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β

β

Φ

Front

Side

Wind

h

nh

mh

height *h*, width *mh*, and length *nh*. The angle Φ

per unit ground area. Suppose the fraction of the

area covered by the sastrugi-like roughness ele-

describes how the mean wind is oriented with

ments is γ. Thus, from Figure 3, the unit area repre-

respect to the sastrugi. When the wind has been

sented by each roughness element is *mnh*2/2γ. The

blowing with constant direction at speeds of

68 m/s, or higher, for several hours, Φ will be

base length of the triangular frontal area that each

roughness element presents to the wind, *L*(Φ), is a

zero.

function of Φ. Likewise, the silhouette area pre-

From the discussion in the penultimate para-

sented, *A*(Φ), is simply

graph, we see that *h *is 520 cm. Descriptions of

drifted snow in the literature (Finney 1939, Mel-

1

lor 1965, Jackson and Carroll 1978) and Plate's

(4)

2

(1971, Figure 4.17) pressure distribution around

Consequently, λ is also a function of Φ

roughness elements similar to that in Figure 3

suggest that *n *is about 10. From Mellor's (1965)

2γ*A*(Φ)

γ*L*(Φ)

description of sastrugi, I assume that *m *is about

λ(Φ) =

=

.

(5)

4. Notice, these parameters imply that, in Figure

3

In Figure 3, we see that there are four Φ regions

β = arctan(*m*/2*n*) = 11.3.

for which a roughness element presents different

(3)

faces to the wind for 0 ≤ Φ ≤ 180 (symmetric for

0 ≥ Φ ≥ 180). These and the associated values of

One of the key parameters in R92's model is λ,

the frontal area of a typical roughness element

3

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