Print Version - Center for the Biology of Natural Systems

More documents

Recommendations

Info

D22303YI ET AL.: DRAINAGE FLOW MODELD22303drag coefficient is independent of stability as wind speedexceeds 2 m s 1 for forests. The value c h D = 0.03 (for u h =2.93 m s 1 ) is close to the range of values observed byMahrt et al. [2001] in representative forests. Drag coefficients(circles and triangle in Figure 4) were obtained ina two-step calculation: half-hour values were first calculatedby equation (2) and then averaged for each level overthe entire nighttime period. The order of calculation willinfluence the estimated values due to the nonlinearity inequation (2). The records with small stress (u *< 0.01 m s 1and weak wind speeds
D22303YI ET AL.: DRAINAGE FLOW MODELD22303speed and air temperature (Figure 8). Using the Richardsonnumber (Ri) [Thom, 1971] defined asRi ¼g @Tq 0 @z@u@z 2!1Figure 6. Dimensionless Reynolds stress profile predictedby equation (8): triangles, total Reynolds stress; diamonds,slope-independent component; squares, slope-dependentcomponent; circles, observations. The observed data pointswere obtained from the same data sets as in Figure 4.Reynolds stress profile (Figure 7). Predictions of the stressprofile using our simple model were similar to those fromthe Wilson and Shaw (WS) model and in better agreementthan other past models.4.3. Prediction of a Very Stable Air Layer Withinthe Canopy[19] The vertical profile of wind speed predicted byequation (6) provides evidence of a layer with relativelylow flow between 3 and 6 m above the ground (Figure 3).This layer lies immediately below the layer of maximumleaf area density. We confirmed the existence of the stablelayer using measurements of the vertical profile in windwith @u/@z = 0 (Figure 8a) and @T/@z 6¼ 0 (Figure 8b), weobserved maximum stability at 6 m when the above-canopyatmosphere was stable (0.05 (z d)/L) and 3 m when theabove-canopy atmosphere was neutral ( 0.05 < (z d)/L
Page 1 and 2: JOURNAL OF GEOPHYSICAL RESEARCH, VO
Page 3 and 4: D22303YI ET AL.: DRAINAGE FLOW MODE
Page 5: D22303YI ET AL.: DRAINAGE FLOW MODE
Page 13: D22303YI ET AL.: DRAINAGE FLOW MODE

Print Version - Center for the Biology of Natural Systems

Create successful ePaper yourself

Delete template?

Save as template?