Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Variability of graupel and ice crystal aggregates observed in tropical oceanic convection by aircraft during TRMM KWAJEX

Ellen M. Sukovich, David E. Kingsmill, and Sandra E. Yuter

Precipitating convective clouds over the tropical oceans play a major role in the global water and energy balance. As surface precipitation measurements are sparse over the ocean, satellite precipitation retrievals are vital for accurately mapping tropical ocean precipitation. In particular, the characterization of ice particles is critical for validating the cloud-resolving models and radiative transfer models upon which rest the scientific foundation of precipitation retrieval algorithms. This work describes the variability of graupel and ice crystal aggregates observed by aircraft in precipitating convective clouds during the Tropical Rainfall Measuring Mission (TRMM) *Kwajalein Experiment** **(KWAJEX) in the western tropical Pacific. *

Microphysics data for this analysis were collected by the University of North Dakota (UND) Citation and the National Aeronautics and Space Agency (NASA) DC-8 aircraft during TRMM KWAJEX. A habit identification algorithm was applied to two-dimensional optical array probe data for the purpose of identifying ice particle ensembles dominated by graupel or aggregates. These ensembles were accumulated along 1-km flight segments at temperatures below 0° C. A third category, mixed graupel/aggregate, has characteristics between those of the predominately graupel and aggregate ensembles and can be used either in combination with the other two categories, or separately.

Aggregate particle ensembles comprise 80% of UND Citation and 98% of NASA DC-8 ensemble data. For the UND Citation, graupel ensembles comprise ~5% of the total with mixed graupel/aggregate ensembles comprising ~15%. There were no graupel ensembles in the NASA DC-8 data, which were collected primarily at temperatures < -35° C. Combining data from both aircraft, aggregate and mixed graupel/aggregate ensembles were evident over the full range of sub-freezing temperatures (0° to -65° C) sampled by the aircraft. In contrast, graupel ensembles were present primarily at temperatures > -10° C. All graupel was either coincident or within a 10-km horizontal distance of radar-identified convective precipitation structures.