An Investigation of the Eddy-Covariance Flux Imbalance in a Year-Long Large-Eddy Simulation of the Weather at Cabauw
| Autor: | H.J.J. Jonker, Jerôme Schalkwijk, A. Pier Siebesma |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Atmospheric Science
Daytime 010504 meteorology & atmospheric sciences Monin–Obukhov length Meteorology Flow (psychology) Eddy covariance 01 natural sciences Wind speed 010305 fluids & plasmas Vortex Physics::Fluid Dynamics Flux (metallurgy) 0103 physical sciences Environmental science Physics::Atmospheric and Oceanic Physics 0105 earth and related environmental sciences Large eddy simulation |
| Zdroj: | Boundary-Layer Meteorology. 160:17-39 |
| ISSN: | 1573-1472 0006-8314 |
| DOI: | 10.1007/s10546-016-0138-9 |
| Popis: | The low-frequency contribution to the systematic and random sampling errors in single-tower eddy-covariance flux measurements is investigated using large-eddy simulation (LES). We use a continuous LES integration that covers a full year of realistic weather conditions over Cabauw, the Netherlands, and emulate eddy-covariance measurements. We focus on the daytime flux imbalance, when the turbulent flux is sufficiently resolved. Averaged over the year, daytime single-tower eddy-covariance flux measurements lead to a significant systematic underestimation of the turbulent flux. This underestimation depends on the averaging period and measurement height. For a 3600-s averaging period at 16-m height, the systematic underestimation reduces to a few percent, but for 900-s averaged tall-tower measurements at 100-m height, the fluxes are systematically underestimated by over 20 %. The year-long dataset facilitates an investigation into the environmental conditions that influence the eddy-covariance flux imbalance. The imbalance problem is found to vary widely from day to day, strongly dependent on the flow regime. In general, the imbalance problem reduces with increased mean wind speed, but days having the largest imbalance (over twice the average) are characterized by roll vortices that occur for average wind speeds, typically having a boundary-layer height (zi) to Obukhov length (L) ratio of 10zi/L<100. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|