Jökull - 01.01.2019, Side 117

Tussetschläger et al.
Figure 7. Photos of snow patches in the head of Úlfsdalir (H. Tussetschläger) and satellite images for 2016
and 2017 used for comparison. The hillshade is derived from the DEM (25 m resolution) provided by LMI. –
Samanburður á notagildi ljósmynda af vettvangi og gervitunglamynda í Úlfsdölum.
ble A3 – appendix). For our study especially, the
winter period is of interest. We calculated the total
precipitation from October until May, when precip-
itation is expected to be mostly snow in the moun-
tain areas. The mean winter precipitation over the
last 19 years in Ólafsfjörður is about 750 mm, the
highest amount of winter precipitation was measured
in 1998/1999 (1016 mm) and the lowest amount in
2002/2003 (481 mm). In all study areas the pattern
of the snow cover is smallest in the period from the
earliest available image until 2017. In Brimnesdalur
and Kerling the largest spatial extent of snow patches
is identified in the time period 1999–2002 during
which the mean winter precipitation is 808 mm, which
is higher than the overall mean winter precipitation.
Similar results are obtained from other weather sta-
tions (Akureyri and Skeiðsfoss). Thus, the periods
with the largest snow patches coincide with the pe-
riods of highest winter precipitation. Similarly, years
with significantly decreased size of snow patches such
as 2016 and 2017 coincide with relatively low win-
ter precipitation (662 mm and 664 mm respectively
which is about 33% less than the 2013–2015 average),
and relatively high mean annual temperature. Interest-
ingly the warmest year is 2014, which also is one of
the years when the snow patches are largest. This pat-
tern in the year 2014 is considered to emphasise the
relative importance of the winter precipitation for the
extent of the snow patches. Furthermore, mass bal-
ance data collected by the Icelandic Institute of Natu-
ral History seem to correlate well with the area distri-
bution of the snow fields in recent years. The cirque
glaciers, Búrfellsjökull, Deildardalsjökull and Teigar-
jökull in Svarfaðardalur displayed positive mass bal-
ance in the years 2013, 2014 and 2015, but negative
mass balance in the years 2016 and 2017 (Brynjólfs-
son, 2018 and 2019).
For an overall estimate of main wind direction,
frequency and speed we used data from the automatic
weather station located on the island of Grímsey.
There, the wind direction is not affected by the moun-
tainous landscape of Tröllaskagi and is considered to
116 JÖKULL No. 69, 2019