Simulation of the Scalar Transport above and within the Amazon Forest Canopy

Edivaldo M Serra-Neto,Paulo R Teixeira,Matthias Sörgel,Luca Mortarini,Raoni A Santana,Antônio O Manzi,Hardiney S Martins,Cléo Q Dias-Júnior,Alessandro C De Araújo,Daiane V Brondani

doi:10.3390/atmos12121631

Abstract

The parallelized large-eddy simulation model (PALM) was used to understand better the turbulent exchanges of a passive scalar above and within a forested region located in the central Amazon. Weak (2 ms−1) and strong (6 ms−1) wind conditions were simulated. A passive scalar source was introduced to the forest floor for both simulations. The simulations reproduced the main characteristics of the turbulent flow and of the passive scalar transport between the forest and the atmosphere. Noteworthily, strong and weak wind conditions presented different turbulence structures that drove different patterns of scalar exchange both within and above the forest. These results show how passive scalar concentration is influenced by the wind speed at the canopy top. Additionally, higher wind speeds are related to stronger sweep and ejection regimes, generating more intense plumes that are able to reduce the passive scalar concentration inside the forest canopy. This work was the first that used PALM to investigate scalar transport between the Amazon rainforest and the atmosphere.

Highlights

As a result of these works, some of the main characteristics of flows above forests, such as the Amazon forest, are already known: the presence of an inflection point in the vertical wind profile [19,20]; the existence of coherent structures in the rolls form at the forest–atmosphere interface [14,21]; the turbulent exchange is dominated by downward sweep motions inside the canopy and by upward ejection motions above it [22]
The turbulent flow is influenced by topography in regions of dense forest [8], and by intermittent gusts of strong wind
We investigated the transport of a passive scalar via the parallelized large-eddy simulation model (PALM) model to the Amazon rainforest under two wind conditions: weak (2 ms−1) and strong (6 ms−1)

Summary

Introduction

The scientific community has been working intensively to better understand such transport at the forest–atmosphere interface, through both experimental studies [6,7,8,9,10,11] and numerical simulations [12,13,14,15,16,17,18]. As a result of these works, some of the main characteristics of flows above forests, such as the Amazon forest, are already known: the presence of an inflection point in the vertical wind profile [19,20]; the existence of coherent structures in the rolls form at the forest–atmosphere interface [14,21]; the turbulent exchange is dominated by downward sweep motions inside the canopy and by upward ejection motions above it [22]. It is known that in the Amazon region, there are frequently convective clouds and strong downdrafts that produce intermittent situations of strong winds at the forest–atmosphere interface [26,27,28,29]

Methods

Results

Conclusion