Inter‐decadal variability in potential glacier surface melt energy at Vestari Hagafellsjökull (Langjökull, Iceland) and the role of synoptic circulation

Abstract

The surface energy balance (SEB) of glaciers, although of considerable importance for understanding the melt response to climate change, is rarely analysed for more than a few melt seasons due to the logistical challenges of meteorological measurement campaigns on glaciers. Insight into low‐frequency (inter‐decadal) changes in the SEB in response to climate warming and variable atmospheric circulation patterns has thus been limited. Here this problem is addressed by using ERA‐Interim reanalysis data to extend glacier‐meteorological records at two locations on Vestari Hagafellsjökull (Iceland) for the period 1979–2012. Trend analysis is conducted for this series before the role of synoptic circulation in modulating surface energetics is investigated. The results indicate that potential melt energy has increased significantly throughout the period of simulation at both locations (by 19.7 and 32.4%), with the largest increase evident for the turbulent heat fluxes (36.3 and 93.1%). The synoptic conditions associated with the recent high melt rates on the proximate Greenland Ice Sheet (GrIS) do not result in similarly extreme melt conditions for our Icelandic location. We also find that the North Atlantic Oscillation Index is significantly correlated with the radiative and latent heat components of the SEB. This association remains hidden if the melt rate is assessed in isolation, highlighting the utility of the SEB approach presented here for assessing synoptic aspects of glacier‐climate interactions.

Atmospheric circulation modulates the spatial variability of temperature in the Atlantic–Arctic region

“…The anomalies of cloud cover and downwards SR are not significant during these regimes (Figure a,b), suggesting that the meridional winds play an important role in the warm anomalies in Iceland. Similarly, Matthews et al () show an association between anticyclonic conditions in the Norwegian Sea and highest glacier melt in Iceland, due to a meridional advection of latent heat flux and an enhancement of longwave IR. Our overall results corroborate Guemas et al () showing an association between SB and warm temperature driven by different processes.…”

Interdecadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures

“…To analyse DDF variability we used the 34 year SEB record presented by Matthews and others (2014a: they term this record ‘REANh’ in that study). Full details of how this dataset was produced are provided in the reference, so we only recap the main points here.…”

“…However, the reanalysis data do not capture the glacier microclimate and so must be downscaled before SEB modelling. Matthews and others (2014a) achieved this by implementing empirical quantile mapping to bias correct the incident radiative fluxes, air temperature, vapour pressure and wind speed relative to AWS reference series available for JJA 2001–2007 and 2001–2009 at VH 500 and VH 1100, respectively. As these bias correction functions are temporally invariant, their use assumes that the relationship between the local (AWS) and large-scale (reanalysis grid-point) climate does not change through time.…”

Statistical summer mass-balance forecast model with application to Brúarjökull glacier, South East Iceland

“…Studies have predicted that increased glacial ablation will result in increased river runoff in Icelandic rivers throughout the 21st century (Jonsdóttir, 2010; Gudmundsson and others, 2011; Matthews and others, 2015). While little prior work exists on summer mass-balance modeling of Icelandic glaciers, several studies have considered the subject in other regions.…”