Dew Formation, Eddy-Correlation Latent Heat Fluxes, and the Surface Energy Imbalance at Cabauw During Stable Conditions

Abstract. Flux tower sites and data are in great demand to provide essential terrestrial climate, water and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based earth observation and monitoring efforts, such as for example assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. Surface energy budget methods for ET estimation rely to a large extend on the basic assumption of a surface energy balance closure, assuming the full conversion of net solar radiation reaching the land surface into soil heat conduction and turbulent fluxes, i.e. the sensible (or convection) and latent heat components of the energy balance. Evapotranspiration is the conversion of the latent heat exchange fraction of the balance. In this paper, the Skukuza flux tower data were analysed in order to verify their use for validation of satellite–based evapotranspiration methods, under development in South Africa.Data series from 2000 until 2014 were used in the analysis. The energy balance ratio (EBR) concept, defined as the ratio between the sum of the turbulent convective and latent heat fluxes and radiation minus soil heat was used. At first typical diurnal patterns of EB partitioning were derived for four different seasons, well illustrating how this savannah-type biome responses to the weather conditions. Also the particular behaviour of the EB components during sunrise and sunset conditions, being important but usually neglected periods of energy transitions and inversions were noted and analysed. Annual estimates of the surface energy balance and its components were generated, including an evaluation of the balance closure. The seasonal variations were also investigated as well as the impact of nocturnal observations on the overall EB behaviour.

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High resolution land surface fluxes from satellite data (HOLAPS v1.0): evaluation and uncertainty assessment

Geoscientific Model Development Discussions ◽

10.5194/gmdd-8-10783-2015 ◽

2015 ◽

Vol 8 (12) ◽

pp. 10783-10841

Author(s):

A. Loew ◽

J. Peng ◽

M. Borsche

Keyword(s):

Surface Energy ◽

Latent Heat ◽

Satellite Data ◽

Land Surface ◽

Global Solar Radiation ◽

Surface Fluxes ◽

Heat Fluxes ◽

Surface Radiation ◽

Water Fluxes ◽

Essential Components

Abstract. Surface water and energy fluxes are essential components of the Earth system. Surface latent heat fluxes provide major energy input to the atmosphere. Despite the importance of these fluxes, state-of-the-art datasets of surface energy and water fluxes largely differ. The present paper introduces a new framework for the estimation of surface energy and water fluxes at the land surface, which allows for temporally and spatially high resolved flux estimates at the global scale (HOLAPS). The framework maximizes the usage of existing long-term satellite data records and ensures internally consistent estimates of the surface radiation and water fluxes. The manuscript introduces the technical details of the developed framework and provides results of a comprehensive sensitivity and evaluation study. Overall the results indicate very good agreement with in situ observations when compared against 49 FLUXNET stations worldwide. Largest uncertainties of latent heat flux and net radiation were found to result from uncertainties in the global solar radiation flux obtained from satellite data products.

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Implied Ocean Heat Transports in the Standard and Superparameterized Community Atmospheric Models

Journal of Climate ◽

10.1175/2009jcli2987.1 ◽

2010 ◽

Vol 23 (7) ◽

pp. 1908-1928 ◽

Cited By ~ 10

Author(s):

Charlotte A. DeMott ◽

David A. Randall ◽

Marat Khairoutdinov

Keyword(s):

