Heat storage and its effect on the surface energy balance closure under advective conditions

Authors: KUTIKOFF, SETH - Kansas State University; LIN, XIAOMAO - Kansas State University; Evett, Steven - Steve; Gowda, Prasanna; Moorhead, Jerry; Marek, Gary; Colaizzi, Paul; AIKEN, ROBERT - Kansas State University; Brauer, David

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2018
Publication Date: 11/15/2018
Citation: Kutikoff, S., Lin, X., Evett, S.R., Gowda, P.H., Moorhead, J.E., Marek, G.W., Colaizzi, P.D., Aiken, R., Brauer, D.K. 2018. Heat storage and its effect on the surface energy balance closure under advective conditions. Agricultural and Forest Meteorology. 265:56-69. https://doi.org/10.1016/j.agformet.2018.10.018.
DOI: https://doi.org/10.1016/j.agrformet.2018.10.018

Interpretive Summary: As irrigation water available from the Ogallala Aquifer decreases, farmers need to better match irrigation applications to water use by the crop. Eddy covariance (EC) is a method for determining crop water use. However, EC routinely underestimates crop water use. ARS scientists at the Bushland, TX and El Reno, OK laboratories, and scientists in the Ogallala Aquifer Program from Kansas State University used EC and the other measurements to find the source of the errors. They concluded that solar energy that was stored in the soil as heat could have accounted for much of the error, especially on hot, sunny and windy days, common to the Southern High Plains. These result brings science closer to an EC method that can deliver accurate estimates of crop water use.

Technical Abstract: High quality estimates of evapotranspiration (ET) are needed for water-limited agriculture where irrigation is necessary to efficiently grow crops. Surface energy budgets are useful for verifying ET estimates, especially in advective conditions that affect energy partitioning in eddy covariance (EC) measurements. Here, we explored the effect of heat storage and advective conditions on surface energy balance closure in the 2014 and 2015 growing seasons in Bushland, Texas. Storage components were estimated near the center of an irrigated sorghum field using an array of soil and surface layer measurements. A comparison of EC estimated turbulent fluxes and available energy consisting of net radiation, soil heat flux, and storage was used to identify advective conditions and assess surface energy balance closure. Our results indicated daytime mean heat storage of approximately 40 W m**-2 with a diurnal pattern featuring a midday peak that exceeded the evening minimum in magnitude, mostly reflective of soil heat storage but also affected by air, water, and biomass heat storage during the morning hours and photosynthesis storage during midday hours. Daytime advective conditions were associated with higher heat storage frequently under stable atmospheric conditions. The surface energy balance was more closed in 2014 than 2015; the 2014 energy balance exhibited a hysteretic pattern with a surplus of turbulent energy in the afternoon, whereas systematic underestimation was common in 2015. This finding is related to a larger proportion of data in 2014 being advective, characterized by a lower Bowen ratio and greater ET, particularly during the late afternoon. Regardless of advection classification, heat storage was demonstrated to be important for daytime energy balance in this irrigated cropland.