کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
82252 158385 2010 10 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Spatiotemporal evolution of CO2 concentration, temperature, and wind field during stable nights at the Norunda forest site
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علم هواشناسی
پیش نمایش صفحه اول مقاله
Spatiotemporal evolution of CO2 concentration, temperature, and wind field during stable nights at the Norunda forest site
چکیده انگلیسی

Unusually high CO2 concentrations were frequently observed during stable nights in late summer 2006 at the CarboEurope-Integrated Project (CEIP) forest site in Norunda, Sweden. Mean CO2 concentrations in the layer below the height of the eddy-covariance measurement system at 30 m reached up to 500 μmol mol−1 and large vertical and horizontal gradients occurred, leading to very large advective fluxes with a high variability in size and direction. CO2 accumulation was found to build up in the second part of the night, when the stratification in the canopy sub-layer turned from stable to neutral. Largest vertical gradients of temperature and CO2 were shifted from close to the ground early in the night to the crown space of the forest late at night, decoupling the canopy sub-layer from the surface roughness layer. At the top of the canopy at 25 m CO2 concentrations up to 480 μmol mol−1 were observed at all four tower locations of the 3D cube setup and concentrations were still high (>400 μmol mol−1) at the 100 m level of the Central tower. The vertical profiles of horizontal advective fluxes during the nights under investigation were similar and showed largest negative horizontal advection (equivalent to an additional CO2-sink) to occur in the crown space of the forest, and not, as usually expected, close to the ground. The magnitude of these fluxes was sometimes larger than −50 μmol m−2 s−1 and they were caused by the large horizontal CO2 concentration gradients with maximum values of up to 1 μmol mol−1 m−1. As a result of these high within canopy CO2 concentrations, the vertical advection also became large with frequent changes of direction according to the sign of the mean vertical wind component, which showed very small values scattering around zero. Inaccuracy of the sonic anemometer at such low wind velocities is the reason for uncertainty in vertical advection, whereas for horizontal advection, instrument errors were small compared to the fluxes. The advective fluxes during these nights were unusually high and it is not clear what they represent in relation to the biotic fluxes. Advection is most likely a scale overlapping process. With a control volume of about 100 m × 100 m × 30 m and the applied spatial resolution of the sensors, we obviously miss relevant information from processes in the mesoscale as well as in the turbulent scale.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Agricultural and Forest Meteorology - Volume 150, Issue 5, 15 May 2010, Pages 692–701
نویسندگان
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