4dVAR : This term refers to a mathematical technique that allows one to very efficiently solve the inverse problem. It uses eh concept of an adjoint model to minimize a large multivariate cost function.
Anomaly : An anomaly is technically a departure from 'normal'. On this website, we show anomalies of fluxes. This means that we first calculate long-term averages of the estimated fluxes, and then see what the departures from this average is in each month and location. Sometimes, the anomalies are further smoothed in time (3-months or a year) to separate noise from signal.
CarbonTracker_EU : This term refers to the carbon dioxide inverse estimates produced with the system developed at the University of Wageningen, the Netherlands.
ECMWF : The European Centre for Medium-Range Weather Forecasts. Many transport models, including TM5 and LMDz, use the ECMWF operational "forecast" model for the meteorological drivers.
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.
EnKF : Ensemble Kalman filter. An inversion scheme based on the classic Kalman filter algorithm. The EnKF uses the power of parallel computers by numerically representing the covariance matrix of parameter uncertainty with a large ensemble of slightly different realizations.
Flux : The flow of mass across a surface. In ICOS, we 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.
Greenhouse Gases : Greenhouse gases are those gases in our atmosphere with the ability to trap radiation from the Earth's surface and thereby warm the air. Carbon dioxide and Methane are amongst the more well known greenhouse gases.
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.
Jena_s96 : This term refers to the carbon dioxide inverse estimates produced with the system developed by the Max Planck Institute for Biogeochemistry in Jena, Germany.
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.
LSCE_miop : This term refers to the carbon dioxide inverse estimates produced with the MIOP system (...?) developed at the Laboratoire Scientifique C... E....
MBL : Marine boundary layer. Technically, the lowest level of the atmosphere over the ocean. Practically, this is an idealized construct of air representing the well-mixed lower atmosphere away from continental sources and sinks of CO2.
Methane : Methane is a greenhouse gas that is formed when carbon containing matter is broken down by bacteria in the absence of oxygen. This occurs for instance deep in the soils, or in rice fields under water, or in landfills. Methane is 23 times more powerful than CO2 in warming the Earth, but there is quite a bit less of it around. Also, methane is broken down in the atmosphere on a time scale of typically a decade making it overall a smaller contributor to warming of the atmosphere than CO2.
Mole Fraction : 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. We use the mole fraction of CO2 in (dry) air because it is a conserved quantity: it does not depend on the pressure, temperature, water vapor or condensed water content, which are all highly variable. The CO2 mole fraction is much less variable, and depends only on the history of its sources and sinks, almost all of which are caused by surface processes such as photosynthesis and respiration, and the burning of coal, oil, or natural gas. It is the magnitudes of these source processes that we want to estimate.
NDVI : Normalized Difference Vegetation Index. A measure of vegetation greenness derived from AVHRR observations.
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.
TM5 : Transport Model, version 5. An off-line model of global atmospheric tracer transport. Uses meteorological driver fields from other sources to model the advection and diffusion of atmospheric gases. Supports two-way nested grids to provide higher-resolution simulations over certain areas of the globe.
TM3 : Transport Model, version 3. An off-line model of global atmospheric tracer transport. Uses meteorological driver fields from other sources to model the advection and diffusion of atmospheric gases.
TransCom : A special project of the International Geosphere-Biosphere Programme (IGBP), Global Analysis, Interpretation, and Modeling (GAIM) Project, the objective of which was to quantify and diagnose the uncertainty in inversion calculations of the global carbon budget that result from errors in simulated atmospheric transport, the choice of measured atmospheric carbon dioxide data used, and the inversion methodology employed.
Uncertainty Estimates : Inversely estimated fluxes 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 the flux estimate as the uncertainty; this means that we believe that there is a 68% probability that the unknown, true flux lies within one standard deviation of our best guess flux.
WMO : World Meteorological Organization