Surface Energy ◽

Latent Heat ◽

Cloud Microphysics ◽

Heat Fluxes ◽

Shortwave Radiation ◽

Trade Wind ◽

Modeling Framework ◽

Marine Stratocumulus ◽

Stratocumulus Clouds ◽

Ice Water

Abstract Implied ocean heat transport (To) based on net surface energy budgets is computed for two versions of the Community Atmospheric Model (CAM, version 3.0) general circulation model (GCM). The first version is the standard CAM with parameterized convection. The second is the multiscale modeling framework (MMF), in which parameterized convection is replaced with a two-dimensional cloud-resolving model in each GCM grid column. Although global-mean net surface energy totals are similar for both models, differences in the geographic distributions of the component errors lead to distinctly different To for each model, with CAM’s To generally agreeing with observationally based To estimates, and the MMF’s To producing northward transport at all latitudes north of ∼50°S. Analysis of component error sources in the To calculation identifies needed improvements in the MMF. Net surface shortwave radiation and latent heat fluxes over the oceans are the primary causes of To errors in the MMF. Surface shortwave radiation biases in the MMF are associated with liquid and/or ice water content biases in tropical and extratropical convection and a deficit of marine stratocumulus clouds. It is expected that tropical ice water contents in the MMF can be made more realistic via improvements to the cloud microphysics parameterization. MMF marine stratocumulus clouds are overly sensitive to low-level relative humidity and form only with nearly saturated conditions and a shallow boundary layer. Latent heat flux errors in the MMF are amplifications of those found in the CAM and are concentrated in the trade wind regime and the Asian monsoon region and the adjacent western Pacific Ocean. Potential improvements to To are estimated by replacing either simulated net surface shortwave or latent heat fluxes with those from observations and recomputing To. When observed shortwave fluxes are used, both CAM and MMF produce greatly improved To curves for both hemispheres. When To is computed using observed latent heat fluxes, CAM To degrades slightly and MMF To improves, especially in the sign of Southern Hemisphere transport.

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Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

Earth Interactions ◽

10.1175/2013ei000523.1 ◽

2013 ◽

Vol 17 (14) ◽

pp. 1-22 ◽

Cited By ~ 27

Author(s):

Allison L. Steiner ◽

Dori Mermelstein ◽

Susan J. Cheng ◽

Tracy E. Twine ◽

Andrew Oliphant

Keyword(s):

Heat Flux ◽

Surface Energy ◽

Latent Heat ◽

Atmospheric Aerosols ◽

Sensible Heat Flux ◽

Surface Fluxes ◽

Heat Fluxes ◽

Surface Energy Budget ◽

Environmental Drivers ◽

Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

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The surface energy balance of a polygonal tundra site in northern Siberia – Part 1: Spring to fall

The Cryosphere ◽

10.5194/tc-5-151-2011 ◽

2011 ◽

Vol 5 (1) ◽

pp. 151-171 ◽

Cited By ~ 60

Author(s):

M. Langer ◽

S. Westermann ◽

S. Muster ◽

K. Piel ◽

J. Boike

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Surface Energy ◽

Snow Cover ◽

Latent Heat ◽

Latent Heat Flux ◽

Surface Energy Balance ◽

Heat Fluxes ◽

Net Radiation ◽

Ground Heat Flux

Abstract. In this article, we present a study on the surface energy balance of a polygonal tundra landscape in northeast Siberia. The study was performed during half-year periods from April to September in each of 2007 and 2008. The surface energy balance is obtained from independent measurements of the net radiation, the turbulent heat fluxes, and the ground heat flux at several sites. Short-wave radiation is the dominant factor controlling the magnitude of all the other components of the surface energy balance during the entire observation period. About 50% of the available net radiation is consumed by the latent heat flux, while the sensible and the ground heat flux are each around 20 to 30%. The ground heat flux is mainly consumed by active layer thawing. About 60% of the energy storage in the ground is attributed to the phase change of soil water. The remainder is used for soil warming down to a depth of 15 m. In particular, the controlling factors for the surface energy partitioning are snow cover, cloud cover, and the temperature gradient in the soil. The thin snow cover melts within a few days, during which the equivalent of about 20% of the snow-water evaporates or sublimates. Surface temperature differences of the heterogeneous landscape indicate spatial variabilities of sensible and latent heat fluxes, which are verified by measurements. However, spatial differences in the partitioning between sensible and latent heat flux are only measured during conditions of high radiative forcing, which only occur occasionally.

