Vertical decoupling of radiation absorption and thermal mass controls the sub-daily timing of canopy heat storage in a tropical dipterocarp forest

Information from the abstract

: Forest eddy-covariance (EC) towers commonly leave a 10%–30% daytime surface energy-balance residual widely attributed to unresolved canopy heat storage. Conventional one-dimensional corrections treat canopy biomass and air as one well-mixed reservoir at a single temperature, but whether this mainly biases daytime-integrated closure or the sub-daily timing of the storage flux is unclear. In a tropical dry evergreen forest at the Sakaerat Environmental Research Station, Thailand, we combine UAV LiDAR, a complete 1,054-stem inventory, and radiometric canopy-top temperature at a 42-m tower. The inventory gives an aboveground biomass of 245 Mg·ha −1 , a woody thermal mass of 113 kJ·m −2 ·K −1 , and an air-column thermal mass of 50 kJ·m −2 ·K −1 . Holding thermal mass fixed, we compare two bulk estimators differing only in thermometric anchor: canopy-anchored ( S canopy ) and air-anchored ( S air ). Across 10,083 daytime quality-controlled half-hours, the baseline energy-balance ratio (EBR) was 0.612. Both anchors gave almost identical daytime-integrated gains (0.650 and 0.649) and daytime means (15.0 and 14.7 W·m −2 ), including the air column raises closure to 0.666. Their diurnal behaviour diverged: S canopy peaked at 44 W·m −2 at 09:00 LST, 46% higher and one hour earlier than the S air peak of 30 W·m −2 at 10:00 LST, with the canopy/air peak ratio reaching 1.49 in the wet season. This is consistent with vertical decoupling between the heights of peak radiation absorption and peak thermal mass, whereby the canopy top leads a morning charging transient that the air anchor cannot reproduce. Both estimators are bulk approximations rather than vertical integrals, and plant area density below 10 m is a lower-bound estimate. The thermometric anchor therefore changes the timing and amplitude, not the daytime-integrated magnitude, of estimated canopy heat storage—relevant to land-surface and soil–vegetation–atmosphere schemes running at sub-daily steps.

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Related topics: Plant Water Relations and Carbon Dynamics · Remote Sensing and LiDAR Applications · Meteorological Phenomena and Simulations