Modulation of Midtropospheric CO_2 by the South Atlantic Walker Circulation

• Published in: Journal of the Atmospheric Sciences
• Main Authors: Jiang, Xun, Olsen, Edward T., Pagano, Thomas S., Su, Hui, Yung, Yuk L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2015
• Subjects: South Atlantic Ocean
• Online Access: https://authors.library.caltech.edu/85258/; https://authors.library.caltech.edu/85258/1/jas-d-14-0340.1.pdf; https://authors.library.caltech.edu/85258/2/10.1175_jas-d-14-0340.s1.doc; https://resolver.caltech.edu/CaltechAUTHORS:20180312-144301289

Midtropospheric CO_2 data from the Atmospheric Infrared Sounder (AIRS) are used in this study to explore the variability of CO_2 over the South Atlantic Ocean. It was found that the area-averaged CO_2 over the South Atlantic Ocean is less than that over South America by about 1 ppm during December–March. This CO_2 contrast is due to the large-scale vertical circulation over this region. During December–March, there is sinking motion over the South Atlantic Ocean. The sinking motion brings high-altitude air with a slightly lower concentration of CO_2 to the midtroposphere. Meanwhile, air rising over South America brings near-surface air with a higher concentration of CO_2 to the midtroposphere. As a result, the AIRS midtropospheric CO_2 concentration is lower over the South Atlantic Ocean than over South America during December–March. The detrended AIRS midtropospheric CO_2 difference correlates well with the inverted and detrended 400-hPa vertical pressure velocity difference between the South Atlantic and South America. Results obtained from this study demonstrate the strong impact of large-scale circulation on the vertical distribution of CO_2 in the free troposphere and suggest that midtropospheric CO_2 measurements can be used as an innovative observational constraint on the simulation of large-scale circulations in climate models.