Climate | Meteorology
In order to understand the microphysical properties of cirrus clouds, it is important to understand the formation and evolution of the environments where ice crystals form and reside on the microscale (~100 m). Uncertainties remain in simulating/parameterizing the evolution of ice crystals, which require more analyses in the Lagrangian view. However, most in situ observations are in the Eulerian view and are restricted from examining the lifecycle of cirrus clouds. In this work, a new method of Diao et al. GRL (2013)* is used to separate out five phases of ice crystal evolution, using the horizontal spatial relationships between ice supersaturated regions (ISSRs) and ice crystal regions (ICRs). In-situ, aircraft-based observations from five flight campaigns are used to compare the evolution processes of ISSRs and ICRs, which include the National Science Foundation HIAPER Pole-to-Pole Observations (HIPPO) Global campaign (2009-2011 Arctic to Antarctic over the central Pacific Ocean), the Stratosphere Troposphere Analyses Regional Transport 2008 (START08) campaign (2008 North America), the Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) campaign (2010 tropical western Atlantic), the Tropical Ocean Troposphere Exchange of Reactive Halogen Species and Oxygenated VOC (2012 Costa Rica), and the Deep Convection, Clouds, and Chemistry (DC3) campaign (2011 Interior North America). To understand the evolution of ICRs and ISSRs on the microscale, we compare the microphysical evolution processes inside ISSRs and ICRs in terms of relative humidity with respect to ice (RHi), ice crystal mean diameter (Dc) and ice crystal number density (Nc) at different meteorological and dynamical backgrounds during these five campaigns. Different phases of ice nucleation and evolution are contrasted to understand how cirrus clouds evolve from clear-sky ISS into fully developed clouds, and finally into sedimentation/evaporation phase. The results show that the ratios of each evolution phase with respect to the total cirrus lifetime vary with different atmospheric conditions. For example, the clear-sky ISS, nucleation/growth and evaporation/sedimentation phases each contribute to 20%, 10% and 70% of the total cirrus lifetime for START08, 30%, 10% and 60% for HIPPO, and 10%, 20% and 70% for DC3. The higher ratio of nucleation/growth phase for DC3 campaign might suggest an influence from deep convection to the continuous coexistence of ISSRs and ICRs. In addition, when comparing the sedimentation/evaporation phase between the Northern and Southern Hemispheres (NH and SH) during the HIPPO Global campaign, larger mean diameters of the ice crystals were observed in the NH, which indicate an interhemispheric difference in ice crystal evolution over the central Pacific Ocean. Further analyses are required upon other campaigns to compare the interhemispheric differences of cirrus evolution over other regions. These results can be used to estimate the influences of dynamical environments on cirrus clouds’ evolution time.
Minghui Diao, Joshua DiGangi, Anthony O’Brien, and Mark Zondlo. "Ice Crystal Formation and Evolution in Five Campaigns: START08, HIPPO Global, DC3, PREDICT and TORERO" Faculty Publications, Meteorology and Climate Science (2013).