On dispersion above a forest—Measurements and methods

Figures & data

Table 1. The 61-m tower locations considered in this work.

Tower	Longitude	Latitude
A	−81.741683	33.346812
C	−81.669158	33.250272
D	−81.741037	33.209064
F	−81.682166	33.278420
H	−81.624719	33.286897
K	−81.658554	33.207485
L	−81.617377	33.215688
P	−81.572696	33.225645

Figure 1. The 61-m tower locations across the Savannah River National Laboratory reservation in South Carolina. In the present analysis, data from tower “D” are used most extensively. Tower “CS” is located in an area surrounded by buildings. Its data will not be used here.

Table 2. Total number of 30-min averages within P-G categories, for different methods of categorization.

Method		P-G Stability Category
		A	B	C	D	E	F
36 m	σθ	136	264	497	841	568	152
	σϕ	356	584	569	568	130	250
61 m	σθ	159	94	785	906	427	389
	σϕ	723	269	196	905	298	69
SRDT		98	528	285	521	309	819

Figure 2. The variation of σ_θ and σ_ϕ with stability category, determined using five different methods as identified: (1) using the 36-m σ_θ data, (2) 36-m σ_ϕ, (3) 61-m σ_θ, (4) 61-m σ_ϕ, and (5) SRDT (see text). The six bars for each case represent the results for P-G categories A, B, C, D, E, and F sequentially, starting from the left for each grouping. Data from tower “D” are used.

Figure 3. The coefficients of variation (CoV ≡ σ_χ/χ) corresponding to the values plotted in Figure 2. Small values indicate a well-ordered statistical distribution. Values increase with an increasing contribution of randomness. Crosses identify cases in which the quantities plotted are sorted according to reported values of the same quantities, so that CoV values are necessarily small.

Figure 4. (a, b) Variation of σ_θ (a) and σ_ϕ (b) with stability for tower “D” and (c, d) corresponding CoVs. Stability is quantified as (z − d)/L, where z is the height above the ground, d is the zero-plane displacement, and L is the Obukhov length scale of turbulence. The heavier line represents data from 36 m, the lighter line, 61 m.

Figure 5. As in Figure 4, except that stability is now quantified as the Richardson number (Ri) derived using the 36-m and 61-m data.

Figure 6. As in Figures 4 and 5, but showing the dependence on time of day (as hours after sunrise).

Figure 7. (a, b) Dependence on wind speed of σ_θ (+) and σ_ϕ (x) for the 61 m and 36 m heights, respectively. (c, d) Corresponding coefficients of variation.

Figure 8. Velocity component statistics versus the relevant velocity scales. Each data point represents a 30-min sampling period. To simplify the presentation, every 25th data point after ordering according to wind speed is plotted. (a, c) σ_θ (+) and σ_ϕ (o); (b, d) results using the same data set for σ_v and σ_w. The upper panels (a, b) are for the peak unstable hours (10:00 a.m. to 4:00 p.m.); the lower panels (c, d) for the peak hours of stable stratification (10:00 p.m. to 4:00 a.m.).

Figure 9. The variation of velocity component standard deviations with stability, represented by Ri. The solid lines link averages of 36-m data; the lighter lines, 61-m. (a, c) Transverse velocity (v) results; (b, d) vertical (w) component results. As in other figures, the lower panels (c, d) show the coefficients of variation corresponding to the upper panels. Note the difference between the 36-m data and the 61-m data in the case of σ_w, such difference is lacking in the case of σ_v.

Figure 10. The dependence on stability of two alternative quantifications of the standard deviations of (a) wind speed (u), (b) the lateral angular component (σ_θ), and (c) the vertical angular departure (σ_ϕ). In each of the panels, circles indicate the average standard deviations in time (e.g., <σ_u>, plotted using the left hand axes) and the pluses the “meander” standard deviations determined from measurements of the corresponding quantities at the eight reporting stations (e.g., σ, referred to the axes on the right). Note that the vertical axes are the same in panel a, and also in panel b. However, in panel c, axis for σ() is scaled differently from that for <σ_ϕ> because the average vertical velocity over each averaging period is close to zero and the standard deviation among these small values is itself necessarily small.

Figure 11. The total effective standard deviations corresponding to the panels of Figure 10, constructed by adding the time and space variances. Values of the amplification factor (A) that could be applied to the single-point estimates of the three different dispersion quantities are plotted as lines joining averages, as A − 1.

Figure 12. For the three quantities illustrated in Figures 10 and 11, the corresponding total CoVs derived by combining the variances in space and in time: for (a) σ_u; (b) σ_θ (crosses) and σ_ϕ (circles).