Does topography affects atmospheric turbulence?

Atmospheric turbulence

Whirling wind motions called turbulence commonly occur in the lowest 100 m of the atmosphere. Here, they play an important role in transporting energy, gases, and particles away from and toward the land surface. Accordingly, these exchanges are crucial for the interaction between the atmosphere and the biosphere. This includes processes such as:

  • transport of latent heat (energy)
  • transport of local methane emissions (gases)
  • rise of forest-produced pollen into the atmosphere, where they might function as condensation nuclei for cloud formation (particles)

Quantifying and predicting the energy available to promote this mixing is therefore critical to better understand how strong these interactions are.

The role of topography

And this is exactly what Marcelo Chamecki and his co-authors are working on. Marcelo Chamecki, Cleo Quaresma Dias‐Júnior, and several researchers of the ATTO project published two papers on the structure of atmospheric turbulence back in 2018 and 2019 (we wrote about this). They found several unexpected results. So now, they and their team followed up on those first results with more details. Specifically, they looked at how gentle topography covered by dense forests affects turbulence.

“Gentle topography” in this case means about 50-70 meters height difference between the highest and lowest points in the area. This terrain is covered by dense rainforest with a canopy height of 35 meters on average.

To approach this, they used daytime observations from two field campaigns in central Amazonia, as well as computer turbulence simulations. The field studies are the GoAmazon campaign and data from ATTO.

And indeed, the scientists found that even the gentle topography underneath the Amazon forest strongly impacts the turbulence in those lowest 100 meters. This is really valuable information. Thus far, studies in the region have interpreted their observations based on the simplified assumption of wind flow over flat topography. If future studies take this effect on turbulence into consideration, they will likely be able to improve existing estimates of energy, gas and pollen fluxes mentioned in the opening.

The shadow and the light of a low sun highlight the gentle topography under the Amazon forest, which affects atmospheric turbulence. © Paulo Brando
The shadow and the light of a low sun highlight the gentle topography under the Amazon forest, which affects atmospheric turbulence. © Paulo Brando

Chamecki et al. recently published the study “Effects of Vegetation and Topography on the Boundary Layer Structure above the Amazon Forest” Open Access in the Journal of the Atmospheric Science.

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