Eddy covariance measurements of evaporation from Great Slave Lake, Northwest Territories, Canada

Abstract

Abstract. The first direct measurements of evaporation from a large high-latitude lake, Great Slave Lake, Northwest Territories, Canada, were made using eddy covariance between July 24 and September 10, 1997, and June 22 and September 26, 1998. The main body of the lake was ice-free between June 20 and December 13, 1997, and June 1, 1998, and January 8, 1999, with the extended ice-free season in 1997-1998 coinciding with 4øC above normal air temperatures and an abnormally strong E1 Nifio. Measurements extending roughly 5.0 to 8.5 km across the lake were made from a small rock outcrop located near the main body of the lake. The lake was thermally stratified between midJuly and September, with the thermocline extending down to approximately 15 m. High winds were effective in mixing warm surface waters downward and, when accompanied by cold fronts, resulted in large, episodic evaporation events typically lasting 45 hours. The daily total evaporation was best described as a function of the product of the horizontal wind speed and vapor pressure difference between the water surface and atmosphere. Seasonally, the latent heat flux was initially negative (directed toward the surface) followed by a steady increase to positive values (directed away from the surface) shortly after ice breakup. The latent heat flux then remained positive for the remainder of the ice-free period, decreasing midsummer and then steadily increasing until freeze-up. The sensible heat flux was small and often negative most of the spring and summer yet switched to positive and began to increase in the early fall. Extrapolation of evaporation measurements for the entire ice-free periods gave totals of 386 and 485 mm in 1997 and 1998-1999, respectively.

Interannual variability in the surface energy budget and evaporation over a large southern inland water in the United States

“…[3] There are a number of long-term eddy covariance measurements and process-based studies for the surface energy budget over inland waters [Blanken et al, 2000;Eaton et al, 2001;Blanken et al, 2003;Rouse et al, 2003;Oswald and Rouse, 2004;Rouse et al, 2005;Vesala et al, 2006;Assouline et al, 2008;Rouse et al, 2008;Tanny et al, 2008;Liu et al, 2009;Blanken et al, 2011;Liu et al, 2011;Nordbo et al, 2011;Liu et al, 2012]. It is noted that, however, most of these measurements were made over highlatitude lakes, such as Great Slave Lake [Blanken et al, 2000;Rouse et al, 2003] and Great Bear Lake [Rouse et al, 2008] in Canada, Lake Valkea-Kotinen in Finland [Vesala et al, 2006;Nordbo et al, 2011], and Lake Superior Spence et al, 2011].…”

“…It is noted that, however, most of these measurements were made over highlatitude lakes, such as Great Slave Lake [Blanken et al, 2000;Rouse et al, 2003] and Great Bear Lake [Rouse et al, 2008] in Canada, Lake Valkea-Kotinen in Finland [Vesala et al, 2006;Nordbo et al, 2011], and Lake Superior Spence et al, 2011]. Liu et al [2012] was the first to report an annual analysis of the surface energy budget over a large southern reservoir.…”

“…For example, the unusually high evaporation rates as a result of high air temperatures have caused a recent record water-level drop in Laurentian Great Lakes over the past 150 years [Assel et al, 2004]. On the other hand, since the surface energy budget over open inland waters is not complicated by the adaptive physiological responses of terrestrial vegetation [Blanken et al, 2000], it may be used as a protocol to detect climate change and variability. Therefore, it is necessary to directly measure the surface energy budget over inland waters to advance our understandings of the physical processes that are responsible for changes in wateratmosphere interactions under climate change and variability [Blanken et al, 2000;Oswald and Rouse, 2004;Liu et al, 2011].…”

“…[4] Previous efforts have also been made to study how seasonal variations are modulated by synoptic weather events [Blanken et al, 2000;Blanken et al, 2003;Rouse et al, 2003;Schertzer et al, 2003;Lenters et al, 2005;Liu et al, 2009]. Over the Great Slave Lake, for instance, more than 50% of the measured evaporation occurs over 25% and 20% of its ice-free season as a result of windy, cold, and dry air masses passing over the lake [Blanken et al, 2000].…”

“…On the other hand, since the surface energy budget over open inland waters is not complicated by the adaptive physiological responses of terrestrial vegetation [Blanken et al, 2000], it may be used as a protocol to detect climate change and variability. Therefore, it is necessary to directly measure the surface energy budget over inland waters to advance our understandings of the physical processes that are responsible for changes in wateratmosphere interactions under climate change and variability [Blanken et al, 2000;Oswald and Rouse, 2004;Liu et al, 2011]. Moreover, in situ observations made at large inland waters can provide useful datasets for validating regional atmospheric models that are applied over regions with abundant inland water bodies [Long et al, 2007].…”