Impact of above and below canopy air temperatures in simulation of sub-canopy longwave radiation in snow-covered boreal forests

2021 ◽  
Author(s):  
Nick Rutter ◽  
Richard Essery
Keyword(s):  
Forest Canopy ◽  
Similarity Theory ◽  
Longwave Radiation ◽  
Snow Surface ◽  
Night Time ◽  
Radiation Emission ◽  
Air Temperatures ◽  
Stable Conditions ◽  
Wide Range ◽  
The Impact

<p>Above canopy air temperatures, as simulated prognostic variables in earth system models or as driving data in snow-physics models, are used as a basis to calculate energy transfers through forest canopies and down to the snow surface. Consequently, simulations of absorption of solar radiation, emission of longwave radiation and coupling between canopy and air temperatures become critical. Parts of the forest canopy, especially the shaded downward-facing elements, are often in equilibrium with sub-canopy air temperatures.</p><p>Measurements of sub-canopy incoming longwave radiation, air temperatures, and forest canopy structure were made in a snow-covered boreal forest, March through April 2012 in Sodankylä, Finland. Accurate simulations of longwave radiation to the snow surface were enabled by using measured sub-canopy air temperatures as a proxy for downward-facing forest canopy temperatures. However, there was a notable decoupling of measured above and below forest canopy air temperatures in stable conditions (air temperatures warmer above the canopy than below), which was enhanced during night-time. Hence, here we present results of an experiment using a multi-physics snow model including a forest canopy (FSM2.1.1) to investigate the impact of above and below canopy air temperature decoupling on simulations of sub-canopy longwave radiation. Simulations compare the use of 1- and 2-layer canopy models, and application of Monin–Obukhov similarity theory across a wide range of forest densities.</p>

scholarly journals The influence of the forest on night-time snow surface temperature

2001 ◽  
Vol 32 ◽  
pp. 217-222 ◽  
Author(s):  
Peter Höller
Keyword(s):  
Surface Temperature ◽  
Open Field ◽  
Air Temperature ◽  
Forest Canopy ◽  
Small Range ◽  
Snow Surface ◽  
Net Radiation ◽  
Night Time ◽  
Near Surface ◽  
Snow Surface Temperature

AbstractSnow surface temperature (Ts) plays an important role in the formation of surface hoar or near-surface faceted crystals The goal of this study was to obtain detailed information on Ts in different forest stands nelr the timberline. The investigations were conducted during clear nights and showed that the snow surface temperature is influenced very strongly by the forest canopy. While the air temperature was very similar on the different experimental sites, Ts was higher in the forest than in the open field; on the south-facing slope the difference between the forest and the open field was 3–4.5°C, and on the north-facing slope approximately 3–7°C. Taking into account that εair is 0.7 and εtree is 0.94, the incoming radiation (I ↓) for the different experimental sites was calculated by the equation of Brunt (the canopy density was estimated using photographs taken with an 8 mm fish-eye). To calculate Ts, air temperature and averaged values of the net radiation (because the net radiation (I) has only a small range of variation during clear nights) were used. The results show that the calculated values were higher than the measured values (by approximately 2°C). However, a better correlation was found by using lower values of the emissivity (εair0.67 and εtree0.91).

An Investigation of the Stability Dependence of SST-Induced Vertical Mixing over the Ocean in the Operational Met Office Model

2017 ◽  
Vol 30 (1) ◽  
pp. 91-107 ◽  
Author(s):  
Qingtao Song ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen ◽  
Andrew R. Brown
Keyword(s):  
Wind Speed ◽  
Weather Prediction ◽  
Surface Wind ◽  
Vertical Mixing ◽  
Surface Wind Speed ◽  
Satellite Observations ◽  
Sea Surface ◽  
Stable Conditions ◽  
Wide Range ◽  
The Impact

