Spatial Patterns and Time Variability of CO2From AIRS.

We investigate the CO₂ spatial-time variability in the troposphere based on the 16-year-long (2002-2018) mid-tropospheric CO₂retrievals obtained from the measurements by the Atmospheric Infrared Sounder (AIRS) and its companion instrument, the Advanced Microwave Sounding Unit (AMSU), onboard of Aqua spacecraft. AIRS retrievals generate CO₂ product at selected atmospheric levels, not averaged in columns. The current version 6 of the retrievals provides high-quality data over the globe (except near the South Pole) for every day and night. The data used are monthly means on a 1°x1° latitude-longitude grid. The data show the expected seasonal /north/south asymmetric variability in the CO₂mixing ratio, as well as regional patterns, including a correlation with El Nino. Spatial patterns and their time variability are evaluated using Principal Component Analysis (PCA). The spectral content of the modes is analyzed with Empirical Mode Decomposition (EMD). To determine the correct spatial distribution of the variance we apply the Sparse PCA algorithm. We discuss potential physical mechanisms driving the observed CO₂variability.