An Overview of Observations of Interstitial Aerosol during ICE-T

Aerosols play a significant role in global climate through their direct and indirect interaction with longwave and shortwave radiation. Of particular importance is the indirect contribution of aerosols to the radiative forcing budget through the formation and evolution of cloud systems. Accurate global climate modeling requires an effective treatment of the indirect effect with simple aerosol-cloud parametric models. Validation of such models requires data from a wide range of cloud systems. Aerosol-cloud model validation efforts have relied mostly on the measurement of activated particles, largely because of a lack of data on the non-activated or interstitial particle populations. Knowledge of interstitial particles in cloud systems enables, not just an improved validation of existing aerosol-cloud models, but also a more complete understanding of the aerosol processing in clouds and the possible role of aerosol in ice nucleation. During the recent ICE-T campaign, comprehensive interstitial aerosol measurements were made in a variety of tropical convective clouds, focused particularly on conditions that permit the formation of ice within these systems. The flight operations were based in St. Croix, U.S. Virgin Islands and sampling was largely conducted within ~ 600 miles of this location. Central to the sampling of interstitial aerosol was the deployment of a new aerosol sampler that provides shatter-free sampling of aerosol particles in ice clouds and significantly reduced shattering in warm clouds (relative to other aircraft aerosol inlets). This inlet samples aerosol particles smaller than ~2 microns. The condensation nuclei (CN) measurements were made with a TSI 3010 condensation particle counter (CPC), while particle size distributions were measured using DMT's ultra-high sensitivity aerosol spectrometer (UHSAS) instrument and a new fast mobility spectrometer. The fast mobility spectrometer consists of a new high-flow dual channel differential mobility analyzer (HD-DMA) and two CPCs operated in a high-flow mode. The combination of these instruments provided size distributions over a size range of 10nm-1000nm in ~ 20 seconds. Measurements of cloud condensation nuclei (CCN) were made in clear air and in clouds using Georgia Tech's CCN instrument operated in scanning flow CCN analysis (SFCA) mode. Results of interstitial aerosol measurements will be presented from various cloud penetrations, focusing on analysis of size distributions of interstitial particles and the correlation of changes in size distribution and CCN characteristics of particles measured inside and outside clouds.