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Theory

 

In the extended model the flowing avalanche core ($\Phi$) consists of clumps and clods of snow (granules); the cloud consists of mixture of air and ice-dust ($\Pi$), see Fig. 1. The core is physically treated as a gravitationally driven, granular shear flow; the cloud is modelled as an inertial, turbulent suspension. Because the snow material in the core is non-suspendable and the ice-dust in the cloud is suspendable, two flow layers exist simultaneously, but with different flow densities ($\rho_{\Phi}$, $\rho_{\Pi}$) and speeds ($\textbf{u}_{\Phi}$, $\textbf{u}_{\Pi}$). The layers are formed by natural segregation because of the large difference in particle sizes – dust (< 1mm) and granules (>1cm) – and therefore settlement speeds. 

Figure 1: The RAMMS::EXT model simulates both the avalanche core ($\Phi$) and the powder cloud ($\Pi$). The core consists of snow granules; the cloud of suspendable ice-dust. The RAMMS model divides the core and cloud into two separate but overlapping flow layers. The densities of the avalanche core and powder cloud vary in the streamwise direction.
 

Random Kinetic Energy

The Random Kinetic Energy (RKE) approach splits the shear work rate into the production of thermal and granular temperatures.

Entrainment

Avalanche interaction with the snowcover is physically treated as an elastic-plastic collision in which snow can be entrained (plastic collision).

Temperature

It has long been recognized that warm, moist snow behaves differently than cold, dry snow.

The Formation of the Powder Cloud

The avalanche cloud is mathematically treated as an inertial, turbulent suspension.

Forest

The forest module applies the detrainment method developed by Feistl et al. 20??.

Pressure Modules

The RAMMS::Extended model contains two pressure modules.