Variations of Solar-Induced Fluorescence, Carbon Dioxide, and Water Cycle

Solar-induced fluorescence (SIF) and column CO₂ data from the Orbiting Carbon Observatory-2 (OCO-2) and the Greenhouse Gases Observing Satellite (GOSAT), precipitation data from the Global Precipitation Climatology Project (GPCP), and evaporation data from the European Centre for Medium-Range Weather Forecasts (ECMWF) are combined to explore the interaction between the biosphere and the atmosphere. SIF data from OCO-2 and GOSAT satellites are used to investigate the CO₂ exchange between the biosphere and the atmosphere. Differences of GPCP precipitation data and ECMWF evaporation data are utilized to estimate the water available to the biosphere. It is found that OCO-2 and GOSAT SIF values are high when there is more water available. Furthermore, high SIF usually correlates with low CO₂ in the atmosphere; there is less CO₂ in the atmosphere when SIF is high in summer. Therefore, there is a negative correlation between atmospheric CO₂ and SIF.

A multiple regression method is further used to estimate the annual cycle amplitudes of SIF, CO₂, and available water. SIF annual cycle amplitudes are large over South America, Central and Southern Africa, and Southeast Asia, where the annual cycle amplitudes of the available water are high. SIF annual cycle amplitudes are also high over the East USA and Europe, which is related to the surface summer-green vegetation. Results in this analysis based on new SIF and CO₂ data from OCO-2 and GOSAT contribute to a better understanding and quantification of the carbon cycle and the interaction between the biosphere and the atmospheric water cycle.