Turbulent Heat Fluxes above a Suburban Reservoir: A Case Study from Germany

Abstract

With the objective of quantifying turbulent sensible Q H and latent Q E heat fluxes above a suburban reservoir, a micrometeorological turbulence measurement campaign using the eddy covariance technique was carried out between June and November 2012 on the Baldeneysee, an artificial lake (2.64 km 2 area with up to 4-m depth) located in Germany. The study was conducted at this site because there is little information on this type of lake and the findings are important for the local water management system. Sensible heat fluxes show a mean diurnal course with maximum positive values during the early morning hours (maximum 5 131.3 W m 22 ) and negative values in the afternoon (minimum 5 212.3 W m 22 ). During daytime, average Q H /Q* ratios (where Q* is the radiation balance) are, in general, smaller than 0.20. Sensible heat fluxes are especially affected by the product of wind speed and water-air temperature difference, as well as the magnitude of global radiation. In contrast, mean hourly values of Q E are, on average, positive over the whole day, with an absolute spread between 1175.1 and 20.8 W m 22 . During daytime in summer, 74% of the radiation balance is transferred via Q E . The measurement values show that during two summer days, 3.72 and 2.84 mm day 21 of water could be evaporated, whereas during two measurement days in autumn, evaporation rates of only 1.36 and 0.94 mm day 21 were registered. The magnitude of Q E is mainly affected by four main parameters: the product of wind speed and vapor pressure deficit, followed by the magnitude of global radiation and water temperature.

The monsoon effect on energy and carbon exchange processes over a highland lake in southwest of China

“…According to the quality control procedure presented above, around 34% of the Hs, 46% of LE and 45% of CO 2 fluxes are removed and the retained data are analyzed in our study. Although the gap ratio is large, it's similar to other studies over 5 lakes (Nordbo et al, 2012;Goldbach and Kuttler, 2015;Shao et al, 2015). A long large gap between August and November of exists in 2014 due to malfunction.…”

“…LE remains at a higher level during three periods, with an average monthly value of 89.1, 103.9 and 82.2 Wm -2 during pre-monsoon, Monsoon and post-monsoon periods, respectively. The average monthly LE/Rn has a smaller annual variation during pre-monsoon period, which ranges from 0.50 to 0.82 for four-year study 30 period. LE/Rn has a larger fluctuation during monsoon period, which varies from 0.53 to 1 from 2012 to 2015.…”

“…The cold fronts and the meteorological properties of the air masses behind cold fronts (e.g., windy, cold and dry) 25 significantly promoted turbulent exchange of sensible heat (Hs) and latent heat (LE) through enhanced turbulent mixing thermally and mechanically, whereas southerly winds with warm and humid air masses generally suppressed turbulent exchanges of Hs and LE over a mid-latitude large reservoir in Mississippi (Liu et al, 2009;Liu et al, 2012). In response to the changes in the weather conditions, the heat balance over a large tropical reservoir in Brazil is substantially altered, and the heat loss can be 30 twice or threefold greater during cold front days than that during the non-cold-front days (Curtarelli et al, 2014). Consistent diurnal peaks in latent heat flux during the afternoon were observed as a result of strong dry winds coinciding with peak water surface temperatures over a small subtropical reservoir in Australia (McGloin et al, 2015).…”

The monsoon effect on energy and carbon exchange processes over a highland lake in the southwest of China

“…The boundary layer method estimates CO 2 flux by the difference in CO 2 concentration between the water and atmosphere and the gas transfer velocity, which is traditionally parameterized only by wind speed (Cole and Caraco, 1998). However, it has been reported that different processes including convection, microwave breaking and stratification could influence the gas transfer velocity (Zappa et al, 2001;Eugster et al, 2003;Podgrajsek et al, 2014). The eddy covariance technique (EC) could provide long-term continuous measurements and the high-resolution data allows for examining the relation between gas exchange velocity and other meteorological variables besides wind speed (Mammarella et al, 2015).…”

“…The summer monsoon induces an abrupt change in large-scale atmospheric circulation and convective activity over Asia, and carries in air mass with distinct atmospheric properties (i.e., air temperature, wind direction, relative humidity; Li and Yanai, 1996;Lau and Yang, 1997;Zhou et al, 2012). The seasonal reversals of atmospheric properties caused by summer monsoon circulation play an important role in regulating landatmosphere heat and water exchange processes (Flohn, 1957;Hsu et al, 1999). The land-atmosphere exchange processes are found to be closely related to the onset and retreat of summer monsoon (Zhang et al, 2012).…”