Title: Methane from the Tropospheric Emission Spectrometer
1- Methane from the Tropospheric Emission
Spectrometer - Vivienne Payne, Mark Shephard
- Atmospheric and Environmental Research, Inc.
- Tony Clough
- Clough Associates
- Brendan Fisher, Greg Osterman, Bill Irion
- JPL
- Ray Nassar
- University of Toronto
- Jennifer Logan
- Harvard University
- AURA Science Meeting
- 27th-30th October 2008
2Methane CH4
Long-term trend
- Important greenhouse gas
- Important for atmospheric chemistry
- Influence on OH concentration
- Factors influencing growth rate
- Wetland emission
- Biomass burning
- Significant increase in growth rate in 2007
- Observed from NOAA flask network
- Long lived
- fairly well mixed in troposphere
- variations are small (lt10 globally)
- latitudinal gradient sources in NH
3TES CH4 Averaging kernels and DOFS
Tropical, over ocean
Low latitude, over desert
- Antarctica (polar winter)
Siberia (polar summer)
TES is most sensitive to CH4 in mid to upper
troposphere.
4Representation of retrievals with limited
vertical information
- TES Level 2 products are supplied on a fine grid
(67 pressure levels) - Number of fine grid levels is much greater than
number of DOFs - Data on single level of the reported fine grid
may contain very little measurement information - Comparisons with other data or global models
without the use of sophisticated data
assimilation systems - e.g. visual inspection of maps, analysis of
latitudinal gradients - Move to a representation that better reflects the
number of DOFS - Report retrieval state in terms of one element
per DOFS (Von Clarmann and Grabowski, ACP, 2007) - For TES CH4, report one quantity a
representative tropospheric VMR - Representative of the mid-upper troposphere
- There are a number of different approaches
- SVD (Ceccherini et al., 2003) partial
eigen-decomposition (Joiner et al., 1998),
analysis of leading eigenvectors (Pan et al.,
1998) - Utilize a straightforward post-retrieval mapping
process that - Reduces the influence of the a priori
- Is performed in physical space
- Retains the sensitivity (level and vertical
resolution) of each profile - Varies spatially and temporally
5Representative Tropospheric VMR resultsPayne et
al. (2008), submitted to JGR
RTVMR for July 2006
July zonal means
Latitudinal Gradients
Difference from GEOS-Chem, after bias removal at
50S-60S
Effective pressure
Latitude
GEOS-Chem CH4 Wang et al. (2004), Xiao et al.
(2004)
6Global spatial features
TES (2006) minus GEOS-Chem (2001), after 3.5
bias removal
7TES CH4 representative tropospheric VMR
TES RTVMR minus GEOS-Chem 2001 RTVMR field (after
removal of 3.5 high bias from TES)
High CH4 over Indonesia in October 2006
associated with increased biomass burning during
the El Nino?
8Northern Hemisphere CH4
High CH4 values Possible sources? Transport
across Pacific?
TES CH4 RTVMR (July 2006)
Effective pressure
Difference from GEOS-Chem
9DACOM flights for INTEX-B Comparisons between
DACOM, TES v003, AIRS v5.0
- DACOM Differential Absorption CO Measurement
- PI Glen Sachse, NASA Langley
- INTEX-B DACOM flights March/April/May 2006
- TES/AIRS
- Both mid-IR instruments, sensitive to CH4 in mid-
to upper troposphere - AIRS CH4 has already been compared with aircraft
measurements from a range of latitudes - Xiong et al, JGR-B (2008)
- Different spectral resolution
- TES 0.06 cm-1 unapodized
- AIRS 1.0 cm-1 in CH4 region
- Different forward models
- AIRS v5.0 CH4 absorption coefficients tuned using
tropical aircraft profiles - Different retrieval techniques
- Retrieval approach
- Retrieval grid
10TES/AIRS/DACOM comparisons example case
- Comparable sensitivity
- TES sensitive lower down
- TES has slightly more DOFS
- Helpful at high latitude
- TES biased high wrt DACOM
- N2O interference
- Plans to address in future versions
- AIRS biased low wrt DACOM
- Plans to re-examine tuning in future versions
11TES/AIRS/DACOM scatter plots
- TES 3.5 bias wrt DACOM
- Investigate physical reasons for bias
- Update N2O profiles in supplemental files
- Try to use microwindows that avoid all N2O lines?
AIRS -2 bias wrt DACOM Tuning to be
re-evaluated for v6.0
12NDACC FTIR comparisons(Network for the Detection
of Atmospheric Composition Change)
FTIR column data publicly available from
http//www.ndsc.ncep.noaa.gov/
- -77.825 166.65 Arrival Heights, Antarctica
- -45.038 169.684 Lauder, New Zealand
- 28.3 343.52 Izana, Tenerife
- 43.66 280.60 Toronto, Canada
- 53.107 8.854 Bremen, Germany
- 60.200 10.800 Harestua, Norway
- 67.84 20.41 Kiruna Sweden
- 76.52 291.24 Thule, Greenland
- 78.92 11.92 Ny-Aalesund, Spitsbergen
- 80.050 273.58 Eureka NDSC
Future work Comparisons with FTIR tropospheric
VMRs through collaboration with instrument teams
(A. Goldman, U. Denver)
13Summary/Future Work
- TES CH4 product contains useful info when viewed
appropriately - TES CH4 is most sensitive in the mid to upper
troposphere with 1 DOF - Representative tropospheric VMR Single
troposphere VMR value specified at an effective
pressure - Sensitivity varies from profile to profile
- TES CH4 RTVMRs show evidence of interesting
features on a global scale - TES latitudinal gradients are realistic
- TES closer to GEOS-Chem than to MOZART a priori
- GEOS-Chem surface values have been validated
against NOAA CMDL measurements (Wang et al, 2004) - Validation of the TES CH4 product is ongoing..
14Summary/Future work
- TES shows high bias of wrt GEOS-Chem
- 3.5 bias at 50S-60S in January
- TES shows high bias of 3.5 wrt DACOM in-situ
aircraft data - Investigation of the high bias in the TES CH4
- Radiance closure studies using DACOM data
- N2O interference in TES microwindows
- Update N2O to present-day values
- Validation against aircraft and ground-based
measurements - FTIR tropospheric volume mixing ratios
- Larger number of aircraft comparisons
- AIRS/SCIAMACHY comparisons on a global scale
- Check whether features of interest are observed
in both datasets