This study presents an assessment of the impact of a March 2006 change in the Met Office operational global numerical weather prediction model through the introduction of a nonlocal momentum mixing scheme. From comparisons with satellite observations of surface wind speed and sea surface temperature (SST), it is concluded that the new parameterization had a relatively minor impact on SST-induced changes in sea surface wind speed in the Met Office model in the September and October 2007 monthly averages over the Agulhas Return Current region considered here. The performance of the new parameterization of vertical mixing was evaluated near the surface layer and further through comparisons with results obtained using a wide range of sensitivity of mixing parameterization to stability in the Weather Research and Forecasting (WRF) Model, which is easily adapted to such sensitivity studies. While the new parameterization of vertical mixing improves the Met Office model response to SST in highly unstable (convective) conditions, it is concluded that significantly enhanced vertical mixing in the neutral to moderately unstable conditions (nondimensional stability [Formula: see text] between 0 and −2) typically found over the ocean is required in order for the model surface wind response to SST to match the satellite observations. Likewise, the reduced mixing in stable conditions in the new parameterization is also relatively small; for the range of the gradient Richardson number typically found over the ocean, the mixing was reduced by a maximum of only 10%, which is too small by more than an order of magnitude to be consistent with the satellite observations.

scholarly journals Urban Lighting Research Transdisciplinary Framework—A Collaborative Process with Lighting Professionals

2021 ◽  
Vol 18 (2) ◽  
pp. 624
Author(s):  
Catherine Pérez Vega ◽  
Karolina M. Zielinska-Dabkowska ◽  
Franz Hölker
Keyword(s):  
Urban Environments ◽  
Practice Research ◽  
Night Time ◽  
Research Knowledge ◽  
Research Production ◽  
Wide Range ◽  
Terrestrial Habitats ◽  
Dual Perspective ◽  
Micro Organisms ◽  
The Impact

Over the past decades, lighting professionals have influenced the experience of the night by brightly illuminating streets, buildings, skylines, and landscapes 24/7. When this became the accepted norm, a dual perspective on night-time was shaped and the visual enjoyment of visitors after dusk was prioritized over natural nightscapes (nocturnal landscapes). During this time, researchers of artificial light at night (ALAN) observed and reported a gradual increase in unnatural brightness and a shift in color of the night-time environment. As a consequence, ALAN has been identified as a relevant pollutant of aquatic and terrestrial habitats, and an environmental stressor, which may adversely affect a wide range of organisms, from micro-organisms to humans. Unfortunately, lighting professionals and ALAN researchers usually attempt to solve today’s sustainable urban lighting problems distinctive to their fields of study, without a dialogue between research and practice. Therefore, in order to translate research knowledge as an applicable solution for the lighting practice and to minimize the impact on the environment, a collaborative framework involving a transdisciplinary process with lighting professionals is crucial to potentially bring the practice, research, production, decision-making, and planning closer to each other. This paper presents a framework to help reduce the existing gap of knowledge, because appropriate lighting applications depend upon it. Access to less light polluted nightscapes in urban environments is just as important as access to unpolluted water, food, and air. This call for action towards sustainable urban lighting should be included in future lighting policies to solve the urgent environmental and health challenges facing our world.

scholarly journals Local flux-profile relationships of wind speed and temperature in a canopy layer in atmospheric stable conditions

2010 ◽  
Vol 7 (3) ◽  
pp. 4505-4537 ◽  
Author(s):  
G. Zhang ◽  
M. Y. Leclerc ◽  
A. Karipot
Keyword(s):  
Richardson Number ◽  
Forest Canopy ◽  
Similarity Theory ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Canopy Layer ◽  
Stability Parameters ◽  
Stable Conditions ◽  
Flux Profile ◽  
The Relationship

