Brasil-flux eddy covariance CO2 flux measurements: Uncertainty analysis, u* threshold and GEP calculation Natalia Restrepo-Coupe, Xubin Zeng, Rafael Rosolem, Brad Christoffersen,, Michel Muza, Luis G. de Goncalves, Koichi Sakaguchi, Alessandro C. da Araujo, Ian Baker, Osvaldo M. R. Cabral, Plinio B. de Camargo, David R. Fitzjarrald, Michael L. Goulden, Bart Kruijt, Jair M. F. Maia, Antonio O. Manzi, Scott D. Miller, Antonio D. Nobre, Celso von Randow, Humberto R. da Rocha, Ricardo K. Sakai, Julio Tota, Fabricio B. Zanchi, Scott R. Saleska

METHODS K77 K67 K83 K34 RJA FNS PDG

METHODS: REFERENCE Barr, A., Hollinger, D., and Richardson, A., 2009, NACP Uncertainty Analysis (11 Aug 2009) Papale, D., Reichstein, M., Canfora, E. et al., 2006, Towards a more harmonized processing of eddy covariance CO2 fluxes: algorithms and uncertainty estimation, Biogeosciences Discussions, 3, Richardson, A., and Hollinger, D. Y., 2007, A method to estimate the additional uncertainty in gap-filled NEE resulting from long gaps in the CO2 flux record, Agricultural and Forest Meteorology, 147m

Method, steps: 1.Remove spikes – Remove values outside the mean plus 3 standard deviations – Based on a double-differenced time series, using the median of absolute deviation about the median (Papale et al., 2006) – Include periods with missing adjacent values (Barr et al., 2009) 2.u* threshold calculation – Look up table (LUT): ta, u* and NEE nighttime – Define u*threshold as min u* that captures 99%, 95%, 90% 85% of the maximum flux. 3.Uncertainty measurements and filling – Calculate Re – Calculate GEP – Synthetic NEE, NEE syn – Remove 10%, 20%, 30% of the Synthetic NEE – Add noise to remaining observations – Calculate Resyn – Calculate GEPsyn – Calculate NEEsyn2syn as NEEsyn2syn = GEPsyn - Resyn – Compare NEE to NEEsyn2syn: seasonal cycle (16-days) and annual sums

1) Results: Remove spikes Remove spikes % removed neighbor % removed w/ missing adjacent values

1) Results: Remove spikes Remove spikes

1) Results: Remove spikes (29032) (10225) zdescription % removed % removed mean+3std(2) (8) 4neighbor0.7 (200) (164) 4w/ missing adjacent values 0.9 (263) (291) 5neighbor0.1 (36) (40) 5 w/ missing adjacent values0.2 (56) (101) 7 neighbor0.2 (68) (4) 7 w/ missing adjacent values0.05 (14) (41) Md = median of the differences z = threshold value 7, 5.5 and 4(conventionally used) For missing adjacent values, is the estimate form the gap-filling model

u* threshold 2) Results u* threshold calculation: Look up table (LUT): ta, u* and NEE nighttime

u* threshold 2) Results u* threshold calculation: Look up table (LUT): ta, u* and NEE nighttime

u* values are required to calculate the avg 2) Results u* threshold calculation: Look up table (LUT): ta, u* and NEE nighttime

95% of the maximum flux is captured 99% of the maximum flux is captured Bootstrap n=100 Bootstrap n=1000 2) Results u* threshold calculation: Bootsrap LUT (ta, u* and NEE nighttime)

90% of the maximum flux is captured 85% of the maximum flux is captured Bootstrap n=100 Bootstrap n=1000 2) Results u* threshold calculation: Bootsrap LUT (ta, u* and NEE nighttime)

Run

% max BootstrapMean Mean 95%CISTD % removed flux captured (n draws) – – ) Results u* threshold calculation: Bootsrap LUT (ta, u* and NEE nighttime)

3) Uncertainty measurements and filling: Calculate Re & GEE (GEE=-GEP)

3) Uncertainty measurements and filling: LUT (month, Ta and NEE nighttime)

3) Uncertainty measurements and filling: LUT (month, Ta and NEE nighttime)

u* threshold =0.228 m s -1 3) Uncertainty measurements and filling: LUT (month, Ta and NEE nighttime) Fourier transform

u* threshold =0.228 m s -1 3) Uncertainty measurements and filling: GEP Fourier transform

– Create a synthetic NEE (NEE syn ) – Remove 10%, 30%, 50% of the sample – Add noise to remaining observations: (Laplace: double – exponential standard deviation). For NEEsyn i >0 For NEEsyn i <=0 3) Uncertainty measurements and filling: Calculate synthetic NEE

– Calculate Re syn – Calculate GEP syn – Calculate NEE syn2syn as NEE syn2syn = GEP syn - Re syn – Compare NEE to NEE syn2syn 3) Uncertainty measurements and filling: Calculate synthetic NEE

3) Uncertainty measurements and filling: Compare NEE to NEE syn2syn % NEE syn Bootstrap Year Annual NEE Annual GEP Annual Re Removed (n draws) spike removal, u* threshold ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.15

3) Uncertainty measurements and filling: Compare NEE to NEE syn2syn % NEE syn Bootstrap Year Annual NEE Annual GEP Annual Re Removed (n draws) spike removal, no u* threshold ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.15

3) Uncertainty measurements and filling: – What happens if we use Re – Add the data – Chec

METHODS

RESULTS Idso, S. (1981), A set of equations for full spectrum and 8-µu-m to 14-µu-m and µu-m to 12.5-µu-m thermal-radiation from cloudless skies, Water Resources Research, 17(2),

RESULTS Idso, S. (1981), A set of equations for full spectrum and 8-µu-m to 14-µu-m and µu-m to 12.5-µu-m thermal-radiation from cloudless skies, Water Resources Research, 17(2),

RESULTS Idso, S. (1981), A set of equations for full spectrum and 8-µu-m to 14-µu-m and µu-m to 12.5-µu-m thermal-radiation from cloudless skies, Water Resources Research, 17(2),

RESULTS

METHODS (uncertainty)

RESULTS

DISCUSSION

CONCLUSIONS

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