Influence of Droughts on CO2

Mid-tropospheric CO2 data from the Atmospheric Infrared Sounder (AIRS) are utilized in this study to explore the impact of droughts on mid-tropospheric CO2 over the southwest USA. It is found for the first time that the mid-tropospheric CO2 concentration is 1 parts per million by volume (ppm) higher during dry years than wet years over the southwest USA from June to September. The mid-tropospheric CO2 differences between dry and wet years are related to CO2 surface fluxes and circulation. During drought conditions, there is less vegetation uptake of CO2 from the biosphere, which leads to high concentration of CO2 in the atmosphere during drought conditions. In addition to the CO2 surface fluxes, vertical pressure velocity from NCEP2 suggest that there is more rising air during dry years over most regions, which can help bring surface high concentration CO2 to the mid-troposphere. Results obtained from this study demonstrate the impact of surface CO2 flux and circulation on the mid-tropospheric CO2. It can help us better understand the impact of droughts on atmospheric CO2 and the interaction between biosphere and atmosphere.