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Urban Energy Balance Obtained from the Comprehensive Outdoor Scale Model Experiment. Part I: Basic Features of the Surface Energy Balance

Journal of Applied Meteorology and Climatology ◽

10.1175/2010jamc1992.1 ◽

2010 ◽

Vol 49 (7) ◽

pp. 1341-1359 ◽

Cited By ~ 38

Author(s):

Toru Kawai ◽

Manabu Kanda

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Surface Energy Balance ◽

Heat Storage ◽

Heat Fluxes ◽

Eddy Correlation ◽

Scale Model ◽

Surface Geometry ◽

Urban Energy Balance ◽

Basic Features

Abstract The objective of this study is to examine the basic features of the surface energy balance (SEB) using the data obtained from the Comprehensive Outdoor Scale Model (COSMO). COSMO is an idealized miniature city that has no vegetation, no human activity, and no heterogeneity of the surface geometry. The basic features of the SEB such as energy balance closure, the ensemble mean of the diurnal variation of the energy balance, and the daytime and daily statistics of the energy balance were investigated. The following were the main findings of the study: 1) A surface energy imbalance was observed. The sum of sensible and latent heat fluxes estimated by the eddy correlation method underestimated the available energy by 1% during the daytime and by 44% during the night. 2) Large heat storage in the daytime and small radiative cooling at night sustained positive sensible heat fluxes throughout the night in all seasons and in all sunshine conditions. 3) The daytime ratio of heat storage ΔQS to net radiation Q*, ΔQS/Q*, depended on the friction velocity u* and decreased with increasing u*. 4) The values of ΔQS/Q* tended to be larger in winter than in summer. The annual averaged value of this ratio was approximately 0.6. 5) The large volumetric heat capacity of the surface materials and the resulting large energetic hysteresis produced nonzero total daily values of heat storage. The total daily values of heat storage largely depended on the weather (i.e., sunshine condition and with or without rainfall) and showed positive and negative values on clear-sky days and rainy days, respectively.

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A Comparison between Simulated and Observed Surface Energy Balance at the Svalbard Archipelago

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-14-0080.1 ◽

2015 ◽

Vol 54 (5) ◽

pp. 1102-1119 ◽

Cited By ~ 9

Author(s):

Kjetil Schanke Aas ◽

Terje Koren Berntsen ◽

Julia Boike ◽

Bernd Etzelmüller ◽

Jón Egill Kristjánsson ◽

...

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Latent Heat ◽

Optical Thickness ◽

Surface Energy Balance ◽

Heat Fluxes ◽

Energy Fluxes ◽

Svalbard Archipelago ◽

Cloud Optical Thickness ◽

The Individual

AbstractThe surface energy balance at the Svalbard Archipelago has been simulated at high resolution with the Weather Research and Forecasting Model and compared with measurements of the individual energy fluxes from a tundra site near Ny-Ålesund (located north of Norway), as well as other near-surface measurements across the region. For surface air temperature, a good agreement between model and observations was found at all locations. High correlations were also found for daily averaged surface energy fluxes within the different seasons at the main site. The four radiation components showed correlations above 0.5 in all seasons (mostly above 0.9), whereas correlations between 0.3 and 0.8 were found for the sensible and latent heat fluxes. Underestimation of cloud cover and cloud optical thickness led to seasonal biases in incoming shortwave and longwave radiation of up to 30%. During summer, this was mainly a result of distinct days on which the model erroneously simulated cloud-free conditions, whereas the incoming radiation biases appeared to be more related to underestimation of cloud optical thickness during winter. The model overestimated both sensible and latent heat fluxes in most seasons. The model also initially overestimated the average Bowen ratio during summer by a factor of 6, but this bias was greatly reduced with two physically based model modifications that are related to frozen-ground hydrology. The seasonally averaged ground/snow heat flux was mostly in agreement with observations but showed too little short-time variability in the presence of thick snow. Overall, the model reproduced average temperatures well but overestimated diurnal cycles and showed considerable biases in the individual energy fluxes on seasonal and shorter time scales.

