CIFEX Experiment #7

Flight # 10

April 9, 2004.

Flight Scientist: O. Lariviere

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Objective:

Make long (+20 min) level flights in aerosol plumes, in order to gather enough data to make a statistical analysis of the aerosol characteristics in each layer.

A high pressure system off the coast was keeping the skies cloud free and RH low, creating perfect conditions to gather data on the aerosol layers that have been observed in previous flights. This flight was similar to the morning flight where a number of layers had been identified at different layers. We flew due west at an altitude of 1300’ in order to resample the aerosol gradient observed in the morning flight at this altitude. The north wind had increased from earlier in the day and averaged around 24 nautical miles/hour. A significant aerosol concentration averaging around 1000#/cc (CPC) and 150#/cc (PCASP) was still evident. The gradient had declined considerably from the morning and concentrations held steady, with occasional dips and peaks. At 126.18W, the CPC reading indicated an abrupt drop to 300 #/cc and began a steady climb back to values averaging 1000#/cc. When we reached 127W, CN values jumped abruptly to ~1700 #/cc. At 127.08W, we performed a vertical spiral profile to 16,000 ft. RH values were between 15% and 40% for the duration of the outbound leg.

I noticed a jump in PCASP values, ~ 400/cc, at 8500 ft, and minor jumps in CN values to 500 or 600 between 13,800 ft and 14,000 ft and again at 14,900ft. We attempted to follow the plume back in at 14,900ft, but soon lost it as aerosol concentrations rapidly decreased. The plane then dropped down to 8,800ft, where CN values were ranging between 600 and 1000/cc. The flight ended with a vertical spiral profile above Trinidad Head. I noticed a layer at 6,600 ft, in which the SMPS may have detected 3 size modes. This must still be verified by statistical data analysis. At 10,300ft, CN concentrations dropped from a fairly constant value of 1000/cc to 100/cc. PCASP values began increasing to greater than 400 at 16,800 ft, and did not decline when we reached 17,500ft. The pilot stated that this was the limit for the profile, so I was not able to determine the full extent of the layer. I detected ultrafine ~10nm particles at concentrations around 900 between 4000 and 5000ft.