1. Tb(10.35)-Tb(3.9) as a function of cloud droplet mean mass diameter (um)
Louie Grasso
CIRA
October 2016

2. Part I
Examine sensitivity of Tb(10.35)-Tb(3.9) on cloud droplet mean mass radius.
Observational examples, are there any?

3. All work was done on rcm02:~/home/grasso/jpss
Mkcld was used in a 1<=X<=15; 1<=Y<=10, 1<=Z<=59 idealized domain
Cloud 3 km <= X <= 13 km; 2 km <= Y <= 8 km; 1 km <=Z<=3 km
Cloud water mixing ratio was varied linearly; increasing from south to north
Cloud number concentration was varied linearly; increasing from west to east
Sounding is the same as rcm02:~/home/grasso/muri for dust stuff
RTM used was oo9_parallel.f90
Mean Mass Radius (um): MMR = 1.0E4 * ( (0.75/PI)*(RCP(K,I,J)/CCP(K,I,J))* 1.0/RHO_LIQ) )**(1.0/3.0)

4. Should be radius (um) X
All axis’s are in km
As particle size increases, Tb(10.35)-Tb(3.9) decreases.
Kelvin

5. Should be radius (um) X

6. Should be radius (um) X
Looks like Tb(10.35)-Tb(3.9) asymptotes to 0.0

7. Part II
Examine correlation between low-level liquid cloud dissipation and cloud top droplet mean mass radius using data from the real-time NSSL 4 KM WRF-ARW
Observational examples?
Can we run real-time GOES-15 particle size retrievals?

8. (A)
(B)
(A) Cloud top mean mass radius (um) from the 4 km NSSL WRF-ARW. This is not a plot from a fixed vertical level in the model output. Rather, fix an (i,j), search downward from the model top until cloud water mass is found; then acquire the mean mass radius. (B) Synthetic GOES-R Tb(10.35)-Tb(3.9)

9. Scatter plot from the entire 3D domain of 3. 9 um extinction (m
Scatter plot from the entire 3D domain of 3.9 um extinction (m**2/kg) as a function of cloud liquid water mass (g/kg).

10. Scatter plot from the entire 3D domain of mean mass radius (um) as a function of cloud liquid water mass (g/kg).

11. Scatter plot from the entire 3D domain of optical depth as a function of 3.9 um extinction (m**2/kg).

12. Scatter plot from the entire 3D domain of optical depth as a function of liquid water path (kg/m**2).

13. Scatter plot from the entire 3D domain of optical depth as a function cloud water mass (g/kg).

14. Scatter plot from the entire 3D domain of 10
Scatter plot from the entire 3D domain of um optical depth as a function 3.9 optical depth.

15. From: Lewis Grasso <Lewis. Grasso@colostate
From: Lewis Grasso Date: Wednesday, October 19, 2016 at 8:28 AM To: Steven Miller Dan Lindsey "Brummer,Renate" Subject: jpss? muri? Tb(10.35)-Tb(3.9) = f(mmr) and fog dissipation = f(cloud top mmr)
Hi Steve and Dan,
   Attached is a small *pptx file with some tools that may be used to further explore
two issues: Tb(10.35)-Tb(3.9) dependence on liquid cloud top particle  size and low-level
liquid water cloud dissipation as a function of retrieved cloud top particle size.
  When I return from Salt Lake City we can discuss this potential project further.
Kind Regards,
Louie
************************************************************************
Sent: Thu 10/20/ :34 AM
To: Grasso,Lewis Brummer,Renate
CC:Rogers,Matthew
Hi Louie,
I have not yet looked into this in detail, but I think that if on Part II you honed in on those two areas of interest (the low clouds off Baja California, and the low clouds over the south/central US) it could help to constrain the analysis.  I think the item of interest would be the time evolution of the cloud top effective radius (which should be able to be related to your mean mass radius value).
If you specify the date/time of your case we can look for the GOES retrieved effective radii—assuming that there was actually a low cloud deck where the model thinks there was one.  Matt could probably help with that since we have GOES running for cloud properties.
Thanks,
-steve

16. Miller,Steven <Steven.Miller@colostate.edu>
Tue 11/15/ :49 PM
Grasso,Lewis Dan Lindsey - NOAA Federal
Louie,
Phew, I was really worried that there was a bug in my Mie code (which would have put a stain on my dissertation results).  Glad to confirm that all is as originally stated!
The move toward more emissive particles as the size decreases for 10.7 micron is consistent with a stronger BTD.  This is born out for liquid clouds whose effective radii are typically 6-15 micron.   Your ice plot says “for pristine” but I take that to be “ice spheres.”    I think that cloud top effective radius for cirrus can be much higher… micron is not uncommon in the retrievals.  If that is the case, then the single scatter albedo at 3.9 and 10.7 are now similar.  That would yield small values of the BTD for optically thick ice clouds. 
Smaller cloud top particle sizes, as might be found in a rapidly rising storm or in a vigorous OT, is where I might expect to still see a possible small positive BTD.  The challenge would be to find a nighttime case where these conditions were met—usually the vigorous convection is associated with daytime heating.  If that can be confirmed, then I guess we have reconciled the single-scatter properties with the observations.  Namely, the main reasons why BTD is useful as a low cloud discriminator have to do with two suppressing factors for high ice clouds:  i) the optically thin nature of many cirrus which allows more upwelling transmittance at 3.9, and ii) the larger particle size for optically thick cirrus which neutralizes the spectral differences between 10.7 and 3.9.  
Importantly, the significance of cloud phase (liquid vs. ice) is mainly associative—the reason the liquid clouds show up better is because liquid clouds are associated with smaller radii and higher water paths.   In other words, if there existed an optically thick, low-level ice cloud with small particles at cloud, it would in theory produce the same positive BTD that we tend to call “low-liquid cloud.”
It still would not explain why the observed BTD goes slightly negative (i.e., 3.9 warmer than 10.7) for thick ice clouds, however.  Unless that has to do with 3.9 weak sensitivity to cold targets leading to saturation and some asymptotic value.
-steve
Steven D. Miller, PhD.
Senior Research Scientist, Deputy Director
Cooperative Institute for Research in the Atmosphere This is relevant to the next slide.
Colorado State University; Foothills Campus
1375 Campus Delivery
Ft. Collins, CO