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Eddy correlation measurements of CO2, latent heat, and sensible heat fluxes over a crop surface

Boundary-Layer Meteorology ◽

10.1007/bf00119792 ◽

1984 ◽

Vol 29 (3) ◽

pp. 263-272 ◽

Cited By ~ 61

Author(s):

Dean E. Anderson ◽

Shashi B. Verma ◽

Norman J. Rosenberg

Keyword(s):

Latent Heat ◽

Heat Fluxes ◽

Eddy Correlation ◽

Sensible Heat

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Permafrost and surface energy balance of a polygonal tundra site in northern Siberia – Part 1: Spring to fall

The Cryosphere Discussions ◽

10.5194/tcd-4-901-2010 ◽

2010 ◽

Vol 4 (3) ◽

pp. 901-947 ◽

Cited By ~ 1

Author(s):

M. Langer ◽

S. Westermann ◽

S. Muster ◽

K. Piel ◽

J. Boike

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Surface Energy ◽

Latent Heat ◽

Latent Heat Flux ◽

Surface Energy Balance ◽

Heat Fluxes ◽

Dominant Factor ◽

Wave Radiation ◽

Ground Heat Flux

Abstract. Permafrost thawing is essentially determined by the surface energy balance, which potentially triggers the activation of a massive carbon source, if previously frozen organic soils are exposed to microbial decomposition. In this article, we present the first part of a comprehensive annual surface energy balance study performed at a polygonal tundra landscape in northeast Siberia, realized between spring 2007 and winter 2009. This part of the study focuses on the half year period from April to September 2007–2008, during which the surface energy balance is obtained from independent measurements of the radiation budget, the turbulent heat fluxes and the ground heat flux at several sites. The short-wave radiation is the dominant factor in the surface energy balance during the entire observation period. About 50% of the available net radiation is consumed by latent heat flux, while the sensible and the ground heat flux are both on the order of 20 to 30%. The ground heat flux is mainly consumed by active layer thawing, where 60% of soil energy storage are attributed to. The remainder is used for soil warming down to a depth of 15 m. The controlling factors for the surface energy partitioning are in particular the snow cover, the cloud cover and the soil temperature gradient. Significant surface temperature differences of the heterogeneous landscape indicate spatial variabilities of sensible and latent heat fluxes, which are verified by measurements at different locations. However, differences in the partition between sensible and latent heat flux for the different sites only exist during conditions of high radiative forcing, which only occur occasionally.

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Surface-to-Atmosphere Exchange in a River Valley Environment

Journal of Applied Meteorology and Climatology ◽

10.1175/jam2517.1 ◽

2007 ◽

Vol 46 (8) ◽

pp. 1169-1181 ◽

Cited By ~ 10

Author(s):

Otávio C. Acevedo ◽

Osvaldo L. L. Moraes ◽

Rodrigo da Silva ◽

Vagner Anabor ◽

Daniel P. Bittencourt ◽

...

Keyword(s):

Latent Heat ◽

Heat Fluxes ◽

Eddy Correlation ◽

Mountainous Area ◽

Sensible Heat ◽

Small Magnitude ◽

Vertical Fluxes ◽

Air Temperatures ◽

The Mean ◽

Increasing Temperature

Abstract Observations of the turbulent exchange between a river surface and the atmosphere in a mountainous area in southern Brazil are presented and discussed. A micrometeorological tower was installed directly above the surface of a 60-m-wide river. This paper describes the observed turbulent fluxes over 12 days of observations at this site. Eddy correlation sensible and latent heat fluxes are directed toward the river during daytime and from the river at night, and they are controlled by differences between water and air temperatures. The magnitude of the vertical fluxes between the river and the atmosphere increases during daytime with increasing temperature gradient up to a threshold, beyond which the increasing stability starts to dampen the fluxes. Water and air temperatures show very little variations across the width of the river, indicating that the measurements taken at one margin may be representative of the mean river exchange. Local scalar budgets show that daytime warming and moistening rates above the river are controlled by local transport from the riverbanks. The main vertical fluxes have a very small magnitude: 0.8 W m−2 for sensible heat and 1.1 W m−2 for latent heat. Events of very large sensible heat fluxes from the river to the atmosphere and very large latent heat fluxes from the atmosphere to the river happened on 3 days, following nights with a very deep fog layer in the valley. These events represented the passage of a warm and dry air mass down the river. A process to explain the occurrence of these large fluxes is suggested that is associated with differential fog dissipation over the valley.

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