scholarly journals Understanding land surface-atmosphere interactions at the diurnal scale from energetic and thermodynamic constraints

2021 ◽  
Author(s):  
Axel Kleidon ◽  
Maik Renner ◽  
Annu Panwar ◽  
Sarosh Alam Ghausi
Keyword(s):  
Energy Balance ◽  
Thermodynamic Limit ◽  
Heat Engine ◽  
Heat Fluxes ◽  
Maximum Power ◽  
Lower Atmosphere ◽  
Turbulent Heat ◽  
First Order ◽  
Atmosphere System ◽  
Turbulent Heat Fluxes

<p>Land-atmosphere interactions are typically evaluated using numerical simulation models of increasingly greater complexity.  But what are the key, major constraints that determine the first-order controls of the land-atmosphere system?  Here, we present an alternative approach that is solely based on energetic and thermodynamic constraints of the coupled land-atmosphere system and show that this approach can reproduce observations at the diurnal scale very well.  The key concept we use is that turbulent heat fluxes are predominantly the result of an atmospheric heat engine that is driven by the heat input from the surface and that operates at the thermodynamic limit of maximum power.  This provides a closure for the magnitude of turbulent fluxes in the surface energy balance.  Interactions enter this approach mainly in two ways: First, the cooling effect of turbulent heat fluxes on surface temperature lowers the engine's efficiency, thereby setting the maximum power limit, and second, by heat storage changes in the lower atmosphere, which represent an entropy term inside the heat engine and alter the thermodynamic limit for power output.  Both effects are, however, well constrained by energy balances, yielding analytical solutions for energy balance partitioning during the day without the need for empirical parameters. The further partitioning into sensible and latent heat fluxes is obtained from the assumption of thermodynamic equilibrium at the surface where heat and moisture is added to the atmosphere (if sufficient soil water is accessible).  We then show that this approach works remarkably well in reproducing FluxNet observations over the diurnal cycle.  What this implies is that these physical constraints determine the first-order dynamics of the land-atmosphere system, enabling us to derive simple, physics-based estimates of climate, the dominant effects of vegetation, and the response of the coupled system to global climate change.</p>

scholarly journals Diurnal land surface energy balance partitioning estimated from the thermodynamic limit of a cold heat engine

2018 ◽  
Author(s):  
Axel Kleidon ◽  
Maik Renner
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Thermodynamic Limit ◽  
Land Surface ◽  
Radiative Forcing ◽  
Surface Energy Balance ◽  
Heat Engine ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Turbulent Heat

Abstract. Turbulent fluxes strongly shape the conditions at the land surface, yet they are typically formulated in terms of semi-empirical parameterisations that make it difficult to derive theoretical estimates of how global change impacts land surface functioning. Here, we describe these turbulent fluxes as the result of a thermodynamic process that generates work to sustain convective motion and thus maintains the turbulent exchange between the land surface and the atmosphere. We first derive a limit from the second law of thermodynamics that is equivalent to the Carnot limit, but which explicitly accounts for diurnal heat storage changes in the lower atmosphere. We then use this limit of a cold heat engine together with the surface energy balance to infer the maximum power that can be derived from the turbulent fluxes for a given solar radiative forcing. The surface energy balance partitioning estimated from this thermodynamic limit requires no empirical parameters and compares very well with the observed partitioning of absorbed solar radiation into radiative and turbulent heat fluxes across a range of climates, with correlation coefficients r2 ≥ 95 % and slopes near one. These results suggest that turbulent heat fluxes on land operate near their thermodynamic limit on how much convection can be generated from the local radiative forcing. It implies that this type of approach can be used to derive first-order estimates of global change that are solely based on physical principles.

scholarly journals Diurnal land surface energy balance partitioning estimated from the thermodynamic limit of a cold heat engine

2018 ◽  
Vol 9 (3) ◽  
pp. 1127-1140 ◽  
Author(s):  
Axel Kleidon ◽  
Maik Renner
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Thermodynamic Limit ◽  
Land Surface ◽  
Radiative Forcing ◽  
Surface Energy Balance ◽  
Heat Engine ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Turbulent Heat

