A description of the assimilation system developed in CARBONES

4D-var: This term refers to a mathematical technique that allows solving the inverse problem with observations that are distributed in space and time. The technique relies on the minimization of multivariate cost function, that quantifies the misfit between the observations and a dynamic model.


Anomaly: An anomaly is technically a departure from 'normal'. On this website, we show anomalies of carbon fluxes and stocks. This means that we first calculate long-term averages of the estimated quantities, and then see what the departures from this average is in each month and location. Sometimes, the anomalies are further smoothed in time to separate noise from signal.


CarbonTracker: This term refers to the carbon dioxide inverse estimates produced with the system developed at NOAA.


CarboScope: CarboScope is an exploring tool for carbon based greenhouse gases ( CO2, CH4 and CO) developed within the framework of the ICOS project. It provides general information on these gases and the scientific methods used to estimate CO2 and CH4 surface fluxes (atmospheric inversion).


Emissions Inventories: In most inverse estimates, fossil fuel inputs of carbon dioxide to the atmosphere are estimated from industry, EPA, and other governmental estimates of the consumption of coal and petroleum. These are called "emissions inventories" for fossil fuels.


fAPAR: fraction of absorbed photosynthetically active radiation. This biophysical variable is directly linked to vegetation primary production and can be used to monitor state and evolution of vegetation cover in space and time. fAPAR is generally estimated from airborne and spaceborne instruments.


Flux: The flow of mass across a surface. In CARBONES, we particularly estimate the transfer of carbon mass between the land and the atmosphere, and the ocean and the atmosphere.


GPP: Gross primary production. Amount of carbon fixed by plants during photosynthesis.


Growth rate of CO2: it traduces the year-over-year change of atmospheric CO2. For a given year, the annual mean rate of growth of CO2 is defined as the the difference in concentration between the end of December and the start of January of that year.


ICOS: ICOS (Integrated Carbon Observation System) is a new European Research Infrastructure for quantifying and understanding the greenhouse balance of the European continent and of adjacent regions.


Inverse Modeling: The process of constraining model predictions to be consistent with observations. Models express our understanding of basic physics and chemistry, but this grounding is often not sufficient to produce a realistic simulation. Observations inform us about the state of the carbon system at one place and at one time, but do not by themselves tell us about other places and times. Data assimilation or inverse modeling brings these together to yield a simulation that is consistent both with theory and with observations.


LMDz: Atmospheric General Circulation Model of the Laboratoire de Meteorologie Dynamique, with a zoom capability. It can be guided by meteorological fields from operational weather centres.


NDVI: Normalized Difference Vegetation Index. A measure of vegetation greenness, usually derived from airborne and spaceborn instruments.


NEE: Net ecosystem exchange. The final balance of carbon surface exchange by an ecosystem, after accounting for photosynthesis, autotrophic and heterotrophic respiration. NEE = NPP - Rh.


NPP: Net primary production. Gross primary production (fixation of carbon via photosynthesis) minus autotrophic respiration (release of CO2 by the same plant).


pCO2: The partial pressure of carbon dioxide. Contribution of CO2 to the total atmospheric pressure. Often the amount of CO2 dissolved in seawater is expressed as pCO2, since differences between atmospheric and oceanic pCO2 imply a disequilibrium that will drive a net exchange of CO2.


PgC/yr: petagram of carbon per year. A unit of emission equal to 1x1015 grams of carbon released per year. Technically, this is not a flux, since flux has dimensions of mass per unit area per unit time. The carbon dioxide emission is larger than the carbon emission by the ratio of molecular mass of CO2 to the atomic mass of carbon: 44/12.


ppm: The mole fraction is defined as the number of molecules of CO2 in any given air parcel divided by the total number of all molecules (except water) in that parcel. For CO2 it is usually expressed as parts per million, abbreviated as ppm.


Rh: Heterotrophic respiration. Conversion of organic carbon compounds into CO2 by microbial processes. "Heterotrophic" refers to the fact that the agent doing this conversion is distinct from the plant which created the organic carbon compound via photosynthesis.


Sink: Any process by which carbon dioxide is removed from the atmosphere. Sinks may be natural (e.g., photosynthesis and reforestation) or due to human activities (e.g., managed forests and other carbon sequestration strategies).


Source: Any process by which carbon dioxide is added to the atmosphere. Sources may be natural (e.g., soil and plant respiration) or due to human activities (e.g., combustion of fossil fuels and deforestation).


Time Series: Observations of a quantity taken regularly over time. The most famous time series in atmospheric carbon dioxide analysis is the Keeling curve, representing CO2 concentrations at Mauna Loa, Hawaii from 1958 onwards.


Uncertainty Estimates: Inversely estimated fluxes and stocks are statistical quantities, which have associated "error bars". These error bars are expressed as estimates of a confidence interval. Generally, we report the standard deviation of an estimate as the uncertainty; this means that we believe that there is a 68% probability that the unknown, true quantity lies within one standard deviation of our best guess.