Asymmetrical response of summer rainfall in East Asia to CO_(2)forcing

Understanding the regional hydrological response to varying CO_(2)concentration is critical for cost-benefit analysis of mitigation and adaptation polices in the near future. To characterize summer monsoon rainfall change in East Asia in a changing CO_(2)pathway, we used the Community Earth System Model(CESM) with28 ensemble members in which the CO_(2)concentration increases at a rate of 1% per year until its quadrupling peak, i.e., 1468 ppm(ramp-up period), followed by a decrease of 1% per year until the present-day climate conditions, i.e., 367 ppm(ramp-down period). Although the CO_(2)concentration change is symmetric in time, the amount of summer rainfall anomaly in East Asia is increased 42% during a rampdown period than that during a ramp-up period when the two periods of the same CO_(2)concentration are compared. This asymmetrical rainfall response is mainly due to an enhanced El Ni?o-like warming pattern as well as its associated increase in the sea surface temperature in the western North Pacific during a ramp-down period. These sea surface temperature patterns enhance the atmospheric teleconnections and the local meridional circulations around East Asia, resulting in more rainfall over East Asia during a ramp-down period. This result implies that the removal of CO_(2)does not guarantee the return of regional rainfall to the previous climate state with the same CO_(2)concentration.

Distinctive impacts of atmospheric intraseasonal oscillations on the net ecosystem exchange of the southeastern China forest between spring and summer

The southeastern China(SEC)forest is an important terrestrial biospheric carbon sink in the global carbon cycle,with its total net ecosystem exchange(NEE)accounting for about 3.2%of the global forest NEE.The prevailing atmospheric intraseasonal oscillations(ISOs)over East Asia strongly modulate climatic conditions over the SEC during spring and summer,thus leading to significant ISOs in the NEE of the SEC forest.As atmospheric ISOs show strong seasonality,this study examined the distinctive impacts of atmospheric ISOs on the NEE of the SEC forest between spring and summer.During spring,the vertical coupling of 10–30-d atmospheric ISOs in the lower and upper troposphere leads to strong 10‒30-d ISOs of solar radiation and temperature over the SEC.The 10‒30-d ISOs of solar radiation and temperature further result in the 10‒30-d ISOs of gross primary productivity(GPP)and terrestrial ecosystem respiration(TER).With the covariation in GPP and TER,the NEE of the SEC forest exhibits significant 10‒30-d ISOs.In contrast,the intraseasonal variations in climatic conditions over the SEC are associated with the 15‒60-d tropical atmospheric ISO during summer.While the induced 15‒60-d ISO of solar radiation leads to that of GPP,the induced 15‒60-d ISO of temperature is small and less effective;thus,the 15‒60-d ISO of NEE mainly originates from that of GPP.