Summary of the Final Report of Research Results1) Title of the proposed research
Southern Hemisphere validation of GOSAT XCO2 and XCH4 from TCCON solar FTS
measurements in Australia and New Zealand
2) Principal Investigator (PI) and Co-Investigators (Co-Is)
PI:
Dr. Vanessa Sherlock
Co-I:
Dr. David Griffith
Dr. Brian Connor
Dr. Osamu Uchino
Dr. Isamu Morino
Dr. Nicholas Deutscher
Dr. Voltaire A. Velazco
3) PI’s affiliation
The National Institute of Water and Atmospheric Research4) Summary of the Final Report of Research Results
GOSAT carbon dioxide and methane retrieval errors need to be well characterized if these data are tobe used to constrain inverse model surface flux estimates. Data from the Total Carbon Column
Observing Network (TCCON) are the primary validation data for GOSAT Short-Wavelength
InfraRed (SWIR) retrievals. However, systematic retrieval errors and uncertainties in calibrationmust be accounted for to make best use of the TCCON data for GOSAT validation. Low inherent
atmospheric variability of CO2 and CH4 in the southern hemisphere (SH), combined with the latitude
range spanned by SH TCCON sites (12◦ S – 45◦ S), provides unique (but not exhaustive) conditions
to validate GOSAT SWIR retrievals and characterise systematic retrieval biases which, ifuncorrected, would lead to spurious surface flux estimates. The goals of the project were:•to characterize XCO2 and XCH4 variability in the Southern Hemisphere and identify andminimise TCCON instrumental artifacts and retrieval biases;•to apply the high quality, self-consistent SH TCCON timeseries thus generated tovalidate NIES GOSAT SWIR L2 retrieval products (XCO2 and XCH4 ); and•to understand the geophysical drivers of observed variability using tagged tracer
modelling, and hence characterise the representativity of SH (Australasian) TCCON
measurements for satellite validation and a posteriori correction of satellite retrieval
biases.

The project also sought to open an effective means of communication between the SH TCCON PI’s
and the NIES GOSAT retrieval team, so that advances in understanding of TCCON data error
characteristics could be rapidly taken up for GOSAT validation.
Over the past five years we have performed a critical appraisal of measurements from thethree Southern Hemisphere (SH) TCCON sites, Darwin and Wollongong (Australia) and Lauder(New Zealand), in order to generate a high quality, self consistent data set for GOSAT validation.
Thanks to activity within this project and network-wide, our understanding of TCCON error budget
and inter-station consistency has evolved markedly over the duration of the RA project. At the closeof this project we are entering a new era for TCCON. The precision and accuracy of satellite
retrieval algorithms has progessed to the point where TCCON inter-station consistency should
ideally be characterised at the 0.05% level for XCO2 [Buchwitz et al., 2012]. Carefulintercomparison and characterisation of the consistency of the Southern Hemisphere sub-network
remains as important and challenging as ever, and will one objective of a future RA project.
Screened and calibrated SH TCCON data have been compared with NIES GOSAT v01.xx
and v02.xx retrievals. NIES GOSAT retrieval error characteristics have been evaluated using boththe comparison of co-located GOSAT and TCCON retrievals and the statistical analysis of GOSAT
retrievals over Australasian land masses. Comparison of v02.xx retrievals with co-located TCCON
measurements in Australia and New Zealand show a substantial reduction in retrieval bias andvariability compared to the v01.xx retrievals. The standard deviation of v02.xx differences with SH
TCCON are 1-2 ppm (0.5%) for XCO2 and 10-20 ppb (0.5-1%) for XCH4. The erroneously skewed
distributions of XCO2 and XCH4 in the austral spring and summer which characterised the v01.xx
retrievals are absent in the v02.xx L2 products.
