Despite advancements over the past several decades in our understanding of processes essential to the formation and evolution of ice in clouds and associated impacts on weather and climate, serious gaps remain. Many of these can be traced to uncertainties and limitations of measurement technologies currently employed aboard cloud-penetrating research aircraft. Descriptions of complex interactions between aerosols (both natural and anthropogenic) and cloud particles are similarly hindered by lack of adequate instrumentation to accurately identify primary modes of ice initiation, discriminate liquid water from ice, and more comprehensively address the chemistry of cloud particles and hydrometeors. Development of a clear and comprehensive description of these gaps, identification of emerging technologies appropriate for bridging them, and discussion of standardized data processing and exchange protocols that would facilitate progress toward these objectives are among topics to be addressed at a summer workshop to be held June 25-27, 2010 at Seaside, Oregon. This location and timing will facilitate participation of instrument builders, aircraft facility managers, and a desirably broad spectrum of both seasoned and early-career cloud microphysical researchers already gathering for the 13th Conference on Cloud Physics, slated for the following week in nearby Portland, Oregon. Support will be offered to defray travel and lodging/per diem expenses of workshop participants, and will be complemented by analogous contributions from two other federal research agencies (NASA and DOE) to facilitate the broad participation viewed as critical to catalyzing rapid progress.
The intellectual merit of this workshop rests in its contribution to advancement of knowledge re: the quality and limitations of currently-available ice cloud measurements, the identification of key obstacles to progress and candidate technologies to surmount these obstacles, and development of plans for improved collaboration and communication (e.g., standardized protocols for instrument calibration and data exchange) to support improved analysis and interpretation of these measurements.
Broader impacts will derive from dissemination of workshop outcomes via a comprehensive Technical Note and through an associated journal publication, via educational opportunities for both early-career workshop participants and students accessing workshop publications, and by facilitating exchange across a diverse group of workshop participants including members of underrepresented groups.
A meeting of 31 international experts on in situ measurements from aircraft was held in Seaside, OR, June 25-7, 2010, to identify unresolved questions concerning ice formation and evolution in ice clouds, assess the current state of instrumentation that can address these problems, introduce emerging technology that may overcome current measurement issues, and recommend future courses of action to improve our understanding of ice cloud microphysical processes and their impact on the environment. The general conclusions and uutcomes of the meeting were: 1) The processes by which ice forms and evolves in cirrus and mixed phase clouds are poorly understood, primarily because of the complexity of ice particle nucleation and the paucity of measurements that accurately provide the properties of ice crystals. Twenty presentations (available at www.uni-leipzig.de/~meteo/en/forschung/airborne_workshop.php) summarized our current understanding of ice processes in clouds, the measurement systems available for characterizing these processes, the limitations and uncertainties of these systems, and emerging technologies for improving our measurement capabilities. 2) The key, unresolved questions concern the relative roles of homogeneous and heterogeneous nucleation, the relationship between ice nuclei (IN) and ice crystal concentration, the mechanisms for secondary ice formation, the optical properties of ice crystals as a function of habit, and the rates of glaciation in mixed phase clouds. 3) Currently available instruments are limited by problems caused by ice crystal shattering and sample volume uncertainties for cloud particles smaller than 50 μm. Although consistent and reliable measurements of ice crystal size distributions can be obtained for particles larger than 400 μm, given sufficiently long integration times, large uncertainties still remain at smaller sizes. 4) New instruments are becoming available to differentiate liquid droplets from ice crystals at sizes less than 50 μm by detecting their shapes from forward light scattering and depolarization signals. 5) More incentives are needed to attract young researchers to the observational sciences.