Abstract. The particularities of the physics of the canopy layer pose challenges to the determination and use of traditional universal functions so helpful in the atmospheric surface layer. Progress toward "universal-like functions" such as those provided by Monin-Obukhov similarity theory for the canopy layer has been modest. One of the challenges lies in that the assumptions underlying Monin-Obukhov similarity theory do not hold within a canopy layer. This paper thus examines the local flux-profile relations for wind (φm) and for temperature (φh) using three different stability parameters, i.e., h/L(h) at tree top, local z/L(z), and local bulk Richardson number (Ri), within a tall forest canopy in nighttime stable (indicated by h/L(h)>0) conditions. Results suggest that the in-canopy φm can be described using the local Richardson number Ri. φm is found to increase linearly with Ri in the upper canopy layer for |Ri|<1. When local |Ri|>1, |φm| decreases with |Ri|, a result consistent for all levels of measurements within the canopy. When both local φh and local Ri are positive, i.e., local downward turbulent heat flux is consistent with local temperature gradient, local φh increases with local Ri when Ri<1 but does not change with Ri (or much more scattered) when Ri>1. The relationship between local φh and Ri disappears when counter-gradient heat transfer occurs in strongly stable conditions. A self-correlation analysis is used to examine the influence of self-correlation and the physical meaning of these relationships.

The Challenges of Turbocharger Matching for North American Freight Locomotives

2019 ◽  
Author(s):  
Thomas Lavertu ◽  
Matthew Hart ◽  
Christopher Homison ◽  
Preeti Vaidya
Keyword(s):  
North American ◽  
Engine Performance ◽  
Ambient Air ◽  
Ambient Conditions ◽  
Efficient Operation ◽  
Engine Efficiency ◽  
Air Temperatures ◽  
Wide Range ◽  
The Impact ◽  
Operating Points

Abstract Engine development is centered on developing a solution for best performance while meeting emissions and operational requirements. This will lead to a tradeoff between engine efficiency and emissions across a wide range of load and ambient operating points. Proper airflow to the engine through turbocharger matching is critical to ensure efficient operation and to meet emissions. This study addresses the challenges of turbocharger matching for vehicle advanced emissions control using a North American freight locomotive application as an example. The airflow trends in moving across the various operating points will be shown along with the impact on both the turbocharger and engine performance. First, the airflow trends across the locomotive load set points will be discussed along with the performance and emissions tradeoffs to meet required airflows. Results on the impact on turbocharger performance such as speed will be shown along with the engine efficiency and emissions implications. Next, the ambient operating requirements for a locomotive will be reviewed and the impact on turbocharger matching. Locomotives operate in a wide range of ambient conditions, including altitudes up to 3,050 meters and across ambient air temperatures ranging from −40 °C to well over 38 °C (including higher temperature operation). This thermal swing provides stress on the turbocharger to efficiently deliver the necessary airflow across all conditions. Trends in turbocharger performance will be reviewed and discussed across this range of ambient conditions. In addition, challenges unique to locomotive applications, such as unventilated tunnel operation and vibrational loading, will be reviewed. Finally, potential for advanced technologies such as variable geometry turbines and their applicability to locomotive operation will be discussed.

scholarly journals Spatially Continuous Characterization of Forest Canopy Structure and Subcanopy Irradiance Derived from Handheld Radiometer Surveys

2019 ◽  
Vol 20 (7) ◽  
pp. 1417-1433 ◽  
Author(s):  
Giulia Mazzotti ◽  
Johanna Malle ◽  
Sarah Barr ◽  
Tobias Jonas
Keyword(s):  
Radiative Transfer ◽  
Land Surface ◽  
Forest Canopy ◽  
Canopy Structure ◽  
Longwave Radiation ◽  
Shortwave Radiation ◽  
Reference Station ◽  
Small Scale ◽  
Wide Range

