Rectifier effect in an atmospheric model with daily biospheric fluxes: impact on inversion calculation

Atmospheric CO2 measurements show strong synoptic variability. To understand the contribution of the synoptic signals on atmospheric CO2 inversion, we simulate the cases of biospheric fluxes with and without synoptic variations (referred to as ‘Synoptic’ and ‘Reference’, respectively) using an atmospheric transport model, and then perform inversion analyses with these biospheric CO2 concentration fields. Results show the monthly and annually averaged CO2 concentration anomalies (Synoptic–Reference) are functions of the distance from the continental biospheric source regions. Remote sites (like Mauna Loa) show averaged monthly amplitude of ∼0.2 ppm, while continental sites show averaged monthly amplitudes of 1–2 ppm with maximum monthly amplitudes up to 7 ppm. Spatial scales of these monthly mean synoptic anomaly patterns may exceed 1000 km. These CO2 concentration patterns are the results of the interaction of the synoptic CO2 flux field and atmospheric transport, and may be referred to as the synoptic Rectifier Effect. Inversion CO2 fluxes for 1992–1995 are obtained using biospheric background fields with and without synoptic biospheric flux variations. The maximum magnitude differences in estimated monthly flux for land and ocean regions are ∼0.4 and ∼0.2 GtC month−1, respectively. The average land sink increases by 0.19 GtC yr−1 while the average ocean sink decreases by 0.30 GtC yr−1.