scholarly journals Modeled Contrast in the Response of the Surface Energy Balance to Heat Waves for Forest and Grassland

2014 ◽  
Vol 15 (3) ◽  
pp. 973-989 ◽  
Author(s):  
Lennert B. Stap ◽  
Bart J. J. M. van den Hurk ◽  
Chiel C. van Heerwaarden ◽  
Roel A. J. Neggers
Keyword(s):  
Boundary Layer ◽  
Surface Energy ◽  
Heat Wave ◽  
Heat Waves ◽  
Surface Model ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Wave Conditions ◽  
The Difference ◽  
The Impact

Abstract Observations have shown that differences in surface energy fluxes over grasslands and forests are amplified during heat waves. The role of land–atmosphere feedbacks in this process is still uncertain. In this study, a single-column model (SCM) is used to investigate the difference between forest and grassland in their energy response to heat waves. Three simulations for the period 2005–11 were carried out: a control run using vegetation characteristics for Cabauw (the Netherlands), a run where the vegetation is changed to 100% forest, and a run with 100% short grass as vegetation. A surface evaporation tendency equation is used to analyze the impact of the land–atmosphere feedbacks on evapotranspiration and sensible heat release under normal summer and heat wave conditions with excessive shortwave radiation. Land–atmosphere feedbacks modify the contrast in surface energy fluxes between forest and grass, particularly during heat wave conditions. The surface resistance feedback has the largest positive impact, while boundary layer feedbacks generally tend to reduce the contrast. Overall, forests give higher air temperatures and drier atmospheres during heat waves. In offline land surface model simulations, the difference between forest and grassland during heat waves cannot be diagnosed adequately owing to the absence of boundary layer feedbacks.

Using Spatial Eddy Covariance to Investigate Energy Balance Closure over a Heterogeneous Ecosystem

2020 ◽  
Author(s):  
Brian Butterworth ◽  
Ankur Desai ◽  
Sreenath Paleri ◽  
Stefan Metzger ◽  
David Durden ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Eddy Covariance ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Land Surface Heterogeneity

<p>Land surface heterogeneity influences patterns of sensible and latent heat flux, which in turn affect processes in the atmospheric boundary layer. However, gridded atmospheric models often fail to incorporate the influence of land surface heterogeneity due to differences between the temporal and spatial scales of models compared to the local, sub-grid processes. Improving models requires the scaling of surface flux measurements; a process made difficult by the fact that surface measurements usually find an imbalance in the energy budget.</p><p>The Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD19) was an observational experiment designed to investigate how the atmospheric boundary layer responds to scales of spatial heterogeneity in surface-atmosphere heat and water exchanges. The campaign was conducted from June – October 2019, measuring surface energy fluxes over a heterogeneous forest ecosystem as fluxes transitioned from latent heat-dominated summer through sensible heat-dominated fall. Observations were made by ground, airborne, and satellite platforms within the 10 x 10 km study region, which was chosen to match the scale of a typical model grid cell. The spatial distribution of energy fluxes was observed by an array of 20 eddy covariance towers and a low-flying aircraft. Mesoscale atmospheric properties were measured by a suite of LiDAR and sounding instruments, measuring winds, water vapor, temperature, and boundary layer development. Plant phenology was measured in-situ and mapped remotely using hyperspectral imaging.</p><p>The dense set of multi-scale observations of land-atmosphere exchange collected during the CHEESEHEAD field campaign permits combining the spatial and temporal distribution of energy fluxes with mesoscale surface and atmospheric properties. This provides an unprecedented data foundation to evaluate theoretical explanations of energy balance non-closure, as well as to evaluate methods for scaling surface energy fluxes for improved model-data comparison. Here we show how fluxes calculated using a spatial eddy covariance technique across the 20-tower network compare to those of standard temporal eddy covariance fluxes in order to characterize of the spatial representativeness of single tower eddy covariance measurements. Additionally, we show how spatial EC fluxes can be used to better understand the energy balance over heterogeneous ecosystems.</p>

scholarly journals Relationships between Recent Pan-Arctic Snow Cover and Hydroclimate Trends

