Jökull - 01.01.2005, Page 130

Sverrir Guðmundsson et al.
Figure 9. Daily energy balance at the three AWSs during the summer 2004. Parameters are defined on page
125. – Orkuþættir í veðurstöðvum á Brúarjökli.
average around 30% at the lowest and highest stations
(Figure 9) and up to 63% for single days at the high-
est station. About 90% of the daily variation in net
radiation (R) was caused by the net short-wave radi-
ation balance (Qi(1 − α)), and the net turbulent heat
flux were driven both by temperature and wind-speed;
97% of the daily variation inH is describedwith TG·u
(Figure 10a,c,d).
High turbulent heat fluxes, driven by exception-
ally strong southerly winds, were observed during the
five days from July 28 to August 1 (Figures 3e,f and
10a,b). These heat fluxes, which were 34 Wm−2
above the July average (1996–2004), were partly
counteracted by low solar radiation resulting in net
radiation of 28 Wm−2 below the July average (Figure
3e,g). The wind-driven turbulent heat fluxes during
those 5 days did, however, increase the melting and
sped up the removal of snow in the ablation area of
Brúarjökull.
A moderate August energy balance and melting
was observed on Brúarjökull during the period of the
first flood (Figure 3e). The intensive melting during
the second flood was driven by both high turbulent
heat fluxes and net radiation (Figures 4, 9 and 10).
During that period, temperatures of 2.7◦C and 6.7◦C
above the August average (1996–2004)were observed
130 JÖKULL No. 55