calculating fine-mode AOD

[mpagowski]

I would like to calculate fine-mode AOD for GOCART_2G. I understand that this would include AOD from all of SU,BC1,BC2,OC1,OC2. Then, it would include only a fraction of the dust from the first bin DU1. For SS1 that is a little more complicated since sea-salt particles grow significantly with relative humidity. Similarly for the recent nitrate.
I learned from literature search that FMF AOD for GOCART was calculated taking these considerations into account
(e.g. Chin et al., 2004, Jones and Christopher, 2011). Rather than reinvent the wheel and make mistakes I would rather rely on procedures that may have already been developed. Can someone comment, possibly direct me to where I can find a solution?
Thanks!

[mathomp4]

I'm going to mention a few people:

• @vbuchard
• @pcolarco
• @amdasilva

one of these should be able to help or point you to someone who can

[pcolarco]

Diagnostics for this already exist (see the GOCART2G and component StateSpecs). For example, under DU there are DUEXTTFM (for PM1 AOD) and DUEXTT25 (for PM2.5 AOD). At the GOCART level there are the TOTEXTTFM and TOTEXTT25 equivalents summed across species. Is that what you want?

[mpagowski]

Yes, that is related to what I am looking for, i.e. I need to calculate extinction in the assimilation code rather than have it given (because mixing ratios of species are adjusted on model levels). So rather than that I am looking for what corresponds to DUMASS25 or SSMASS25 but for 1um. Can you direct mu to the place in the code where the calculations are done?

Also, I think the common attitude is that the fine mode is diameter below 1um. Do you know if this is how fine-mode-fraction AOD is calculated in MODIS DT. E.g. from
https://darktarget.gsfc.nasa.gov/content/what-aerosol-fine-mode-fraction#:~:text=The%20smaller%20particles%20are%20referred,between%201.0%20and%202.5%20microns.

"Atmospheric aerosols generally have a bimodal distribution. The smaller particles are referred to as the fine mode or accumulation mode aerosols. These particles have radii between 0.1 and 0.25 microns. The larger particles comprise the coarse mode. These particles generally have radii between 1.0 and 2.5 microns. The aerosol fine mode fraction is the proportion of fine mode aerosols to the total. This is an optical measurement of the proportion by volume."

[pcolarco]

Hi Mariusz, There is presently not a calculation of the dust and sea salt fine mode mass concentrations (e.g., DUMASSFM). This would be straightforward to add analogously to how the PM2.5 is done (e.g., DUMASS25). I believe the steps would be: 1. Create the variables in the DU and SS StateSpecs resource files 2. Create the calculation in the Process_Library/GOCART2G_Process.F90:Compute_Aero_Diags subroutine, adding the optional outputs to the subroutine arguments 3. Add those arguments in the respective DU and SS Fortran code The needed information should be present in the existing code (fPMfm). I hope that makes sense, and it would be welcome. Something analogous would need to be done for NI, but see how there are two calls to Compute_Aero_Diags in NI code; the second one is where you would introduce the hooks for the desired fine mode output (we are implicitly assuming the FM and PM2.5 portions of the nitrate are equivalent, looking at how we already handle the optical calculations). The other species are generally assumed fine mode. I believe your interpretation of the MODIS FM AOD is correct; I would defer to Rob Levy for a definitive answer. Pete From: Mariusz Pagowski ***@***.***> Date: Wednesday, January 8, 2025 at 2:01 PM To: GEOS-ESM/GOCART ***@***.***> Cc: Colarco, Peter R. (GSFC-6140) ***@***.***>, Mention ***@***.***> Subject: [EXTERNAL] [BULK] Re: [GEOS-ESM/GOCART] calculating fine-mode AOD (Issue #297) CAUTION: This email originated from outside of NASA. Please take care when clicking links or opening attachments. Use the "Report Message" button to report suspicious messages to the NASA SOC. Yes, that is related to what I am looking for, i.e. I need to calculate extinction in the assimilation code rather than have it given (because mixing ratios of species are adjusted on model levels). So rather than that I am looking for what corresponds to DUMASS25 or SSMASS25 but for 1um. Can you direct mu to the place in the code where the calculations are done? Also, I think the common attitude is that the fine mode is diameter below 1um. Do you know if this is how fine-mode-fraction AOD is calculated in MODIS DT. E.g. from https://darktarget.gsfc.nasa.gov/content/what-aerosol-fine-mode-fraction#:~:text=The%20smaller%20particles%20are%20referred,between%201.0%20and%202.5%20microns. "Atmospheric aerosols generally have a bimodal distribution. The smaller particles are referred to as the fine mode or accumulation mode aerosols. These particles have radii between 0.1 and 0.25 microns. The larger particles comprise the coarse mode. These particles generally have radii between 1.0 and 2.5 microns. The aerosol fine mode fraction is the proportion of fine mode aerosols to the total. This is an optical measurement of the proportion by volume." — Reply to this email directly, view it on GitHub<#297 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/ANW73YCRUSDQYNZNVEKQTE32JVYW3AVCNFSM6AAAAABUYQH6KSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNZYGQYTEMBRG4>. You are receiving this because you were mentioned.Message ID: ***@***.***>

[mpagowski]

Thanks Pete, that should do it, I will follow your advice,
Mariusz