Case 3: Heavy drizzle bin microphysics test

The objective is to further test the performance of “component-method” in I3RC for a heavy drizzle case

Case setup:

The microphysics of the cloud is from a Large-Eddy simulation model with bin microphysics.  As shown in Figure 1 the particle size distribution has two modes, the cloud mode from 2µm~30µm and the drizzle mode from about 30µm~1000µm

Cloud parameters:                           0.5km~1.5km, LWC =0.1g/m^3; no atmosphere, black surface

Total optical depth @0.86µm:         3.63411

Solar angles:                                   µ0=0.9397 (20 degree); phi0 = 0 degree

Observing angle:                             a total of 131 observing directions in the upper hemisphere

Wavelengths:                                  0.86µm, 1.65µm, 2.13µm and 3.7µm 

Number concentration

Mass concentration

re~40µm

Veff=2.6

Phase Function @ 0.86µm

Phase Function @ 2.13µm

external average

component-method

external average

component-method

Figure 1 Microphysics of the cloud

Figure 2 Cumulative extinction of first i bin

Drizzle mode accounts for about 20% of total extinction

RT simulation results

Reflectance @ 0.86µm

Reflectance @ 1.65µm

Reflectance @ 2.13µm

Reflectance @ 3.75µm

Corr 

Std of rel dif.

     0.937153      6.57597

     0.979431      3.36402

     0.989679      2.44790

     0.997366      1.79874

Component method agrees very well with the external mixing method

Spectral invariant test for Sasha

single scattering albedo

0.86µm 0.999810   

1.65µm 0.980027    

2.13µm 0.934289    

3.75µm 0.800542

Spectral invariant test: Nadir viewing example

Spectral invariant test:all viewing directions

radiance/albedo=a*(radiance)+b

good fit when “a” is close to unity

Less than perfect when “a” becomes significantly smaller than 1