Paquita Zuidema , Seethala Chellappan, Simon Kirschler, Christiane Voigt, Brian Cairns, Ewan C. Crosbie, Richard Ferrare, Johnathan Hair, David Painemal, Taylor Shingler, Michael Shook, Kenneth L. Thornhill, Florian Tornow, Armin Sorooshian

Five cold-air outbreaks are investigated with aircraft offshore of continental northeast American. Flight paths aligned with the cloud-layer flow span cloud-top temperatures of -5 to -12 0C, in situ liquid water paths of up to 600 g m-2, while in situ cloud droplet number concentrations exceeding 500 cm-3 maintain effective radii below 10 micron. Ice is usually present at cloud initiation. Further downstream, ice particle number concentrations (N_i) of 0.1-2.5 L-1 indicate secondary ice production. This is enhanced near cloud top, consistent with collisional breakup of graupel and vapor-grown ice particles, and near cloud base, where ice aggregates near 0 0C. Rime-splintering is clearly evident. The highest ice water contents coincide with temperatures favoring dendritic growth. Warmer clouds and weaker surface fluxes correlate to fewer ice particles. Buoyancy fluxes reach 400-600 W m-2 near the Gulf Stream's western edge, with updrafts reaching five m s-1 supporting closely-spaced convective cells. Upper-level detrainment maintains a high overall cloud fraction despite decoupled boundary layer vertical structures. The near-surface liquid rainfall rates of three more intense cold-air outbreaks are a maximum near the Gulf Stream's eastern edge, just before the clouds transition to more open-celled structures, and correspond to higher cloud liquid water paths. The milder two cold-air outbreaks transition to lower-albedo cumulus through cloud thinning.