|HICKS, BRUCE - Metcorps|
|O'DELL, DEB - University Of Tennessee|
|EASH, NEAL - University Of Tennessee|
|Sauer, Thomas - Tom|
Submitted to: Agriculture and Forest Meterology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2014
Publication Date: 10/15/2014
Citation: Hicks, B.B., O'Dell, D., Eash, N.S., Sauer, T.J. 2014. Nocturnal intermittency in surface CO2 concentrations in sub-Saharan Africa. Agriculture and Forest Meterology. 200:129-134.
Interpretive Summary: Traditionally, the movement of gases like carbon dioxide and water vapor between plant canopies and the atmosphere was considered to be a steady exchange process driven by differences in concentrations. Measurement techniques were developed based on this understanding of gas exchange. Recent data has suggested that this way of thinking about gas exchange may not be correct. New information suggests that the exchange occurs in large events that only occur periodically. This objective of this study was to measure carbon dioxide exchange from four fields in Zimbabwe. Instruments were located in each field with different plants or bare soil that included sensors to measure carbon dioxide concentration. When this data was looked at closely, cycles in the observed concentrations were noticed. These cycles were found to be related to air temperature and humidity differences and changes in wind speed, especially at night. The results indicate that some of the assumptions regarding carbon dioxide exchange may be incorrect and measurement practices may need to be adjusted to avoid errors. This research is important to scientists and policymakers interested in the accuracy and reliability of long-term carbon dioxide exchange between plant canopies and the atmosphere.
Technical Abstract: Data obtained over four adjacent fields of differing management practices in Zimbabwe illustrate the role of atmospheric intermittency as a mechanism for transferring CO2 between the surface and the atmosphere above. At night, limited atmospheric mixing permits CO2 concentrations to increase to levels well above those conventionally reported (exceeding a spatial average of 450 ppm on some nights), but these high levels are moderated by a periodic intermittency that appears to be generated by wind shear aloft. This intermittency (slightly more rapid than once per hour) is a frequently observed atmospheric phenomenon, often associated with the “sweeps” observed in forested environments. The availability of CO2 data with adequate time resolution facilitates investigation of the general behavior, which is suspected to be a common although rarely observed feature of the lower atmosphere. If true, this means that the nocturnal vertical transfer of momentum, heat and mass is not solely through a constrained spectral continuum of turbulence as much as by regular sudden bursts, propagating from above and penetrating the surface boundary layer.