#vEMS21: Our updates on using #thermodynamics for land-atmosphere interactions, the precipitation response to #globalwarming, and the #windenergy potential in the German bight

With summer coming to a close, we are back to present new insights from ongoing research in extreme precipitation events, offshore wind energy and thermodynamics at the European Meteorological Society Annual Meeting 2021. The event, which will be held online next week (6 – 10 September 2021), focuses on weather and climate research and services for the achievement of the UN Sustainable Development Goals. Read on to find out more details about when and what each of us will be presenting.

On Monday, Axel presents the current status of applying physical constraints, and thermodynamics in particular, to better understand land-atmosphere interactions at the diurnal scale. The key ingredients in this approach are energy balances and thermodynamics, which both enter twice, and can explain a lot of what is seen in observations. It includes (1) the surface energy balance, obviously, as a starting point, but also (2) the energy balance of the whole atmospheric column. The latter represents the storage term that buffers the strong diurnal variation in the solar radiation input over land and manifests itself in the diurnal growth of the convective boundary layer. The thermodynamic part involves (3) the maximum power limit to infer how much heat is transported from the surface to the atmosphere, and (4) the partitioning of this heat into the sensible and latent heat fluxes, a concept sometimes referred to as “equilibrium partitioning” and reflects thermodynamic equilibrium at the surface. As we show, the combination of these physical concepts can explain observed energy balance partitioning and evaporation rates very well. So it seems that it does not require much detail to understand the land-atmosphere system. The system appears to be very strongly constrained by these energetic and thermodynamic concepts, making them highly predictable. This is quite a different, and, hopefully, illuminating view of land-atmosphere interactions to be developed further in future work. He presents a lightning talk on 6 September at 14:15 CEST as part of the session UP1.2 “Atmospheric boundary-layer processes, turbulence and land-atmosphere interactions.

On Wednesday, Sarosh presents in the session UP3.1 on climate change, trends, and extremes his update on assessing the precipitation response to global warming using observations. Extreme precipitation is expected to increase with temperature at rate of 7%/K; a limit set by thermodynamics based on the amount of moisture the atmosphere can hold (based on the Clausius-Clapeyron relationship, CC in short). However, observations from tropical regions show large deviations in the precipitation sensitivities from the CC rate. Sarosh uses observations from India and shows that a large part of the uncertainty in this response comes from the radiative effect of clouds on surface temperatures during the precipitation events. This results in a covariation between precipitation and temperature that needs to be accounted for when using observations to infer how precipitation events scale with temperature. He minimises this uncertainty by removing the cloud effects on surface temperature using the maximum power approach and estimated sensitivities that are consistent with physical arguments and model projections. To find out more about his work, see his abstract and listen to him presenting on 8 September at 11:15 CEST.

On Thursday, Jonathan presents his progress in evaluating the wind resource potential for proposed wind farms in the North sea, as simulated by Weather Research and Forecasting (WRF-EWP) simulations and our Kinetic Energy budget of the Atmosphere (KEBA) approach. Both these approaches predict that per turbine yields could be reduced by up to 25% if the proposed capacity is installed because of the response of the atmosphere. The aim throughout his investigation has been to identify the key atmospheric information which needs to be included when estimating the yields from future large wind farm deployment which may range in capacity from a few 10s to 100s of GW. He has found that while the kinetic energy (KE) budget of the boundary layer represents the predominant control on the yields from proposed large wind farms, impacts from atmospheric stability, or the propensity of the boundary layer to mix and transfer KE and momentum to the turbines also affects the yields to some extent for certain conditions. His results show that on average KEBA overestimates yields during stable or very stable atmospheric conditions by up to 1.7 to 2 times i.e. when the amount of mixing in the atmosphere is low and the deficit created by the KE extraction by the turbines is replenished slower leading to lower per turbine efficiencies. The insights from his research should allow us to provide renewable energy policy makers with a simple understanding of the key atmospheric controls on large wind farm yields while enabling the use of KEBA as a potential policy design tool. His presentation titled “How much atmospheric dynamics do we need to capture yield reductions from proposed large wind parks in the German Bight?” is scheduled on 9 September 2021 at 14:45 CEST as a part of the OSA2.3 Energy Meteorology session.

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