Corona is still around, also in Vienna, but the EGU General Assembly will nevertheless happen again, in a hybrid form. We are thrilled to be there physically, giving our 6 minute short talks on our work, and look forward to seeing and talking to you there!
Sarosh presents in the session CL4.1: Land-atmosphere interactions and asks the question “How much of the surface energy partitioning can be explained by controls imposed by thermodynamics?”. The answer is “a lot”. The laws of thermodynamics set limits and directions to energy conversions and thus constrain several physical processes within the Earth system. While the first law (energy conservation) is widely considered in form of the surface energy balance to study land-surface processes, the use of the second law (entropy budget) in understanding land-atmosphere interactions is mostly absent. Sarosh applies the second law on the exchange of heat between the surface and atmosphere and shows that the turbulent fluxes are constrained as the system evolves to operate at its thermodynamic limit. This limit is associated with maximum amount of work the lower atmosphere can perform to generate buoyancy and sustain vertical mixing within convective boundary layer. He evaluates this approach and found that these constraints alone can explain more than 95% of the climatological variations in surface temperatures and turbulent fluxes over continents. On further partitioning of available energy into sensible and latent heat he shows that while it is water limitation (and thermodynamic equilibrium when water availability does not limit) which governs the tradeoff between evaporation and buoyancy, the total turbulent fluxes are predominantly shaped by local radiative conditions and thermodynamic limits. To know more about his work, attend his presentation on 24th May at 15:59 CEST in room 0.14.
Yinglin, presents in the session CL4.7 “Energy and dynamics in the climate system “. Her work focuses on understanding the temperature extremes over the Tibetan Plateau based on the surface energy balance. The Tibetan Plateau, known as the “roof of the world” with an average elevation exceeding 4000 m, has witnessed a significant increase in extremely warm days and nights, making attributing these extremes very importance. Previous work has found that temperature extremes are closely correlated to characteristics of large-scale circulation patterns, the connection between which was statistically attributed to heat advection. It seems to make sense that the warm air or cold spell intrusions can modulate local temperature. However, if we look at it from the perspective of the surface energy balance, heat advection cannot directly influence the surface temperature; after all, the balance consists mostly of the absorption of solar radiation, exchange of terrestrial radiation, surface turbulent fluxes, and heat storage and this balance directly determines variations in surface temperature. One might further think that heat advection can play an indirect role, considering that warmer or moister air will enhance the downwelling flux of longwave radiation. No doubt, it is a kind of possibility. But there are also cases where variations in the circulation can be translated into changes in radiation by changing clouds, but not heat convergence. In this context, is it this indirect effect of heat advection that caused the extremes over the Tibetan plateau? In this work, we found the daytime extremes are controlled by solar radiation, and the nighttime extremes are dominated by longwave radiation. Furthermore, radiation is modulated by clouds that are affected by changes in the atmospheric circulation. But heat advection is absent during daytime extremes and only plays a limited role during nighttime or extremes. She presents on 25 May 2022 at 10:44 CEST.
Jonathan will present on Wednesday 25th of May 2022 at 8:58 AM in the session on Spatial and Temporal Modelling of Renewable Energy Systems (ERE 2.2). He will focus on the incorporation of the effects of key atmospheric controls on wind turbine yields within large deployments in the estimation of technical wind energy potential for policy applications. It is well-known that wind turbines remove kinetic energy (KE) to generate electricity and that this results in slower winds behind the turbines. However, the standard approach for resource potential estimation implicitly assumes that KE removed by large-scale deployments would not affect winds. This means that the effect of slower winds from KE removal are not yet included regional wind energy resource evaluations. Jonathan evaluates the extent to which the impacts of large scale KE removal on wind speeds can be captured by using a simple yet physical approach that frames wind energy as the removal of KE from a fixed atmospheric budget (KEBA). This is consistent with the physics of atmospheric KE generation – more on this from Axel (see below). Jonathan shows that KEBA captures the key trends in wind speed reductions which explain why numerically modelled (WRF) nighttime yields from a hypothetical large deployment in Kansas are lower than daytime, despite higher wind speeds. Consequently, a revaluation of Kansas’ technical potential using KEBA is significantly more consistent with WRF than the standard approach. This means that KEBA results in more physically representative estimates of technical potential and is, thus, better suited for use in policy applications compared to the standard approach. If this has piqued your interest and you would like to know more about the atmospheric limits on large scale wind energy, please reach out to Jonathan directly at EGU or by mail.
Axel asks a rather general question of “How much kinetic energy can the large-scale atmospheric circulation at best generate?“. He provides an answer based on thermodynamics in his talk in session CL4.7 “Energy and dynamics in the climate system” on Wednesday, 25 May 2022 at 09:08. The answer comes from the application of the maximum power limit to the different solar heating across latitudes. The outcome is very similar to the proposed Maximum Entropy Production principle, yet the application is more specific – it is the atmosphere that works as hard as it can, yielding maximum power. This, in turn, then sets a constraint and upper limit to atmospheric dynamics. He also links this outcome to the more established framework of the Lorenz Energy Cycle and shows that at maximum power, the estimated mean available potential energy is similar to observed values. The implications of this dynamical constraint from thermodynamics is that it allows to derive simple, physically-based climate estimates as well as hard limits on the renewable wind energy resource. If you are interested to read more on this, his talk is based on a recently published review article in the Meteorologische Zeitschrift and is summarized in this blogpost.