Metscan reads in a single (often annual) temperature I/O API meteorology data file (created from either the MET_CRO_2D or MET_CRO_3D files) and determines the first freeze date and last freeze date of a year, by grid cell. It outputs a gridded file with a daily (24-hour) time step that contains a single variable. For each grid cell, that variable has a value of 0 (zero) when the date being modeled indicates that the cell is experiencing winter conditions; otherwise it has a value of 1, indicating summer conditions. The program can be set to run in the Northern Hemisphere or in the Southern Hemisphere (it will not work on global meteorology datasets). In the Northern Hemisphere, the first freeze date in the fall marks the start of winter, and the last freeze date in the spring marks the end of winter; all other days are considered summer days. The seasons are reversed in the Southern Hemisphere, and the program accommodates this accordingly.

Both the BEIS2 and BEIS3 models operate using the assumption of either winter or summer emission factors. There are no spring or fall factors available, which is why this program is limited to the choice of summer or winter. The use of the freeze date to determine summer or winter emission factors is based on EPA’s recommendation.

The program reads in the name of the temperature variable as an option, so that the ground temperature, 1.5-meter temperature, or 10-meter temperature can be used from the MET_CRO_2D file, or the layer-1 temperature can be used from the MET_CRO_3D file. See the TMPR_VAR option below for more information on the names of the temperature variables that are acceptable.