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History Interval becomes different in wrfout d01

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I'm running 3 domains where history intervals are 60, 15, 5 sometimes 60, 30, 10.
Every time for domain 1 the interval becomes like following,

Times =
"2019-03-31_00:00:00",
"2019-03-31_01:00:18",
"2019-03-31_02:00:36",
"2019-03-31_03:00:00",
"2019-03-31_04:00:18",
"2019-03-31_05:00:36",
"2019-03-31_06:00:00",
"2019-03-31_07:00:18",
"2019-03-31_08:00:36",
"2019-03-31_09:00:00",
"2019-03-31_10:00:18",
"2019-03-31_11:00:36",
"2019-03-31_12:00:00",
"2019-03-31_13:00:18",
"2019-03-31_14:00:36",
"2019-03-31_15:00:00",
"2019-03-31_16:00:18",
"2019-03-31_17:00:36",
"2019-03-31_18:00:00",
"2019-03-31_19:00:18",
"2019-03-31_20:00:36",
"2019-03-31_21:00:00",
"2019-03-31_22:00:18",
"2019-03-31_23:00:36",
"2019-04-01_00:00:00" ;

where does this extra 18 second come from in the interval?
What should i do for getting the output 1 hour interval for domain 1 while running 3 domains together???

my namelist is attached here.
 

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Your problem is your dynamics timestep:
time_step = 54,

You want to output information every hour, but 3600 is not dividable by 54 (or, at least, you don't get an integer answer). If the next scheduled output time falls in the middle of a dynamics timestep, rather than stop that timestep WRF will wait until it is finished to write the output file, so you'll end up with the pattern of irregular output times that you're seeing.

The solution is simple - change your dynamics timestep to match your output step. The advice of using 6*dx (in km) for your dynamics timestep is intended as the *minimum* sensible timestep length - so you can change to 60 seconds and it'll run fine.
 
Thanks a lot. Just now, I've got the point.


douglowe said:
Your problem is your dynamics timestep:
time_step = 54,

You want to output information every hour, but 3600 is not dividable by 54 (or, at least, you don't get an integer answer). If the next scheduled output time falls in the middle of a dynamics timestep, rather than stop that timestep WRF will wait until it is finished to write the output file, so you'll end up with the pattern of irregular output times that you're seeing.

The solution is simple - change your dynamics timestep to match your output step. The advice of using 6*dx (in km) for your dynamics timestep is intended as the *minimum* sensible timestep length - so you can change to 60 seconds and it'll run fine.
 
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