Constraints on Free Tropospheric Ozone from the
Tropospheric Emission Spectrometer (TES)
Dylan Jones
University of Toronto
Thomas Walker (University of Toronto)
Mark Parrington (University of Edinburgh)
Kevin Bowman, John Worden (JPL)
Anne Thompson (Penn State)
David Tarasick (Environment Canada)
Ivanka Stajner (Noblis)
Lee Murray (Harvard U.)
Tropospheric Emission Spectrometer (TES)
Averaging kernels for retrieval at 30°N, 87°W
150 - 50 hPa
500 - 150 hPa
1000 - 500 hPa
70-90 hPa
• One of four instruments on the NASA Aura
spacecraft (launched July 2004)
400 hPa
• Infrared Fourier transform spectrometer
(3.3 - 15.4 m)
• Nadir footprint = 8 km x 5 km
• Orbit repeats every 16 days
700 hPa
x̂TES = xapriori + A(xtrue - xapriori )
¶x̂TES
A = true = averaging kernel
¶x
Objective: Assess the impact of assimilating TES data on surface ozone in GEM-MACH
Ozone Analysis for Aug 1-15th, 2006
Without assimilation (7 km)
With TES assimilation (7 km)
•
TES data were assimilated from 1 Jul. to 31 Aug. 2006 into GEOS-Chem using a
sequential Kalman filter
•
Assimilation of TES data significantly increased ozone abundances across the
extratropics
Ozone Analysis Over North America (at 5 km on 15 August 2006)
Before assimilation
After assimilation
ppb
[Parrington et al., JGR, 2008]
• Assimilation of TES data increased O3 across North America by up to 40%
• Large increases in O3 in the eastern Pacific, in the vicinity of a stratospheric
intrusion, and across Canada, linked to stratosphere-troposphere exchange
• The summertime O3 maximum over the southeast is more pronounced after
assimilation
Modelled O3 Over North America along 40°N
NOx
O3 without TES assim
O3 with TES assim
[Parrington et al., JGR, 2008]
The upper tropospheric ozone maximum is linked to NOx emissions from lightning, which
were 0.068 Tg N for North America (in August), a factor of 4 lower than recommended by
Hudman et al. [JGR, 2007] based on comparisons of the model with aircraft data.
Comparison with IONS-06 Ozonesondes Over North America
Mean (August 2006) O3 profile over North America (model sampled at the
ozonesonde observation time and location)
Mean Profiles
Difference relative to sondes
Sonde
profile
Before assim
After assim
[Parrington et al., JGR, 2008]
Significant improvement in fee tropospheric O3 (300 - 800 hPa) after assimilation.
The bias was reduced from a maximum of -35% to less than 5% (between 300-800 hPa).
Comparison of TES analysis with assimilation of OMI and MLS
GMAO OMI+MLS ozone assimilation GEOS-Chem ozone (7-8 km) for Aug. 2006
Northern midlatitude in
better agreement after
assimilation of TES data
GEOS-Chem with TES assimilation
GMAO – GEOS-Chem differences
GMAO – G-C with TES
GMAO – G-C without TES
Over Asia, the biased
between GMAO ozone and
GEOS-Chem decreased
from 6.8 ppb to 1.4 ppb
after TES assimilation
[Worden et al., JGR, 2009]
Mean Ozone (Aug. 2006) Along 45°E
GMAO OMI+MLS analysis
TES assimilation
Comparison of TES ozone analysis
with assimilation of OMI and MLS
• The O3 distribution in the TES analysis is more
consistent with OMI+MLS
• The Middle East ozone maximum is reduced in
the TES assimilation, relative to the free
running simulation
Without TES assimilation
[Worden et al., JGR, 2009]
Impact of TES Assimilation on Surface Ozone (Aug. 2006)
Before assimilation
After assimilation
• The model overestimates
surface ozone in the east and
underestimates it in the west
Surface O3 difference (assim - no assim)
AQS and NAPS surface O3 data
• Assimilation increases
surface O3 by as much as
9 ppb, with the largest
increase in western North
America
• TES-based estimates of
background O3 are 20-40 ppb
Background O3 at the surface before assim
Background O3 at the surface after assim
[Parrington et al., GRL, 2009]
Evaluation with surface ozone measurements
Location
Mean bias
before (ppb)
Mean bias
with TES
Kelowna, AB
-1.81
4.52
Bratt’s Lake, SK
0.99
4.96
Glacier NP, MT
-5.61
0.65
Pinnacles NM, CA
-6.36
0.19
Theodore Roosevelt
NP, ND
-8.39
-4.49
Table Mt., CA
0.64
6.47
Boulder, CO
-3.90
-0.37
Dallas, TX
5.14
8.74
Egbert, ON
1.63
4.90
Narragansett, RI
8.21
11.26
Coffeeville, MS
11.76
13.70
Sumatra, FL
16.05
17.66
Sites sensitive to
background
O3:
TES assimilation
reduced the bias
Sites sensitive to
local O3 production:
bias enhanced
• Assimilating TES data reduces the model bias in western North America at the sites
most sensitive to background ozone
• Large residual bias at sites such as Egbert, Sumatra, and Table Mt. due to the coarse
model resolution
Summary and Future Work
•
•
•
Assimilation of TES data provides sufficient information to constrain the vertical
structure of ozone in the free troposphere
We are interested in assimilating the TES data to assess their impact on the
ozone simulation in GEM-MACH, with a focus on surface ozone forecasts in
North America. (We will use MLS data to constrain stratospheric ozone.)
Since the TES observational coverage is poor, an important issue to examine is
the trade-off between vertical resolution and spatio-temporal coverage of free
tropospheric ozone observations
o We are interested in comparing the impact of TES and OMI data on the
surface ozone fields
Comparison of the new model with assimilated ozone
v8 GEOS-Chem O3 Aug 2006, 5 km
O3 in v8 of GEOS-Chem with
new lightning NOx source
(and with biomass burning
emissions based on GFED3)
TES Assimilation Aug 2006, 5 km
In the middle troposphere,
relative to the TES
assimilation, the mean bias
between 20º-50ºN in the
model decreased from about
-7 ppb to 2 ppb with the new
lightning NOx source
Chemical Data Assimilation Methodology
Sequential sub-optimal Kalman filter:
Observation Operator:
Kalman Gain Matrix:
Analysis Error Cov. Matrix:
x̂a = x f + K[xobs - H(x f )]
H(x f ) = xa + A(x f - xa )
K = P f HT (HP f HT + R)-1
Pa = (I - KH)P f
Model
• GEOS-Chem model with detailed nonlinear tropospheric chemistry
• Linearized (LINOZ) O3 chemistry in the stratosphere
• Model transport driven by assimilated meteorological fields (GEOS-4) from the NASA GMAO
(at a resolution of 2° x 2.5° or 4° x 5° )
• O3 and CO profile retrievals from TES are assimilated from 1 Jul. - 31 Aug. 2006
• 6-hour analysis cycle
• Assumed initial forecast error of 50% for CO and O3
• Neglected horizontal correlations in forecast and observation error covariance matrices