Revised eddy covariance flux calculation methodologies - effect on urban energy balance

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Nordbo, Annika ; Jarvi, Leena ; Vesala, Timo (2012)
  • Publisher: Tellus B
  • Journal: Tellus B (issn: 1600-0889, eissn: 0280-6509)
  • Related identifiers: doi: 10.3402/tellusb.v64i0.18184
  • Subject: CENTRAL-EUROPEAN CITY | OPEN-PATH | flux error | QUALITY-CONTROL | 114 Physical sciences | eddy covariance; urban; energy balance; flux uncertainty; flux error | energy balance | WATER-VAPOR | eddy covariance | SURFACE-ATMOSPHERE INTERACTIONS | FREQUENCY-RESPONSE CORRECTIONS | CORRELATION SYSTEMS | SONIC ANEMOMETER | urban | ANTHROPOGENIC HEAT | flux uncertainty | CO2 FLUXES

Eddy covariance (EC) measurements of turbulent fluxes of momentum, sensible heat and latent heat – in addition to net radiation measurements – were conducted for three consecutive years in an urban environment: Helsinki, Finland. The aims were to: (1) quantify the detection limit and random uncertainty of turbulent fluxes, (2) assess the systematic error caused by EC calculation-procedure choices on the energy balance residual and (3) report the energy balance of the world's northernmost urban flux station. The mean detection limits were about 10% of the observed flux, and the random uncertainty was 9–16%. Of all fluxes, the latent heat flux – as measured with a closed-path gas analyser – was most prone to systematic calculation errors due to water vapour interactions with tube walls: using a lag window that is too small can cause a 15% lack of data (due to the dependency of lag time on relative humidity) and omitting spectral corrections can cause on average a 26% underestimation of the flux. The systematic errors in EC calculation propagate into the energy balance residual and can be larger than the residual itself: for example, omitting spectral corrections overestimates the residual by 13% or 18% on average, depending on the analyser.Keywords: eddy covariance; urban; energy balance; flux uncertainty; flux error(Published: 19 April 2012)Citation: Tellus B 2012, 64, 18184, http://dx.doi.org/10.3402/tellusb.v64i0.18184
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