Title: 2.8. Snow Hydrology — ctsm CTSM master documentation

URL Source: https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Snow_Hydrology/CLM50_Tech_Note_Snow_Hydrology.html

Markdown Content:
The parameterizations for snow are based primarily on [Anderson (1976)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#anderson1976), [Jordan (1991)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#jordan1991), and [Dai and Zeng (1997)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#daizeng1997). The snowpack can have up to twelve layers. These layers are indexed in the Fortran code as \\(i=-11,-10,...,-1,0\\) where layer \\(i=0\\) is the snow layer next to the top soil layer and layer \\(i=-11\\) is the top layer of a twelve-layer snow pack. Since the number of snow layers varies according to the snow depth, we use the notation \\(snl+1\\) to describe the top layer of snow for the variable layer snow pack, where \\(snl\\) is the negative of the number of snow layers. Refer to [Figure 2.8.1](#figure-three-layer-snow-pack) for an example of the snow layer structure for a three layer snow pack.

![Image 1: ../../_images/image16.png](https://escomp.github.io/ctsm-docs/versions/master/html/_images/image16.png)

Figure 2.8.1 Example of three layer snow pack (\\(snl=-3\\)).[¶](#id14 "Permalink to this image")

Shown are three snow layers, \\(i=-2\\), \\(i=-1\\), and \\(i=0\\). The layer node depth is \\(z\\), the layer interface is \\(z\_{h}\\), and the layer thickness is \\(\\Delta z\\).

The state variables for snow are the mass of water \\(w\_{liq,i}\\) (kg m\-2), mass of ice \\(w\_{ice,i}\\) (kg m\-2), layer thickness \\(\\Delta z\_{i}\\) (m), and temperature \\(T\_{i}\\) (Chapter [2.6](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Soil_Snow_Temperatures/CLM50_Tech_Note_Soil_Snow_Temperatures.html#rst-soil-and-snow-temperatures)). The water vapor phase is neglected. Snow can also exist in the model without being represented by explicit snow layers. This occurs when the snowpack is less than a specified minimum snow depth (\\(z\_{sno} < 0.01\\) m). In this case, the state variable is the mass of snow \\(W\_{sno}\\) (kg m\-2).

Section [2.8.1](#snow-covered-area-fraction) describes the calculation of fractional snow covered area, which is used in the surface albedo calculation (Chapter [2.3](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Surface_Albedos/CLM50_Tech_Note_Surface_Albedos.html#rst-surface-albedos)) and the surface flux calculations (Chapter [2.5](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Fluxes/CLM50_Tech_Note_Fluxes.html#rst-momentum-sensible-heat-and-latent-heat-fluxes)). The following two sections ([2.8.2](#ice-content) and [2.8.3](#water-content)) describe the ice and water content of the snow pack assuming that at least one snow layer exists. Section [2.8.4](#black-and-organic-carbon-and-mineral-dust-within-snow) describes how black and organic carbon and mineral dust particles are represented within snow, including meltwater flushing. See Section [2.8.5](#initialization-of-snow-layer) for a description of how a snow layer is initialized.

