| Institution: | (1) Research Institute for Humanity and Nature, Kyoto 602-0878, Japan;(2) Present address: Oki/Kanae Lab, Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan;(3) Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan;(4) University Forests in Aichi, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 11-44 Goizuka-cho, Seto Aichi, 489-0031, Japan |
| Abstract: | Wind speed profiles above a forest canopy relate to scalar exchange between the forest canopy and the atmosphere. Many studies have reported that vertical wind speed profiles above a relatively flat forest can be classified by a stability index developed assuming wind flow above a flat plane. However, can such a stability index be used to classify vertical wind speed profiles observed above a sloping forest at nighttime, where drainage flow often occurs? This paper examines the use of the bulk Richardson number to classify wind speed profiles observed above a sloping forest at nighttime. Wind speed profiles above a sloping forest were classified by the bulk Richardson number Ri B . Use of Ri B distinguished between drainage flow, shear flow, and transitional flow from drainage flow to shear flow. These results suggest that Ri B is useful to interpret nighttime CO2 and energy fluxes above a sloping forest. Through clear observational evidence, we also show that the reference height should be high enough to avoid drainage-flow effects when calculating Ri B . |
