# 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`

: Glen’s flow law (Glen [19], Nye [51]) with stress exponent \(n=3\).`2`

: Goldsby-Kohlstedt [22, 23] flow law with stress exponent \(n=1.8\) and grain-size exponent \(p=1.4\). Average grain size defined by the parameter`GR_SIZE`

.`3`

: Flow law by Durham et al. [16] with stress exponent \(n=4\).`4`

: Polynomial flow law by Smith and Morland [60] (summarized by Greve and Blatter [31], Section 4.3.3).

For the cases `FLOW_LAW = 1, 2 or 3`

, 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 [31], Section 4.3.2).

Note

The rate factor \(A(T')\) must fit the flow law unit- and value-wise. It 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.