Abstract
Abstract. In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a novel method based on semi-automatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = −0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (Cr) equal to 6 g m−2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).
Highlights
1.1 Research motivation and study aimsAn understanding of how albedo varies in response to changes in the state of the surface is a crucial component in modeling ice melt and in describing the climate of the ice-covered regions and the climate in general
In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface
We proposed a novel method based on semi-automatic image analysis to quantify fine debris coverage (d) on glacier ice
Summary
1.1 Research motivation and study aimsAn understanding of how albedo varies in response to changes in the state of the surface is a crucial component in modeling ice melt and in describing the climate of the ice-covered regions and the climate in general (see Grenfell, 2011). In recent climate modeling studies, attention is paid to the ice–albedo feedback and to its action in modulating the changes in the total energy balance of the analyzed area (Grenfell, 2011). Dust and black carbon deposition on glacier accumulation areas (i.e., at the surface of snow and firn) have been of increasing interest to the scientific community due to accelerated snow melting rates affecting glaciers in the highelevation glacierized areas of Asia (Flanner et al, 2009; Yasunari et al, 2010). Clarke and Noone (1985) found that the black carbon deposition caused an Arctic snow albedo reduction of 1–3 % in fresh snow and by an additional factor of 3 as the snow ages. Dumont et al (2014) found that the Greenland springtime darkening since 2009 stems from a widespread increase in the amount of light-absorbing impurities in snow, as well as in the atmosphere. Clarke and Noone (1985) found that the black carbon deposition caused an Arctic snow albedo reduction of 1–3 % in fresh snow and by an additional factor of 3 as the snow ages. Hansen and Nazarenko (2004) modeled this decreased albedo in Arctic snow and sea ice and found this resulted in a hemispheric radiative forcing of +0.3 W m−2, which may have substantially impacted the Northern Hemisphere climate in recent decades
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
