Observations of Chain Aggregates in Florida Cirrus Cloud Anvils

Abstract:

Multiple aircraft field projects have obtained in-situ observations of chain-like aggregates of crystals in cirrus clouds of tropical thunderstorms. Observations of these chain aggregates date back to 2002 when the 2D-C cloud imaging probe sampled the cloud tops of convection produced over the Amazon Rainforest. More recently, these chain aggregates were observed during research flights of the North Dakota Citation Research Aircraft over Florida in 2015 and 2019 (CAPE2015 & CAPE2019). In 2019, the airborne Particle Habit Imaging and Polar Scattering (PHIPS) probe obtained higher resolution stereographic images and angular light scattering functions of individual ice particles. With over 170,000 PHIPS images available from the field project, manually classifying images to determine locations of the chain aggregates is time consuming. The aircraft’s position in conjunction with concurrent, multi-radar observations are utilized to determine if chain aggregates occur more often adjacent to the convective cores or at different altitudes within the cirrus cloud anvil. An analysis of the CAPE2019 flight on August 3, 2019 showed that of a total of 17,146 PHIPS images, 7,151 where classified as chain aggregates. Since these chain aggregates can contain multiple plates and columns connected by small joints, these chains are sufficiently larger than individual 100-300 μm diameter plates themselves. Determining the process which generate these large chain aggregates in cirrus cloud anvils should enable models to predict their occurrence.