Hydra Home FAQ

Wind speed profile

The wind speed increases with height. How much depends on the roughness of the terrain and the stability of the atmosphere (is there much convection, or not?). In the table below and this figure the wind speed profile is given for a cloudy day (neutral), a shiny day (unstable), and a clear night (stable).

	Wind speed (m/s)
Height (m)	Neutral	Unstable	Stable
1.0	1.8	1.9	1.7
1.5	2.3	2.4	2.2
2.0	2.7	2.9	2.6
3.0	3.3	3.4	3.2
4.0	3.7	3.8	3.6
4.8	4.0	4.1	3.9
7.1	4.5	4.6	4.5
10	5.0	5.0	5.0
15	5.5	5.4	5.6
21	6.1	5.8	6.3
29	6.5	6.1	6.9
42	7.0	6.5	7.7
60	7.5	6.8	8.6
88	8.1	7.1	9.8
117	8.5	7.3	10.9

Technical details

The logarithmic wind speed profile has been used. This is not valid close to the surface (< 20 x z0). Roughness length z0 = 0.3 m. In stable conditions large deviations in wind speed and large differences in wind direction are possible at larger heights.

	Heat flux (W m-2)	Obukhov length (m)
Neutral	1	-17.000
Unstable	300	-76
Stable	-50	286