Effect of fetch length on latent heat flux data accuracy calculated by Bowen ratio energy balance method

0426787 - ÚVGZ 2014 eng A - Abstract
Pozníková, Gabriela - Fischer, Milan - Trnka, Miroslav - Orság, Matěj - Kučera, J. - Žalud, Zdeněk
Effect of fetch length on latent heat flux data accuracy calculated by Bowen ratio energy balance method.
Geophysical Research Abstracts. EGU, 2013. 8279-2-8279-2. ISSN 1607-7962.
[EGU General Assembly 2013. 07.04.2013-12.04.2013, Vienna]
R&D Projects: GA MŠMT(CZ) ED1.1.00/02.0073; GA MŠMT(CZ) EE2.3.20.0248
Institutional support: RVO:67179843
Keywords : flux data accuracy * Bowen ratio * energy balance
Subject RIV: EH - Ecology, Behaviour

Bowen ratio energy balance (BREB) is one of the most widely used indirect methods for deriving latent heat (LE) and sensible heat fluxes. The BREB technique relies on net radiation, ground heat flux, and air temperature and humidity gradients measurements. Whilst the first two mentioned can be practically considered as point measurements, the source area of temperature and humidity gradients is at least one order of magnitudes larger. Therefore, the horizontal, homogeneous and extensive area is necessary prerequisite for correct flux determination by BREB method. An ideal fetch for BREB has been reported to be within 10 to 200 times the height of upper measuring level above zero plane displacement. This broad range is a result of different atmospheric stratifications and surface roughness, but the fetch to height ratio 100:1 has become generally acknowledged as a rule of thumb. In this study, data from four different BREB systems above various covers (two poplar plantations, grassland and turf grass field) will be used to calculate and analyse LE for different fetches. Data were recorded in Domanínek near Bystˇrice nad Pernštejnem in Czech-Moravian highlands where two BREB systems have measured above poplar plantation and turf grass since summer 2008 until present and two more systems have been placed above grassland and another poplar plantation at the beginning of 2011 and have measured until present time. During the measurements changing wind direction limited the fetch of particular BREB systems on the sites. That is why LE calculated for particular fetch lengths will be split into three categories - fetch classes (“good”, “medium”, and “bad”) according to prevailing wind direction and corresponding fetch. These categories will be delimited using the simple footprint model. Fetches with more than 75% of the measured entities coming from the area of interest will be considered as the “good” ones. The “medium” class will contain fetches with 50-75% of the flux data coming from the area of interest and the category “bad” embraces fetches with less than 50% of the LE from the area of interest.
Permanent Link: http://hdl.handle.net/11104/0232527