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. CT-NRT.v2017 uses CO2 observational data from GLOBALVIEW+ and from a Near-Real-Time (NRT) ObsPack. The NRT data are made available through special arrangement with data providers and are provisional in that in most cases, they have not undergone full quality-control procedures. Also, there are fewer data available in the NRT. For more information, please see the NRT ObsPack release notes.
CT-NRT.v2017 uses data from four ObsPacks as detailed below. Most of the observations come from just two products, however. Prior to 2016-Jan-01, data are extracted primarily from the GLOBALVIEWplus_v2.0_2016-08-05 ObsPack. After 2016-Jan-01, data come from the_NRT_v3.3_2017-04-19 ObsPack.
Source Online availability Comment GLOBALVIEW+ v2.0 ObsPack download Main source of observations prior to 2016 NRT v3.3 ObsPack download Measurements in 2016, after end of GLOBALVIEW+ 2.0 ORCAS ObsPack download Data were first released in stand-alone ObsPack, but now are formally available in GLOBALVIEWplus releases ASCENDS ObsPack download Data were first released in stand-alone ObsPack, but now are formally available in GLOBALVIEWplus releases
- 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, CT2016. Since the majority of flux variability comes from the land biosphere, a land flux anomaly model was also developed. This is a regression of CT2016 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.
- CT-NRT.v2017 has a 12-week assimilation window. This release represents a major increase of the CarbonTracker assimilation window length, from 5 weeks to 12. This is in response to the 2015-2016 El Niño and our sparse observational network in the tropics.
- CT-NRT.v2017 now uses a temporally-varying model-data mismatch for assimilation constraints. Previous products 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 MDM and other decisions about assimilation constraints are taken from CT2016.
Versions This CT-NRT release is CT-NRT.v2017. It extends from 2015-Dec-12 through 2017-Apr-29. Results can be downloaded from /aftp/products/carbontracker/co2/CT-NRT.v2017/. CT-NRT.v2017 starts from a CT2016 initial condition at 2015-Dec-12 using the eic-b2oifmi suite member.