Moustafa Chahine, lead study author and AIRS science team leader at NASA's Jet Propulsion Laboratory, Pasadena, Calif., said the maps, which cover from September 2002 to July 2008, will be used by scientists to refine how climate models represent the processes that transport carbon dioxide within Earth's atmosphere. 'These data capture global variations in the distribution of carbon dioxide over time that are not represented in the existing models used to determine where carbon dioxide is created and stored,' he said.
Chahine said the previous scientific consensus was that carbon dioxide was evenly mixed in the free troposphere, decreasing as you move farther south of the equator. 'Our results show carbon dioxide there can vary by nearly one percent and that the free troposphere is like international waters-what's produced in one place is free to travel elsewhere,' he said.
This visualization is a time-series of the global distribution and variation of the concentration of mid-tropospheric carbon dioxide observed by the Atmospheric Infrared Sounder (AIRS) on the NASA Aqua spacecraft. For comparison, it is overlain by a graph of the seasonal variation and interannual increase of carbon dioxide observed at the Mauna Loa, Hawaii observatory. The AIRS data show the average concentration (parts per million) over an altitude range of 3 km to 13 km, whereas the Mauna Loa data show the concentration at an altitude of 3.4 km and its annual increase at a rate of approximately 2 parts per million (ppmv) per year.
The two most notable features of this visualization are the seasonal variation of CO2 and the trend of increase in its concentration from year to year. The global map clearly shows that the CO2 in the northern hemisphere peaks in April-May and then drops to a minimum in September-October. Although the seasonal cycle is less pronounced in the southern hemisphere it is opposite to that in the northern hemisphere. This seasonal cycle is governed by the growth cycle of plants. The northern hemisphere has the majority of the land masses, and so the amplitude of the cycle is greater in that hemisphere. The overall color of the map shifts toward the red with advancing time due to the annual increase of CO2.
Although the mid-latitude jet streams are not visible in the map, we can see their influence upon the distribution of CO2 around the globe. These rivers of air occur at an altitude of about 5 km and rapidly transport CO2 around the globe at that altitude. In the northern hemisphere, the mid-latitude jet stream squirms like a released garden hose over the period of a few days due to the continental landmasses.
In the southern hemisphere the jet stream flow is more directly West to East, and during the period from July to October the CO2 concentration is enhanced in a belt delineated by the jet stream and lofting of CO2 into the free troposphere by the high Andes is visible in this period. The zonal flow of CO2 around the globe at the latitude of South Africa, southern Australia and southern South America is readily apparent.
Eastward flow of CO2 from Indonesia and the Celebes sea can be seen in the November to February time frame.