PALM-4U provides a standardized way via the NetCDF data format to input e.g. global attributes, topography data or surface properties, vegetation properties, etc., as well as initialization data and boundary conditions for the prognostic variables.

Input variables are distinguished between static, dynamic, radiation and chemistry variables, while for each type a separate input file exists. The static input file, indicated by the filename supplement _STATIC, contains all static information, such as topography, geographical latitude and longitude, surface property and vegetation information. The dynamic input file, indicated by the filename supplement _STATIC, contains dynamic information on the initial state of the atmosphere or time-dependent boundary conditions. The radiation input file, indicated by _RAD, contains static and dynamic information on radiation properties such as trace gas profiles or sky-view factors. The chemistry input file, indicated by _CHEM, contains static and dynamic information on chemical species and emissions.

The initialization procedure for the surface elements follows a multi-step approach, depending on the given level of detail. In a first step, surfaces elements are initialized horizontally homogeneous with a bulk classification for each type (e.g. vegetation or soil), either set by a default value or set by a namelist-provided value, while the bulk classification provides standard values for a variety of parameters. In a second step, surface elements are initialized individually by providing the bulk classification at each grid point. In case more detailed information is available, all/single parameters can also initialized individually at each grid point.

The provided input data is used to classify each surface element according to its treatment, i.e. default-, natural- or urban-type, in order to treat each surface element accordingly. In case no land-surface or urban-surface scheme is applied, all surfaces are classified as default-type. If a surface element has vegetation, pavement or water, it will be classified as natural-type and is treated by the land-surface scheme, while building surfaces will be treated by the urban-surface scheme.

After reading the input files, PALM-4U performs consistency checks on the provided data. All applied input variables are listed and explained below and additional remarks on restrictions and initialization are given. More detailed information on variable attributes can be found in the PIDS-1.7.

Topography:

Input variable	Type	Explanation / Remarks
orography_2D(y,x)	NC_FLOAT	Terrain height in m above sea level. The relative model height is orography_2D - origin_z. If not provided, orography_2D - origin_z will be set to 0 all over the model domain. Please note, orography_2D must not contain any _FillValues.