Seasonal changes in physical processes controlling evaporation over inland water

Abstract

While previous studies have shown the distinct characteristics of water surface energy fluxes in different seasons, much less analysis is conducted about how seasonal changes in physical processes and environmental variables in the atmospheric surface layer (ASL) cause variations in flux exchange.Here we analyzed and compared eddy covariance fluxes of sensible heat (H) and latent heat (LE) and other microclimate variables that were measured over a large inland water surface in the winter season (January, February, and March) and the summer season (June, July, and August) of 2008. Our analysis was primarily focused on LE using half-hour time series data on a short-term basis. Our results show that an increase in wind speeds (U) or vapor pressure difference in the ASL (Δe) or ASL instability did not necessarily cause an increase in LE, and the opposite changes in LE with changes in these variables were observed. Relative regulations of LE by different environmental variables depended largely on Δe magnitudes. Under low Δe conditions, diurnal LE variations were not sensitive to changes in Δe and U but were controlled primarily by changes in the ASL stability. Under high Δe conditions, diurnal LE variations were mainly determined by changes in Δe, though alternate controls by U and Δe were observed, whereas ASL stability played minor roles in affecting LE variations. Whether these highly nonlinear responses of LE to environmental variables are adequately reflected in the bulk transfer relations requires further studies. ZHANG AND LIU

Non-closure of the surface energy balance explained by phase difference between vertical velocity and scalars of large atmospheric eddies

“…The post-field data processing procedures are documented elsewhere (Zhang et al 2010, Zhang and Liu 2014, Gao et al 2016. Briefly, these procedures include: 1) removing physically impossible values and spikes from the time series; 2) double rotation for the sonic anemometer measured w (Kaimal and Finnigan 1994); 3) calculation of averages, variances and covariances using a 30 min block average; 4) sonic temperature correction (Schotanus et al 1983, Liu et al 2001, oxygen cross sensitivity correction for KH20 (Tanner et al 1993), density correction applied to LE (Webb et al 1980), and correction for flux attenuation due to spatial separation of CSAT3 and KH20 ; and 5) quality check for stationary and developed turbulent conditions (Foken et al 2004).…”

Physical controls on half‐hourly, daily, and monthly turbulent flux and energy budget over a high‐altitude small lake on the Tibetan Plateau

“…As is well understood, latent heat fluxes ( LE ; with E as evaporation, in other words) and sensible heat fluxes ( H ) from lakes are primarily controlled by water vapor and temperature gradients, together with turbulent mixing intensity, which is influenced by surface roughness length, wind speed, and atmospheric stability [ Assouline et al ., ; Blanken et al ., ; Blanken et al ., ; Granger and Hedstrom , ; Heikinheimo et al ., ; Liu et al ., ; Rouse et al ., ; Wang et al ., ; Zhang and Liu , ]. The question of what factors drive turbulent flux exchange between lakes and the atmosphere remains highly relevant.…”

“…In addition to the widely observed positive correlations between temperature and water vapor gradients on the one hand and sensible and latent heat fluxes on the other [ Blanken et al ., ; Blanken et al ., ; Liu et al ., ; Liu et al ., ; Liu et al ., ; Zhang and Liu , ], net radiation is an important parameter for estimating evaporation over longer periods, such as 1 day, 10 days, or 1 month [ Rosenberry et al ., ; Yao , ]. However, no clear positive correlations have been observed between net radiation and turbulent heat flux in deep or large lakes [ Blanken et al ., ; Blanken et al ., ; Liu et al ., ; Zhang and Liu , ]. This result contrasts with the positive correlations from shallow lakes over periods longer than a week [ Granger and Hedstrom , ; Nordbo et al ., ].…”

“…For small lakes, a positive correlation is found between wind speed and latent heat flux [ Assouline et al ., ; Granger and Hedstrom , ], while a poor correlation between these factors has been observed for a 0.041 km 2 boreal lake [ Nordbo et al ., ]. For large lakes, wind speed has no relationship with latent heat flux at Ross Barnett Reservoir [ Liu et al ., ; Liu et al ., ; Zhang and Liu , ]; however, a positive correlation has been observed for the Great Slave Lake for wind speeds greater than a particular threshold value [ Blanken et al ., ]. It has also been found that the presence of unstable (stable) atmosphere boundary layers causes H and LE to increase (decrease) [ Brutsaert , ].…”

Variability of Surface Heat Fluxes and Its Driving Forces at Different Time Scales Over a Large Ephemeral Lake in China

“…Many studies have revealed that the diurnal LE and H variations in lakes are out of phase with net radiation ( R n ) and are primarily governed by the wind speed, temperature, and humidity gradient of the atmospheric surface layer (Assouline et al, ; Granger & Hedstrom, ; Lenters et al, ; Nordbo et al, ; Q. Zhang & Liu, ). The relationships can be described using the bulk aerodynamic methods (Garratt, ; Stull, ).…”