6.6. Flow law

Several options for the flow law of polycrystalline ice are available. They can be selected by the parameter FLOW_LAW in the run-specs headers:

• 1: Nye-Glen flow law (Glen [18], Nye [51]) with stress exponent \(n\).

• 4: Polynomial flow law by Smith and Morland [60], modified by Greve and Staroszczyk [40].

The rate factor \(A(T')\) is defined as a list for integer temperature values, to be read from a file specified in the run-specs header (parameter RF_KAPPA_C_FILE). Between integer temperatures, linear interpolation is applied. To avoid problems with varying units and numerical values, a dimensionless formulation is chosen (Greve [29]).

For the case FLOW_LAW = 1, the stress exponent \(n\) is defined by the parameter N_POWER_LAW. The additional parameter FIN_VISC allows choosing between the unmodified flow law with an infinite-viscosity limit for low strain rates (FIN_VISC = 1), or using a regularized flow law with a finite-viscosity limit (FIN_VISC = 2). The latter is defined by a non-vanishing residual stress \(\sigma_0\) (parameter SIGMA_RES; see Greve and Blatter [30], Section 4.3.2; recommended value \(10^4\,\mathrm{Pa}\)).

An alternative flow-law regularization that affects only non-SIA dynamics can be done via defining a minimum value for the effective strain rate \(d_\mathrm{e,min}\) (parameter D_E_MIN, recommended value \(10^{-9}\,\mathrm{a^{-1}}\)).