Which factors make forests cooler: Evaporation or their high aerodynamic conductance? Our paper just published in HESS suggests that it is the latter.

Trees and plants moderate the Earth’s surface temperature. Generally, the cooling effect of vegetation is mainly attributed to the process of evapotranspiration. In our paper just published in HESS, we used observations to unravel the importance of evaporative cooling for short vegetation and forest in shaping diurnal variations in temperatures and found that, actually, it is not only evaporation that keeps the forests cool.

Continue reading “Which factors make forests cooler: Evaporation or their high aerodynamic conductance? Our paper just published in HESS suggests that it is the latter.”

More wind turbines should lead to less wind and less efficient wind turbines, but how to account for this? We showed that our simple spreadsheet KEBA model is about as good as complex WRF simulations to describe this effect.

Wind energy has seen a tremendous increase over the last decades, a trend that is likely to continue into the future with the transition towards a sustainable energy system. Yet, each wind turbine removes energy from the atmosphere, so the more wind turbines there are within a region, the more wind speeds should decline, making each turbine less efficient. This effect has clearly been shown by atmospheric simulation models (e.g., in our previous work), but this effect has typically not been accounted for in regional to continental wind energy resource estimates and energy scenarios for the future. The effect sounds complicated, so what should be done?

Continue reading “More wind turbines should lead to less wind and less efficient wind turbines, but how to account for this? We showed that our simple spreadsheet KEBA model is about as good as complex WRF simulations to describe this effect.”

Solar radiation is the main cause for diurnal variations on land. Looking at this slightly differently than how it is normally done helps to better understand observations and evaluate models of the land surface

My former postdoc, Maik Renner, just got his paper published in the Journal of Hydrometeorology, in which he evaluated the performance of common land surface models at the diurnal time scale using FluxNet observations. The evaluation was based on a simple concept that we developed in my group: that solar radiation is the main driver of the diurnal variation of variables that characterize the land-atmosphere system. This sounds trivial. Of course solar radiation is the dominant driver, so what novel insights can be gained from this view? Continue reading “Solar radiation is the main cause for diurnal variations on land. Looking at this slightly differently than how it is normally done helps to better understand observations and evaluate models of the land surface”

Does thermodynamics limit photosynthesis? It probably does, but not as you may think

Fig Leaf picturePhotosynthesis is the process which powers life on Earth.  It takes the energy contained in sunlight, uses carbon dioxide, and generates chemical energy that is stored in form of sugars and similar compounds that fuel the activity of the biosphere, including us humans.  And just as any other Earth system process, in doing so it follows the laws of thermodynamics.  But does thermodynamics also restrict the efficiency by which photosynthesis can use sunlight? 

Continue reading “Does thermodynamics limit photosynthesis? It probably does, but not as you may think”

Are you looking for a stimulating Postdoc opportunity? Our group has a position open, applying thermodynamics and optimality to Earth system science.

I have an opening for a Postdoc position available in my group that is rather flexible and provides a lot of freedom because it is unattached to any research project (it is the succession of my co-worker Maik Renner, who advanced to a permanent position elsewhere).  I would like the research to broadly focus on advancing the application of thermodynamics and optimality principles to Earth system science, but the concrete topic is up to you.  So if you are curious to learn more about thermodynamics and how to apply it, I’d like you to think about a topic and apply!  The formal details are provided on our homepage here. Continue reading “Are you looking for a stimulating Postdoc opportunity? Our group has a position open, applying thermodynamics and optimality to Earth system science.”

Does global warming behave the same on rainy and sunny days? No, it doesn’t, and our new JGR paper explains why.

Global warming, the increase in near-surface temperature due to the enhanced greenhouse effect at global scale, has clearly been reflected in observations over the last 50 years. However, the severities of warming in different regions and different period differs a lot. Scientists have considered many factors which may contribute to shape the temperature trends.  For example, our ESD paper explained the stronger temperature trends over land compared to oceans by the different ways by which the diurnal variation in solar radiation is buffered on land and ocean. Here we introduce another simple but significant factor, sunny and rainy days. Continue reading “Does global warming behave the same on rainy and sunny days? No, it doesn’t, and our new JGR paper explains why.”

More offshore wind energy is likely to reduce turbine efficiencies, but still a lot of renewable energy can be generated. This is what a new @AgoraEW study shows to which we contributed.

Winds over the ocean typically have higher wind speeds, resulting in high efficiencies of wind turbines and making this an attractive environment for generating a lot of renewable energy.  But how efficient are turbines going to be when offshore wind farms become larger and larger? Continue reading “More offshore wind energy is likely to reduce turbine efficiencies, but still a lot of renewable energy can be generated. This is what a new @AgoraEW study shows to which we contributed.”

Do roughness changes of tropical deforestation affect surface energy balance partitioning? No, they don’t. That’s what we found when we estimated the effects from first principles.

Cutting down tropical rainforests and replacing them with soybean fields alters how the land surface functions, and this affects the atmosphere.  Rainforests have a heterogeneous canopy that absorbs sunlight very well and is aerodynamically rough, and they have deep-reaching root systems that allow them to draw water from deep within the soil, especially during the dry season when water input by precipitation is limited.  When trees are cut down and replaced by soybean fields, these physical aspects of the land surface are changed, thus impacting how the absorbed solar energy is partitioned at the surface, and how this energy is transferred into the overlying atmosphere.  Tropical deforestation is one of the many aspects of global change that has been dealt with over the last decades, evaluated with observations and climate models, so what else can add new insights?  And what can these insights be used for? Continue reading “Do roughness changes of tropical deforestation affect surface energy balance partitioning? No, they don’t. That’s what we found when we estimated the effects from first principles.”

If you think surface and air temperature are basically the same thing, think again. Or read our new paper.

In meteorology, air temperature measurements are typically taken 2m above the surface.  It is a routine measurement at weather stations, and this temperature is the basis for analyzing trends, such as global warming.  The temperature of the surface is not so often measured, but it can be inferred by satellites from how much radiation is being emitted by the surface.  Being only 2m apart, one may think that the temperatures basically reflect more or less the same, given their close proximity. We actually found out that this is not the case: surface temperature responds much more strongly to a lack of water than air temperature.  This finding was just published in our article in the journal Geophysical Research Letters. Continue reading “If you think surface and air temperature are basically the same thing, think again. Or read our new paper.”