Validation, Analysis of Annual Cycle, and Biogenic Sequestration of CO2, and Modulation of CH4
Greenhouse gases, such as carbon dioxide (CO2) and methane (CH4), play a critical role in the processes of global warming and climate change. Retrieved CO2 from satellites (e.g., OCO 2, GOSAT, AIRS, TES) offer a fresh opportunity to understand the variability of CO2 over the global domain that was unattainable before due to sparse in situ measurements. First, two innovative satellite data sets, Orbiting Carbon Observatory (OCO-2) and Greenhouse Gases Observing Satellite (GOSAT), which have vertical sensitivities in the lower atmosphere were compared, with ground-based measurements to validate the new retrievals. This established that the GOSAT and OCO-2 CO2 data sets are close to the in situ measurements. The overall GOSAT CO2 uncertainty was -0.63 ppm; whereas, OCO-2 uncertainty was 0.23 ppm. Second, the long-term trend and annual variability of CO2 using satellite retrievals were explored. A multiple regression method was used to estimate CO2 seasonal cycle from the satellite CO2 retrievals and in situ CO2 measurements to better understand surface, mid-tropospheric, and column CO2 seasonal cycles. Third, novel satellite-retrieved Solar-induced Fluorescence (SIF) datasets were studied to investigate the contributions of the biosphere to CO2. This analysis allows for a better understanding of how the biosphere acts as a source and also a sink for global CO2, yielding a better understanding of the CO2 global cycle. An inverse relationship was found between atmospheric CO2 and SIF. During each hemisphere’s summer season, SIF values are high because there is more photosynthesis, which leads to a low levels of atmospheric CO2. Finally, the influence of El Niño-Southern Oscillation on mid-tropospheric methane was studied. Enhanced rising air in the central Pacific during El Niño months advects lower surface concentrations of CH4 over the ocean to the middle troposphere, with less CH4 over the central Pacific than the western Pacific. Furthermore, rising air can transport low surface concentrations of CH4 to the middle troposphere over the western Pacific in La Niña months, contributing to lower CH4 concentrations over the western Pacific than the central Pacific during La Niña months.