# 5.1. Overview of fields computation: PREP

The prognostic fields (temperature, humidity, ice, snow, etc...) are averaged or interpolated on the specified grid by the program PREP. They are stored in the surface file. The computation is done separately for each surface scheme.

During the PREP facility :

1. You initializes the date of the surface
2. You initializes the prognostic variables of the chosen sea scheme
3. You initializes the prognostic variables of the chosen lake scheme
4. You initializes the prognostic variables of the chosen vegetation scheme
5. You initializes the prognostic variables of the chosen town scheme

Here are presented the initialization procedures for the schemes that need such information (for example, scheme "IDEAL " does not need any information here, but modificaton of the code source init_ideal_flux.f90).

Note that for each scheme, and for some for each variable of the scheme, it is possible to initialize the prognostic fields either form an operationnal or research model, or using prescribed (usually uniform) fields.