The influence of atmospheric intraseasonal oscillations on terrestrial biospheric CO2 fluxes in Southeast China Forest

Abstract

With its strong carbon sequestration capacity and significantly expanding trend, forest over southeast China (SEC) is an important biospheric carbon sink. As intraseasonal oscillation (ISO) is a remarkable variability of the East Asian summer monsoon—the major climate system influencing the carbon exchange of SEC forest, the objective of this study is to examine the impact of atmospheric intraseasonal oscillation on CO2 fluxes in SEC forest based on daily CO2 fluxes and meteorological data. Significant 15‒60-day ISO of CO2 fluxes is identified in SEC forest during May‒August of 1980‒2013. The 15‒60-day ISO of net ecosystem exchange between atmosphere and biosphere mainly results from that of gross primary productivity (GPP), with the explained variances greater than 50% over most SEC forest areas. Due to the high drought-resistance of SEC forest, the 15‒60-day ISO of its GPP is controlled primarily by local solar radiation, which is in turn associated with the northward-propagating atmospheric ISO. Suppressed (active) convection anomaly and the thermally induced anomalous anticyclone (cyclone) on its northwestern side initiate from the southern South China Sea and then propagate northward to SEC coherently in the form of a Rossby wave-like pattern. Decreased (increased) cloud cover associated with the suppressed (active) convection anomaly leads to more (less) solar radiation reaching the SEC forest canopy, thus promoting (impairing) forest productivity.