Impact of coordinate rotation on eddy covariance fluxes at complex sites

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dc.contributor University of Helsinki, Micrometeorology and biogeochemical cycles en
dc.contributor University of Helsinki, Institute for Atmospheric and Earth System Research (INAR) en
dc.contributor University of Helsinki, Finnish Meteorological Institute en
dc.contributor University of Helsinki, Institute for Atmospheric and Earth System Research (INAR) en
dc.contributor University of Helsinki, INAR Physics en
dc.contributor.author Rannik, Üllar
dc.contributor.author Vesala, Timo
dc.contributor.author Peltola, Olli
dc.contributor.author Novick, Kimberly A.
dc.contributor.author Aurela, Mika
dc.contributor.author Järvi, Leena
dc.contributor.author Montagnani, Leonardo
dc.contributor.author Mölder, Meelis
dc.contributor.author Peichl, Matthias
dc.contributor.author Pilegaard, Kim
dc.contributor.author Mammarella, Ivan
dc.date.accessioned 2020-05-20T15:37:02Z
dc.date.available 2020-05-20T15:37:02Z
dc.date.issued 2020-06-15
dc.identifier.citation Rannik , Ü , Vesala , T , Peltola , O , Novick , K A , Aurela , M , Järvi , L , Montagnani , L , Mölder , M , Peichl , M , Pilegaard , K & Mammarella , I 2020 , ' Impact of coordinate rotation on eddy covariance fluxes at complex sites ' , Agricultural and Forest Meteorology , vol. 287 , 107940 . https://doi.org/10.1016/j.agrformet.2020.107940 en
dc.identifier.issn 0168-1923
dc.identifier.other PURE: 133227230
dc.identifier.other PURE UUID: f4f3e615-8107-4d19-a4b4-a8181eede75a
dc.identifier.other RIS: urn:343B511F16C4FE94A8D0DE684A974F4F
dc.identifier.other WOS: 000531095900013
dc.identifier.other ORCID: /0000-0002-8516-3356/work/75461784
dc.identifier.other ORCID: /0000-0002-1744-6290/work/75464038
dc.identifier.uri http://hdl.handle.net/10138/315085
dc.description.abstract The choice of coordinate system to calculate eddy covariance fluxes becomes particularly relevant at complex measurement sites. The traditional way is to perform double rotation (DR) of the coordinate system i.e., to calculate turbulent fluxes in a coordinate system that is aligned with the flow streamlines within the flux averaging period (e.g., Kaimal and Finnigan, 1994). The second approach, the so-called planar-fitted (PF) coordinate system, averages the flow over a longer period of time, in practice a month or more. The PF method allows to derive an intercept coefficient of the vertical wind speed which can be attributed to the offset of the sonic anemometer or the average vertical flow related to meteorological conditions. We evaluated the variants of the PF methods using data from a variety of sites ranging from complex urban and forest sites to nearly ideal forest and peatland sites. At complex sites, we found that the intercept of the vertical wind speed derived from the PF method is a function of wind direction, time of day and/or stability. The sector-wise PF (SPF) method frequently led to insignificant statistical relationships. We tested a continuous PF (CPF) method where the relationship establishing the coordinate frame was represented as the continuous function in the form of Fourier series. The method enabled to obtain the PF with lower uncertainty as compared to the SPF method, by selecting necessary number of harmonics for each site based on confidence intervals of estimated parameters. Therefore, we recommend to use the CPF method in cases when the number of observations in some wind direction interval is low or the obtained SPF is insignificant due to large variance in measurements. We also showed that significant systematic difference can exist in cumulative turbulent fluxes between the DR and PF methods over a longer period of time. Derived vertical advection of carbon dioxide exhibited large variability with wind direction due to topography at complex sites and therefore, without considering horizontal advection, cannot be used to improve the net ecosystem exchange estimation during nocturnal, low turbulence conditions. en
dc.format.extent 23
dc.language.iso eng
dc.relation.ispartof Agricultural and Forest Meteorology
dc.rights en
dc.subject 114 Physical sciences en
dc.subject Coordinate rotation en
dc.subject Planar fit en
dc.subject Eddy covariance en
dc.subject Stability en
dc.subject Complex sites en
dc.title Impact of coordinate rotation on eddy covariance fluxes at complex sites en
dc.type Article
dc.description.version Peer reviewed
dc.identifier.doi https://doi.org/10.1016/j.agrformet.2020.107940
dc.type.uri info:eu-repo/semantics/other
dc.type.uri info:eu-repo/semantics/publishedVersion
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