CO2 Annual and Semiannual Cycles from Satellite Retrievals and Models

Abstract:

We have compared satellite CO₂ retrievals from the Greenhouse gases Observing SATellite (GOSAT), Atmospheric Infrared Sounder (AIRS), and Tropospheric Emission Spectrometer (TES) with in-situ measurements from the Earth System Research Laboratory (NOAA-ESRL) Surface CO₂ and Total Carbon Column Observing Network (TCCON), and utilized zonal means to characterize variability and distribution of CO₂. In general, zonally averaged CO₂ from the three satellite data sets are consistent with the surface and TCCON X_CO2 data. Retrievals of CO₂ from the three satellites show more (less) CO₂ in the northern hemisphere than that in the southern hemisphere in the northern hemispheric winter (summer) season. The difference between the three satellite CO₂ retrievals might be related to the different averaging kernels in the satellites CO₂ retrievals. A multiple regression method was used to calculate the CO₂ annual cycle and semiannual cycle amplitudes from different satellite CO₂ retrievals. The CO₂ annual cycle and semiannual cycle amplitudes are largest at the surface, as seen in the NOAA-ESRL CO₂ data sets. The CO₂ annual cycle and semiannual cycle amplitudes in the GOSAT X_CO2, AIRS mid-tropospheric CO₂, and TES mid-tropospheric CO₂ are smaller compared with those from the surface CO₂. Similar regression analysis was applied to the Model for OZone And Related chemical Tracers-2 (MOZART-2) and CarbonTracker model CO₂. The convolved model CO₂ annual cycle and semiannual cycle amplitudes are similar to those from the satellite CO₂ retrievals, although the model tends to under-estimate the CO₂ seasonal cycle amplitudes in the northern hemisphere mid-latitudes from the comparison with GOSAT and TES CO₂ and underestimate the CO₂ semi-annual cycle amplitudes in the high latitudes from the comparison with AIRS CO₂. The difference between model and satellite CO₂ can be used to identify possible deficiency in the model and improve the model in the future.