From: Cynthia Twohy
Organization: Oregon State University/NCAR

Research Area: AEROSOLS

Mission Scenario: New Particle Production Near Convective Cloud Outflow

Recent studies suggest that the production of new particles may be favored downstream of the outflow of convective cloud systems in the upper troposphere. Cold temperatures, low particle surface area, and high levels of gas-phase precursers carried up by the convection provide ideal conditions for the nucleation of ultrafine sulfuric acid particles. These will then grow by coagulation to larger particles, which may be important for chemical reactions or cloud formation. Although the tropical upper troposphere provides widespread convection and cold temperature extremes, these events may occur near mid-latitude storms as well. Measurements of new particle formation have been sporadic, since the nucleation process requires special conditions and the environment is difficult to sample. Also, observations may occur inadvertently while conducting other measurements. Existing data sets are incomplete because instruments and flight plans have not been selected specifically for this problem. HIAPER, with its long range, high ceiling, and large payload capacity, should be ideal to study the problem.

Flight Plan: Similar flights would be planned for both mid-latitude and tropical regions on different days, so an intermediate base, perhaps in Mexico, might be appropriate. Using forecasts and satellite imagery to target regions of active convection, the aircraft would ferry to the equatorial region (2.75 hrs), receiving on-board satellite updates to refine the target area. Once there, we would sample the ambient aerosol at high altitude and select an isolated cloud system in active development with anvil just beginning to form (0.5 hrs). Aircraft would descend to just above the surface at 1000 ft/min (0.75 hrs). If possible, aircraft would then circumnavigate the storm near the surface to measure chemistry and state parameters of the inflow region, then ascend (1.5 hrs). The first upper level would be 1000 ft below the cirrus outflow, at its furthest downwind end. A race track pattern would be conducted across the cirrus band, half below the visible cloud and half downwind. This would be repeated at the cirrus level and 1000 ft above it (1.25 hrs). (If additional time is available, the aircraft would loiter in the downwind region attempting to measure particle evolution over time.) Ferry home (2.75 hrs). Total flight time: 9.5 hrs.

Alternately, the mid-latitude portions of the experiment could be based in Jeffco, with the aircraft moving to Panama for the tropical missions. With more time on station in both sites, these flights could perhaps be combined with some of the related missions of others (Clarke, Young, Toon).

Instrumentation:

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