NPZ-model/Physical-Processes.md

@@ -19,18 +19,26 @@ The underwater light conditions is depending on the the irradiation and the exti
 I_{z} = I_{0} \cdot e^{-k_{d} \cdot z}
 ```
 
-The extinction coefficient ($`k_{d}`$) is depending on the amount of Total Particulate Matter in the water.  
+The extinction coefficient ($`k_{d}`$) is depending on the amount of Total Particulate Matter (TPM) in the water that varies over the season (described by cosine function). The extinction coefficient is calculated from the TPM concentration using a simplified version of the function that is used by Los and Wijsman (2007), based on Van Gils and Tatman (2003).  
 Los and Wijsman (2007) use the relation from Van Gils and Tatman (2003)  
 
 
+```math
+k_{d} = 0.24 + 0.036 \cdot TPM
+```
+
+Where the background extinction is 0.25 m<sup>-1</sup> (including the extinction due to dissolved humic substances) and TPM is the concentration of suspended sediment particles (mg l<sup>-1</sup>)
+
 The average light ($`I_{avg}`$) is calculated by integration of the function over the whole water column divided over the waterdepth. 
 
 ```math
 I_{avg} = \frac{ \int_{z=0}^{z=Depth} \cdot I_{z} \cdot dz}{Depth}
 ```
 
-It is assumed that about 50% of the light is photosynthetic active radiation (PAR) $`PAR = 0.5 \cdot I_{avg}`$
-
+It is assumed that about 50% of the light is photosynthetic active radiation (PAR) .
+```math
+PAR = 0.5 \cdot I_{avg}
+```
 
 
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