The short variable names given in the tables have been selected to be unique and easy to understand. In order to easily analyze results from multiple models it is necessary that all output is returned with the same variable names. However, we recognize that to change the name of output variables in an existing model may be very difficult as it changes habits of the users. The program "ncrename" of the NCO package can be used to rename variable in the netCDF output file before it is send to the inter-comparison centre. In any case the quality screening program will prompt the user to provide alias names for variables when the standard ALMA variables are not encountered. The aliased variables will then be automatically replaced with the ALMA standard in the netCDF file to be returned for analysis.
This column provides the long name of the variable which describes properly the content. This description should be included in the netCDF files as it is much more explicit than just the name of the variable. The long name depends much less than the variable names on personal preferences.netCDF attribute for variable description : long_name
Much thought and discussion has gone into the choice of a standard set of units which will be logically defined and easy to analyze. We have decided that it is most appropriate to use SI units in all cases. Since in some cases the choice of SI units is not intuitive a program is provided which can be used to transfer between units.netCDF attribute for variable units : units
For the convenience of the user, it has been decided to allow the choice of sign convention between two options. Each scheme must consistently follow one of these conventions. For the 'traditional approach', all variables are positive in their 'dominant' direction, i.e. precipitation, and radiation positive towards the surface; evaporation, sensible heat and runoff are positive away from the surface. For the 'mathematical approach', the sign is chosen so water and energy fluxes will balance, i.e. precipitation, and radiation are positive towards the surface; evaporation, sensible heat and runoff are negative away from the surface. A netCDF global attribute is used to specify in the file the sign convention used. The quality check software will use this attribute to evaluate the data. The unit conversion program also allows for the sign change of variables.netCDF global attribute for sign convention : SurfSgn_convention
This column indicates the level of importance associated with each variable. Variables considered "Mandatory" must be included for all LSS inter-comparison projects. It is encouraged that "Recommended" variables be included for most inter-comparisons. Those variables marked "Optional" refer to properties which may only be significant in some climates or for some applications and therefore may not be used for all inter-comparison projects. Each project within GLASS may choose to make any of the recommended or optional output variables mandatory for its inter-comparison. This depends on the type of analysis which is intended during the project. The mandatory variables on the other hand should always be provided as they allow to check the general behavior of the scheme.
There is a small but important distinction to be made between these two variables. The average surface temperature is the mean of all temperatures resulting from the energy balances performed by the schemes within the grid-box. This averaging process should be representative of the modeled interactions of the surface with the lower variables of the atmosphere. It thus needs to take into account the assumptions made in the land-surface scheme on the fractions of vegetation present in the grid-box as well as the way the relation between the ground and vegetation temperatures are considered for the calculation of the turbulent fluxes to the atmosphere.
The radiative temperature, on the other hand, is the average of all
temperatures used by the model to compute the outgoing long-wave flux of
the grid-box. Obviously this averaging process needs to take into account
the fact that the outgoing long-wave flux has to be conserved. It is thus
different from the one for the surface temperature as the T4
variables needs to be averaged. Other differences between
both temperatures may arise from the numerical implementation of
the energy balance. It is not given that the same temperature is
used to compute the turbulent flux and the long-wave
radiation. Thus the distinction between both temperatures is
needed but very simple model may not show any difference between
This variable should
include the fast component of runoff response. This includes any
surface runoff generated as infiltration excess runoff or
saturation excess runoff (or the parameterized equivalent). In
addition it should include any subsurface lateral quick-flow, which
based on modelers experience is best routed as a fast storm-flow
component, rather than a drainage or base-flow component. This variable represents
streamflow which leaves the channel network and returns to the
grid cell interface. The sign will always be opposite to that of
surface runoff and the recharge quantity should not be subtracted
from the surface runoff variable when recharge is specified. This variable should
include the slow drainage component of runoff response. This
includes gravity drainage and lateral base-flow.
Change in Storage These variables
represent the accumulated change in storage from the beginning of
each archiving time step to the end. These are the quantities
which are required to resolve the water balance at any time scale.
They differ from the storage terms (SurfStor, SoilMoist, etc.)
which represent the average storage for each time step.
This variable should include the fast component of runoff response. This includes any surface runoff generated as infiltration excess runoff or saturation excess runoff (or the parameterized equivalent). In addition it should include any subsurface lateral quick-flow, which based on modelers experience is best routed as a fast storm-flow component, rather than a drainage or base-flow component.
This variable represents streamflow which leaves the channel network and returns to the grid cell interface. The sign will always be opposite to that of surface runoff and the recharge quantity should not be subtracted from the surface runoff variable when recharge is specified.
This variable should include the slow drainage component of runoff response. This includes gravity drainage and lateral base-flow.
These variables should contain the average soil temperature for each simulated soil layer. The thickness and number of layers may not be identical for all schemes for all applications. In the case of a large number of simulated layers, participants may choose to combine results for some layers. For models which do not explicitly track soil layer boundaries it is left to the discretion of the modeler to define boundaries, or to return only one depth-averaged quantity.
This variable should contain the average non-frozen moisture content for each simulated soil layer, as described above. If soil freezing is not represented, this quanity will be equal to SoilMoist.
To be calculated as the total simulated soil moisture (minus the soil moisture at wilting point) divided by the maximum allowable soil moisture (minus the soil moisture at wilting point). This will give an indication of the degree of saturation of the soil and allow calculation of the maximum available soil moisture, in conjunction with the total simulated soil moisture provided in table O.2.
Sea-ice refers to all ice, whether formed on oceans, seas or lakes. The sea-ice fraction is given relative to the area of the entire grid cell, even if only a portion of the grid cell contains oceans or lakes.
Although the atmospheric state variables needed to force land-surface schemes are two dimensional, it was chosen to save them in arrays of rank 3. This allows to specify the vertical dimension even if its size is equal to one. On this axis the hight of the atmospheric variables will be specified. There are two advantages to including the vertical axis : First the height of the variable does not need to be provided outside of the forcing data file and it can evolve over time, secondly if for future land-surface scheme inter-comparisons data on more than one atmospheric level will be provided the format does not need to change.