We have assessed the consistency between the XCO2 timeseries at SH TCCON sites andthe CarbonTracker CT2011 oi CO2 analysis [Deutscher et al., 2013]. While agreement between themodel analyses and the TCCON timeseries is generally good, significant differences between model
analyses and TCCON observations are found at times, particularly at Darwin, which we do notbelieve are due to instrument errors. The observed intra-seasonal variability of XCO2 and XCH4 at
Wollongong is greater than that observed at either Darwin or Lauder. It is also greater than XCO2variability in CarbonTracker analyses.
Differences between the model simulations and the observations have been interpretedusing tagged tracer modelling. Sensitivity of model-observation mismatch to the prescribed fluxes
and transport has been evaluated by considering multiple terrestrial biosphere flux models (CASAand SiB) and multiple transport models (TM3, TM5 and GEOS-Chem). The Darwin XCO timeseries
has been used to evaluate the timing and magnitude of modelled biosphere burning contributions toobserved XCO2 variability. Based on these analyses we conclude that large eposodic differences
between model and observed XCO2 at Darwin are most likely due to errors in the analysed terrestrial
biosphere fluxes for the Australian Northern Territory region.

5) List of publications relating to the proposed research
N. Deutscher, V. Sherlock, S. Mikaloff-Fletcher, D.W.T. Griffith, J. Notholt, R. Macatangay, B.J.
Connor, J. Robinson, H . Shiona, V.A. Velazco, P.O. Wennberg, and D. Wunch. Drivers of XCO2variability at southern hemisphere Total Carbon Column Observing Network sites. Atmos. Chem.
Phys. Discuss., 13:14331–14376, 2013. doi: 10.5194/acpd-13-14331-2013.
(Accepted for publication in ACP)
S. Dohe, V. Sherlock, F. Hase, M. Gisi, J. Robinson, E. Sepulveda, M. Schneider, and T.
Blumenstock., A method to correct sampling ghosts in historic near-infrared Fourier Transform
Spectrometer (FTS) measurements. Atmos. Meas. Tech., 6(8), 1981–1992, 2013.
F. Hase, B. J. Drouin, C. M. Roehl, G. C. Toon, P. O. Wennberg, D. Wunch, T. Blumenstock, F.
Desmet, D. G. Feist, P. Heikkinen, M. De Mazière, M. Rettinger, J. Robinson, M. Schneider, V.
Sherlock, R. Sussmann, Y. Té, T. Warneke, and C. Weinzierl. Calibration of sealed HCl cells used for
TCCON instrumental line shape monitoring. Atm. Meas. Tech., 6(12):3527–3537, 2013. doi:
10.5194/amt-6-3527-2013. URL http://www.atmos-meas-tech.net/6/3527/2013/.
Y. Yoshida, N. Kikuchi, I. Morino, O. Uchino, S. Oshchepkov, A. Bril, T. Saeki, N. Schutgens, G.C.
Toon, D. Wunch, C.M. Roehl, P.O. Wennberg, D.W.T. Griffith, N.M. Deutscher, T. Warneke, J.
Notholt, J. Robinson, V. Sherlock, B. Connor, M. Rettinger, R. Sussman, P. Ahonen, P. Heikkinen, E.
Kyro, and T. Yokota. Improvement of the retrieval algorithm for GOSAT SWIR XCO2 and XCH4and their validation using TCCON data, Atmos. Meas. Tech, 6(6), 1533–1547, 2013.
I. Morino, O. Uchino, M. Inoue, Y. Yoshida, T. Yokota, P.O. Wennberg, G. C. Toon, D. Wunch, C.M.
Roehl, J. Notholt, T. Warneke, J. Messerschmidt, D.W.T. Griffith, N.M. Deutscher, V. Sherlock, B.
Connor, J. Robinson, R. Sussmann, and M. Rettinger. Preliminary validation of column-averaged
volume mixing ratios of carbon dioxide and methane retrieved from GOSAT short-wavelength
infrared spectra. Atmos. Meas. Tech., 4:1061–1076, 2011.