Lisø PhD Dissertation Manuscript - NTNU

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Frequency
(a)
Frequency
(b)
Frequency
(c)
Frequency
(d)
10
20
15
10
5
0
5
0
10
5
0
from the north (from about 3101 to 601) and also from
the south (from about 1701 to 2201). In Oslo, maxima
occurred from a direction slightlyeast of north, from the
sector 20 to 601, and to a slightlylesser degree from a
sector in the southerlydirection, bounded approximatelyby1601
and 2001. Otherwise, there were
relativelyfew rain observations with wind from the west
and northwest (from about 2501 to 3501).
The next step was to convert the frequencydistributions
in Fig. 2 into directional rainfall totals. Though
percentages of rainfall events coded as moderate or
heavy, shown in Table 3, varysomewhat from station to
station, the relative frequencyversus wind direction at
each station is verysimilar to the normalized frequency
distribution of total rainfall events at each of these
stations. To illustrate this point, a comparison of the
relative frequencies of observations coded as moderate
or heavy(codes 62–65, 81 and 82) with those coded as
some type of rain (codes 60–65 and 80–82) for Bergen is
shown as an example in Fig. 3. The moderate/heavy
values for each angle are normalized bythe total
number of moderate/heavycodes observed in the
period, and the ‘all types’ values are taken from Fig.
ARTICLE IN PRESS
J.P. Rydock et al. / Building and Environment 40 (2005) 1450–1458
Oslo
10 40 70 100 130 160 190 220 250 280 310 340
Degrees from north
Bergen
10 40 70 100 130 160 190 220 250 280 310 340
Degrees from north
Trondheim
10 40 70 100 130 160 190 220 250 280 310 340
Degrees from north
Tromsø
20
15
10
5
0
10 40 70 100 130 160 190 220 250 280 310 340
Degrees from north
Fig. 2. Relative frequencyvs. wind direction of observations coded as rain for the period 1974–2003 for (a) Bergen, (b) Trondheim, (c) Oslo and (d)
Tromsø.
2b. This figure suggests perhaps a slightlyhigher
incidence of moderate/heavyevents from the principal
direction at Bergen (1301–1701, as discussed above),
which might indicate a need for an incrementally
stronger weighting of rainfall from that direction than
is obtained from Fig. 2b. This is also evident in the
principal directions at Tromsø and Trondheim, and
from the southerlydirection in comparison to the
northeasterlydirection at Oslo, but the differences in
all cases are small. Use of the frequencydistributions in
Fig. 2 for decomposing average annual rainfall amounts
into directional rainfall totals at each of the stations,
therefore, is probablya reasonable approximation.
For driving rain considerations it is important to
distinguish between liquid and solid precipitation. While
annual precipitation is recorded at literallyhundreds of
stations around the country, the percentage of precipitation
falling as rain is not. For stations where
snowfall is not common, this is not a problem. At many
stations in Norway, however, precipitation in frozen
form represents a substantial percentage of the annual
total. For the stations considered here, Bergen has the
lowest relative occurrence of snowfall and Tromsø the