REGRID Tutorial : Introduction

Program REGRID is the second program in the suite of MM5 system programs. This program creates meteorological fields on the mesoscale grid you designed in program TERRAIN. This is also the first place you will select the time period of the case. You should not be here if you have not successfully run TERRAIN program.

REGRID has two sequential programs: pregrid and regridder. Program pregrid pre-processes gridded, pressure-level meteorological fields from another source (such as the NCAR archive, and NCEP's ftp server) and puts the data in an intermediate format. Program regridder takes the intermediate-format data and output file from TERRAIN, and creates what we call a "first-guess" for subsequent programs. The output file from REGRID will have 3-dimensional meteorological fields of wind, temperature, relative humidity, geopotential height, and 2-dimensional fields like sea-level pressure and sea-surface temperature.

 

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Because MM5 is a regional model, it requires initial condition as well as lateral boundary condition to run. The requirement of lateral boundary conditions means that you will need to obtain data to cover the entire model integration period during pre-processing. For example, if you plan on doing a 24-h model run, and your first-guess is available at 12 hourly intervals, you will need to obtain data at 0, 12 and 24-h times in order to make the MM5 run. Even if you only want to integrate the model for less than 24 hours, it is a good practice to obtain data for at least one whole day. This is because the surface air temperature will be averaged (in INTERPF) to calculate what is called the 'substrate temperature' or 'deep soil' temperature for MM5 to use as a lower boundary condition. Averaging daily temperature would give you a better estimate than using temperatures for day time or night time alone.