Ice microphysics and aerosol indirect effects based on in-situ observations collected during the ISDAC field project

The objective of this work is to study 1) ice crystal number concentration (Ni) parameterizations that represent heterogeneous nucleation through ice nuclei (IN) at cold temperatures and 2) aerosol indirect effects on Arctic clouds. The earlier parameterizations (Meyers et al. 1995 and Fletcher, 1945) were based on limited observations and did not represent cold air temperatures (T) properly but are often used in the modeling community. Observations collected during the ISDAC (Indirect and Semi-direct Aerosol Campaign) project were analyzed to derive a relationship between Ni and T, and Ni and Na (aerosol number concentration). Preliminary results suggest that the earlier parameterizations underestimated Ni by more than 1-2 orders of magnitude at cold temperatures when Na reached about 600 cm-3 on April 24. After removing shattering particles with inter-arrival times, a 2DC optical probe with size ranges>100 ƒÝm at 25 ƒÝm bins and SPEC 2DS (two-dimensional stereographic) with sizes >10 micron were used in the analysis. The FSSP/CDP observations were only used qualitatively because of shattering issues. Aerosol observations from the Particle Cavity Aerosol Spectrometer Probe (PCASP) with size range of 0.3 to 3 ƒÝm over 15 channels were further used to describe the environmental conditions where polluted weather conditions played an active role in cloud microphysical processes and estimating indirect aerosol effect on the radiative budget. In this work, using broadband radiative fluxes, and aerosol and ice particle measurements from polluted and clean environments, the aerosol indirect effects on Arctic clouds will be discussed.