Turbulence Spectra above a Vegetated Surface under Conditions of Sensible Heat Advection

Raymond P. Motha Center for Agricultural Meteorology and Climatology, Department of Agricultural Engineering and Natural Resources, University of Nebraska, Lincoln 68583

Search for other papers by Raymond P. Motha in
Current site
Google Scholar
PubMed
Close
,
Shashi B. Verma Center for Agricultural Meteorology and Climatology, Department of Agricultural Engineering and Natural Resources, University of Nebraska, Lincoln 68583

Search for other papers by Shashi B. Verma in
Current site
Google Scholar
PubMed
Close
, and
Norman J. Rosenberg Center for Agricultural Meteorology and Climatology, Department of Agricultural Engineering and Natural Resources, University of Nebraska, Lincoln 68583

Search for other papers by Norman J. Rosenberg in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

Spectra of vertical and horizontal velocity, air temperature and humidity fluctuations were analyzed from measurements made over a well-watered alfalfa crop under conditions of sensible heat advection. Vertical velocity and air temperature spectra as well as cospectra of momentum, sensible heat and water vapor were found to be dependent on atmospheric thermal stratification. These spectra and cospectra were shifted toward higher frequencies under advective as compared to lapse conditions. These results indicate that the predominant eddy sizes are relatively smaller under advective conditions. Humidity spectra, on the other hand, were independent of daytime thermal stratification conditions but were influenced by conditions of the crop. The humidity spectra over a transpiring crop were shifted toward lower frequencies as compared to those over a less well-developed crop canopy.

Abstract

Spectra of vertical and horizontal velocity, air temperature and humidity fluctuations were analyzed from measurements made over a well-watered alfalfa crop under conditions of sensible heat advection. Vertical velocity and air temperature spectra as well as cospectra of momentum, sensible heat and water vapor were found to be dependent on atmospheric thermal stratification. These spectra and cospectra were shifted toward higher frequencies under advective as compared to lapse conditions. These results indicate that the predominant eddy sizes are relatively smaller under advective conditions. Humidity spectra, on the other hand, were independent of daytime thermal stratification conditions but were influenced by conditions of the crop. The humidity spectra over a transpiring crop were shifted toward lower frequencies as compared to those over a less well-developed crop canopy.

Save