Abstract Small-scale variations in radiative transfer through forest canopies are strongly linked to canopy structural heterogeneity. To date, upscaling of radiative transfer parameterizations developed at the point scale is hampered by (i) poor representation of canopy structure variability and (ii) limited spatially explicit subcanopy irradiance data to assess the performance of radiative transfer schemes at typical resolutions of land surface models. This study presents a novel approach for efficient in situ characterization of canopy structure and subcanopy irradiance over large spatial extents. The method involves a handheld radiometer assembly mounted on a motorized gimbal developed for nonstationary continuous measurements of shortwave and longwave radiation along forest transects. In combination with radiation and temperature data from a stationary reference station, spatially resolved estimates of sky-view fraction, canopy transmissivity, and longwave enhancement could be obtained. Under favorable meteorological conditions, validation against sky-view fraction data from hemispherical photographs yielded an RMSE of 0.03 (i.e., 3%). Irradiance measurements under heterogeneous canopy cover revealed strong spatial coherence between longwave radiation enhancement, shortwave radiation attenuation, and sky-view fraction on overcast days. Under clear-sky conditions, however, sun flecks caused highly variable shortwave radiation transmissivity patterns. This study demonstrates the potential of handheld radiometer surveys to deliver valuable spatially distributed datasets of collocated canopy structure and subcanopy irradiance which can be used (i) as reference data for alternative approaches to derive canopy structure parameters, (ii) to improve modeling of subcanopy radiation across a wide range of canopy distributions, and (iii) to support respective model upscaling efforts.

scholarly journals Flexible Charging of Electric Vehicles: Results of a Large-Scale Smart Charging Demonstration

2021 ◽  
Vol 12 (2) ◽  
pp. 82
Author(s):  
Pieter C. Bons ◽  
Aymeric Buatois ◽  
Friso Schuring ◽  
Frank Geerts ◽  
Robert van den Hoed
Keyword(s):  
Large Scale ◽  
Peak Load ◽  
Real World Data ◽  
Night Time ◽  
Electricity Grid ◽  
Charging Station ◽  
Wide Range ◽  
Smart Charging ◽  
Charging Current ◽  
The Impact

Flexible charging can be applied to avoid peak loads on the electricity grid by curbing demand of electric vehicle chargers as well as matching charging power with availability of sustainable energy. This paper presents results of a large-scale demonstration project “Flexpower” where time-dependent charging profiles are applied to 432 public charging stations in the city of Amsterdam between November 2019 and March 2020. The charging current on Flexpower stations is reduced during household peak consumption hours (18:00–21:00), increased during the night-time, and dynamically linked to solar intensity levels during the day. The results show that the EV contribution to the grid peak load can be reduced by 1.2 kW per charging station with very limited user impact. The increased charging current during sunny conditions does not lead to a significantly higher energy transfer during the day because of lack of demand and technical limitations in the vehicles. A simulation model is presented based on empirical power measurements over a wide range of conditions combining the flexibility provided by simulations with the power of real-world data. The model was validated by comparing aggregated results to actual measurements and was used to evaluate the impact of different smart charging profiles in the Amsterdam context.

scholarly journals Quantifying the Impact of Light Pollution on Sea Turtle Nesting Using Ground-Based Imagery

2020 ◽  
Vol 12 (11) ◽  
pp. 1785
Author(s):  
James Vandersteen ◽  
Salit Kark ◽  
Karina Sorrell ◽  
Noam Levin
Keyword(s):  
Remote Sensing ◽  
Land Cover ◽  
Cloud Cover ◽  
Sea Turtle ◽  
Spatial And Temporal Variation ◽  
Light Pollution ◽  
Night Time ◽  
Wide Range ◽  
Remote Sensing Techniques ◽  
The Impact