2013 ◽  
Vol 26 (6) ◽  
pp. 2048-2064 ◽  
Author(s):  
Xiaogang Shi ◽  
Stephen J. Déry ◽  
Pavel Ya. Groisman ◽  
Dennis P. Lettenmaier
Keyword(s):  
Surface Energy ◽  
Snow Cover ◽  
North American ◽  
Maximum Temperature ◽  
Daily Minimum Temperature ◽  
Daily Maximum Temperature ◽  
Surface Model ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Snow Cover Extent

Abstract Using the Variable Infiltration Capacity (VIC) land surface model forced with gridded climatic observations, the authors reproduce spatial and temporal variations of snow cover extent (SCE) reported by the National Oceanic and Atmospheric Administration (NOAA) Northern Hemisphere weekly satellite SCE data. Both observed and modeled North American and Eurasian snow cover in the pan-Arctic have statistically significant negative trends from April through June over the period 1972–2006. To diagnose the causes of the pan-Arctic SCE recession, the authors identify the role of surface energy fluxes generated in VIC and assess the relationships between 15 hydroclimatic indicators and NOAA SCE observations over each snow-covered sensitivity zone (SCSZ) for both North America and Eurasia. The authors find that surface net radiation (SNR) provides the primary energy source and sensible heat (SH) plays a secondary role in observed changes of SCE. As compared with SNR and SH, latent heat has only a minor influence on snow cover changes. In addition, these changes in surface energy fluxes resulting in the pan-Arctic snow cover recession are mainly driven by statistically significant decreases in snow surface albedo and increased air temperatures (surface air temperature, daily maximum temperature, and daily minimum temperature), as well as statistically significant increased atmospheric water vapor pressure. Contributions of other hydroclimate variables that the authors analyzed (downward shortwave radiation, precipitation, diurnal temperature range, wind speed, and cloud cover) are not significant for observed SCE changes in either the North American or Eurasian SCSZs.

scholarly journals Modelling seasonal and spatial variations in the surface energy balance of Haut Glacier d’Arolla, Switzerland

2000 ◽  
Vol 31 ◽  
pp. 53-62 ◽  
Author(s):  
Ben W. Brock ◽  
Ian C. Willis ◽  
Martin J. Sharp ◽  
Neil S. Arnold
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Roughness Length ◽  
Meteorological Conditions ◽  
Aerodynamic Roughness Length ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Aerodynamic Roughness ◽  
The Impact

AbstractThe impact of spatial and temporal variations in the surface albedo and aerodynamic roughness length on the surface energy balance of Haut Glacier d’Arolla, Switzerland, was examined using a semi-distributed surface energy-balance model (Arnold and others, 1996). The model was updated to incorporate the glacier-wide effects of albedo and aerodynamic roughness-length variations using parameterizations following Brock (1997). After the model’s performance was validated, the glacier-wide patterns of the net shortwave, turbulent and melt energy fluxes were examined on four days, representative of surface conditions in late May, June July and August. In the model, meteorological conditions were held constant on each day in order that the impact of albedo and aerodynamic roughness-length variations could be assessed independently. A late-summer snowfall event was also simulated. Albedo and aerodynamic roughness-length variations, particularly those associated with the migration of the transient snowline and the decay of the winter snowpack, were found to exert a strong influence on the magnitude of the surface energy fluxes The importance of meteorological conditions in suppressing the surface energy fluxes and melt rate following a fresh snowfall was highlighted

scholarly journals Distinguishing between early- and late-covering crops in the land surface model Noah-MP: impact on simulated surface energy fluxes and temperature

