232 research outputs found
The Maximum Entropy Production Principle: Its Theoretical Foundations and Applications to the Earth System
The Maximum Entropy Production (MEP) principle has been remarkably successful in producing accurate predictions for non-equilibrium states. We argue that this is because the MEP principle is an effective inference procedure that produces the best predictions from the available information. Since all Earth system processes are subject to the conservation of energy, mass and momentum, we argue that in practical terms the MEP principle should be applied to Earth system processes in terms of the already established framework of non-equilibrium thermodynamics, with the assumption of local thermodynamic equilibrium at the appropriate scales
Towards understanding how surface life can affect interior geological processes: a non-equilibrium thermodynamics approach
Life has significantly altered the Earth’s atmosphere, oceans and crust. To what extent has it also affected interior geological processes? To address this question, three models of geological processes are formulated: mantle convection, continental crust uplift and erosion and oceanic crust recycling. These processes are characterised as non-equilibrium thermodynamic systems. Their states of disequilibrium are maintained by the power generated from the dissipation of energy from the interior of the Earth. Altering the thickness of continental crust via weathering and erosion affects the upper mantle temperature which leads to changes in rates of oceanic crust recycling and consequently rates of outgassing of carbon dioxide into the atmosphere. Estimates for the power generated by various elements in the Earth system are shown. This includes, inter alia, surface life generation of 264 TW of power, much greater than those of geological processes such as mantle convection at 12 TW. This high power results from life’s ability to harvest energy directly from the sun. Life need only utilise a small fraction of the generated free chemical energy for geochemical transformations at the surface, such as affecting rates of weathering and erosion of continental rocks, in order to affect interior, geological processes. Consequently when assessing the effects of life on Earth, and potentially any planet with a significant biosphere, dynamical models may be required that better capture the coupled nature of biologically-mediated surface and interior processes
Predictive use of the Maximum Entropy Production principle for Past and Present Climates
In this paper, we show how the MEP hypothesis may be used to build simple
climate models without representing explicitly the energy transport by the
atmosphere. The purpose is twofold. First, we assess the performance of the MEP
hypothesis by comparing a simple model with minimal input data to a complex,
state-of-the-art General Circulation Model. Next, we show how to improve the
realism of MEP climate models by including climate feedbacks, focusing on the
case of the water-vapour feedback. We also discuss the dependence of the
entropy production rate and predicted surface temperature on the resolution of
the model
Two methods for estimating limits to large-scale wind power generation
Wind turbines remove kinetic energy from the atmospheric flow, which reduces wind speeds and limits generation rates of large wind farms. These interactions can be approximated using a vertical kinetic energy (VKE) flux method, which predicts that the maximum power generation potential is 26% of the instantaneous downward transport of kinetic energy using the preturbine climatology. We compare the energy flux method to the Weather Research and Forecasting (WRF) regional atmospheric model equipped with a wind turbine parameterization over a 105 km2 region in the central United States. The WRF simulations yield a maximum generation of 1.1 We⋅m−2, whereas the VKE method predicts the time series while underestimating the maximum generation rate by about 50%. Because VKE derives the generation limit from the preturbine climatology, potential changes in the vertical kinetic energy flux from the free atmosphere are not considered. Such changes are important at night when WRF estimates are about twice the VKE value because wind turbines interact with the decoupled nocturnal low-level jet in this region. Daytime estimates agree better to 20% because the wind turbines induce comparatively small changes to the downward kinetic energy flux. This combination of downward transport limits and wind speed reductions explains why large-scale wind power generation in windy regions is limited to about 1 We⋅m−2, with VKE capturing this combination in a comparatively simple way
HESS Opinions: Functional units: a novel framework to explore the link between spatial organization and hydrological functioning of intermediate scale catchments
This opinion paper proposes a novel framework for exploring how spatial organization alongside
with spatial heterogeneity controls functioning of intermediate scale catchments of organized
complexity. Key idea is that spatial organization in landscapes implies that functioning of
intermediate scale catchments is controlled by a hierarchy of functional units: hillslope scale
lead topologies and embedded elementary functional units (EFUs). We argue that similar soils and
vegetation communities and thus also soil structures "co-developed" within EFUs in an adaptive,
self-organizing manner as they have been exposed to similar flows of energy, water and nutrients
from the past to the present. Class members of the same EFU (class) are thus deemed to belong to
the same ensemble with respect to controls of the energy balance and related vertical flows of
capillary bounded soil water and heat. Class members of superordinate lead topologies are
characterized by the same spatially organized arrangement of EFUs along the gradient driving
lateral flows of free water as well as a similar surface and bedrock topography. We hence
postulate that they belong to the same ensemble with respect to controls on rainfall runoff
transformation and related vertical and lateral fluxes of free water. We expect class members of
these functional units to have a distinct way how their architecture controls the interplay of
state dynamics and integral flows, which is typical for all members of one class but dissimilar
among the classes. This implies that we might infer on the typical dynamic behavior of the most
important classes of EFU and lead topologies in a catchment, by thoroughly characterizing a few
members of each class. A major asset of the proposed framework, which steps beyond the concept of
hydrological response units, is that it can be tested experimentally. In this respect, we reflect
on suitable strategies based on stratified observations drawing from process hydrology, soil
physics, geophysics, ecology and remote sensing which are currently conducted in replicates of
