Ice-producing processes in a North Dakota cumulus cloud

Abstract

The early development of ice particles in a convective cloud is monitored using radar and instrumented aircraft. Observed ice particle concentrations (∼ 1000 m −3) at the −13°C level in updraft regions are consistent with recent suirvey of ice nuclei concentrations but are high compared to earlier surveys. An adiabatic parcel model with an ice nucleation parameterization based on the more recent surveys produces an initial ice particle population at the −13°C level that closely resembles that observed. The observations suggest that in this cloud ice particles first nucleated in the air rising in the updraft region below this level. These particles began to grow to precipitation sizes just as the updraft began to collapse. Due to lack of supercooled cloud water, ice particles that nucleated later at higher and colder levels did not grow to precipitation sizes. Maximum concentrations of small graupel particles reached only 2 × 10 4 m −3 near the −10°C level in the cloud even though cloud-top temperatures as low as −40°C were attained.