Where has all the energy gone? Quantifying advective energy fluxes with dense tower networks

Abstract

Accurate and extensive measurements of the exchange of energy between the land surface and atmosphere are needed for building and improving models of the earth’s climate system. The eddy covariance (EC) method, used to measure the exchange of energy and gasses between the land surface and atmosphere, consistently measures an imbalance in the surface-atmosphere energy budget with greater incoming energy fluxes than outgoing fluxes. Studies have suggested that large-scale secondary circulations (SCs) may be responsible for some of the energy transport that is not measured by EC systems. This missing portion of the energy budget may be captured by quantifying the advective energy fluxes with dense tower networks. In this study, we investigated whether, and under what conditions, advective fluxes of sensible and latent heat may be estimated from a high-density network of tower measurements such as those taken during the CHEESHEAD19 experiment. We applied horizontal and vertical interpolation methods to measurements of temperature and humidity in order to calculate x,y, and z gradients across each EC measurement site within the CHEESEHEAD19 domain. These gradients were used, in addition to wind measurements, to quantify horizontal and vertical advective energy fluxes. Inclusion of the advective fluxes did not consistently improve energy budget closure, indicating that our method fails to provide accurate estimates of advective energy transport. Results suggest that a greater spatial density of measurements and an alternative vertical velocity measurement method may allow for improved advection estimates from a similar tower network. While this work lends insight into the nature of advective energy transport over heterogeneous land surfaces, further investigation is needed to improve our understanding of the contribution of advective fluxes to the surface-atmosphere energy balance.