1. Regional tower network of CO2 mixing ratio measurements in North Wisconsin
Six systems are distributed on a circle of roughly 150-km radius centered at the WLEF tower. All measurements are taken at a height of 76m. Field tests prior to deployment in which the six systems sampled the same air indicate agreement of the systems to within 0.5-1.0 ppm from the mean during relatively quiescent periods. The high precision and accuracy of the systems ensure the data will detect horizontal gradients in CO2 mixing ratios caused by net ecosystem-atmosphere exchange. These horizontal gradients will be the basis for using atmospheric budget methods to derive regional fluxes with spatial and temporal resolution find enough to warrant comparison to the ChEAS regional flux tower network.
2. Virtual tall tower (VTT) network in AmeriFlux sites
The same systems or methodology as project 1 will be used at 10 or more AmeriFlux towers (click here for a VTT map) to ensure the CO2 mixing ratio measurements are well-calibrated and able to detect the regional gradients of CO2 mixing ratios. Sites will be chosen to optimize our ability to derive both Midwestern and continental-scale fluxes of CO2. To convert the measurements at the surface layer towers into virtual tall tower data, VTT technique is used. The method is simple, robust and accurate, and will be re-evaluated at every opportunity.
(1) Using the same systems to establish high-precision, high-accuracy CO2 mixing ratio measurements at selected AmeriFlux towers
(2) Intersite calibration of field sites is assured by using four tanks of standard gases at each site.
(3) Correction for the surface layer to mid-CBL bias is achieved using mixed-layer similarity theory. (for details, click < here >)
(4) Applying the data to determine regional and continental NEE of CO2