THE SEASONAL CYCLE OF ATMOSPHERIC CO2 - A STUDY BASED ON THE NCAR COMMUNITY CLIMATE MODEL (CCM2)

Citation
Dj. Erickson et al., THE SEASONAL CYCLE OF ATMOSPHERIC CO2 - A STUDY BASED ON THE NCAR COMMUNITY CLIMATE MODEL (CCM2), JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 101(D10), 1996, pp. 15079-15097
Citations number
57
Categorie Soggetti
Metereology & Atmospheric Sciences
Volume
101
Issue
D10
Year of publication
1996
Pages
15079 - 15097
Database
ISI
SICI code
Abstract
A global three-dimensional atmospheric model, the NCAR CCM2 general ci rculation model, has been adapted to study the hourly to yearly variab ility of CO2 in the atmosphere. Features of this CCM2-based model incl ude high spatial resolution (2.8 degrees x 2.8 degrees latitude/longit ude), 18 vertical levels, a 15-min time step, and an explicit, nonloca l atmospheric boundary layer parameterization. The surface source/sink relationships used include exchange with the ocean, the terrestrial b iosphere, biomass burning, and fossil fuel release of CO2. The timing and magnitude of the model seasonal cycle are compared to observationa l data for 28 sites. The seasonal cycle of atmospheric CO2 is generall y well predicted by the model for most of the northern hemisphere, but estimates of the amplitude of the seasonal cycle in the southern hemi sphere are overpredicted. To address this aspect more rigorously, we h ave used the monthly surface ocean pCO(2) maps created by the Max-Plan ck-Hamburg ocean general circulation model to asses the ocean seasonal ity on the atmospheric surface CO2 seasonality. The globally averaged interhemispheric gradient in atmospheric CO2 concentrations, as comput ed with the chosen source/sink distributions, is a factor of two too h igh compared to data, and selected longitudinal bands may be up to 50% higher than the zonal mean. The high temporal resolution of this mode l allows the infrequent yet real extrema in atmospheric CO2 concentrat ions to be captured. The vertical attenuation of the seasonal cycle of atmospheric CO2 is well simulated by the boundary layer/free troposph ere interaction in the model in the northern hemisphere. Conversely, a n increasing amplitude of the seasonal cycle aloft is found in the mid latitude southern hemisphere indicating interhemispheric transport eff ects from north to south. We use two different models of the terrestri al biosphere to examine the influence on the computed seasonal cycle a nd find appreciable differences, especially in continental sites. A gl obal three-dimensional chemical transport model is used to assess the production of CO2 from the oxidation of CO throughout the volume of th e atmosphere. We discuss these CO + OH --> CO2 + H results within the context of inverse model approaches to ascertaining the global and reg ional source/sink patterns of CO2. Deficiencies in the model output as compared to observational data are discussed within the context of gu iding future research.