candidate functional units in the Attert basin (Luxembourg), to search for typical and similar
functional and structural characteristics. A second asset of this framework is that it blueprints
a way towards a structurally more adequate model concept for water and energy cycles in
intermediate scale catchments, which balances necessary complexity with falsifiability. This is
because EFU and lead topologies are deemed to mark a hierarchy of "scale breaks" where
simplicity with respect to the energy balance and stream flow generation emerges from spatially organized
process-structure interactions. This offers the opportunity for simplified descriptions of these
processes that are nevertheless physically and thermodynamically consistent. In this respect we
reflect on a candidate model structure that (a) may accommodate distributed observations of states
and especially terrestrial controls on driving gradients to constrain the space of feasible model
structures and (b) allows testing the possible added value of organizing principles to understand
the role of spatial organization from an optimality perspective
Global NO and HONO emissions of biological soil crusts estimated by a process-based non-vascular vegetation model
The reactive trace gases nitric oxide (NO) and nitrous acid (HONO) are
crucial for chemical processes in the atmosphere, including the formation of
ozone and OH radicals, oxidation of pollutants, and atmospheric
self-cleaning. Recently, empirical studies have shown that biological soil
crusts are able to emit large amounts of NO and HONO, and they may therefore
play an important role in the global budget of these trace gases. However,
the upscaling of local estimates to the global scale is subject to large
uncertainties, due to unknown spatial distribution of crust types and their
dynamic metabolic activity. Here, we perform an alternative estimate of
global NO and HONO emissions by biological soil crusts, using a process-based
modelling approach to these organisms, combined with global data
sets of climate and land cover. We thereby consider that NO and HONO are
emitted in strongly different proportions, depending on the type of crust and
their dynamic activity, and we provide a first estimate of the global
distribution of four different crust types. Based on this, we estimate global
total values of 1.04 Tg yr−1 NO–N and 0.69 Tg yr−1 HONO–N
released by biological soil crusts. This corresponds to around 20 % of
global emissions of these trace gases from natural ecosystems. Due to the low
number of observations on NO and HONO emissions suitable to validate the
model, our estimates are still relatively uncertain. However, they are
consistent with the amount estimated by the empirical approach, which
confirms that biological soil crusts are likely to have a strong impact on
global atmospheric chemistry via emissions of NO and HONO.</p
Surface Energy Budgets of Arctic Tundra During Growing Season
This study analyzed summer observations of diurnal and seasonal surface energy budgets across several monitoring sites within the Arctic tundra underlain by permafrost. In these areas, latent and sensible heat fluxes have comparable magnitudes, and ground heat flux enters the subsurface during short summer intervals of the growing period, leading to seasonal thaw. The maximum entropy production (MEP) model was tested as an input and parameter parsimonious model of surface heat fluxes for the simulation of energy budgets of these permafrost‐underlain environments. Using net radiation, surface temperature, and a single parameter characterizing the thermal inertia of the heat exchanging surface, the MEP model estimates latent, sensible, and ground heat fluxes that agree closely with observations at five sites for which detailed flux data are available. The MEP potential evapotranspiration model reproduces estimates of the Penman‐Monteith potential evapotranspiration model that requires at least five input meteorological variables (net radiation, ground heat flux, air temperature, air humidity, and wind speed) and empirical parameters of surface resistance. The potential and challenges of MEP model application in sparsely monitored areas of the Arctic are discussed, highlighting the need for accurate measurements and constraints of ground heat flux.Plain Language SummaryGrowing season latent and sensible heat fluxes are nearly equal over the Arctic permafrost tundra regions. Persistent ground heat flux into the subsurface layer leads to seasonal thaw of the top permafrost layer. The maximum energy production model accurately estimates the latent, sensible, and ground heat flux of the surface energy budget of the Arctic permafrost regions.Key PointThe MEP model is parsimonious and well suited to modeling surface energy budget in data‐sparse permafrost environmentsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150560/1/jgrd55584.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150560/2/jgrd55584_am.pd
Using phase lags to evaluate model biases in simulating the diurnal cycle of evapotranspiration: a case study in Luxembourg
While modeling approaches of evapotranspiration (λE) perform
reasonably well when evaluated at daily or monthly timescales, they can show systematic
deviations at the sub-daily timescale,
which results in potential biases in modeled λE to global climate
change. Here we decompose the diurnal variation of heat fluxes and
meteorological variables into their direct response to incoming solar
radiation (Rsd) and a phase shift to Rsd. We analyze data from an
eddy-covariance (EC) station at a temperate grassland site, which experienced a
pronounced summer drought. We employ three structurally different modeling
approaches of λE, which are used in remote sensing retrievals, and
quantify how well these models represent the observed diurnal cycle under
clear-sky conditions. We find that energy balance residual approaches, which
use the surface-to-air temperature gradient as input,
are able to reproduce the reduction of the phase lag from wet to dry conditions. However, approaches
which use the vapor pressure deficit (Da) as the driving gradient
(Penman–Monteith) show significant deviations from the observed phase lags,
which is found to depend on the parameterization of surface conductance to
water vapor. This is due to the typically strong phase lag of 2–3 h
of Da, while the observed phase lag of λE is only on the order of
15 min. In contrast, the temperature gradient shows phase differences in
agreement with the sensible heat flux and represents the wet–dry difference
rather well. We conclude that phase lags contain important information on
the different mechanisms of diurnal heat storage and exchange and, thus,
allow a process-based insight to improve the representation of
land–atmosphere (L–A) interactions in models.</p
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