Experimental Study on the Dependency of Ice Nucleation Active Surface Site Density on ATD Aerosol Size

In light of the percentage of Earth’s cloud coverage, heterogeneous ice nucleation in clouds is the most important global-scale pathway. More recent parameterizations of ice nucleation processes in the atmosphere are based on the concept of ice nucleation active surface site density (ns). It is usually assumed that ns is independent of time and aerosol size distribution, i.e. that the surface properties of aerosols of the same species do not vary with size. However, the independence of ns on aerosol size for every species has been questioned. This study presents the results of ice nucleation processes of ATD laboratory-generated aerosol (particle diameters of 0 - 3 μm). Ice nucleation in the condensation mode was performed in a Dynamic Filter Processing Cham- ber at temperatures of -18°C and -22°C, with a saturation ratio with respect to water of 1.02. Results show that ns increased by lowering the nucleation temperature, and was also dependent on the particle size. The ns of particles collected on the filters, after a 0.5 μm D50 cut-off cyclone, resulted statistically higher with respect to the values obtained from the particles collected on total filters. The results obtained suggest the need for further investigation of ns dependence of same composition aerosol particles with a view to support weather and climate predictions.

Distributions of crystals and gas bubbles in reservoir ice during growth period

In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.

Analysis on the crystals of sea ice cores derived from Weddell Sea,Antarctica

In order to understand the sea ice types and its region of origin frozen in Weddell Sea,27 ice cores were taken from Weddell Sea,Antarctica during September and October,2006.Their crystals were analyzed,and their ice forming processes were evaluated based on the crystals.Photos of the thin sections from two whole ice cores,and from polygonal granular superimposed ice were taken as well as corresponding stratigraphy descriptions.Vertical profiles of salinity, density and grain size were also obtained.Based on ice core structural texture,the findings include that： 1） although large and smooth ice floes were selected as the investigation sites, the ice sheet at the sampling position may be formed by rafted ice,consolidated ice ridges and second-year ice which were affected by dynamic and thermodynamic processes together subsequently.Ice formed in pure thermal growth comprises minority.The polygonal granular superimposed ice from refrozen wetted dense snow is one type of the ice in Antarctica.2） Of the all 27 ice cores,the granular,mixed granular-columnar and columnar crystals in sea ice occupy 28.7%,14.4% and 55.2%,respectively.3） The pure thermal growth ice is predominant in marginal sea ice zone;the rafted ice and consolidated ice ridges,even second-year ice and polygonal granular superimposed ice from dynamic and thermal effects were found in front of Larsen A Ice Shelf;the thermal growth ice froze in the polynyas of Larsen A,and was transferred outwards.