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kb:lbc [2012/07/30 23:22] enviadminkb:lbc [2012/07/30 23:49] enviadmin
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 ====== Lateral Boundary Conditions ====== ====== Lateral Boundary Conditions ======
 +Lateral boundary conditions define the way, the model behaves at its lateral boundaries. This is a very specific setting and you normally do not need to change these settings.\\
 +**From Version 4 on, it is recomended to use at least the "Simple Forcing" for temperature and humidity. This overcomes almost all problems that have been observed with the lateral boundaries in the former versions.** 
  
 ===== What Kind of LBCs are available in ENVI-met? ===== ===== What Kind of LBCs are available in ENVI-met? =====
  
 Three different kinds of LBC can be selected in ENVI-met: Three different kinds of LBC can be selected in ENVI-met:
-  * **open LBC**: The values of the next grid point close to the border are copied to the border for each time step +  * **Open LBC**: The values of the next grid point close to the border are copied to the border for each time step 
-  * **forced (or closed) LBC**: The values of the one dimensional model are copied to the border  +  * **Forced (or closed) LBC**: The values of the one dimensional model or from the forcing data are copied to the border  
-  * **cyclic LBC**: The values of the downstream model border are copied to the upstream model border+  * **Cyclic LBC**: The values of the downstream model border are copied to the upstream model border
  
  
-You can choose the LBCs for temperature, humidity and for the turbulence variables. For the flow field, an open LBC will be used in any case.+You can choose the LBCs for temperature, humidity and for the turbulence variables. For the flow field, an open LBC will be used in a non-forced or "Simple-forced" configuration. 
 +If you use **Forcing** (either Simple Forcing or Full Forcing), the LBCs will be in any case "Forced" so that your pre-defined profils (temperature, humidity, wind,..) will be copied to the main model.
  
  
 ===== Which LBC is the best one? ===== ===== Which LBC is the best one? =====
  
-The is no general clue, which LBC is the best for your case. Each LBC type represents some kind of situation in the model and you have to check which one is the most appropriate assumption for your case. At the end of this section you will find an illustrated example which might help you in your choice.+The is no general clue, which LBC is the best for your case. Each LBC type represents some kind of situation in the model and you have to check which one is the most appropriate assumption for your case. At the end of this section you will find an illustrated example which might help you in your choice.\\ 
  
 The **open LBC** is the condition with the minimum effect of the model boundary to the inner parts of the model. For most cases, this is the recommended LBC. But as the open LBC copies the values from the inner parts of the model to the boundaries, there is a certain danger of numerical instabilities. The **open LBC** is the condition with the minimum effect of the model boundary to the inner parts of the model. For most cases, this is the recommended LBC. But as the open LBC copies the values from the inner parts of the model to the boundaries, there is a certain danger of numerical instabilities.
  
-The **forced LBC** is the most stable condition because the mostly independent 1D model is used to obtain the boundary values which stabilises the 3D model. On the other hand, the 1D profile will have a significant effect on the data in the main model. If the 1D profile is not representative for your average conditions, this will cause a certain error. At the moment beingthe inflow profile for the forced LBC is obtained from the internal 1D model. In future versions it will also be possible to use external given data (e.g. from mesoscale models or from radio soundings) to force the 3D model.+The **forced LBC** is the most stable condition because the mostly independent 1D model is used to obtain the boundary values which stabilises the 3D model. On the other hand, the 1D profile will have a significant effect on the data in the main model. If the 1D profile is not representative for your average conditions, this will cause a certain error. If you use the "Simple Forcing" optionforced LBC will be applied for the temperature and the humidity. The values applied to the model border are taken from your given profileIf you use the "Full Forcing" mode, a forced LBC will be applied to all variables, that are actually forced in your configuration, including the wind
  
 Finally, the **cyclic LBC** assumes that the average conditions upstream of your model area (which produce the inflow profile) are similar to your model area. As the values of the outflow boundary are copied to the inflow boundary there is also a certain danger of undesired feedback inside the model which might cause numerical instabilities. Finally, the **cyclic LBC** assumes that the average conditions upstream of your model area (which produce the inflow profile) are similar to your model area. As the values of the outflow boundary are copied to the inflow boundary there is also a certain danger of undesired feedback inside the model which might cause numerical instabilities.