LEVEL 3 – VARIABLES DECRIPTION Level 3 data are obtained from the level 2 products, data are quality checked using standardized techniques and NEE is calculated. Data are not changed but descriptive variables (‘flags’) are added. - Month: from 1 to 12 - Day: day of the month - Hour: from 0 to 23.5, indicates the end of the half hour of measurement - DoY: decimal day of the year - CO2: carbon dioxide concentration measured at top of the tower [umol/mol] - H2O: water vapour concentration measured at top of the tower [mmol/mol] - ZL: atmosphere stability parameter - Fc: carbon dioxide flux [umolCO2 m-2 s-1] - qf_Fc: fluxes quality flags (see below) - NEE_st: Net Ecosystem Exchange standardized - calculated using the storage obtained with the discrete approach (single point on the top of the tower) with the same method for all the sites [umolCO2 m-2 s-1] - qf_NEE_st: fluxes quality flags (see below) - NEE_or: Net Ecosystem Exchange original - calculated using the storage sent by the PI that can be obtained with the discrete approach or using the profile system (see others information below) [umolCO2 m-2 s-1] - qf_NEE_or: fluxes quality flags (see below) - H: sensible heat flux [W m-2] - LE: latent heat flux [W m-2] - Ustar: friction velocity [m s-1] - qf_ust: quality flag: 0 = ok, 1 = possible spike. Calculated starting from the linear regration between ustar and wind speed. Flagged as 1 if the residual are bigger than 5 times the standard deviation. - Precip: precipitation [mm] - Rg: global radiation [W m-2] - PPFD: photosynthetic photon flux density [umol m-2 s-1] - R_pot: potential radiation (‘at top of atmosphere’) calculated from time and geographic coordinates [W m-2] - qf_Rg: quality flag for Rg: 0=ok, 1=possible bad values. Calculated comparing measured Rg and potential radiation. - qf_Rad: quality flag for Rg and PPFD: 0 = ok, 1 = possible bad values. Calculated starting from the linear regration between the two variables. Flagged as 1 if the residual are bigger than 5 times the standard deviation. - Rr: reflected radiation [W m-2] - Rn: net radiation [W m-2] - Rd: diffuse radiation (global) [W m-2] - APAR: light interception [umol m-2 s-1] - Ta: air temperature [°C] - Ts1: soil temperature depth 1 [°C] - Ts2: soil temperature depth 2 [°C] - SWC1: soil water content depth 1 [%vol] - SWC2: soil water content depth 2 [%vol] - G1: soil heat flux [W m-2] - G2: soil heat flux [W m-2] - Rh: relative humidity [%] - WD: wind direction [degrees] - WS: wind horizontal speed [m s-1] Flux quality flags explanation: The qc_flag is a 9 bits number. See below the explanation: Bit 9: QC from PI 0 = ok (class 0-1 of QA/QC method based on raw data – Foken et al.) 1 = not ok (class 2) Bit 8: Marginal point (at the border to a gap) 0 = no 1 = marginal point Bits 7-6: ustar criterion 00 = ok 01 = below threshold 10 = preceding values is below threshold 11 = below threshold and preceding below threshold Bits 5-4: Spike detection 00 = no spike 01 = spike as outside 4 SD 10 = spike as outside 5.5 SD 11 = spike as outside 7 SD or out of range. Bit 3: Low variability 0 = ok 1 = low variability (e.g. when pump is broken etc.) Bits 2-1: Summary 00 = best 01 = medium (not used) 10 = bad 11 = missing