with a combination of stratospheric
  air intrusions through wave breaking events and
  enhancements at 2 km and 6 km due to influence
  of cross-Pacific transport.

Compared to the 6-day period before case 1, an
ozone enhancement of about 10 ppb was indicated
from the surface to 300 mb along 35oN (where
Santa Barbara is located). The same cross-section
for case 2 indicates similar and but a stronger
enhancement along 35oN . Based on the location
of the tropopause, there are indications of
stratospheric influence near the tropopause in
both cases.
Good agreement (corr 0.8) has been found between
the GEOS-CHEM model and satellite TCO data in the
principal features of the distribution in spring.
An area of enhancement over the extra-tropical
region divides into one TCO high over the Eastern
Pacific near the Baja peninsula and another over
the Gulf of Mexico, the Eastern United States and
the adjacent North Atlantic. The TCO enhancements
increase from March to May and from spring to
summer, driven by the changes in the locations of
stratosphere/troposphere exchange, tropospheric
photo-chemical production from surface emissions,
and lightning NOx,, and the area of TCO
enhancement shifts northward over the US East
Coast in 2005 (see discussion in Choi et al.,
2008). OMI-MLS and GEOS-CHEM agree well in the
locations of enhancements in summer although
there is disagreement in the month to month
variations. The strongest TCO enhancement occurs
in June based on OMI-MLS, but it occurs in August
in GEOS-CHEM.
6. References
Choi, Y., Y. Wang, Q. Yang, D. Cunnold, T. Zeng,
C. Shim, M. Luo, A., Eldering, E. Bucsela, and J.
Gleason (2008), Geopys. Res. Lett., 35, L04818,
doi10.1029/2007GL032276. Jing, P., D. M.
Cunnold, Y. Choi, and Y. Wang (2006), Geophys.
Res. Lett, 33, L17817, doi 10.1029/2006GL026473.
Yang, Q., D. M. Cunnold, H.-J. Wang, L.
Froidevaux, H. Claude, J. Merrill, M. Newchurch,
and S. J. Oltmans (2007), J. Geophys. Res., 112,
D20305, doi 10.1029/2007JD008528. Schoeberl, M.
R., et al. (2007), J. Geophys. Res., 112, D24S49,
doi10.1029/2007JD008773.
Meridional pressure by latitude cross-sections of
ozone (in ppb) at 120oW (crossing Santa Barbara)
based on the GEOS-CHEM for 6-day period before
case 1, the case 1 period,, the case 2,period and
the 6-day period after case 2. The solid and
dashed lines in red represent the dynamic (3.5
PVU) and thermal tropopause (from the National
Center for Environmental Protection (NCEP)
reanalysis 1 dataset ), respectively.