Comparison of the aerosol scattering and absorption coefficients measured on Ron Brown and on the C130 aircraft during a flyby

Anne Jefferson, Pat Sheridan and John Ogren - NOAA/CMDL
Patricia Quinn - NOAA/PMEL

Contact: ajefferson@cmdl.noaa.gov

The C130 aircraft performed a flyby of the NOAA Ron Brown ship on Feb. 28th of the INDOEX IOP. Both the CMDL instruments on board the C130 and the PMEL instruments on the Ron Brown had identical model nephelometers (TSI model 3563) and Particle Soot Absorption Photometers (Radiance Research PSAP). The relative humidity in the nephelometers was 54% and 58% for the C130 and RB instruments, respectively. The C130 was flying about 30 meters above the ocean surface. The Ron Brown instruments were measuring absorption and scattering coefficients in the sub-10 micron size range throughout the intercomparison time period. The C130 had 3 minutes of measurements in this size range out of the 11minute C130 flyby-time past the ship. The remainder of the time period for the C130 was spent in the submicron measurement mode or was removed because of heater edits. The Ron Brown measurements were averaged for plus and minus 68 minutes on either side of the CMDL sub-10 micron aerosol measurements. The Ron Brown average time was calculated by the aircraft speed (106 m/s), the ambient wind speed (4.9 m/s) and the CMDL measurement time (3 min). Aerosol absorption and scattering coefficient measurements compared quite well between the two platforms. Below is a table with the mean values of each parameter:( absorption (l =565 nm), total scattering (l =450, 550 and 700 nm), hemispheric backscattering ((l =450, 550 and 700 nm), single scattering albedo (wo) and hemispheric backsattering ratio (b). The single scattering albedo, hemispheric backscatter fractions and Ångstrom exponent were calculated from the mean scattering coefficients. The small differences between the two measurements are less than the instrument uncertainties (see explanation of instrument uncertainty in CMDL C130/KCO intercomparison). Typical instrument uncertainties for submicron absorption and green total scattering coefficients are +/- 2 to 3 Mm-1 for the mean values given below. The uncertainty associated with the sub-10 micron size range is expected to be greater and more susceptible to differences in aerosol losses between the inlets. The smaller Ångstrom exponent for the Ron Brown instrument may designate a somewhat larger aerosol.
 
 
 
Parameters
Absorption
Scat_B
Scat_G
Scat_R
Bscat_B
Bscat_G
Bscat_R
wo
b
Ang_GR
C130 (stdev)
14.4 (3.3)
83.0 (0.7)
62.6 (0.6)
39.6 (0.7)
6.9 (0.3)
5.8 (0.1)
4.7 (0.3)
0.81
0.09
1.91
Ron B (stdev)
11.3 (0.3)
75.5 (2.0)
59.0 (1.6)
39.8 (1.1)
7.3 (0.3)
6.5 (0.2)
5.6 (0.2)
0.84
0.11
1.63