CIFEX Experiment # 13
April 17, 2004.
Flight Scientist for Flight # 18: Greg Roberts
Flight Scientist for Flight #19: Eric Wilcox
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Flight 19: 4:00 - 8:00 p.m.
Objectives: Sample stratocumulus clouds and aerosols below cloud.
Small bands of stratocumulus clouds appeared in the satellite image ahead of an advancing storm. Skies were clear at the coast and shallow cumulus clouds began appearing about 30 n. miles offshore. Aerosols were sampled in clear air above and between these clouds at about the elevation of the highest cloud tops (5500ft <65 n. miles offshore and 8000ft from 65 to 75 n. miles offshore). At 5500ft CN concentrations were high (3200/cc at 20 n. miles) and slowly decreasing offshore, though still very high (1800/cc at 60 n. miles). These aerosols were mostly small with the size distribution showing two peaks, one at 20nm and another at about 40nm. Above 6000ft, the aerosol concentration indicated clean free-troposphere conditions (CN=200/cc; PCASP=100/cc). At 100 n. miles we rose to 10,000ft to sample the above a more substantial deck of cloud topping out at about 8000ft. Cirrus cloud associated with the leading edge of the advancing storm was visible just to the west. North-south transects of approx. 15 minutes of level flight were performed at 5550ft, 2500ft, and 1000ft thru a line of clouds including the well organized cumulus system with the 8000ft top. Significant ice was sampled at 5550ft and occasional rain extending to the surface was observed in the cloud radar. At 2500ft a thin stratus layer was present. Where there was not thin stratus there was precipitating cumulus. At 1000ft CN concentrations were 400/cc between rain bands. Continuing to the north of the first set of sampled clouds we encountered more benign cumulus and stratocumulus, only a few of which were raining. Cloud bases at 3000ft and tops mostly at 4500ft. Level flight at 3500ft included penetrations of several cloud elements. CN concentrations were 800-1100/cc between clouds. A higher transect at 4500ft included passes thru more cloud elements and occasional thin stratus. CN concentrations were still high (1500/cc) between clouds. Drop concentrations were 6-18/cc, LWC about .25 g/m^3 and mean diameters 12-20um. A profile beginning at 10,000ft was performed through a precipitating cumulus cloud. Level flight at 1000ft back to Arcata indicating rising CN concentrations from 1500/cc at 50 n. miles offshore to 2000/cc at 20 n. miles. Several cargo ships were spotted during this flight. We flew directly over Trinidad Head at 1400ft at 7:37pm.