Balloon Icing Research

Icing is the formation of ice on the balloon. There's much more information available about heaver-than-air craft (airplanes) than lighter-than-air craft (balloons). Most information presented here is relevant to heavier-than-air craft, and it's applicability to balloons will be specifically stated, if known.

Balloon Icing Studies

The Occurrence of Icing on Constant Level Balloons

Abstract

The remarkably short lifetime of many pressurized balloon flights at 300 mb had been tentatively explained by overloading with ice. This phenomenon was definitely observed and well documented in one recent flight. When the balloon entered a dense cirrus cloud the observed ice layer growth rate was very fast, 2 μm min−1. This transport of ice particles cannot be accounted for by eddy diffusion alone in the vicinity of the craft. The proposed explanation of the observed accretion rate of ice is the fall of the large ice particles on the top of the balloon.

Altitudes

Icing is usually restricted to the lower 30,000 feet (9,140 m) of the troposphere1).

Types of Icing

Clear Ice

This is caused by average size freezing rain or drizzle drops hitting an aircraft surface and spreading out before freezing on the sub-zero aircraft surface2). It will most likely occur in the troposphere, below the jet stream. It is very heavy, and hard to get rid of.

Rime Ice

This occurs when tiny super-cooled liquid water droplets in a cloud freeze instantly on contact with a sub-zero aircraft surface. It forms a rough, crystalline, brittle deposit that has many airspaces inside. Temperatures possible: 0C to -40C, most likely from -10C to -20C3).

Hoar Frost

Frost occurs when moist air comes in contact with a sub-zero surface. The water vapor forms ice deposits directly on the surface without going through the liquid phase. It forms a fluffy rough coating that can be brushed off easily. Typical conditions required for frost require a clear night, calm air, and high humidity. Frost can occur when an aircraft descends from sub-zero air into warmer, moist air.4)

Icing in clouds

Our research has show that cirrus clouds are not uncommon along the jet stream, and are likely caused by the low pressure in the jet stream. A cirrus cloud that forms at 300mb to 200mb altitudes should form ice crystals, not liquid water droplets5).

Cumulus clouds that extend upward through these altitudes are uncommon, however they do occur. Cumulonimbus cloud formations from storm cell lifting can carry supercooled liquid water droplets to and beyond the level of 200mb. Liquid droplets in cumulonimbus clouds are likely to be present in temperatures from 0C to -20C, and uncommon from -20C to -40C, and very unlikely below -40C6)7).

Risk of airframe icing in certain types of clouds8):

Risk Cumuliform Clouds Stratiform Clouds Freezing Rain/Drizzle
High 0 to -20C 0 to -15C 0C and below
Med -20C to -40C -15C to -30C
Low -40C and below -30C and below
science/icing/research.txt · Last modified: 2010/10/14 16:43 by steamfire
 
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