Journal article
Eddy covariance measurements of surface energy budget and evaporation in a cool season over southern open water in Mississippi
Journal of Geophysical Research: Atmospheres, Vol.114(D4), pp.D04110-n/a
02/27/2009
Handle:
https://hdl.handle.net/2376/110572
Abstract
Eddy covariance measurements of sensible (H) and latent (LE) heat fluxes were made over a large southern open water surface of Ross Barnett Reservoir (the Reservoir hereafter) in Mississippi during the cool season with frequent incursions of cold fronts from 1 September 2007 to 31 January 2008. The eddy covariance tower was located in the middle of the main body of the Reservoir with the tower fetches exceeding 2.0 km in all directions. The Reservoir was ice‐free in winter and the water temperatures always decreased with depth. Over the entire cool season, the averaged water surface temperatures were 1.8°C higher than the overlying air (i.e., positive temperature gradients that led to thermally convective conditions) and the averaged vapor pressure near the water surface was 0.8 kPa greater than the overlying air (i.e., positive vapor pressure gradients), though occasionally negative gradients for temperature and vapor pressure were also observed for short periods. On average, the wind speeds were considerably large (3.9 m s−1) to maintain adequate turbulent mixing mechanically. As a consequence of the combined effect of thermally and mechanically generated turbulent mixing, consistently positive H (with a mean H of 20.0 W m−2) and LE (with a mean LE of 80.0 W m−2) occurred during the entire season. These continuous energy losses via H and LE resulted in release of a large amount of energy stored in the water to the atmosphere. The mean Bowen ratio was low for this open water surface (i.e., 0.3), suggesting that most of the energy released from the water fueled evaporation rather than sensible heating of the atmosphere. Nighttime evaporative water losses were substantial, contributing to 45% of the total evaporative water loss in this cool season. Frequent incursions of cold fronts with windy, cold, and dry air masses significantly promoted turbulent exchanges of sensible and latent heat through enhanced turbulent mixing thermally and mechanically, leading to large H and LE events. Daily H and LE (i.e., evaporation) during the passages of cold fronts were on average 2.7 and 7.3 times those in nonevent days, respectively. Given the fact that large H and LE events occurred 26% of the time for our site, these cold front events caused an increase in the seasonal H by 42% and LE by 157%. Therefore changes in frequency, intensity, and duration of synoptic weather events, particularly the incursions of cold fronts, have significant impacts on the surface energy budget and evaporation over water at this site.
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Details
- Title
- Eddy covariance measurements of surface energy budget and evaporation in a cool season over southern open water in Mississippi
- Creators
- Heping Liu - Jackson State UniversityYu Zhang - Jackson State UniversityShuhua Liu - Peking UniversityHaimei Jiang - Peking UniversityLi Sheng - Peking UniversityQuinton L Williams - Jackson State University
- Publication Details
- Journal of Geophysical Research: Atmospheres, Vol.114(D4), pp.D04110-n/a
- Academic Unit
- Civil and Environmental Engineering, Department of
- Number of pages
- 13
- Identifiers
- 99900547027701842
- Language
- English
- Resource Type
- Journal article