Atmospheric boundary layer

Can turbulence survive the cold?

Aim: To understand the turbulence processes responsible for the occurrence of for example ground frost.

How can we explain ground frost? And why are weather models not very good at predicting these phenomena? In this project, we seek answers to these questions. Ground frost is just one application, but the dynamics of turbulence at night can also be responsible for fog formation, limited pollution ventilation or ice growth in the arctic.

Ground frost on the Dutch Veluwe. Source: - Cannonball

After sunset the surface temperature can drop rapidly in some nights and may lead to ground frost, while in other nights the surface temperature remains higher. Broadly speaking the cold nights occur under clear-sky conditions with weak winds, while cloudy, stormy nights are generally warmer.

By a recent breakthrough in our group, we can explain the impact that cloud coverage and wind speed have on the dynamics of near-surface turbulence and hence on near-surface temperatures. In our research we now focus on a deeper analysis both fundamentally and practically. Hereto, our research is pillared by three main areas: theoretical analysis, numerical studies and field observations.

The theoretical part is focussed on using strongly simplified models. This type of models can help to obtain a deeper understanding of the dynamics in a complex system like the atmospheric boundary layer. Can you make it simpler, without destroying the dynamics?

Detailed numerical studies can be used to benchmark the simple models. With different designs of numerical experiments, different parts of the dynamics can be magnified. And, unlike in the real atmosphere, the dynamics are undisturbed, so we obtain insight in the dynamics in great detail.

The final pillar is to compare the results with measurements from the real atmosphere (e.g. from the Royal Dutch Meteorological Institute, KNMI). Here, the main challenge is to separate the dynamics of interest from all the disturbances that are abundant in the real atmosphere.

Weather tower at Cabauw. Source: KNMI

Group members

Ivo van Hooijdonk, Herman Clercx

Bas van de Wiel (Delft University of Technology)