Abstract. Turbulent fluxes strongly shape the conditions at the land surface, yet they are typically formulated in terms of semiempirical parameterizations that make it difficult to derive theoretical estimates of how global change impacts land surface functioning. Here, we describe these turbulent fluxes as the result of a thermodynamic process that generates work to sustain convective motion and thus maintains the turbulent exchange between the land surface and the atmosphere. We first derive a limit from the second law of thermodynamics that is equivalent to the Carnot limit but which explicitly accounts for diurnal heat storage changes in the lower atmosphere. We call this the limit of a “cold” heat engine and use it together with the surface energy balance to infer the maximum power that can be derived from the turbulent fluxes for a given solar radiative forcing. The surface energy balance partitioning estimated from this thermodynamic limit requires no empirical parameters and compares very well with the observed partitioning of absorbed solar radiation into radiative and turbulent heat fluxes across a range of climates, with correlation coefficients r2≥95 % and slopes near 1. These results suggest that turbulent heat fluxes on land operate near their thermodynamic limit on how much convection can be generated from the local radiative forcing. It implies that this type of approach can be used to derive general estimates of global change that are solely based on physical principles.

scholarly journals The Surface Energy Balance System (SEBS) for estimation of turbulent heat fluxes

2002 ◽  
Vol 6 (1) ◽  
pp. 85-100 ◽  
Author(s):  
Z. Su
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Heat Fluxes ◽  
Physical Parameters ◽  
Turbulent Heat ◽  
Evaporative Fraction ◽  
Balance System ◽  
Turbulent Heat Fluxes

Abstract. A Surface Energy Balance System (SEBS) is proposed for the estimation of atmospheric turbulent fluxes and evaporative fraction using satellite earth observation data, in combination with meteorological information at proper scales. SEBS consists of: a set of tools for the determination of the land surface physical parameters, such as albedo, emissivity, temperature, vegetation coverage etc., from spectral reflectance and radiance measurements; a model for the determination of the roughness length for heat transfer; and a new formulation for the determination of the evaporative fraction on the basis of energy balance at limiting cases. Four experimental data sets are used to assess the reliabilities of SEBS. Based on these case studies, SEBS has proven to be capable to estimate turbulent heat fluxes and evaporative fraction at various scales with acceptable accuracy. The uncertainties in the estimated heat fluxes are comparable to in-situ measurement uncertainties. Keywords: Surface energy balance, turbulent heat flux, evaporation, remote sensing

scholarly journals Strong Summer Atmospheric Rivers Trigger Greenland Ice Sheet Melt through Spatially Varying Surface Energy Balance and Cloud Regimes

2020 ◽  
Vol 33 (16) ◽  
pp. 6809-6832 ◽  
Author(s):  
Kyle S. Mattingly ◽  
Thomas L. Mote ◽  
Xavier Fettweis ◽  
Dirk van As ◽  
Kristof Van Tricht ◽  
...  
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Heat Fluxes ◽  
Water Vapor Transport ◽  
Turbulent Heat ◽  
Atmospheric Rivers ◽  
Turbulent Heat Fluxes

ABSTRACTMass loss from the Greenland Ice Sheet (GrIS) has accelerated over the past two decades, coincident with rapid Arctic warming and increasing moisture transport over Greenland by atmospheric rivers (ARs). Summer ARs affecting western Greenland trigger GrIS melt events, but the physical mechanisms through which ARs induce melt are not well understood. This study elucidates the coupled surface–atmosphere processes by which ARs force GrIS melt through analysis of the surface energy balance (SEB), cloud properties, and local- to synoptic-scale atmospheric conditions during strong summer AR events affecting western Greenland. ARs are identified in MERRA-2 reanalysis (1980–2017) and classified by integrated water vapor transport (IVT) intensity. SEB, cloud, and atmospheric data from regional climate model, observational, reanalysis, and satellite-based datasets are used to analyze melt-inducing physical processes during strong, >90th percentile “AR90+” events. Near AR “landfall,” AR90+ days feature increased cloud cover that reduces net shortwave radiation and increases net longwave radiation. As these oppositely signed radiative anomalies partly cancel during AR90+ events, increased melt energy in the ablation zone is primarily provided by turbulent heat fluxes, particularly sensible heat flux. These turbulent heat fluxes are driven by enhanced barrier winds generated by a stronger synoptic pressure gradient combined with an enhanced local temperature contrast between cool over-ice air and the anomalously warm surrounding atmosphere. During AR90+ events in northwest Greenland, anomalous melt is forced remotely through a clear-sky foehn regime produced by downslope flow in eastern Greenland.

scholarly journals Modeling experiments on seasonal lake ice mass and energy balance in Qinghai-Tibet Plateau: A case study

