Fig. 1.
An overview of the surrounding area of the EC tower: white height contour lines (m) superimposed on a Google Earth picture. The locations of the SMEAR III tower and the auxiliary meteorological instruments are marked with a red star and circle, respectively. Black lines indicate the borders of the three sectors (urban 320–40°, road 40–180° and vegetation 180–320°).
Table 1. Calculation procedure comparison. The steps in eddy covariance raw data post-processing are shown in the columns, and the affected fluxes are in brackets: sensible heat (H) and open- and closed-path latent heat, (LE OP, LE CP). The names of the different calculation method combinations and their ID numbers are referred to in the text as rows. The calculation steps that are within the iteration are marked with a grey background. See text for further details
[i] aExperimental (exp) or theoretical (theor) spectral correction for LE CP .
[ii] bPF=planar fitting somewhat as in Wilczak et al. (2001).
[iii] cTheoretical lag window for LE CP as shown in Fig. 7.
Table 2. Flux omittance percentages for momentum (τ), sensible heat (H) and closed- and open-path latent heat (LE CP, LE OP). Values are given for omittance due to all criteria for all data and for day- and night-time data, and for omittance only due to flux stationarity and intermittency. Also, the percentage of unacceptable skewness and kurtosis of the zonal wind (u), meridional wind (v), vertical wind (w), temperature (T), H2O concentration from the open-path analyser (q OP) and closed-path analyser (q CP) are given. Values are calculated for raw 10 Hz data after despiking. See text for further details.
Fig. 2.
(a) 5-d running means of air temperature (T, °C) and wind speed (U, ms−1) at 31 m height. (b) Daily precipitation (mm d−1) and 5-d running mean of relative humidity (RH,%).
Table 3. Flux error analysis for momentum (τ), sensible heat (H) and closed- and open-path latent heat (LE CP, LE OP). Mean random flux error (units of flux), the ratio between the random flux error and the observed flux (%), the detection limit (units of flux) and the ratio between the detection limit and the observed flux (%) for all quality checked data in 2009.
Fig. 3.
(a) The ratio of the flux detection limit to the observed flux for momentum (τ), sensible heat (H) and closed- and open-path latent heat (LE CP, LE OP). Values are given for three wind direction sectors: urban (320–40°), road (40–180°) and vegetation (180–320°). Bars indicate means, and errorbars the 25th and 75th percentiles. (b) Same as (a) but for the ratio between the random flux error and the observed flux. Data are quality checked (as per text) and covers 2009.
Fig. 4.
Time series of net radiation (R n ), sensible heat flux (H), latent heat flux measured with a closed- and open-path analyser (LE CP , LE OP), and residuals of the energy balance (Res CP , Res OP), which is defined Res=R n −H−LE. Grey dots indicate 30 min average fluxes, and the continuous and dashed lines are the 5-d running mean averages of day-time and night-time data, respectively. Turbulent flux data have been quality screened according to the text.
Fig. 5.
Average diurnal cycles for 20 degree wind direction sectors. Hours are labelled with 2-hour resolution and run from 1:00 (local time) closest to the centre to 23:00 (local time) on the outside of the subplots. Colours indicate the median of the energy flux divided by the absolute value of net radiation (R n); see colourbar. The energy fluxes are (a) sensible heat flux (H), (b) closed-path latent heat flux (LE CP), (c) open-path latent heat flux (LE OP), (d) residual of the energy balance using LE CP and (e) residual of the energy balance using LE OP. All turbulent fluxes have been quality checked (see text), ratios exceeding 10 have been omitted from the plot, and data cover the whole period from October 2007 to September 2010 inclusive.
Table 4. Heat fluxes in cities with a cold temperate climate (latitude >45°N). The ranges of mean diurnal courses are given for the sensible (H) and latent (LE) heat fluxes, the energy balance residual (Res=R n −H−LE=ΔQ S −Q F) in addition to the anthropogenic heat flux (Q F).
[i] aAnnual means obtained by summing up contributions of human metabolism, vehicular traffic and buildings, using, e.g., energy consumption and population statistics.
[ii] bDaily means.
[iii] cIndividual values.
[iv] dSame as footnote ‘a’ but for the range of values in a diurnal course.
[v] eAnnual average estimated assuming that ΔQ S has to be zero over a year.
[vi] fΔQ S is obtained using the Element surface temperature method, where element surface temperatures are measured and the heat transfer through the elements are modelled. Q F=H+LE+ΔQ S −R n .
[vii] gMean of the whole period.
[viii] hRange is from autumn night to summer day.
[ix] iValues for open-path and closed-path gas analysers.
Fig. 6.
Calculation procedure effects on turbulent flux magnitudes for momentum (τ), sensible heat (H) and closed- and open-path latent heat (LE CP, LE OP), in addition to effects on energy balance residuals (Res CP, Res OP). Bars give the means over all stabilities; and means for different stability classes are denoted by ∇ (stable, ζ>0.01), o (neutral, −0.01<ζ<0.01), Δ (unstable, ζ<−0.01). Errorbars denote 25th and 75th percentiles, and the median is denoted by a filled circle (•). Red crosses show fluxes that are not affected by a certain calculation procedure. Deviations are calculated as (flux-fluxStandard) except for Res where an absolute value of the denominator is used since corrections can easily change the sign of Res.
Fig. 7.
Lag time (s) of closed-path H2O measurements as a function of relative humidity (%) and an exponential with 95% confidence intervals. The theoretical lag time (t lag,theor) and the theoretical lag window (rectangle) are also given. The colourbar gives the latent heat flux magnitude (LE, W m−2). Data are from May and June 2010.
Fig. 8.
Normalised cross-correlation functions of closed-path H2O measurements as a function of time shift (s) for different relative humidities. The time lag has been taken into account and negative time shifts correspond to H2O signal lagging the vertical wind speed signal. Thick lines are means and shaded patches are standard deviations. Data are from September 2009.
Fig. 9.
Flux convergence for momentum (τ), sensible heat (H) and closed- and open-path latent heat (LE CP, LE OP). Proportion of flux Ogives that converge within a 30 min averaging period (black) or have an extreme value before converging within 219 min (white). No quality-checked data fell into the class of non-convergent Ogives.
Fig. 10.
(a) Monthly mean residual of the surface energy balance (W m−2, eq. 2) with closed-path (Res CP) and open-path (Res OP) analyser evaporation, (b) difference between a modified Res CP and the standard Res CP, (c) same for Res OP. Values in (b) and (c) are given for different calculation procedures: no spectral correction, theoretical spectral correction of LE CP, no iteration, planar fitting, surface heat correction of LE OP and theoretical lag time of LE CP. Only times when the data for all calculation types are available are included, and some months are thus omitted due to a lack of data. See text for further details.
