To inflate a balloon, hold the inflation hose 2 to 3
inches from the connection to the balloon nozzle and
allow the gas to flow into the balloon until the balloon
just supports the weight of the inflation nozzle assembly
(to achieve neutral buoyancy). It is a good idea to shut
off the valve when the balloon is about half-full and
listen for any leaking air from holes that may be in the
balloon. Finally, shut off the gas flow and tie off the
If balloon inflation weights are not available,
balloons may be inflated using only the regulator. You
may inflate the balloons with the required amount of gas
by using the inner (cubic feet) scale of the high-pressure
dial. To achieve approximately 700 grams of free lift, a
100-gram balloon will take about 40 cubic feet of
helium. To achieve 900 grams of free lift, a 300-gram
balloon will need about 70 cubic feet of helium. In any
case, the balloon should produce a fairly strong pull or
tug on the nozzle and hose.
A D J U S T M E N T S T O I N F L A T I O N .
Ascension rates should be calculated for all soundings.
Because of environmental conditions, free lift weight is
adjusted to better target the 900 to 1,000 feet per minute
desired ascension rate. During precipitation or icing,
you must increase the free lift to compensate for the
additional weight of water, snow, or ice on the balloon.
For example, during light rain or drizzle, you must
increase free lift (weight of inflation nozzle assembly)
by 100 grams or increase the helium in the balloon by 3
to 4 cubic feet. When light to moderate icing or
moderate to heavy precipitation is anticipated, increase
the free lift by 200 to 300 grams or increase the helium
by 7 to 11 cubic feet. However, increasing the free lift
by more than 300 grams during severe icing conditions
may slow the ascent rate because of the increased
surface area on which ice may collect.
Tying the Balloon
After inflation, it is imperative that the balloon neck
be tied properly to prevent leakage of gas and to allow
for attachment of the instrument. Most balloons can be
sealed by using a single loop over the unwinder gripper
and a plastic tie. If no plastic ties are available, use a 3-
to 4-foot length of cotton textile tape (balloon tape) or a
medium thickness cotton twine. Fold the twine in half
to obtain a double thickness. While the balloon is still
on the inflation nozzle, tie a tight square knot around the
balloon neck about 1 1/2 to 2 inches below the body of
the balloon. Remove the balloon from the nozzle and
loop the excess balloon neck up and over the first knot
by about an inch. Then, wrap the loop tightly with the
remaining cord ends, and tie it securely with a second
square knot. The loop in the balloon neck must be large
enough to insert the gripper of the balloon winder
through the loop (fig. 1-6). The remaining excess cord
is used to handle the balloon before release. The
balloon cord should be attached to the unwinder gripper
with a double square knot prior to release. Tying the
cord to the gripper will help prevent the gripper from
chaffing the balloon loop during gusty wind conditions.
Allow no more than 6 to 8 feet of train from the
Use of Parachutes
Parachutes are neither required nor recommended
for use during an MRS sounding. The 250-gram RS-80
series radiosonde instrument, even when in free-fall
after balloon burst, has sufficient drag that even a direct
strike to a person on the ground will cause no serious
injury. However, the National Weather Service does
require their use. If a parachute is elected for use at land
stations, the parachute is tied to the balloon, and the
radiosonde is affixed to the bottom of the parachute.
Use of the 6-foot paper parachute or the 6-foot cloth
parachute requires that an extra 100 grams be added to
the nozzle weight during Inflation to maintain proper
free lift. Meteorological parachutes are never used at
Use of Balloon Shrouds
A balloon shroud is recommended for use to protect
and securely hold or move the balloon and radiosonde
prior to launch during windy conditions. The fabric
balloon shroud may be used to hold balloons up to 7 1/2
feet in diameter. When moving a balloon, use the
handles at the comers of the shroud. The cloth bands at
the apex of the shroud may be used to attach an
anchoring line, which is used to pull the shroud off the
balloon as the handles are released during launch.
Balloon shrouds must be hung to dry if used during rain,
and must contain an antistatic electricity treatment if
used with hydrogen or natural-gas-filled balloons.
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