Two modes of sea‐ice gravity drainage: A parameterization for large‐scale modeling

Abstract

[1] We present a new one-dimensional parameterization of gravity drainage implemented in an all-new thermodynamic component of the Los Alamos Sea Ice Model (CICE), based on mushy layer theory. We solve a set of coupled, nonlinear equations for sea-ice temperature (enthalpy) and salinity using an implicit Jacobian-free Newton-Krylov method. Time resolved observations of gravity drainage show two modes of desalination during growth. Rapid drainage occurs in a thin region just above the ice/ocean interface, while slower drainage occurs throughout the ice. Parameterizations are designed to represent each of these modes and work simultaneously. Near the interface, desalination occurs primarily via the fast drainage, while slow drainage continues to desalinate ice above the interface. The rapid desalination is convectively driven and is parameterized based on a consideration of flow driven upward within the mush and downward in chimneys, modified by the Rayleigh number. The slow desalination is represented as a simple relaxation of bulk salinity to a value based on a critical porosity for sea-ice permeability. It is shown that these parameterizations can adequately reproduce observational data from laboratory experiments and field measurements.Citation: Turner, A. K., E. C. Hunke, and C. M. Bitz (2013), Two modes of sea-ice gravity drainage: A parameterization for large-scale modeling,

Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model

“…In the following discussion, we denote R the correlation and R the detrended correlation. Summarizing figures 12, 13 and 14, one can conclude that introducing the new physical parametrizations schemes described in §2 and, in particular, the new mushy-layer thermodynamic approach of Turner et al [37] can improve the main basin average characteristics of the sea ice with respect to the SFFT14 set-up. The improvement is particularly clear for the August SIA and SIE and the September SIA.…”

“…We solve the system of equations (2.4)-(2.6) separately for each ice thickness category and save T 0 , S 0 as well as all fluxes as output variables. Note that this parametrization scheme is only operational in CICE when the mushy layer parametrization of Turner et al [37] is switched on.…”

“…In SST_TIME, we use a timedependent SST from the MYO reanalysis which is equivalent to modifying the oceanic flux F adv shown on figure 1. As clearly demonstrated in Turner & Hunke [38], by introducing a new mushy layer thermodynamic scheme [37] (NO_3EQTN and REF), we also modify the flushing parametrization used in the earlier set-up of CICE [36] (NO_MUSHY). This results in less melt pond water being flushed in the summer in NO_MUSHY as opposed to in NO_3EQTN (or REF) which lowers the albedo and increases the incoming shortwave radiation penetrating the sea ice and ML system, resulting in a strong reduction in SIV as shown in figure 12g-i.…”

Sea-ice thermodynamics and brine drainage

“…Indeed, the model of Turner et al [19] is now included as an option within CICE v. 5 [22]. They share the common assumption, based on the observations above of more detailed models, that the brine flux varies linearly with the Rayleigh number.…”

“…Turner et al [19] take the flow rate to be the largest of the flow rates they calculate for layers at or above the layer in question. The dominant character of this choice is illustrated by the expression…”