Wave-like wind fluctuations observed in the stable surface layer over a plant canopy(2)

Abstract

Observations of wind velocity and air temperature fluctuations were made in the nocturnal surface inversion layer over a sorghum field. Wave-like fluctuations of temperature and wind velocity with a period of 15-20 min were observed for about 2 hours, 3 to 5 hours before sunrise. Wave-like fluctuations of temperature were observed in the air layer above and within a plant canopy and were most noticeable at the top of the plant canopy. Spectral analysis of temperature and wind velocity fluctuations reveals a separation of energy into wave-like and turbulent fluctuations. Cospectral analysis shows that for both momentum and heat, vertical transports are partitioned almost equally in the frequency ranges characteristic of wave-like and turbulent fluctuations. This suggests waveturbulence interactions at low frequencies in the air layer near a plant canopy.

Joint probability analysis of momentum and heat fluxes at a deciduous forest

“…(4) We have considered mainly the supply of kinetic energy from the mean flow of the upper layer as an energy source for the sweep-ejection cycle. Energy supplies from convection in very unstable conditions, or gravity waves in very stable conditions) might also be important as an energy source to maintain such a cycle (e.g., Ohtaki, 1987 andMaitani, 1989).…”