Update effective radius bin ranges for new MODIS ice-cloud CER-CWP joint histograms

[brandonduran]

The new MODIS CER-CWP joint histograms introduced to COSP in PR #85 and #87 by @caseywall7926 include the following CER (cloud effective radius) bin edges for ice-topped clouds:
5, 10, 20, 30, 40, 50, 60 microns
The justification for these bin edges was to match the observational data from Pincus et al. (2023).

Further testing suggests some GCMs have a substantial amount of ice clouds with CER > 60 microns. With the current bin edges, these clouds are not included in the MODIS joint histogram output. See the attached figure of an example within E3SM of an added 60-90 micron bin capturing ~25% of ice-topped clouds that are omitted / missed by the simulator given the current bin boundaries.

To include these clouds that are simulated in some GCMs, we propose the addition of one more bin, such that updated bin edges are as follows:
5, 10, 20, 30, 40, 50, 60, 90 microns

[klein21]

Quick question: Do you want the new bin to have an upper limit? Why not just Re > 60?

[brandonduran]

@klein21 We have only tested with an upper limit of 90 microns. There doesn't seem to be any harm in adding a bin to capture the remaining clouds with Re > 60, so I believe this can be adjusted. Do you agree @caseywall7926 @qinyia ?

[caseywall7926]

@klein21’s suggestion sounds ideal. Thanks! -CaseySent from my iPhoneOn 13/02/2025, at 6:39 PM, brandonduran ***@***.***> wrote: @klein21 We have only tested with an upper limit of 90 microns. There doesn't seem to be any harm in adding a bin to capture the remaining clouds with Re > 60, so I believe this can be adjusted. Do you agree @caseywall7926 @qinyia ?—Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***> brandonduran left a comment (CFMIP/COSPv2.0#109) @klein21 We have only tested with an upper limit of 90 microns. There doesn't seem to be any harm in adding a bin to capture the remaining clouds with Re > 60, so I believe this can be adjusted. Do you agree @caseywall7926 @qinyia ? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***>

[caseywall7926]

***@***.***’s suggestion sounds ideal. Thanks! -CaseySent from my iPhoneOn 13/02/2025, at 6:39 PM, brandonduran ***@***.***> wrote: @klein21 We have only tested with an upper limit of 90 microns. There doesn't seem to be any harm in adding a bin to capture the remaining clouds with Re > 60, so I believe this can be adjusted. Do you agree @caseywall7926 @qinyia ?—Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***> brandonduran left a comment (CFMIP/COSPv2.0#109) @klein21 We have only tested with an upper limit of 90 microns. There doesn't seem to be any harm in adding a bin to capture the remaining clouds with Re > 60, so I believe this can be adjusted. Do you agree @caseywall7926 @qinyia ? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***>

[qinyia]

@brandonduran I agree with @klein21 's suggestion.

[brandonduran]

What is the preferred practice within COSP for this? I’d propose a placeholder threshold upper limit of 10000 (1E4) microns as the upper bin edge. This should be large enough to capture all clouds with Re > 60 microns and is much less restrictive than 90 microns. Happy to implement a different approach if the arbitrary threshold isn’t ideal.

[caseywall7926]

That sounds good, @brandonduran. Thanks! Sent from my iPhoneOn 13/02/2025, at 7:29 PM, brandonduran ***@***.***> wrote: What is the preferred practice within COSP for this? I’d propose a placeholder threshold upper limit of 10000 (1E4) microns as the upper bin edge. This should be large enough to capture all clouds with Re > 60 microns and is much less restrictive than 90 microns. Happy to implement a different approach if the arbitrary threshold isn’t ideal.—Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***> brandonduran left a comment (CFMIP/COSPv2.0#109) What is the preferred practice within COSP for this? I’d propose a placeholder threshold upper limit of 10000 (1E4) microns as the upper bin edge. This should be large enough to capture all clouds with Re > 60 microns and is much less restrictive than 90 microns. Happy to implement a different approach if the arbitrary threshold isn’t ideal. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***>

[klein21]

I don't know if there is a fixed practice for COSP on this. Rather, the practice is determined by the science you have.

When Mark Webb and I built the ISCCP simulator, we wanted to make sure that all GCMs clouds would be recorded within the histogram somewhere, so there is no upper limit on tau imposed on the largest optical depth bin.

The bin boundary for optical depth of 0.3 was added (it's not present in the ISCCP observations) as a way to delineate GCM clouds which can be detected by ISCCP (i.e. 1.3 > tau > 0.3) and those GCM clouds which are too thin to be detected by ISCCP (i.e. tau < 0.3).

These are the types of considerations you should take when designing your histogram. I asked just to be sure that you and Casey have intentionally thought about these concerns.