A novel approach to evaluate soil heat flux calculation: An analytical review of nine methods

Abstract

There are no direct methods to evaluate calculated soil heat flux (SHF) at the surface (G0). Instead, validation and cross evaluation of methods for calculating G0 usually rely on the conventional calorimetric method or the degree of the surface energy balance closure. However, there is uncertainty in the calorimetric method itself, and factors apart from G0 also contribute to nonclosure of the surface energy balance. Here we used a novel approach to evaluate nine different methods for calculating SHF, including the calorimetric method and methods based on analytical solutions of the heat diffusion equation. The SHF (Gz) measured by a self‐calibrating SHF plate at a depth of z = 5 cm below the surface (hereafter Gm_5cm) was deployed as a reference. Each SHF calculation method was assessed by comparing the calculated Gz at the same depth (hereafter Gc_5cm) with Gm_5cm. The calorimetric method and simple measurement method performed best in determining Gc_5cm but still underestimated Gm_5cm by 19% during the daytime. Possible causes for this underestimation include errors and uncertainties in SHF measurements and soil thermal properties, as well as the phase lag between Gc_5cm and Gm_5cm. Our results indicate that the calorimetric method achieves the most accurate SHF estimates if self‐calibrating SHF plates are deployed at two depths (e.g., 5 cm and 10 cm), soil temperature and water content measurements are made in a few depths between the two plates, and soil thermal properties are accurately quantified.

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

“…Nevertheless, we have made initial efforts to install eddy covariance systems at the site (see description in Sect. 3.1 of Gao et al, 2017), but the processing of the flux data is still preliminary. We will report flux observations and validations of the surface energy budget simulations in future studies.…”

Mechanistic links between underestimated CO 2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem

“…These soil data were sampled at 1 Hz and stored as 30 min averages. G 0 was then determined by the calorimetric method (Liebethal et al 2005, Russell et al 2015, Gao et al 2017b combining the measured soil heat flux at 5 cm depth and the change in heat storage in the layer above 5 cm depth. We used two sublayers (0-2.5 cm and 2.5-5 cm) between the surface and 5 cm depth to calculate the change in heat storage.…”

Uncertainties in Turbulent Statistics and Fluxes of CO2 Associated With Density Effect Corrections

“…A mixture of shrubs and grasses dominates in the area (Figure S1 in the supporting information). During the spring with adequate soil water availability, the vegetation is active, whereas in summer months the vegetation activities are largely constrained due to the decreased water availability (Gao et al, 2017, 2019; Missik et al, 2019). One three‐dimensional sonic anemometer (model CSAT3, Campbell Scientific, Inc.) and one open‐path infrared gas analyzer (model LI‐7500A, LI‐COR, Inc.) were installed on the tower at 5 m above the ground with a separation distance of 0.2 m. The sonic anemometer measured longitudinal ( u ), lateral ( v ), and vertical ( w ) wind components and sonic temperature ( T s ), and the gas analyzer measured ρ v and ρ c .…”