Extended Abstract (104K)P1.16A
Convective boundary layer development over a midlatitude deciduous forest (Formerly Paper Number 7.4)
H. N. Zutter, Indiana University, Bloomington, IN; and C. S. B. Grimmond, A. J. Oliphant, H. P. Schmid, H. B. Su, and L. Ciasto
Knowledge of convective boundary layer (CBL) development, particularly the mixing layer height (zi), aids in the interpretation of surface-atmosphere exchanges because of its influence on the ability of the atmosphere to exchange heat, momentum, carbon dioxide, and water vapor. This study examines the development of the CBL over a deciduous forest in the midwestern United States (Morgan-Monroe State Forest - MMSF, Indiana) and evaluates the ability of a simple slab-model to predict zi
Profiles of potential temperature ( ) and specific humidity (q) were collected with airsondes for 26 anticyclonic days through a 12-month period (2000-01). Profile characteristics (particularly zi) were compared to surface fluxes (collected from a 46 m tower), canopy cover, and synoptic conditions. Mixing layer heights follow trends in cumulative and daytime total sensible heat flux (QH). However, changes in forest canopy, particularly leaf emergence and senescence, indicated that QH alone could not explain the variation observed in zi in the spring, summer and fall. For these seasons, changes in energy partitioning, incoming solar radiation, and synoptic conditions were documented to be important.
A simple slab model is found to estimate zi well compared with observations for MMSF. Observed profiles of and q and surface data from MMSF were used as initial conditions and surface forcing for modeling the boundary layer growth . Model performance remains relatively good when profiles from regional National Weather Service (NWS) locations are used to initialize the model and/or when the surface fluxes are modeled, rather than observed. Thus we conclude that it is quite reasonable to use the slab model to predict the CBL characteristics for interpretation of surface-atmosphere exchanges, even in the absence of observed fluxes or site-observed profile information.
Poster Session 1, Agricultural and Forest Meteorology
Wednesday, 22 May 2002, 3:30 PM-3:30 PM
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