Fróðskaparrit - 01.01.2002, Blaðsíða 102

100
ARCTIC MOUNTAIN METEOROLOGY AT THE SORNFELLI MOUNTAIN
IN YEAR 2000 IN THE FAROE ISLANDS
230
^Anemometer
Unshielded air
temperature
Shielded air
temperature
on the boom
100 cm
Figure 5. Tlie Sornfelli meteorological station, with
the instrument cylinder in an icing situation. Notice
that a thick icing covers the sensor on the boom. Large
photo by Egil Rasmussen, 29 December 1999 and
small photo by Lis Mortensen, 2001.
logical station was installed on 19 Novem-
ber 1999. It is remotely controlled, with fa-
cilities for remote downloading of data. In-
side the 80 cm high cylinder, which is
standing on a 2.3 m mast, the instruments
are fíxed upright onto a platform, which is
lifted out through the cylinder top lid for 10
minutes every half hour (Fig. 5). The lid
hole is covered with plastic brushes to keep
out snow. Heaters, fans and thermostats in-
side the cylinder keep the inside tempera-
ture above a minimum of 3 °C. At the plat-
form air temperature is measured at 725.6
m asl., and the wind recordings at 725.7 m
asl. (Fig. 5). Air temperature is also record-
ed every half hour by a sensor fíxed to a 50
mm round boom extending 1 m from the
cylinder (Fig. 5).
For wind speed and wind direction
recording, a 2 axis ultrasonic anemometer,
Solent Wind Observer model 1172T, is
used. At each axis a transducer sends a
sound pulse across to its paired transducer
and the flight time is measured. A sound
pulse is then sent in the opposite direction,
the wind speed along the axis being given
by the difference in the two flight times.
Unlike conventional cup anemometers, this
type of anemometer has no moving items,
which eliminates the possibility of damage
by strong winds. Sonic anemometers are,
however, susceptible to ice formation on
the transducers, but this is prevented by
storage of the instruments in the heated
cylinder.
The military station supplies 230V elec-
tricity to the station. To prevent severe
lightning damage, the electronic systems
are protected with fuses and relays, and the
site is firmly connected to a lightning con-
ductor system.
Two cabinets attached to the mast (Fig.
5) house the station computers and devices
for control and communication. Recorded
data are stored on computers. The comput-
ers are set up in a WindowsNT network
with a server and connected PC’s. Every
hour the station connects to the internet and
raw data are transmitted to a receiving serv-
er at Metsupport in Denmark. Here the