CO2 annual and semiannual cycles from multiple satellite retrievals and models

Abstract

Satellite CO2 retrievals from the Greenhouse gases Observing SATellite (GOSAT), Atmospheric Infrared Sounder (AIRS), and Tropospheric Emission Spectrometer (TES) and in situ measurements from the National Oceanic and Atmospheric Administration - Earth System Research Laboratory (NOAA-ESRL) Surface CO2 and Total Carbon Column Observing Network (TCCON) are utilized to explore the CO2 variability at different altitudes. A multiple regression method is used to calculate the CO2 annual cycle and semiannual cycle amplitudes from different data sets. The CO2 annual cycle and semiannual cycle amplitudes for GOSAT XCO2 and TCCON XCO2 are consistent but smaller than those seen in the NOAA-ESRL surface data. The CO2 annual and semiannual cycles are smallest in the AIRS midtropospheric CO2 compared with other data sets in the Northern Hemisphere. The amplitudes for the CO2 annual cycle and semiannual cycle from GOSAT, TES, and AIRS CO2 are small and comparable to each other in the Southern Hemisphere. Similar regression analysis is applied to the Model for OZone And Related chemical Tracers-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 models tend to underestimate the CO2 seasonal cycle amplitudes in the Northern Hemisphere midlatitudes and underestimate the CO2 semiannual cycle amplitudes in the high latitudes. These results can be used to better understand the vertical structures for the CO2 annual cycle and semiannual cycle and help identify deficiencies in the models, which are very important for the carbon budget study.