Remote sensing of anthropogenic light has substantial potential to quantify light pollution levels and understand its impact on a wide range of taxa. Currently, the use of space-borne night-time sensors for measuring the actual light pollution that animals experience is limited. This is because most night-time satellite imagery and space-borne sensors measure the light that is emitted or reflected upwards, rather than horizontally, which is often the light that is primarily perceived by animals. Therefore, there is an important need for developing and testing ground-based remote sensing techniques and methods. In this study, we aimed to address this gap by examining the potential of ground photography to quantify the actual light pollution perceived by animals, using sea turtles as a case study. We conducted detailed ground measurements of night-time brightness around the coast of Heron Island, a coral cay in the southern Great Barrier Reef of Australia, and an important sea turtle rookery, using a calibrated DSLR Canon camera with an 8 mm fish-eye lens. The resulting hemispheric photographs were processed using the newly developed Sky Quality Camera (SQC) software to extract brightness metrics. Furthermore, we quantified the factors determining the spatial and temporal variation in night-time brightness as a function of environmental factors (e.g., moon light, cloud cover, and land cover) and anthropogenic features (e.g., artificial light sources and built-up areas). We found that over 80% of the variation in night-time brightness was explained by the percentage of the moon illuminated, moon altitude, as well as cloud cover. Anthropogenic and geographic factors (e.g., artificial lighting and the percentage of visible sky) were especially important in explaining the remaining variation in measured brightness under moonless conditions. Night-time brightness variables, land cover, and rock presence together explained over 60% of the variation in sea turtle nest locations along the coastline of Heron Island, with more nests found in areas of lower light pollution. The methods we developed enabled us to overcome the limitations of commonly used ground/space borne remote sensing techniques, which are not well suited for measuring the light pollution to which animals are exposed. The findings of this study demonstrate the applicability of ground-based remote sensing techniques in accurately and efficiently measuring night-time brightness to enhance our understanding of ecological light pollution.

scholarly journals Features of the generation of fast particles from microstructured targets irradiated by high intensity, picosecond laser pulses

2019 ◽  
Vol 37 (2) ◽  
pp. 176-183 ◽  
Author(s):  
M.V. Sedov ◽  
A.Ya. Faenov ◽  
A.A. Andreev ◽  
I.Yu. Skobelev ◽  
S.N. Ryazantsev ◽  
...  
Keyword(s):  
Front Surface ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Laser Target ◽  
Radiation Emission ◽  
Particle In Cell ◽  
Laser Absorption ◽  
Wide Range ◽  
Micro Structures ◽  
The Impact

AbstractThe use of targets with surface structures for laser-driven particle acceleration has potential to significantly boost the particle and radiation energies because of enhanced laser absorption. We investigate, via experiment and particle-in-cell simulations, the impact of micron-scale surface-structured targets on the spectrum of electrons and protons accelerated by a picosecond laser pulse at relativistic intensity. Our results show that, compared with flat-surfaced targets, structures on this scale give rise to a significant enhancement in particle and radiation emission over a wide range of laser–target interaction parameters. This is due to the longer plasma scale length when using micro-structures on the target front surface. We do not observe an increase in the proton cutoff energy with our microstructured targets, and this is due to the large volume of the relief.

scholarly journals Light pollution is associated with earlier tree budburst across the United Kingdom

2016 ◽  
Vol 283 (1833) ◽  
pp. 20160813 ◽  
Author(s):  
Richard H. ffrench-Constant ◽  
Robin Somers-Yeates ◽  
Jonathan Bennie ◽  
Theodoros Economou ◽  
David Hodgson ◽  
...  
Keyword(s):  
Urban Areas ◽  
Species Interactions ◽  
Ecological Impact ◽  
Plant Phenology ◽  
Deciduous Tree ◽  
Light Pollution ◽  
Spring Temperature ◽  
Night Time ◽  
Wide Range ◽  
The Impact

The ecological impact of night-time lighting is of concern because of its well-demonstrated effects on animal behaviour. However, the potential of light pollution to change plant phenology and its corresponding knock-on effects on associated herbivores are less clear. Here, we test if artificial lighting can advance the timing of budburst in trees. We took a UK-wide 13 year dataset of spatially referenced budburst data from four deciduous tree species and matched it with both satellite imagery of night-time lighting and average spring temperature. We find that budburst occurs up to 7.5 days earlier in brighter areas, with the relationship being more pronounced for later-budding species. Excluding large urban areas from the analysis showed an even more pronounced advance of budburst, confirming that the urban ‘heat-island’ effect is not the sole cause of earlier urban budburst. Similarly, the advance in budburst across all sites is too large to be explained by increases in temperature alone. This dramatic advance of budburst illustrates the need for further experimental investigation into the impact of artificial night-time lighting on plant phenology and subsequent species interactions. As light pollution is a growing global phenomenon, the findings of this study are likely to be applicable to a wide range of species interactions across the world.

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