Aircraft Measurements of Vertical Profiles from Cloud Base to Anvils of Cloud Drops, Precipitation and Ice Particles in Relations to the CCN (Invited Presentation)

The ACRIDICON campaign of DLR's HALO aircraft in September 2014 was devoted in part for cloud microphysical measurements. The aircraft measured convective cloud clusters from base to anvils in unprecedented detail for tropical clouds. This provided extremely valuable details of the vertical evolution of cloud drop size distribution, the formation of warm rain, the initiation of ice phase by various processes such as freezing of supercooled rain drops, ice multiplication and homogeneous freezing of cloud drops near -38°C. The documentation of the convective cores continued into the glaciated tops and the outflow of the anvil. Vertical profiles of cloud drop effective radius, cloud and rain water content, and ice hydrometeor concentrations show a clear partitioning into several distinctly different groups, which are determined mainly by the aerosol concentrations below cloud base, as follows:

1. Blue Ocean or pristine marine clouds: Cloud drop concentrations (Nd) < 200 cm-3; Warm rain starts below 2 km; Nd is depleted quickly to < 30 cm-3 above that height, but below the freezing level.

2. Green Ocean or pristine Amazonian clouds: Nd is 200-300 cm-3; Warm rain starts above height of 2.5 to 3 km; Glaciation occurs above the -15°C isotherm.

3. Modified Green Ocean, or slightly hazy Amazonian clouds: The Manaus plume is included in this category. Nd is 400-600 cm-3; Warm rain starts above the height of 3.5 to 4 km. Glaciation occurs between -20 and -30°C.

4. Smoky clouds: Nd is between 800 and 1110 cm-3, depending on the smoke density. Heavy smoke comparable to the 2002 SMOC campaign was not encountered. Supercooled warm rain was initiated above the 0°C level when cloud base Nd<1000 cm-3, and was completely suppressed for higher Nd. The clouds glaciate between -30°C and the homogeneous ice nucleation temperature of -38°C, depending on the updraft speeds at that height and the CCN below cloud base.

5. Pyro-cumulus. This category was not sampled sufficiently for a reliable characterization.

This represents a vast range of microphysical and thermodynamic cloud behavior, which can be ascribed to the aerosol effects. This classification provides the basis for more in depth analyses, simulations, and intercomparisons with satellite retrievals.