Guy Cascella, in association with MPO531, presents: Featuring: African dust aerosols as atmospheric nuclei, DeMott et al, 2003 Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation, Twohy and Poellet, 2005 experiment designed to test the importance of African dust in cloud properties over Florida July 2002 part of the NASA CRYSTAL-FACE program three main motivations: understanding cold cloud dynamics: ice phase transitions dust is a fairly common atmospheric substance anthropogenic activity: land use change CFDC collects all type of aerosol how are dust aerosol identified? Answer: LIDAR LIDAR identifies the geometry of the aerosol calculates the linear depolarization ratio, , which is the ratio between the alignment of the planes both parallel and perpendicular to the laser thus, for spherical aerosol, = 0 dust aerosol are non-spherical, so we expect > 0 Koren et al, 2001 African dust significantly impacts IN concentrations in cirrus anvils over Florida an increase to >1 cm -3 from a mean of.01 cm -3 favors heterogeneous freezing Effects in cloud microphysical and radiative properties, latent heating, and precipitation Atmospheric dust levels should be monitored desert dust, anthropogenic factors, etc. Previous experiment emphasized geometry, but could not discern chemical composition Also part of the NASA CRYSTAL-FACE program Main motivations: analyze the chemical composition of varying sizes of ice nuclei both in anvils and in immediate surrounding (ambient) air determine how homogeneous and heterogeneous ice formation contribute samples particles >5 m, smaller particles deflected by counterflow particles removed of water two impacting stages (large and small) ~.56 m and ~.38 m samples sized and analyzed for chemical composition with electron microscope 45 wedge multiply by 8 for total particle count 45 wedge multiply by 8 for total particle count total particles: O(100)/Liter 1/3 of particles composed of salts which are soluble But so are sulfates; ~40% of observed particles are soluble highly favors homogeneous freezing! 1/3 of particles composed of salts which are soluble But so are sulfates; ~40% of observed particles are soluble highly favors homogeneous freezing! Industrial substances; ~15% of total particles (anthropogenic forcing) 1/3 of particles composed of salts which are soluble But so are sulfates; ~40% of observed particles are soluble highly favors homogeneous freezing! Industrial substances; ~15% of total particles (anthropogenic forcing) ~15% of particles have crustal origin (e.g. African dust as we saw earlier) 1/3 of particles composed of salts which are soluble But so are sulfates; ~40% of observed particles are soluble highly favors homogeneous freezing! Industrial substances; ~15% of total particles (anthropogenic forcing) ~15% of particles have crustal origin (e.g. African dust as we saw earlier) ~25% carbon based particles, function is not clear and is in need of further research ? ? ? ? 1/3 of particles composed of salts which are soluble But so are sulfates; ~40% of observed particles are soluble highly favors homogeneous freezing! Industrial substances; ~15% of total particles (anthropogenic forcing) ~15% of particles have crustal origin (e.g. African dust as we saw earlier) ~25% carbon based particles, function is not clear and is in need of further research ~5% other/unknown/mixed particles, most likely Carbon based ? ?? ? high variability at different altitudes despite convincing average results shown in previous slides homogeneous processes dominate at the coldest temperatures we expect this with soluble particles as temperatures rise, heterogeneous processes take over; also expected at the warmest temperatures, virtually no ice processes occur, so this can be excluded from the perspective of this study salts and sulfates (soluble) dominated the findings anthropogenic activity again plays a large role industrial based aerosol land use leading to increases in atmospheric dust carbon based aerosol and their role in ice nucleation processes require further study convective processes are important for distributing various aerosol throughout the atmosphere here, the distributions of salts was of particular value and importance homogeneous freezing processes are much more important than theory leads us to believe! but is this only for coastal areas?