Regional surface momentum flux derived from atmospheric boundary layer bulk similarity approach

Abstract

Abstract. Wind speed data in the atmospheric boundary layer (ABL) observed during two recent experiments over a wide stability range and over different experimental areas allowed an extensive test of the ABL bulk similarity equation with the similarity functions B w previously proposed and calibrated with the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) data set in order to obtain regional surface momentum fluxes. It was found that FIFE-calibrated Bw functions produced similarly good results with the two new data sets; furthermore, one similarity function B w based on a simple dual-layer ABL model which worked best with the FIFE data set was also found to perform best with the new data sets. Recalibration of the constant of this B• function with all three combined data sets resulted in the same value as that calibrated with the FIFE data set. IntroductionThe knowledge of surface momentum fluxes of a region is needed in many Earth science disciplines such as hydrology and meteorology. Because of its importance, there has been steady progress in the method of determining the regional fluxes. One possible approach is to determine the regional surface roughness parameters and to use them together with wind data in the atmospheric boundary layer ( Another formulation one can employ on is the ABL bulk similarity approach. It can be derived from two governing equations for the mixed layer and for the surface layer by assuming an overlap region of the two, and by "patching" these two equations [e.g., Brutsaert, 1982]. For this equation to be valid over a complex region, the same conditions that need to be satisfied for the application of the profile equation over such a region must also be satisfied. However, since the height of measurements for the ABL bulk similarity equation is higher than that for the surface layer profile equation, the restrictions for use of the ABL bulk similarity equation over a complex region are expected to be relaxed to some extent.The ABL bulk similarity equations have been known for a long time, but only recently have they come to be recognized as a practical tool for determining surface momentum fluxes. Brutsaert and and Sugita and Brutsaert [1992]

How universal is the C function in the bulk atmospheric boundary layer similarity approach for estimating surface sensible heat flux?

“…As mentioned in section 1, five data sets were analyzed in the present study. Among them, three data sets are identical to those used for the study of the B w function by Sugita et al [1999], namely, the data sets obtained in (1) the Tsukuba Atmospheric Boundary Layer Experiment (TABLE) [ Sugita et al , 1993], (2) the Northern Hemisphere Climate Processes Land Surface Experiment (NOPEX) [ Halldin et al , 1999], and (3) the First ISLSCP Field Experiment (FIFE) [ Sellers et al , 1988]. The fourth data set came from (4) the GEWEX Asian Monsoon Experiment (GAME), where GEWEX stands for Global Energy and Water Cycle Experiment.…”

“…Also in the same manner as Sugita and Brutsaert [1992a], b = ln ( az 0 / z 0 h , r ) was treated as a constant to be determined using calibrations. From previous studies, a = 69 derived from the height range of the surface layer 48 ≤ ( z − d )/ z 0 ≤ 101 found for FIFE [ Brutsaert and Sugita , 1991; Sugita and Brutsaert , 1992a], a = 40 for TABLE from 18 ≤ ( z − d )/ z 0 ≤ 90 [ Hiyama et al , 1996], and a = 30 from 16 ≤ ( z − d )/ z 0 ≤ 56 in NOPEX [ Sugita et al , 1999] were adopted in the following analysis, and the mean value of a = 112 was obtained for the GAME data set by determining the surface layer extent from visual inspection of θ profiles. For the RAISE data set, the information is not available, and an overall mean of a = 63 for all data sets was simply adopted.…”

“…Values of h i were determined for GAME at the lowest height where d θ/ dz ≥ 6.0 K km −1 in radio sounding profiles, as for previous studies ( Brutsaert and Sugita [1991] and Sugita and Brutsaert [1992a] for FIFE, Sugita et al [1999] for TABLE, and Hiyama et al [1999] for NOPEX). To avoid possible spurious values due to small oscillations in the radiosonde profiles, the validity of the selected height was confirmed visually on a θ versus z plot.…”

“…To answer this question, a test with as many experimental data sets as possible (not only similarity considerations to verify that all relevant variables are included and that there are no redundant variables involved in the formulation [see, e.g., Brutsaert and Sugita , 1991]) obtained for a range of different conditions reflecting surface features, climatic conditions, atmospheric conditions, geographic location, etc., needs to be carried out in a consistent manner. To some extent, for the B w function, Sugita et al [1999] performed this task using three data sets, and their result indicates that B w can be treated as a universal function of atmospheric stability. For the C function a comprehensive study of this kind has not been carried out yet.…”

“…For the C function a comprehensive study of this kind has not been carried out yet. In this work, the three data sets in the work by Sugita et al [1999] and two additional data sets, one obtained in a dry season in the central part of Thailand and one obtained in an extensive steppe region in Mongolia, were used to study the universality of the C function, especially for the purpose of flux estimation by means of the BAS. Since the new data sets were obtained under different conditions than the others, especially in terms of surface dryness and higher surface temperatures, a better and more thorough examination of the C function should be possible.…”