fix: force shortest_time_between_assimilations to be at least the mod…

…el dt

Previous code would let you set assimilation_period_seconds = 0
which gave you a 0 sized assimilation window
#404 (comment)

models/wrf/model_mod.f90

@@ -134,7 +134,6 @@ module model_mod
 ! module variables
 character(len=256), parameter :: source   = "wrf/model_mod.f90"
 logical :: module_initialized = .false.
-type(time_type) :: assimilation_time_step
 
 integer, parameter :: MAX_STATE_VARIABLES = 100
 integer, parameter :: NUM_STATE_TABLE_COLUMNS = 4
@@ -209,6 +208,7 @@ module model_mod
   integer :: wes, sns ! west-east staggered, south-north staggered number of grid points
   integer :: bt ! bottom-top number of grid points
   integer :: bt_stag ! staggered bottom-top number of grid points
+  real(r8) :: dt ! time step
 
   ! wrf options, apply to domain 1 only.
   logical :: polar = .false.
@@ -251,7 +251,6 @@ subroutine static_init_model()
 integer :: nfields
 logical, allocatable :: domain_mask(:)
 integer :: i, field ! loop indices
-integer :: model_dt, assim_dt
 character (len=1)     :: idom ! assumes <=9
 
 module_initialized = .true.
@@ -266,11 +265,6 @@ subroutine static_init_model()
 
 call set_calendar_type(calendar_type)
 
-model_dt = 1
-print*, 'FAKE model_dt', model_dt
-assim_dt = (assimilation_period_seconds / model_dt) * model_dt
-assimilation_time_step = set_time(assim_dt) ! assimilation window
-
 allocate(wrf_dom(num_domains), grid(num_domains), stat_dat(num_domains))
 
 call verify_state_variables(nfields, varname, state_qty, update_var, in_domain)
@@ -451,10 +445,17 @@ end subroutine model_interpolate
 function shortest_time_between_assimilations()
 
 type(time_type) :: shortest_time_between_assimilations
+integer :: model_dt
 
 if ( .not. module_initialized ) call static_init_model
 
-shortest_time_between_assimilations = assimilation_time_step
+model_dt = nint(grid(1)%dt) ! model time step in seconds lowest res domain
+
+if (assimilation_period_seconds < model_dt ) then
+   shortest_time_between_assimilations = set_time(model_dt)
+else
+   shortest_time_between_assimilations = set_time(assimilation_period_seconds)
+endif
 
 end function shortest_time_between_assimilations
 
@@ -952,7 +953,8 @@ subroutine read_grid()
     call nc_get_global_attribute(ncid, 'TRUELAT1', grid(i)%truelat1)
     call nc_get_global_attribute(ncid, 'TRUELAT2', grid(i)%truelat2)
     call nc_get_global_attribute(ncid, 'STAND_LON', grid(i)%stand_lon)
-
+    call nc_get_global_attribute(ncid, 'DT', grid(i)%dt)
+
     grid(i)%bt = nc_get_dimension_size(ncid, 'bottom_top', routine)
     grid(i)%bt_stag = nc_get_dimension_size(ncid, 'bottom_top_stag', routine)