Time-series analysis of albedo on the Agassiz Ice Cap, Canada

The final glacier analysed was the Agassiz Ice Cap (AIC) shown in Fig. 1.

agassizSS

Figure 1: Study site map for Agassiz Ice Cap. Coordinates refer to UTM (Universal Trans Mercator)
zone 18N. Contour spacing is marked at 500 m and AWS refers to the automatic weather station from which
data was collected. The inset shows shows the location of AIC within the Canadian  Archipelago with coordinates referring to the NSIDC sea ice polar stereographic north system.

The results were broken down into three sections. Firstly, daily albedo measurements provide an overview of the behaviour of albedo throughout the melt season and allow short term fluctuations from the norm to be quantified (Fig. 2).

agassizEvolution

Figure 2: Seasonal evolution of daily albedo on AIC.

Secondly, yearly averages were calculated including maximum and minimums (Fig. 3).

agassizSDMaxMinFinal

Figure 3: Yearly evolution of albedo on AIC.

Continue reading

Advertisements

Time series analysis of albedo on Humboldt Glacier, Greenland


Following on from the previous post, the second glacier analysed was the Humboldt Glacier (HG) shown in Fig. 1; the largest in Greenland. This was used to provide method validation with Box et al (2012), which encompassed the whole of the Greenland Ice Sheet (GrIS), as well as a more detailed and localised analysis of individual glacier albedo behaviour. A small yearly discrepancy of 0.0006 was seen which provides confidence in the methods to replicate both short and long – term albedo variability.

Figure 1: Study site map for Humboldt Glacier. Coordinates refer to UTM (Universal Trans Mercator)
zone 20N. Contour spacing is marked at 200 m and AWS refers to the automatic weather station from which
data was collected. The inset shows shows the location of Humboldt Glacier within Greenland and the
Canadian Archipelago with coordinates referring to the NSIDC sea ice polar stereographic north system.

The results were broken down into three sections. Firstly, daily albedo measurements provide an overview of the behaviour of albedo throughout the melt season and allow short term fluctuations from the norm to be quantified (Fig. 2).

Figure 2: Seasonal evolution of daily albedo on HG.

Secondly, yearly averages were calculated including maximum and minimums (Fig. 3).

Figure 3: Yearly evolution of albedo on HG.

Finally, regional maps were created highlighting the spatial relationship of albedo fluctuations throughout the time series (Fig. 4).

Figure 4: Regional evolution of albedo on HG.


Key points from these figures are as follows:

  •  Average albedo across the glacier (αyearly) is decreasing at a rate of 0.0042 ± 0.0011 year-1 with minimum and maximum trends following suit.
  • Analysing average monthly albedo shows that June and July were largely responsible for yearly declines with July albedo decreasing at rate twice that of αyearly (0.0086 ± 0.0023 year.-1). Almost no trend existed for August and September.
  • Regionally 87% of the glacier has seen a decline in albedo.
  • Two seasons saw significant deviations (σ) from daily average albedo (αdaily) with mid-June to early-August 2008 measuring 1 σ below, and early-June to mid-August 2012 measuring 2 σ below at peak melt.
  • Daily melt season anomalies, defined as > 1 σ below αdaily, were five times more common in the period 2008 – 2013 than 2001 – 2007.
  • Albedo standard deviations are at their largest during times of higher melt.

References: Box, J. E., Fettweis, X., Stroeve, J., Tedesco, M., Hall, D., Ste en, K., 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. The Cryosphere 6 (4), 821 – 839.

Time-seies analysis of albedo on Svalbard (Part 2)

Further analysis involved calculating yearly averages as well as the spatial representation of albedo change across Austfonna.

svalbardSDMaxMinFinalaustfonnaAverageQGISFinal


Key points from these figures are as follows:

  • Yearly averages (αyearly) disclose no overall trend, but this masks an almost sinusoidal pattern whereby early and late trends cancel one another. Initial multi-year decline of 0.018 ± 0.0034 year􀀀-1is halted in 2005. Increases are then seen until 2008, whereby another significant forcing reversed the trend once again,into a decreasing trend at 0.0194 ± 0.0029 year􀀀-1.
  • Average monthly albedos also show a slight change in pattern from the eastern Arctic glacier’s with July not providing the greatest proportion of albedo decline and June the only month showing any real decline (0.0063 ± 0.0016 year􀀀-1).
  • Regionally 86% of the glacier has seen a decline in albedo.
  • In contrast to Humboldt Glacier, αdaily exhibits greater short term variability throughout June, July and August. Defining an extreme variance shift as a five unit swing over a period of 3 days, the current declining period (2008 – 2013) has 41 shifts, compared to 16 on Humboldt Glacier