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Pilot Balloon Selection and Procedures
Balloons used for upper level wind observation are spherically shaped films of natural or synthetic rubber which are inflated with a lighter-than air gas (helium or hydrogen) so that they are buoyant in air.
Storage and Handling
Balloons should be stored in their original, sealed containers and , if possible, stored at temperatures between 65 and 85 degrees F. If balloons are subjected to below freezing temperatures, they must be returned to a temperature of >65 degrees of 12 hours or more prior to removal from their containers. This will prevent damage that the balloon might receive if it were manipulated when cold. Exposure to temperatures above 120 degrees F is extremely detrimental. Additionally exposure to ozone (commonly produced by large electrical generators and motors) is harmful to most rubber compounds.
No part of the balloon except the neck should be touched with bare hands. Soft rubber gloves, soft cloth gloves or some other non-abrasive material should be used to protect the balloon when it is necessary to handle any portion of the balloon other than the neck. If gloves are not worn, make certain that hands are clean, fingernails are clipped, and rings are removed. Dust hands with talc.
Selection of Balloons
There are 4 sizes of balloons commonly available for pibal use. 10,20, 30 and 100 grams with protocols for 30 and 100 gram sizes specified and used in the weather service and military publications.
10 gram balloons are often called ceiling balloons as there traditional use has been for determining cloud height. However their relatively slow ascent rate, and thrifty use of helium (about 1.5 CF verses 5 CF for a 30 gram balloon) makes them an ideal candidate for use in relatively light winds (under 20 knots) and low altitude work (under 6 thousand feet MSL). This includes applications such as wind measurement for fire weather, hot air ballooning, and aerobatic competitions.
30 and 100 gram balloons ascent faster and reach a higher altitude than 10 gram balloons before bursting. Using the protocols developed for these two balloon sizes 30 gram balloons ascend at a predicted rate of 180 meters per minute and 100 gram balloons at a predicted rate of 270 meters per second. The 100 gram balloon will attain a higher altitude before bursting and is larger (easier to track at a given altitude), it does however use a significantly larger amount of gas, and in the case of low speed winds may be less accurate.
Weather, and military service protocols are outlined below:
Night Tracking a pibal at night can be made possible by attaching a lightweight, self-illuminating or battery-operated lighting unit to the balloon. Attach the lighting unit directly to the balloon with a length of cord. The length of the train should generally be limited to 2 meters (6 feet). No lighting unit should be used for a release more than 15 minutes after the unit has been activated. The lighting unit should be activated just prior to the release in accordance with accompanying manufacturer's instructions.
Attachments should not be made to pilot balloons used in observations taken during daylight hours.