Seminar: Dieu Anh Tran

The eddy covariance technique allows for direct methane flux measurements through high-frequency operations of atmospheric turbulences. But while several tens of stations are in service in the North American boreal zone, the Siberian region is only sparsely covered by such measurements. In Siberia, the predominant way to determine CH4 fluxes has been by chamber measurements. This motivates the exploitation of existing data sets in Siberia to gain spatially and temporally better-resolved carbon budgets. The ZOtino Tall Tower Observatory (ZOTTO; 60° 48’ N, 89° 21’ E) observations of CH4 mole fractions, as well as meteorological parameters from six different heights up to 301 m a.g.l, allow for an additional estimate of surface-atmosphere fluxes of CH4 for the middle Siberian region since beginning 2009. We will study the long-term variations in atmospheric CH₄ in inland Eurasia by evaluating 11 years of in situ observations at ZOTTO, focusing on temporal patterns, seasonal and diurnal variations, and long-term trends. We will next apply a complementary approach to infer CH4 surface flux – the mixed-layer theory. The theory is based on boundary layer budget methods valid under convective conditions. Under these conditions, we can assume that well-mixed conditions prevail a mixed-layer value of CH4 that is representative of the entire boundary layer, and relatively small differences in the regions with concentration gradients (above the canopy and in the entrainment zone) are used to estimate CH4 fluxes on local scales.