thumbnail

Variability in surface energy flux partitioning during Washita '92: Resulting effects on Penman-Monteith and Priestley-Taylor parameters

Agricultural and Forest Meteorology

By:
, , and
DOI: 10.1016/0168-1923(96)02334-9

Links

Abstract

During the Washita '92 field experiment, the local surface energy balance was evaluated at four locations in the USDA-ARS Little Washita River Watershed near Chickasha, OK, using the Bowen ratio-energy balance (BREB) approach. For any given day, differences in the partitioning of the available energy appeared to be mostly a function of the type of vegetation at the site, while the actual magnitude of the fluxes was mostly affected by cloud cover. The soil surface was initially wet, and gradually dried during the field experiment. However, there was not a corresponding decrease in the evaporative fraction, which would have indicated a decreasing contribution of soil evaporation to the total latent heat flux. Ground weather data indicated a large shift in the direction and magnitude of the surface winds, and a significant increase in air temperature and vapor pressure deficit. During this period, the evaporative fraction actually increased at two of the four sites. The response of the different sites to the changing near- surface atmospheric conditions was studied in more detail by evaluating the canopy resistance (r(c)) to evaporation using the Penman-Monteith equation and the Priestley-Taylor parameter (??). Midday averages of r(c) and (??) tended to decrease (increase) with increasing vapor pressure deficit for two of the sites while such a trend was not evident for the other two sites. Estimates of stomatal resistances indicated that significant plant physiological differences existed between the sites containing weedy vegetation versus the grasses at the pasture/rangeland sites. Even though soil moisture conditions were relatively wet, ?? was less than 1 at all sites and there was no trend in ?? as a function of surface soil moisture conditions. These findings suggest that vegetation types in mixed agricultural/rangeland ecosystems can have significantly different responses to similar atmospheric forcing conditions.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Variability in surface energy flux partitioning during Washita '92: Resulting effects on Penman-Monteith and Priestley-Taylor parameters
Series title:
Agricultural and Forest Meteorology
DOI:
10.1016/0168-1923(96)02334-9
Volume
82
Issue:
1-4
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Agricultural and Forest Meteorology
First page:
171
Last page:
193
Number of Pages:
23