Wind resources at Horns Rev

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5. Stability and climate
The atmospheric stability is a derived quantity, which is based on the Richardson
number, as defined by the formula:
The temperature difference is based on temperature recordings from level 13 and 55 m,
while the wind speed difference is based on wind speeds from level 15 and 45 m:
Table 5.1 Stability distribution for 5 = CUP62M < 25 m/s
Stability Interval Distribution
Very stable 0.12 = Ri < 1 37%
Stable 0.045 = Ri < 0.12 11%
Near neutral -0.06 = Ri < 0.045 9%
Unstable -0.30 = Ri < -0.06 12%
Very unstable -2.00 = Ri < -0.30 31%
The stability analysis is based on 11,550 hours of measurements recorded in the wind
speed interval 5–25 m/s, and Figure 5.1 shows the stability distribution representing the
Horns Rev site, according to the definition given in Table 5.1.
pdf [%]
40
30
20
10
Ri
5.1 Shear exponent distribution
0
Very stable
g Δt
Δh
= ×
T ( ΔV
Δh
2
)
Stability measured at Horns Rev
5 < CUP62M < 25 m/s
Slightly stable
Near neutral
Slightly unstable
Figure 5.1 Stability distribution
Very unstable
The shear exponent a is a derived quantity, which is used to represent the mean wind
gradient:
Report no.: D-160949
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