Daily course of skewness and kurtosis within and above a crop canopy

Abstract

A measurement program is carried out within as well as above a maize crop canopy. Statistical characteristics are analyzed for the velocity components as well as for temperature for a clear weather day as well as a cloudy day. During daytime it appears that the above and within-canopy characteristics are dominated by sweeps, which means a positive u-skewness and a negative w-skewness. During daytime the within-canopy w-kurtosis is extremely high due to strong turbulence events of sweeps as well as ejections. During night-time, hot plumes released from the soil surface dominate the extremes, which results in a positive w-skewness, above as well as within the canopy. The temperature skewness is mostly positive within as well as above the canopy. After mid-day on the clear day with low wind conditions, however, the within-canopy skewness for temperature is negative nearly throughout the whole canopy due to sweeps from a relatively high and cool level.