Investigation of the structure of the stablely stratified atmospheric surface boundary layer
Abstract
It is often observed that the turbulence in the stably stratified boundary layer is not very continuous but rather consisting of intermittent events or turbulent bursts. This behavior does not conform to the M-O theory. The objective of the present study is to investigate the reasons for the intermittency, with the two working hypotheses being described below. The first mechanism is internal to the surface layer: As the surface cools radiatively, the cooled surface layer is decoupled, because of the decreased turbulent mixing. The surface friction then becomes negligible and the flow aloft accelerates. When the wind shear is sufficiently high, the critical Richard-son number is exceeded, a burst of turbulence is created, sending a heat flux down-wards, reversing the process, but since the radiative cooling of the surface is an on-going process the process can be repeated several times during the night. The resulting non-stationary behaviour of the flow is described by Businger (1973) Another mechanism that would be producing intermittent flux behaviour is the possible presence of breaking internal gravity waves in the stable boundary layer. These could interact with the flow causing intermittent event of turbulence and thereby again making the simple M-O similarity not applicable. This mechanism is explored by (Zilitinkevich and Calanca, 2000). We have explored data from an experiment in Boris, a military range western Jutland, and from the SABLES99 experiment to evaluate the relative importance between the two mechanisms above. Unsurprisingly it is found that both mechanisms are important. References Businger, J.A. (1973) Turbulent transfer in the atmospheric surface layer. Workshop on Micrometeorology, D.A. Haugen, Ed., Amer. Meteor. Soc., 67-100. Zilitinkevich, S. and P. Calanca (2000) An extended similarity-theory for the stably stratified surface layer. Quart. J. Roy. Meteorol. Soc. 126, 1913-1923.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....14812J