Rit (Vísindafélag Íslendinga) - 01.06.1976, Qupperneq 87

lying farthest from the isobaric cooling line. Hólar, with ðD —
— 89%0 and mean air temperature t = 3.4°C, is located in a deep
valley partly surrounded by mountains approximately 1000 m high
Assuming that the average altitude of condensation is approxima-
tely 500 m higher than it would be if the station were unshielded
and that the air temperature decreases by 0.6 °C per 100 m eleva-
tion, which is a mean value for Iceland found experimentally
(Einarsson 1976), the temperature measured at the station Hólar,
t = 3.4°C, should be replaced by the value t = 0.4°C. This cor-
rected value for Hólar would lie very close to the isobaric cooling
line in Fig. 21.
The anomalous behaviour of inland stations may be explained
in a similar way, viz. by the fact that before the air masses bring-
ing the precipitation reach the inland station, they frequently
have to pass mountainous areas with an altitude higher than the
station itself.
The conclusion drawn from the ðD—t relationship is that the
isotopic fractionation of precipitation in Iceland does not follow a
fractionation process which can be described as moist-adiabatic
cooling. Even in central Iceland the distance from the coast is not
sufficient for moist-adiabatic conditions to be reached.
The high scatter of the data indicates that the isotopic fraction-
ation not only depends on the air temperature at the place in ques-
tion but also on other parameters such as the landscape and wind
direction when precipitation occurs. Consequently a detailed pic-
ture of the deuterium distribution in Icelandic precipitation cannot
be obtained by other means than direct measurements.
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