Hi CTSM developers,
I have a question about how nbedrock is used when initializing excess ground ice in CTSM5.3.026.
In WaterStateType.F90, excess ice is initialized only when
j >= nexice .and. j < nbedrock
so the layer j = nbedrock is always excluded from excess-ice initialization.
However, my understanding is that nbedrock represents the last standard soil layer associated with the prescribed bedrock depth. For example, the code classifies
1:nbedrock
as LEVGRND_CLASS_STANDARD, while layers below nbedrock are classified as bedrock.
This leads to a few cases that I am having difficulty interpreting physically.
For the default configuration with 20 soil layers, the bedrock depth is set to the bottom interface of layer 20. Therefore, layer 20 is entirely above the bedrock interface and is still a standard soil layer. However, because the excess-ice condition is j < nbedrock, excess ice can only be initialized through layer 19, and layer 20 is excluded.
A similar issue occurs with a shallower prescribed bedrock depth. For example, if zbedrock = 3.2 m, this depth falls within layer 14 (approximately 2.72–3.26 m), so nbedrock = 14. Layer 14 is still classified as a standard layer, but excess ice is only allowed through layer 13. This means that the soil portion between about 2.72 m and 3.2 m cannot contain initialized excess ice.
An even clearer case is when the prescribed bedrock depth is exactly at the bottom interface of layer 14, approximately 3.26 m. In this case, layer 14 is entirely above bedrock, yet it is still excluded from excess-ice initialization because j < nbedrock
This also seems to introduce a discontinuity. For example, if the bedrock depth changes from exactly 3.26 m to slightly deeper than 3.26 m, nbedrock changes from 14 to 15, and layer 14 suddenly becomes eligible for excess ice. Thus, a very small change in bedrock depth can add or remove an entire soil layer of excess ice.
Could you please clarify the intended behavior here?
Specifically:
Thank you!
I have a question about how nbedrock is used when initializing excess ground ice in CTSM5.3.026.
In WaterStateType.F90, excess ice is initialized only when
j >= nexice .and. j < nbedrock
so the layer j = nbedrock is always excluded from excess-ice initialization.
However, my understanding is that nbedrock represents the last standard soil layer associated with the prescribed bedrock depth. For example, the code classifies
1:nbedrock
as LEVGRND_CLASS_STANDARD, while layers below nbedrock are classified as bedrock.
This leads to a few cases that I am having difficulty interpreting physically.
For the default configuration with 20 soil layers, the bedrock depth is set to the bottom interface of layer 20. Therefore, layer 20 is entirely above the bedrock interface and is still a standard soil layer. However, because the excess-ice condition is j < nbedrock, excess ice can only be initialized through layer 19, and layer 20 is excluded.
A similar issue occurs with a shallower prescribed bedrock depth. For example, if zbedrock = 3.2 m, this depth falls within layer 14 (approximately 2.72–3.26 m), so nbedrock = 14. Layer 14 is still classified as a standard layer, but excess ice is only allowed through layer 13. This means that the soil portion between about 2.72 m and 3.2 m cannot contain initialized excess ice.
An even clearer case is when the prescribed bedrock depth is exactly at the bottom interface of layer 14, approximately 3.26 m. In this case, layer 14 is entirely above bedrock, yet it is still excluded from excess-ice initialization because j < nbedrock
This also seems to introduce a discontinuity. For example, if the bedrock depth changes from exactly 3.26 m to slightly deeper than 3.26 m, nbedrock changes from 14 to 15, and layer 14 suddenly becomes eligible for excess ice. Thus, a very small change in bedrock depth can add or remove an entire soil layer of excess ice.
Could you please clarify the intended behavior here?
Specifically:
- Is the exclusion of the nbedrock layer from excess-ice initialization intentional?
- What is the intended physical interpretation of nbedrock in this context: the deepest soil layer, or the layer containing the soil-bedrock interface?
- If the bedrock depth lies within the nbedrock layer, is the whole layer intentionally excluded to avoid assigning excess ice below the actual bedrock interface?
- If the bedrock depth lies exactly at the bottom interface of the nbedrock layer, should that entire layer physically be allowed to contain excess ice?
- Could the condition j < nbedrock be an off-by-one issue, or is this a deliberate discretization choice?
Thank you!