CarbonTracker CT-NRT is an extension of the standard CarbonTracker CO2 analysis system, designed to provide more timely model results. It was created under funding from NASA, for use in the OCO-2 program.
CT-NRT differs from our standard CarbonTracker projects in several ways:
- Assimilation of provisional CO2 observations. In collaboration with measurement scientists from NOAA Global Monitoring Division and Environment Canada's Greenhouse Gas Measurement Program. (i.e., fewer obs and less quality control). CT-NRT uses observational data from two near-real time ObsPacks: obspack_co2_1_CarbonTracker-NRT_v1.0_2015-10-06 from 2012 through 2015-07-25 and obspack_co2_1_CarbonTracker-NRT_v2.0_2016-02-12 after that time.
Note: Environment Canada data are not available in obspack_co2_1_CarbonTracker-NRT_v2.0_2016-02-12, and do not constrain CT-NRT v2015-2 results after 2015-07-25.
- Use of a different prior flux model. Our standard land biosphere flux prior is not available in near-real time, so we had to develop an alternative first-guess flux estimate. For this, we take the climatology of optimized land, wildfire, and ocean fluxes from the latest standard CarbonTracker release. Since the majority of flux variability comes from the land biosphere, a land flux anomaly model was also developed. This is a simple regression of CT2013B land flux anomalies as a function of anomalies of precipitation, shortwave radiation, and temperature. The statistical flux anomaly model was developed for each CarbonTracker ecoregion, and provides daily estimates of NEE anomaly. The radiation and temperature data for this model come from the ERA-interim meteorology used by TM5; the precipitation anomaly comes from the Global Precipitation Climatology Project. Although this flux prior does not reliably reproduce interannual variability, it is arguably a more statistically optimal prior than that for our standard release since it already represents the long-term mean CO2 sinks that we know exist. Since the priors for our standard release do not represent these sinks, the standard CarbonTracker requires that CO2 observations correct these biased priors.
- Use of "real-time" ERA-interim transport in TM5 Importantly, it does use “real-time” TM5 transport, since the ERA-interim winds are operationally available from ECMWF and the TM5 users group. In v2015-2 we use temporally-interpolated meteorology, whereas v2015-1 used temporally constant winds within each 3-hour window. This has little impact on TM5 performance, but is more consistent with developments being made by the TM5 community. The temporal interpolation also changes how the flux anomalies are generated.
- CT-NRT v2015-2 now uses a temporally-varying model-data mismatch for assimilation constraints. Previous products, including CT-NRT v2015-1 and CT2013B used temporally-constant MDM (although this mismatch varied by dataset). This "adaptive" model-data mismatch is developed from posterior residuals of a previous inversion, and is designed to handle the larger variability of lower atmosphere CO2 in local summer. The adaptive MDM model will be used in our next CarbonTracker release, CT2015.
Versions Our most current CT-NRT release is v2015-2 which extends through 2015-11-27. Results can be downloaded from ftp://aftp.cmdl.noaa.gov/products/carbontracker/co2/CT-NRT.v2015-2/. CT-NRT v2015-2 starts from a CT2013B initial condition of 2012-06-09 using the eic-b2oifmi suite member.
The previous release is v2015-1, available from ftp://aftp.cmdl.noaa.gov/products/carbontracker/co2/CT-NRT.v2015-1/.