2018 ◽  
Author(s):  
Wenfeng Huang ◽  
Bin Cheng ◽  
Jinrong Zhang ◽  
Zheng Zhang ◽  
Timo Vihma ◽  
...  
Keyword(s):  
Energy Balance ◽  
Mass Balance ◽  
Open Water ◽  
Heat Fluxes ◽  
Tibet Plateau ◽  
Turbulent Heat ◽  
Lake Ice ◽  
Ice Surface ◽  
Turbulent Heat Fluxes ◽  
Ice Mass Balance

Abstract. The lake-rich Qinghai-Tibet Plateau (QTP) has significant impacts on regional and global water cycles and monsoon systems through heat and water vapor exchange. The lake-atmosphere interactions have been quantified over open-water periods, yet little is known about the lake ice thermodynamics and heat and mass balance during ice-covered season due to a lack of field data. Modeling experiments on ice evolution and energy balance were performed in a shallow lake with a high-resolution snow and ice thermodynamic model. The bottom ice growth and decay dominated the seasonal evolution of the thickness of lake ice. Strong surface sublimation was a crucial pattern of ice loss, which was up to 40 % of the maximum ice thickness. Simulation results matched well with the observations with respect to ice mass balance components, net ice thickness, and ice temperature. Strong solar radiation, consistent freezing air temperature, and low air moisture were the major driving forces controlling the seasonal ice mass balance. Energy balance was estimated at the ice surface and bottom, and within the ice interior and under-ice water. Particularly, almost all heat fluxes showed significant diurnal variations including short- and long-wave radiation, turbulent heat fluxes, water heat fluxes at ice bottom, and absorbed and penetrated solar radiation. The calculated ice surface temperature indicated that the atmospheric boundary layer was consistently stable and neutral over the ice-covered period. The turbulent heat fluxes between the lake ice and air and the net heat gain by the lake were much lower than those during open-water period. Ice surface sublimation (vapor flux) was demonstrated to be a vital seasonal water balance component, accounting for 41 % of lake water loss during the ice seasons.

The Role of Turbulent Heat Fluxes in the Energy Balance of High Alpine Snow Cover

1994 ◽  
Vol 25 (1-2) ◽  
pp. 25-38 ◽  
Author(s):  
C. Plüss ◽  
R. Mazzoni
Keyword(s):  
Energy Balance ◽  
Snow Cover ◽  
Correlation Method ◽  
Heat Fluxes ◽  
Eddy Correlation ◽  
Turbulent Heat ◽  
Net Radiation ◽  
Melting Snow ◽  
Measuring Period ◽  
Turbulent Heat Fluxes

Energy balance measurements over a seasonal snow cover were performed near Davos, Switzerland at 2,540 m a.s.l. The energy fluxes were studied over dry and melting snow covers. The beginning of snowmelt clearly coincides with the beginning of positive daily sums of net radiation. During snowmelt, net radiation is the dominant energy source. Latent and sensible heat fluxes do not show a significant seasonal change and remain slight over most of the measuring period. This minor contribution of the turbulent heat fluxes can be attributed to generally low wind speeds in this inner alpine region and to frequent inversions over the melting snow cover. In a changing climate the turbulent heat fluxes could become increasingly important in the energy balance. Therefore, evaluations of the turbulent heat fluxes from profile measurements and the eddy correlation method are compared with simple approximations commonly used in snowmelt models. The conditions under which these approximations can be used for routine discharge forecasts are identified.

scholarly journals An Analysis of Turbulent Heat Fluxes and the Energy Balance During the REFLEX Campaign

2015 ◽  
Vol 63 (6) ◽  
pp. 1516-1539 ◽  
Author(s):  
Christiaan van der Tol ◽  
Wim Timmermans ◽  
Chiara Corbari ◽  
Arnaud Carrara ◽  
Joris Timmermans ◽  
...  
Keyword(s):  
Energy Balance ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

scholarly journals Thermal resistances in the Everest Area (Nepal Himalaya) derived from satellite imagery using a nonlinear energy balance model

2014 ◽  
Vol 8 (1) ◽  
pp. 887-918 ◽  
Author(s):  
D. R. Rounce ◽  
D. C. McKinney
Keyword(s):  
Energy Balance ◽  
Temperature Gradient ◽  
Satellite Imagery ◽  
Heat Fluxes ◽  
Energy Balance Model ◽  
Shortwave Radiation ◽  
Balance Model ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes ◽  
Nonlinear Temperature

