Can seasonal and interannual variation in landscape CO2 fluxes be detected by atmospheric observations of CO2 concentrations made at a tall tower?

[摘要] The coupled numerical weather model WRF-SPA (Weather Research and Forecastingmodel and Soil-Plant-Atmosphere model) has been used to investigate a 3 yrtime series of observed atmospheric CO₂ concentrations from a tall towerin Scotland, UK. Ecosystem-specific tracers of net CO₂ uptake and netCO₂ release were used to investigate the contributions to the tower signalof key land covers within its footprint, and how contributions varied atseasonal and interannual timescales. In addition, WRF-SPA simulatedatmospheric CO₂ concentrations were compared with two coarse globalinversion models, CarbonTrackerEurope and the National Oceanic andAtmospheric Administration's CarbonTracker (CTE-CT). WRF-SPA realisticallymodelled both seasonal (except post harvest) and daily cycles seen inobserved atmospheric CO₂ at the tall tower (R² = 0.67,rmse = 3.5 ppm, bias = 0.58 ppm). Atmospheric CO₂ concentrationsfrom the tall tower were well simulated by CTE-CT, but the inverse modelshowed a poorer representation of diurnal variation and simulated a largerbias from observations (up to 1.9 ppm) at seasonal timescales, compared tothe forward modelling of WRF-SPA. However, we have highlighted a consistentpost-harvest increase in the seasonal bias between WRF-SPA and observations.Ecosystem-specific tracers of CO₂ exchange indicate that the increasedbias is potentially due to the representation of agricultural processeswithin SPA and/or biases in land cover maps. The ecosystem-specific tracersalso indicate that the majority of seasonal variation in CO₂ uptake forScotland's dominant ecosystems (forests, cropland and managed grassland) isdetectable in observations within the footprint of the tall tower; however,the amount of variation explained varies between years. The between yearsvariation in detectability of Scotland's ecosystems is potentially due toseasonal and interannual variation in the simulated prevailing winddirection. This result highlights the importance of accurately representingatmospheric transport used within atmospheric inversion models used toestimate terrestrial source/sink distribution and magnitude.

[学科分类] 地球化学与岩石