Ice in Clouds Experiment—Layer Clouds. Part I: Ice Growth Rates Derived from Lenticular Wave Cloud Penetrations

Abstract

Lenticular wave clouds are used as a natural laboratory to estimate the linear and mass growth rates of ice particles at temperatures from 2208 to 2328C and to characterize the apparent rate of ice nucleation at water saturation at a nearly constant temperature. Data are acquired from 139 liquid cloud penetrations flown approximately along or against the wind direction. A mean linear ice growth rate of about 1.4 mm s 21 , relatively independent of particle size (in the range 100-400 mm) and temperature is deduced. Using the particle size distributions measured along the wind direction, the rate of increase in the ice water content (IWC) is calculated from the measured particle size distributions using theory and from those distributions by assuming different ice particle densities; the IWC is too small to be measured. Very low ice effective densities, ,0.1 g cm 23 , are needed to account for the observed rate of increase in the IWC and the unexpectedly high linear growth rate.Using data from multiple penetrations through a narrow (along wind) and thin wave cloud with relatively flat airflow streamlines, growth rate calculations are used to estimate where the ice particles originate and whether the ice is nucleated in a narrow band or over an extended period of time. The calculations are consistent with the expectation that the ice formation occurs near the leading cloud edge, presumably through a condensation-freezing process. The observed ice concentration increase along the wind is more likely due to a variation in ice growth rates than to prolonged ice nucleation.

Perspectives on the Future of Ice Nucleation Research: Research Needs and Unanswered Questions Identified from Two International Workshops

“…For example, previous field campaigns have targeted the roles of ice initiation and secondary ice multiplication in clouds such as the Ice in Clouds Experiment-Layer Clouds (ICE-L; 2007) in Colorado, ICE-Tropical Clouds (ICE-T; 2011) in St. Croix, and ICE-Dust (ICE-D; 2015) in Cape Verde (e.g., [187][188][189][190][191][192][193][194]). Although these and other previous, parallel studies have yielded noteworthy results, our overall understanding of heterogeneous ice nucleation remains limited due to: (1) the complexities involved with heterogeneous ice nucleation processes and their role in modulation of precipitation phase, location, and quantity relative to secondary ice and atmospheric dynamical processes and (2) variability of these processes within different cloud regimes.…”

Ice particle production in mid-level stratiform mixed-phase clouds observed with collocated A-Train measurements

“…Below the liquiddominated cloud layer, ice crystals continue to grow during the fall until they reach a level that is sub-saturated with respect to ice. The less complex dynamic environment and straightforward ice growth trajectory in mid-level stratiform mixed-phase clouds provides an ideal scenario for studying cloud thermodynamic-phase partitioning and aerosol impacts on ice formation in clouds, and for retrieving cloud microphysical properties with remote sensing measurements (Wang et al, 2004;Larson et al, 2006;Heymsfield et al, 2011;Zhang et al, 2012Zhang et al, , 2014Bühl et al, 2016). Zhang et al (2010) show for the first time the climatology of midlevel stratiform clouds and their macrophysical properties using A-Train satellite remote sensing measurements.…”

Axis Ratios and Flutter Angles of Cloud Ice Particles: Retrievals from Radar Data

“…Ice crystals are the foundation for much precipitation worldwide and ice clouds play a significant role in the radiation balance of the earth system. Large amounts of data on particle shapes have been obtained with laboratory experiments and onboard probes (e.g., Pruppacher and Klett 1997, section 2.2.1; Korolev and Isaac 2003;Hallett 2004, 2009;Heymsfield et al 2011). Direct cloud measurements with onboard probes are very costly and provide data along airplane tracks (i.e., in areas with extremely small volumes compared to cloud volumes available from radar).…”