Abstract
Abstract. During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign at mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between −87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were further distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. The dimensions and aspect ratios (AR, the dimension of the major axis divided by the dimension of the minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' orL') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50 ± 1.35 during three campaigns and 6.32 ± 1.34 (5.46 ± 1.34; 4.95 ± 1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67 < T < -35 °C and at −40 < T < −15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L–W relationships of columns derived using current data exhibited a strong dependence on temperature; similar relationships determined in previous studies were within the range of the current data.
Highlights
The impacts of ice clouds on the energy budget of the Earth and their representation in climate models have been identified as important and unsolved problems (IPCC, 2013)
Ice crystals were sampled at lower temperatures during Tropical Warm Pool International Cloud Experiment (TWP-ICE) compared with SPARTICUS and Indirect and Semi-Direct Aerosol Campaign (ISDAC) sampling at progressively higher T
Larger numbers of ice crystals were analyzed during SPARTICUS (i.e., 13 919 crystals) compared to TWP-ICE (4799 crystals) and ISDAC (3787 crystals) because a greater number of relevant flight hours were available from that campaign
Summary
The impacts of ice clouds on the energy budget of the Earth and their representation in climate models have been identified as important and unsolved problems (IPCC, 2013). Ice clouds consist almost exclusively of non-spherical ice crystals with various shapes (i.e., habits) and sizes (e.g., Liou, 1986). The fundamental building blocks of the most common ice crystal habits are hexagonal prisms (i.e., hexagonal columns and plates) because of the hexagonal lattice structure of water molecules in an ice crystal. The other common habit frequently found in cirrus is a bullet rosette and its basic component (i.e., branch or arm) is a hexagonal prism. Since initial work that identified crystal shapes using in situ ob-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
