Air motion within and above forest vegetation in non-ideal conditions

Gaining a good knowledge of air motion in forest vegetation is a necessary step towards a better understanding of a number major abiotic impacts on th e trees such as wind risk, pollutant and nutrient deposition, frost, materi al dispersion and transport, and energy, water and carbon exchanges. In a r ecent survey study, Raupach et al. [Raupach, M.R., Finnigan, J.J., Brunet, Y., 1996. Bound.-Layer Meteorol. 78, 351-382] reviewed the current state of knowledge about air flow under ideal conditions (neutral to slightly unsta ble conditions, homogeneous and extensive canopy, flat terrain). This paper extends the knowledge by employing advances in our understanding of the fl ow in 'non-ideal' situations. The paper is divided into four topic areas: c anopy flow under stable stratification, disturbed flow (forest edge, forest clearing, sparse canopy), canopy flow over complex terrain, and extreme wi nd events. Discussion of the latter two topics is of limited scope because of the scanty literature. A detailed account is given to the nighttime cano py wave phenomenon, broad patterns of the transitional flow across forest e dges, and models of various complexities of the disturbed flows. Both obser vational and modeling aspects are discussed wherever possible. This synthes is study has identified a number of important questions in need of further research. (C) 2000 Elsevier Science B.V. All rights reserved.