Lisø PhD Dissertation Manuscript - NTNU

Fig. 1. Map of Norwayshowing the locations of the four weather
stations used in this study.
Table 2
Average annual precipitation and wind speed for Oslo, Bergen,
Trondheim and Tromsø, Norwayfor normal period 1961–1990
Location Average annual
precipitation (mm/
yr)
Oslo 763 2.7
Bergen 2250 3.5
Trondheim 892 3.9
Tromsø 1031 4.0
events. Oslo had the lowest number of annual rain
observations (less than half the number observed in
Bergen) but the highest percentage of moderate or heavy
events (23%). Though receiving less annual precipitation
than Tromsø, Trondheim exhibited a greater
number of rain events (about 167 versus 133 per year).
This is probablyat least in part because a larger
ARTICLE IN PRESS
J.P. Rydock et al. / Building and Environment 40 (2005) 1450–1458 1453
Average wind speed
(m/s)
Table 3
Average annual observations coded as rain (codes 60–65 and 80–82)
and percentage coded as moderate or heavyrain (codes 62–65 and
81–82) from 1974–2003 at Oslo, Bergen, Trondheim and Tromsø,
Norway
Location Synoptic
observations coded
as rain (per year)
Oslo 98 23
Bergen 255 18
Trondheim 167 10
Tromsø 133 15
Moderate/heavyas
a percentage of total
(%)
percentage of precipitation in Tromsø is in the form of
snow. Trondheim had the lowest number of moderate or
heavyobservations of the four weather stations examined
here, with 17 per year (or 10% of the Trondheim
average yearly total).
The relative frequencies of rainfall events versus wind
direction (in 101 increments) for each station are shown
in Figs. 2a–d. The values shown are the percentages as a
function of the total number of observations coded as
rain in the analysis period at each station. If the
frequencies shown in the figure are thought of as
percentages, then, the sum over all directions plus the
percentage of rain events with no wind, at each station,
will equal 100. This is just a simple wayof expressing
how often the wind was blowing from a particular
direction when rain was observed at a station.
Interestingly, the distribution pattern is distinctly
different for each station. Bergen and Tromsø are
perhaps the most striking, with 58% of events in Bergen
associated with a wind from the sector 1301 to 1701
(where 1801 is due south and 901 is due east) and 53% of
the events for Tromsø with wind from the sector 1901 to
2301. Otherwise, particularlyin Bergen, there are
proportionallyveryfew events from other directions at
these stations, with the exception of the hint of a
secondarymaximum from 3001 to 3301 in Fig. 2b.
Rather surprisinglyin fact, there were less than 10 rain
observations recorded at the Bergen station with a wind
from 101, 201 or 301. This is in contrast to almost 1500
observations in the 30-year period with a wind direction
from 1501. Similarly, in Tromsø, there were less than 10
rain observations recorded with a wind direction from
1001, 1101 and 1301, while there were 639 from 2101. At
both Oslo and Trondheim there is a clear directional
dependence that is perhaps more pronounced at
Trondheim. A westerlywind direction defined bythe
sector 2301 to 3001 was associated with 56% of the rain
observations at the Trondheim airport. A small secondarymaximum
occurred with a wind direction slightly
north of east, between 801 and 1301. Otherwise in
Trondheim there were few rain observations with wind