Results from SPartICus (Small Particles in Cirrus) project

From a mass-weighted perspective, cirrus clouds exert an enormous influence on the radiative energy budget of the earth's climate system. Owing to their location in the cold upper troposphere, cirrus can reduce significantly the outgoing long-wave radiation while, at the same time, remain relatively transmissive to solar energy. Thus, cirrus clouds are the only cloud genre that can exert a direct radiative warming influence on the climate system. The DOE ARM Small Particle in Cirrus (SPartICus) field project takes place from 4 January through 15 May 2010. The SPEC Learjet is instrumented with state-of-the-art microphysical sensors that have been designed to minimize the effects of large ice particles shattering on probe inlets, which has contaminated results from most previous projects. The instrument compliment includes fast FSSP, CDP, CPI, 2D-S, 2D-P and Nevzorov IWC probes, along with air motion sensing. Data were collected in cirrus clouds over the ARM ACRF site near Lamont, Oklahoma, and in cirrus under various locations coincident with CloudSat/Calipso satellite overpasses. The overarching scientific goal of SPartICus is to collect a dataset with statistical relevance that documents the nature and variability of the particle size distribution in cirrus. Given the uncertainty in previous measurements (mainly due to the effects of ice particle shattering), SPartICus aims to determine to what degree small particles (i.e., < 50 microns diameter) contribute to the mass and radiative properties of mid-latitude cirrus. Characterization of the contribution of small particles to the total number concentration is critical for developing and evaluating model parameterizations and improving algorithms to retrieve microphysical properties using remote sensors. SPartICus measurements reshape our understanding of the bimodality of the ice crystal size distribution. Improving and evaluating cloud property retrieval algorithms is fundamental to utilizing the long-term time record of remote sensing observations at the ACRF sites. Initial results from in-situ measurements in cirrus will be presented, including fast FSSP. CDP, CPI, 2D-S, 2DP and Nevzorov measurements of particle size, area and mass distribution, coincident with remote retrievals from Raman lidar, millimeter radar and other remote sensors.