Lecture Revision Questions (Glaciers)

What is glacier mass balance, and what are the three ways of collecting data to calculate it? (1)

Glacier mass balance is the relationship between accumulation and ablation, from this an equilibrium line can be calculated that determines the topography of a glacier over time. Data can be collected using the glaciological method (in-situ, surface measurements using stakes), geodetic (satellites, GPS) or geodetic methods (GRACE and GRACE-FO).

What are the key considerations you need before beginning modelling glacier mass balance? (1)

Spatial domain (what dimension you will model in), mathematical descriptions (which model and calculation will be used), inputs and observations that are used to calibrate models.

What does the degree day model calculate, what are the pros and cons of this model? (1)

The degree day model calculates the empirical relationship between air temperature and melting per positive degree day and also tracks refreezing due to air temperatures. This is useful as it is easy, only requires air temperature measures and can predict future melt but is empirical, offers limited insights into processes and gives limited information on temporal patterns.

What does the energy balance model calculate, what are the pros and cons of this model? (1)

The energy balance model calculates how much energy is available at the glacier surface to melt ice or snow taking into account many variables and calculating conduction. This is useful as it provides good insight into processes, useful over spatial and temporal scales and can be applied to other glaciers but is expensive and requires many inputs.

What have hybrid models been used to calculate, how have these been useful? (1)

Hybrid models are variants on the degree day model and have been used to account for potential clear sky radiation (patterns of shading) and cloud cover. This is useful for future predictions and accounting for alternative spatial methods.

Where do inputs to models come from, and how are the models then used to reveal information about glaciers? (1)

Inputs can come from automatic weather stations, climate models and observations but these must be extrapolated over whole glaciers and calibrated. Once this has occurred models can be used to understand glacial sensitivity to other factors, inter-comparison of other models and global assessments of contributions to processes such as sea level rise.