Abstract
When measuring the energy balance at the earth’s surface using the Eddy covariance technique, the obtained budgets seldom produce a closed energy balance. The measurements often miss some of the energy fluxes. A possible reason is the neglect of non-turbulent surface fluxes of latent heat and sensible heat, i.e. advective fluxes of these quantities. We present estimates of advective latent and sensible heat fluxes for three different sites across Europe based on the ADVEX dataset. The obtained horizontal and vertical advective fluxes were site-specific and characterized by large scatter. In relative terms, the data indicated that the sensible heat budget was less affected by advection than the latent heat budget during nighttime; this is because vertical turbulent latent heat fluxes were very small or close to zero during the night. The results further showed that the additional energy gain by sensible heat advection might have triggered enhanced evaporation for two sites during nighttime. Accounting for advective fluxes improved the energy balance closure for one of the three ADVEX sites. However, the energy balance closure of the other two sites did not improve overall. A comparison with energy balance residuals (energy missed by the measurements without accounting for advection) indicated a large influence of systematic errors. An inspection of the energy balance for the sloped site of the ADVEX dataset underlined the necessity of slope-parallel measurement of radiation.
Highlights
The energy balance is fundamental in the interconnected earth-atmosphere system (Odum 1983; Oke 1987)
An energy balance closure gap between 10 and 30% is reported for most sites and often the sum of the latent and sensible heat flux is underestimated in relation to available energy (AE) (Wilson et al 2002; Foken 2008; Franssen et al 2010; Stoy et al 2013)
We only present a cautious interpretation of corresponding budgets here because of weaknesses and limitations in calculating advective fluxes, which became apparent when inspecting diurnal courses and relationships to turbulence and atmospheric stratification
Summary
The energy balance is fundamental in the interconnected earth-atmosphere system (Odum 1983; Oke 1987). Tsvang et al 1991; Kanemasu et al 1992; Wilson et al 2002; Foken 2008; Franssen et al 2010; Stoy et al 2013; Gerken et al 2018; McGloin et al 2018); that is, the sum of the measured fluxes of the left and right hand side of Eq 1 and Eq 2, respectively, is not equal This is known as lack of energy balance closure, or energy balance closure gap. There are a few studies (Heusinkveld et al 2004; Mauder et al 2007a) which report an almost closed energy balance for measurements above rather homogeneous terrain
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