There are lots of different timesteps and substepping going on in the ACME v1 model (much of which is inherited from v0). This page is an attempt to clarify what values we typically use for these substeps. Note that most of the substep values for dynamics are illustrated in this slide:
This table provides the values we've been using and explanation of what each quantity means.
ne30 v0 | ne30 v1 | ne120 before 8/10/16 | ne120 after 8/10/16 | Explanation | |
|---|---|---|---|---|---|
| dtime | 30 min | 15 min | 15 min | Timestep used for most physics processes and for coupling between physics and dynamics | |
| se_nsplit | 2 dt_remap=900s | 4 | 6* | dtime/se_nsplit = time between vertical remaps of the semi-Lagrangian vertical coordinate. | |
| se_rsplit | 3 dt_tracer = 300s | 3 | 2* | dtime/(se_nsplit*se_rsplit) = timestep used for tracer timestep For ne30, dt_tracers = 360s is probably stable, but we usually use 300s For ne120, dt_tracers = 90s is probably stable, but we usually use 75s. | |
| se_qsplit | 1 | 1 | 1 | 1 | dtime/(se_nsplit*se_qsplit*se_rsplit) = timestep used for dynamics calculations This should always be 1, so that dt_dyn = dt_tracers. |
| hypervis_subcycle | 3 dt_vis = 100s | 4 | 4 | dtime/(se_nsplit_se_qsplit*se_rsplit*hypervis_subcycle) = timestep used for hyperviscosity calculation | |
| hypervis_subcycle_q | 1 | 1 | 1 | dtime/(se_nsplit_se_qsplit*se_rsplit*hypervis_subcycle_q) = timestep used for hyperviscosity calculation in tracer advection (namelist_definition.xml indicates that only '1' is supported in CAM?) | |
| cld_macmic_num_steps | 6 | 3* | 3 | Number of times the code surrounding macrophysics + microphysics is subcycled. This means that dtime/cld_macmic_num_steps = timestep used for macrophysics and microphysics. | |
| clubb_timestep | 300 sec | 300 sec | 300 sec | I'm not sure what this means or how it relates to cld_macmic_num_steps | |
| IRADSW | 2 steps | 4 steps (1 hr) | 4 steps (1 hr) | How frequently to compute SW radiation (in multiples of dtime). Radiation tendencies are taken from previous steps for steps when radiation is not recalculated. I think some scaling is made to account for zenith angle changes? | |
| IRADLW | 2 steps | 4 steps | 4 steps | How frequently to compute LW radiation (in multiples of dtime). Radiation tendencies are taken from previous steps for steps when radiation is not recalculated. | |
| *since AV1C-04 | *suggest to use |