Adjustments to the law of the wall above an Amazon Forest explained by a spectral link

Forests have a profound influence on the atmospheric flow above them. This influence manifests itself in the formation of a roughness sublayer above canopies. The roughness sublayer affects a plethora of physical, chemical, and biological processes. A better understanding of the wind velocity field above tall, forested canopies might also lead to a better handshake between the forest and the atmosphere in numerical weather predictions and Earth Systems Models.

In a new study, Luca Mortarini and his colleagues introduce a novel approach to the study of the roughness sublayer, using a cospectral budget model. Its originality lies in not considering the mixing layer analogy to parameterize the turbulence statistics. Instead, it relates them to the different scales of the wind velocity spectrum without making any assumption on the property of the flow. It is a shift of perspective that also naturally takes into account eventual terrain effects. This might come in handy at the ATTO site, where scientists have just begun to explore the influence of orography on forest dynamics.

A side result of the paper is a new formulation for the turbulent eddy viscosity. This quantity is crucial and widely used to estimate fluxes. Better quantification of the eddy viscosity traduces in a better estimation of the fluxes.

In this study, only neutral stability conditions and wind velocity statistics were considered. However, a new development for temperature and scalars might be on the way.

view from the ATTO tall tower over the rainforest below that extends all the way to the horizon. Shadows clearly mark hills and valleys crisscrossing the landscape
The Amazon rainforest is not at all flat. The early morning light clearly shows the the hills and valleys crisscrossing the landscape. © Martin Kunz / MPI-BGC

Mortarini et al. published the study “Adjustments to the law of the wall above an Amazon forest explained by a spectral link” Open Access in the journal Physics of Fluids.

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