Numerical simulations of glacier evolution performed using flow-line models of varying complexity

Abstract

Abstract. The performance of two numerical models of different complexity, i.e., a Shallow Ice Approximation (SIA) and a Full-Stokes Model (FSM), is studied by analyzing glacier evolutions at various bed geometries and by applying different climatic forcings. Glacier bed geometry changes from a constant slope and a uniform width to a superimposed Gaussian bump or ice-fall on a constant slope and an exponentially varying width. Constant slopes of 0.1, 0.2 and 0.3 are chosen to study the evolution of a large, medium and small glacier, respectively. A specific mass balance serves as a climatic forcing. The steady 5 state is reached 60, 30 and 10 years, respectively faster for large, medium and small glacier, when simulations are performed using SIA instead of FSM. Glaciers time response is studied by using step and periodic changes, and by imposing natural variability in the equilibrium-line altitude. Glacier length response time is up to 14 years longer when FSM is used compared to SIA. When periodic and natural variability are enforced, glaciers simulated using SIA lag in phase compared to the forcing up to 81.2°for glacier length and up to 56.5°for volume. Contrary to that, glaciers simulated with FSM show greater lag in 10 phase compared to the forcing for glacier length and smaller lag for volume. The models differ in their treatment of glacier flow mechanics and differences in physical variables become apparent with increasing glacier bed slope and bed profile complexity.

Spin-up Characteristics with Three Types of Initial Fields and the Restart Effects on the Forecast Accuracy in GRAPES Global Forecast System

“…Due to different types and usages of numerical models, the spin-up time in different models is greatly different. For example, in global climate models, glacial models, and ocean circulation models, the spin-ups usually take decades to hundreds of 65 years (Scher & Messori 2019;Danek et al, 2019;Rimac et al, 2017). But in a regional climate model or a land surface model, only several weeks to several months are needed (Zhong et al, 2008;Rimac et al, 2017;Senatore et al, 2015;Giorgi & Mearns 1999;Chen et al, 1997).…”

Referee’s report on “Numerical simulations of glacier evolution performed using flow-line models of varying complexity” by Antonija Rimac, Sharon van Geffen, and Johannes Oerlemans

“…In order to merit for publication, the authors must relate their results with respect to these papers. How much is actually new here and how much can be deduced from the results in [1] and [2]?…”

“…What is perhaps the most problematic issue with this paper is that it lacks references to [1] and [2] that deal with comparisons between SIA, Second Order Shallow Ice Approximation (SOSIA) and FSM. Moreover, in these papers the validity of the assumptions behind SIA and SOSIA is thouroughly investigated, theoretically and numerically.…”

“…-Overall, the references are fairly old. Apart from [1] and [2] it should be possible to include more relevant and up-to-date references.…”

“…To summarize, my opinion is that if the authors rewrite the paper thoroughly in relation to [1] and [2], it might be acceptable for publication. However, that strongly depends on how much is found to be new in the present paper when this is included.…”