2020 ◽  
Vol 17 (10) ◽  
pp. 2791-2805
Author(s):  
Kristina Bohm ◽  
Joachim Ingwersen ◽  
Josipa Milovac ◽  
Thilo Streck
Keyword(s):  
Land Use ◽  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Land Surface Model ◽  
Surface Model ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract. Land surface models are essential parts of climate and weather models. The widely used Noah-MP land surface model requires information on the leaf area index (LAI) and green vegetation fraction (GVF) as key inputs of its evapotranspiration scheme. The model aggregates all agricultural areas into a land use class termed “cropland and pasture”. In a previous study we showed that, on a regional scale, the GVF has a bimodal distribution formed by two crop groups differing in phenology and growth dynamics: early-covering crops (ECC; e.g., winter wheat, winter rapeseed, winter barley) and late-covering crops (LCC; e.g., corn, silage maize, sugar beet). That result can be generalized for central Europe. The present study quantifies the effect of splitting the land use class cropland and pasture of Noah-MP into ECC and LCC on surface energy fluxes and temperature. We further studied the influence of increasing the LCC share, which in the study area (the Kraichgau region, southwest Germany) is mainly the result of heavily subsidized biomass production, on energy partitioning at the land surface. We used the GVF dynamics derived from high-resolution (5 m × 5 m) RapidEye satellite data and measured LAI data for the simulations. Our results confirm that the GVF and LAI strongly influence the partitioning of surface energy fluxes, resulting in pronounced differences between simulations of ECC and LCC. Splitting up the generic crop into ECC and LCC had the strongest effect on land surface exchange processes in July–August. During this period, ECC are at the senescence growth stage or already harvested, while LCC have a well-developed ground-covering canopy. The generic crop resulted in humid bias, i.e., an increase in evapotranspiration by +0.5 mm d−1 (latent heat flux is 1.3 MJ m−2 d−1), decrease in sensible heat flux (H) by 1.2 MJ m−2  d−1 and decrease in surface temperature by −1 ∘C. The bias increased as the shares of ECC and LCC became similar. The observed differences will impact the simulations of processes in the planetary boundary layer. Increasing the LCC share from 28 % to 38 % in the Kraichgau region led to a decrease in latent heat flux (LE) and a heating up of the land surface in the early growing season. Over the second part of the season, LE increased and the land surface cooled down by up to 1 ∘C.

scholarly journals CONNECTING LAND-ATMOSPHERE INTERACTIONS TO SURFACE HETEROGENEITY IN CHEESEHEAD19

2020 ◽  
pp. 1-71
Author(s):  
BRIAN J. BUTTERWORTH ◽  
ANKUR R. DESAI ◽  
STEFAN METZGER ◽  
PHILIP A. TOWNSEND ◽  
MARK D. SCHWARTZ ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Spatial Heterogeneity ◽  
Regional Scale ◽  
Surface Heterogeneity ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

CAPSULE SUMMARYA regional-scale observational experiment designed to address how the atmospheric boundary layer responds to spatial heterogeneity in surface energy fluxes.

scholarly journals Analysis of wind power under heat wave conditions in southern Europe

2021 ◽  
Author(s):  
María Ofelia Molina ◽  
Enrique Sánchez ◽  
Claudia Gutiérrez ◽  
María Ortega
Keyword(s):  
Wind Energy ◽  
Wind Power ◽  
Heat Wave ◽  
Energy Supply ◽  
Energy Demand ◽  
Energy Production ◽  
Heat Waves ◽  
Maximum Temperature ◽  
Wave Conditions ◽  
The Impact

<p>In recent years, renewable energy is gaining importance in the energy mix, increasing the dependence of the energy system on the weather. Studies have been mainly focused on atmospheric patterns related to wind energy production in winter, as wind resource in Europe is higher for this season, but also because it is when there is a larger and more stable heating demand in Europe as a whole. However, it can be seen that summer energy demand can be as high as in winter in southern European countries, especially on heat wave days (calculated from E-OBS maximum temperature observations). Therefore, the objective of this work is to study the effect of heat waves on wind power generation. Summer climate conditions present reduced wind values, so a potential increase in energy demand due to heat wave conditions could compromise the total energy supply. We analyse the main atmospheric patterns in summer (1989-2019) and how these are related to changes in wind energy production. The relationship between weather regimes and wind energy is examined using an energy model from ERA5 wind speed data at 100 m. Results show a demand increase in heat wave days and different responses in wind power, depending on the country and weather regime studied. The impact of extreme climate events, such as heat waves, on wind energy in conditions of high energy demand, should be considered in the energy supply strategic planning and control to minimize the impact of these events on an electricity system with high penetration of renewables.</p>

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