Average fluxes from heterogeneous vegetated regions

Klaassen, Wim

doi:10.1007/bf00120236

Cited by 52 publications

(27 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The micro-meteorological model is based on a model by Klaassen (1992) for heat and momentum fluxes in heterogeneous, vegetated landscapes. It is a two-dimensional model with a horizontal x-axis in the wind direction and a vertical z-axis.…”

Section: The Micro-meteorological Modelmentioning

confidence: 99%

“…It was concluded that the multi-layer representation of vegetation is essential to realistically simulate momentum fluxes near forest edges. At the micro-scale this is explained by the airflow into the forest edge (Klaassen, 1992) and at the landscape scale it is the obstacle drag of transitions in vegetation height that explains the large drag of forest edges (Klaassen and Claussen, 1995).…”

Section: The Micro-meteorological Modelmentioning

confidence: 99%

“…Above homogeneous surfaces lm= kz, resulting in logarithmic profiles. Above heterogeneous landscapes, lm varies because of advection and adjustment as described by Klaassen (1992). Changes in the concentration profile are calculated from mass conservation, using:…”

Section: The Micro-meteorological Modelmentioning

confidence: 99%

See 2 more Smart Citations

Simulated dry deposition of nitric acid near forest edges

Jong

Klaassen

1997

Atmospheric Environment

View full text Add to dashboard Cite

Section: The Micro-meteorological Modelmentioning

confidence: 99%

Section: The Micro-meteorological Modelmentioning

confidence: 99%

See 1 more Smart Citation

Simulated dry deposition of nitric acid near forest edges

Jong

Klaassen

1997

Atmospheric Environment

View full text Add to dashboard Cite

“…They included a multilayer representation of the forest biomass, pressure effects and first-order closure. In a further development of this approach Klaassen (1992) Oke, 1990;Schmid, 1994). (1992) model.…”

mentioning

confidence: 99%

Forest edges and the soil-vegetation- atmosphere interaction at the landscape scale: the state of affairs

Veen

Klaassen

Kruijt

et al. 1996

Progress in Physical Geography: Earth and Environment

Self Cite

View full text Add to dashboard Cite

Although the soil-vegetation-atmosphere exchange of momentum and heat is fairly well understood for many types of homogeneous surfaces, the disturbances created by transitions of one surface type to another remain to be analysed more fully. This is especially true for the impact which a large transition such as the forest edge has on the average fluxes in a small-scale heterogeneous landscape with forest. Recently acquired experimental evidence appears to some extent contradictory and at variance with conventional concepts.Key words: forest edges, momentum fluxes, energy balance, land surface heterogeneity, advection, area averaging of fluxes. I IntroductionObservations on the water balance of forests have shown that the generally high water use of forests -as compared to, for example, low agricultural crops -is mainly caused by high evaporative losses of intercepted rainfall. One-dimensional modelling, reviewed by Veen and Dolman (1989), suggests that a high evaporation rate of intercepted water is explained to a large extent by the high aerodynamic roughness of forests. This can be easily understood. Strong absorption of the kinetic energy of the air flowing over the rough canopy creates strong turbulence. The upward motions in the eddies very quickly transport water vapour away from the wet, evaporating surface. When the leaves are dry, turbulence is no less intensive. But in a dry canopy the stomata at University of Groningen on October 12, 2011 ppg.sagepub.com Downloaded from 293 regulate the transpiration rate. The surface resistance of forests is, therefore, much larger than the aerodynamic resistance. As in low vegetation it increases with decreasing availability of -among others -light and soil moisture. Water losses through transpiration in forests have turned out to be similar to those of other vegetation types.The notion that forests present a very rough surface to the flow of air is important not only for the fluxes of water vapour but also for the other quantities that are transported by turbulent diffusion. The downward motions in eddies of the strongly turbulent wind field over forests transport gases and aerosols towards the land surface more efficiently than in the much quieter flow patterns across smooth, i.e., low vegetation. The flux of acidifying air pollutants from the atmosphere towards the forest soil is, therefore, significantly larger than the flux to arable soils. Measurements and calculations, for example, in the Dutch ACIFORN project (Van Aalst and Erisman, 1991) have demonstrated this.Aerodynamic roughness also plays a role in the influence of forest on climate. The direct effect of forests on the atmosphere stems from high roughness in combination with low albedo. Low albedo causes much radiative energy to be available for conversion into sensible and latent heat. High roughness makes for low resistance to heat fluxes from the forest to the atmosphere. Extensive regions covered by forest significantly affect the properties of air masses overhead. At the continental scale...

show abstract

“…The large variability of NH x deposition near sources is known to depend critically on the canopy structure surrounding the source (roughness, side fluxes) (Klaassen, 1991;Draaijers et al, 1994;De Jong and Klaassen, 1997;Theobald et al, 2001;, the NH 3 emissions from the canopy (Schjoerring et al, 1998;Riedo et al, 2002), the litter (Nemitz et al, 2000a(Nemitz et al, , 2000b, or from the soil (Génermont and Cellier, 1997), as well as the non-stomatal NH 3 fluxes (van Hove et al, 1989;Erisman and Wyers, 1993;Sutton et al, 1995a;Fléchard et al, 1999;. Less known, are wet deposition fluxes and chemical transformations of NH x near intensive sources, as well as direct emissions of particulate NH 4 + (McCulloch et al, 1998).…”

mentioning

confidence: 99%

Ammonia Deposition Near Hot Spots: Processes, Models and Monitoring Methods

Loubet¹,

Asman

Theobald

et al.

Atmospheric Ammonia

View full text Add to dashboard Cite

ABSTRACT. Atmospheric reduced nitrogen (NH x ) mainly originates from hot spots, which can be considered as intensive area or point sources. A large fraction of the emitted NH x may be recaptured by the surrounding vegetation, hence reducing the contribution of these hot spots to long-range transport of NH x . This paper reviews the processes leading to local recapture of NH x near hot spots as well as existing models and monitoring methods. The existing models range from research models to more operational models that can be coupled with long-range transport model provided the necessary information on emissions is available. Local recapture of NH 3 ranges from 2% to 60% within 2 km of a hot-spot and it is sensitive to source height, atmospheric stability, wind speed, structure of the surrounding canopies, as well as stomatal absorption, which mainly depends on green leaf area index and stomatal NH 3 compensation point of vegetation, and finally, cuticular deposition, which depends primarily on vegetation wetness. The main uncertainties and limitations on NH x recapture models and monitoring techniques are discussed.

show abstract

Average fluxes from heterogeneous vegetated regions

Cited by 52 publications

References 41 publications

Simulated dry deposition of nitric acid near forest edges

Simulated dry deposition of nitric acid near forest edges

Forest edges and the soil-vegetation- atmosphere interaction at the landscape scale: the state of affairs

Ammonia Deposition Near Hot Spots: Processes, Models and Monitoring Methods

Contact Info

Product

Resources

About