HHMMSS = 10000 * hour + 100 * minutes + seconds YYYYDDD = 1000 * year + daywhere the year is 4-digits (1994, say, rather than just 94), and the day is the Julian day-number (1,...,365 or 366).
A time step sequence is a sequence of dates and times
{ [date(0),time(0)], [date(1),time(1)], ... [date[N],time[N] }having a starting date and time [date(0),time(0)], a time increment dT, and such that each [date(K),time(K)] is exactly dT away from [date(K-1),time(K-1)]. Note that each file has a time step sequence (where by convention, time increment dT=0 means that the data in the file is time-independent, and routines like READ3() and WRITE3() which deal with time-independent files ignore the date-and-time arguments.
There are a number of utility routines available for manipulating dates and times, in addition to programs gregdate and juldate for converting back and forth between model-convention Julian dates and ordinary calendar dates. Note that for these utility routines, time increments may perfectly well be negative -- just make sure you keep the parts all positive or all negative; a time increment of -33000 means to step three and a half hours into the past, for example; the hours part is -3, the minutes part is -30, and the seconds part is 0. This way of representing dates and times is easy to understand and manipulate when you are watching code in the debugger (you don't have to turn the UNIXism "seconds since Jan. 1, 1970" into something meaningful for your model run, nor do you have to remember whether April has 30 days or 31 when your model run crosses over from April to May). The utility routines for manipulating dates and times are the following:
Next Section: Calling from Fortran
To: Models-3/EDSS I/O API: The Help Pages