Impact of coordinate rotation on eddy covariance fluxes at complex sites

Show simple item record Rannik, Üllar Vesala, Timo Peltola, Olli Novick, Kimberly A. Aurela, Mika Järvi, Leena Montagnani, Leonardo Mölder, Meelis Peichl, Matthias Pilegaard, Kim Mammarella, Ivan 2020-05-20T15:37:02Z 2020-05-20T15:37:02Z 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 .
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.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 cc_by
dc.rights.uri info:eu-repo/semantics/openAccess
dc.subject 114 Physical sciences
dc.subject Coordinate rotation
dc.subject Planar fit
dc.subject Eddy covariance
dc.subject Stability
dc.subject Complex sites
dc.title Impact of coordinate rotation on eddy covariance fluxes at complex sites en
dc.type Article
dc.contributor.organization Micrometeorology and biogeochemical cycles
dc.contributor.organization Institute for Atmospheric and Earth System Research (INAR)
dc.contributor.organization Viikki Plant Science Centre (ViPS)
dc.contributor.organization Ecosystem processes (INAR Forest Sciences)
dc.contributor.organization Helsinki Institute of Sustainability Science (HELSUS)
dc.contributor.organization Urban meteorology
dc.contributor.organization Helsinki Institute of Urban and Regional Studies (Urbaria)
dc.contributor.organization INAR Physics
dc.description.reviewstatus Peer reviewed
dc.relation.issn 0168-1923
dc.rights.accesslevel openAccess
dc.type.version publishedVersion

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