Data description

Document containing the description of the current CARBONES data (V0.5).

The objective of this document is to give the users of the CARBONES portal a brief and synthetic overview of the available products and services. This document contains three sections:

• Section 1: gives a rapid overview of the data assimilation system used (CCDAS) in the generation of the data currently available on the portal;
• Section 2: contains a list of products available on the portal;
• Section 3: contains a description of the display processing available;

1. Description of the CCDAS version used to generate the data

This is a description of the data currently available on the portal. The document will be updated after each new release of data on the portal. The data currently displayed on the portal correspond to version 0.5 (released in January 2012).

The products were generated as follows:

• The assimilation system including the atmospheric transport model (LMDz) was used to invert atmospheric CO2 observations in order to optimize :
o Net ecosystem fluxes using a priori estimates from the ORCHIDEE model
o Biomass burning fluxes
o And ocean fluxes using a priori estimates from the climatology of Takahashi
• The remaining products (land carbon stocks and land gross fluxes) were obtained from the ORCHIDEE model forward simulation (no assimilation) for the concerned 20 year period.

2. Description of products available on the CARBONES portal

The Carbon Data Assimilation System delivers fluxes and stocks of carbon, as well as latent heat and sensible fluxes over land. These products were generated for a 20 year period (1990-2009) at a resolution of 1° x 1° degrees. The calculations for the current version (V0.5) were done at a coarser resolution of 2.5° x 3.75° and were then interpolated on the 1°x1° degree grid. Future versions will provide an estimate of the uncertainty (Bayesian uncertainty calculated by the CCDAS). The CCDAS products available with the current version are listed in Table 1 below:

Table 1: List of products provided by the current version of the CCDAS

3. Description of processing available on the CARBONES portal

The processing available with the current version of the CARBONES portal (V0.5) concerns two types of filtering:

• Temporal filtering
• Spatial averaging

3.1 Temporal filtering
The portal allows displaying the products either at their original temporal resolution or for coarser temporal means (Table 2)

  Carbon fluxes Heat fluxes Carbon stocks LAI
3 hourly values Original resolution Original resolution No No
24 hour means Yes Yes Original resolution Original resolution
Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes

Table 2: Information on the original resolution of the products and on the temporal means available.

The units depend on the type of temporal averaging and spatial aggregation: for instance flux in kgC/m²/hr is transformed into kgC/m²/day or kgC/m²/month or kgC/m²/year, and the spatial aggregates are transformed into kgC or GtC (see below)

In addition to calculating the means, the time filtering algorithm can be applied to fit the data to a polynomial of degree 2, with 3 harmonics. The residuals are filtered in the frequency space using a low-pass filter of 667 days and a high-pass filter of 80 days. The output variables from the temporal filtering are listed in Table 3.

CARBONES post-processing output parameter Description
Means Algebraic means (Table 2)
Smoothed trend The polynomial fit plus the low-pass filtered residuals using a cut-off value at 667 days
Smoothed curve The fitted function plus the low-pass filtered residuals using a cut-off value at 80 days
Re-centred parameter The original data minus the period mean

Table 3: Types of temporal filtering available

3.2 Spatial Averaging:
All variables (fluxes and stocks) can be aggregated onto predefined regions for the visualization of the time series of fluxes and stocks (not for displaying 2D maps). This aggregation is performed based on 2D masks describing each of the preselected regions at 1°x1° resolution.

• There are 3 general types of regions:
o Land only,
o Ocean only,
o Land + ocean.

All available regions are listed in the Table 4 below.
Table 4: List of available regions for spatial aggregation

Note: For the ocean regions there are no carbon stocks and no estimation of the latent heat and sensible heat fluxes.