Energy partitioning between latent and sensible heat flux during the warm season at FLUXNET sites

Abstract

[1] The warm season (mid-June through late August) partitioning between sensible (H ) and latent (LE ) heat flux, or the Bowen ratio (b = H/LE ), was investigated at 27 sites over 66 site years within the international network of eddy covariance sites (FLUXNET). Variability in b across ecosystems and climates was analyzed by quantifying general climatic and surface characteristics that control flux partitioning. The climatic control on b was quantified using the climatological resistance (R i ), which is proportional to the ratio of vapor pressure deficit (difference between saturation vapor pressure and atmospheric vapor pressure) to net radiation (large values of R i decrease b). The control of flux partitioning by the vegetation and underlying surface was quantified by computing the surface resistance to water vapor transport (R c , with large values tending to increase b).There was a considerable range in flux partitioning characteristics (R c , R i and b) among sites, but it was possible to define some general differences between vegetation types and climates. Deciduous forest sites and the agricultural site had the lowest values of R c and b (0.25-0.50). Coniferous forests typically had a larger R c and higher b (typically between 0.50 and 1.00 but also much larger). However, there was notable variability in R c and R i between coniferous site years, most notably differences between oceanic and continental climates and sites with a distinct dry summer season (Mediterranean climate). Sites with Mediterranean climates generally had the highest net radiation, R c , R i , and b. There was considerable variability in b between grassland site years, primarily the result of interannual differences in soil water content and R c .

Energy budget above a temperate mixed forest in northeastern China

“…This was similar to a broadleaved temperate deciduous forest in North America, where a study showed thatř anged from 0Ð68 to 0Ð78 over three observation years (Wilson and Baldocchi, 2000). However, theˇvalue at the mixed broadleaved-pine forest was generally high compared with those in other temperate deciduous forests, and even higher than most temperate coniferous forests, which typically had a highˇvalue (Wilson et al, 2002b). For example, the mean annualˇfor a temperate deciduous forest in south-central Indiana, USA, was 0Ð59 (Oliphant et al, 2004).…”

Quality control of CarboEurope flux data – Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems

“…Law et al, 2002;Hibbard et al, 2005;Reichstein et al, 2007b;Yuan et al, 2007) and ecosystem responses to climate anomalies and interannual variability (e.g. Wilson et al, 2002;Ciais et al, 2005;Reichstein et al, 2007a), or conducting inverse modeling studies to constrain carbon fluxes (e.g. Gerbig et al, 2003;Wang et al, 2007).…”

A more accurate scheme for calculating Earth’s skin temperature

“…In general, during the daylight hours, aerodynamic and canopy resistances are much lower than those during the nights (Blondin 1991;Tsai et al 2007). Typical values of daytime aerodynamic and canopy resistances observed in various land covers in the summer can be found in Wilson et al (2002). Therefore, from the Fig.…”

“…In addition, qG 0 * /qT 0 * of the diurnal frequency component is also shown in the figure. At the site, the daytime aerodynamic and canopy resistances in the summer are about 37 and 60 s m -1 , respectively (Wilson et al 2002). Following the method of Wilson et al (2002), r a is derived from the sum of the resistance to momentum transport and an excess resistance for scalar fluxes (Verma et al 1986) and r c is determined according to the PenmanMonteith approximation to the big leaf equations (Jarvis and McNaughton 1986;Shuttleworth et al 1984).…”

“…At the site, the daytime aerodynamic and canopy resistances in the summer are about 37 and 60 s m -1 , respectively (Wilson et al 2002). Following the method of Wilson et al (2002), r a is derived from the sum of the resistance to momentum transport and an excess resistance for scalar fluxes (Verma et al 1986) and r c is determined according to the PenmanMonteith approximation to the big leaf equations (Jarvis and McNaughton 1986;Shuttleworth et al 1984). It can be seen that at this site, typical value for winter nighttime qG 0 * /qT 0 * (qG 0 /qT 0 ) was about 1.8 (29.04 W m -2 K -1 ), and that of summer day was about 4.4 (70.93 W m -2 K -1 ), of which the annual mean was 2.86 (46 W m -2 K -1 ) with the median value at 2.64 (42 W m -2 K -1 ), when T 0 during wintertime (November-January) was usually \273 K. Table 6 shows the bias, RMSE and normalized RMSE of skin temperature, and the bias, RMSE and normalized RMSE for surface ground heat of Case 7 simulated by ''A74'', ''D78'', ''op(0,0,0)'', ''op(1,0,0)'', ''op(1,1,0)'', ''op(2,1,0)'', ''echam'', ''ecmwf'', ''ecmwf ?…”