Cirrus Particle “Cloud-Catcher”: A New Balloon-Borne Technique for High-Resolution Imaging of Cirrus Ice Particles

Instrument design and initial observations are presented from the TCNJ “Cloud Catcher” – a novel balloon-borne device designed to capture, preserve, and return cirrus particles for transfer and imaging via high-resolution Environmental Scanning Electron Microscopy (ESEM). The 5 pound prototype payload houses a custom-fabricated insulated cryo-containment chamber which is carried aloft by weather balloon, returned to earth by parachute, and tracked by GPS. A 1 cm2 top-side aperture on the containment chamber is operated by a pressure switch, allowing ice particles to fall gently into the containment vessel as the catcher ascends slowly through the cirrus cloud and only when the pressure (and cirrus altitude) is within a pre-defined range (typically 400 to 50 mb). The cryo-containment chamber has been designed to maintain equilibrium ice saturation and isothermal temperatures at approximately -50°C (for up to ~12 hours outside the lab, or longer in cold-storage), such that captured ice particle surfaces can be preserved as closely as possible to their state of capture. The sealed central storage cell within the containment chamber has been designed so that it can be sealed, removed, and transferred directly to the ESEM cold stage without altering the ice/vapor equilibrium around the captured crystals. Once the equilibrium conditions are matched within the ESEM chamber environment, the sealed orifice to the cell is peeled off through motion of the ESEM stage, allowing direct imaging at equilibrium conditions. The Cloud Catcher includes the pre-chilled cryo-container, aperature control electronics, 2 GPS tracking devices, HD video camera, and temperature, pressure, and humidity loggers along with a 6-legged construction intended to promote upright landing. The device, parachute (5 ft. Rocketman) , and balloon (300 gram Kaymont) assembly is launched during cirrus coverage from a location determined by trajectory modeling to result in a landing/recovery site in an agricultural corridor just west of Princeton to promote easy recovery and access to the ESEM. Trial flights have verified intended operation: balloons ascended to ~60,000 feet at ~3 m/s, burst, and the payload descended at ~ 5 m/s. Payloads where recovered on all but the first trial and were confirmed to have captured and preserved cirrus particles on one instance (9/2/13). Unfortunately, the Princeton ESEM malfunctioned on this date and ESEM images could not be acquired. Nevertheless, proof-of-concept was achieved. We are confident of achieving successful capture and ESEM imaging of cirrus particles.