Abstract. Debris thickness is an important characteristic of many debris-covered glaciers in the Everest region of the Himalayas. The debris thickness controls the melt rates of the glaciers, which has large implications for hydrologic models, the glaciers response to climate change, and the development of glacial lakes. Despite its importance, there is little knowledge of how the debris thickness varies over these glaciers. This paper uses an energy balance model in conjunction with Landsat7 ETM+ satellite imagery to derive thermal resistances, which is the debris thickness divided by the thermal conductivity. The developed model accounts for the nonlinear temperature gradient in the debris cover to derive accurate thermal resistances. Fieldwork performed on Lhotse Shar/Imja glacier in September 2013 was used to validate the satellite-derived thermal resistances. Results indicate that accounting for the nonlinear temperature gradient is crucial. Furthermore, correcting the incoming shortwave radiation term for the effects of topography and including the turbulent heat fluxes is imperative to derive accurate thermal resistances. Since the topographic correction is important, the model will improve with the quality of the DEM. The main limitation of this work is the poor resolution (60 m) of the satellite's thermal band. The derived thermal resistances are accurate at this resolution, but are unable to derive trends related to slope and aspect on a finer scale. Nonetheless, the study finds this model derives accurate thermal resistances on this scale and is transferable to other debris-covered glaciers in the Everest region.

scholarly journals The residual method for determination of the turbulent exchange coefficient applied to automatic weather station data from Iceland, Switzerland and West Greenland

2005 ◽  
Vol 42 ◽  
pp. 367-372 ◽  
Author(s):  
C. Rolstad ◽  
J. Oerlemans
Keyword(s):  
Energy Balance ◽  
Heat Fluxes ◽  
Turbulent Exchange ◽  
Turbulent Heat ◽  
Weather Station ◽  
Automatic Weather Station ◽  
Exchange Coefficient ◽  
Residual Method ◽  
Turbulent Heat Fluxes ◽  
Turbulent Exchange Coefficient

AbstractThe surface energy balance of glaciers is studied to determine their sensitivity to climate variations. It is known that the turbulent heat fluxes are sensitive to increases in temperature. Automatic weather station data from ablation regions are used to measure melt rates, radiative fluxes and the meteorological data required to determine turbulent heat fluxes using bulk formulas. The turbulent exchange coefficient must be determined for closure of the energy budget. The available methods are the eddy correlation method, the profile method and the residual method, which is applied and tested here. In the residual method the coefficient is determined by fitting a calculated melt curve to an observed melt curve. The coefficients are estimated for three sites: for Vatnajökull, Iceland, Ch = (1.3 ± 0.55) × 10–3 (1998) and Ch = (2.5 ±1.1) × 10–3 (1999); for Morteratschgletscher, Switzerland, Ch = (2.1 ±0.55) × 10–3 (1998); and for West Greenland, Ch = (2.0 ±0.52) × 10–3 (1998-2000). It is found that the coefficient can be determined to within 26% uncertainty under the following conditions: all terms in the energy balance are measured, there is no differential melt on the glacier surface, the melt curves are fitted when the entire snow layer has melted, and the measurement period is several weeks.

scholarly journals Energy-balance model validation on the top of Kilimanjaro, Tanzania, using eddy covariance data

2007 ◽  
Vol 46 ◽  
pp. 227-233 ◽  
Author(s):  
Nicolas J. Cullen ◽  
Thomas Mölg ◽  
Georg Kaser ◽  
Konrad Steffen ◽  
Douglas R. Hardy
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Longwave Radiation ◽  
Heat Fluxes ◽  
Balance Model ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes ◽  
Roughness Lengths ◽  
Order Of Magnitude ◽  
Important Input

AbstractEddy covariance data collected over a horizontal surface on the largest ice body on Kilimanjaro, Tanzania, over 26–29 July 2005 were used to assess the uncertainty of calculating sublimation with a surface energy balance (SEB) model. Data required for input to the SEB model were obtained from an existing automatic weather station. Surface temperatures that were solved iteratively by the SEB model were used to compute emitted longwave radiation, turbulent heat fluxes using the aerodynamic bulk method and the subsurface heat flux. Roughness lengths for momentum and temperature, which were found to be the most important input parameters controlling the magnitude of modelled (bulk method) turbulent heat fluxes, were obtained using eddy covariance data. The roughness length for momentum was estimated to be 1.7×10–3 m, while the length for temperature was one order of magnitude smaller. Modelled sensible and latent heat fluxes (bulk method) compared well to eddy covariance data, with root-mean-square differences between 3.1 and 4.8 Wm–2 for both turbulent heat fluxes. Modelled sublimation accounted for about 90% of observed ablation, confirming that mass loss by melting is much less important than sublimation on the horizontal surfaces of the remaining plateau glaciers on Kilimanjaro.

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