Upper-Air Instruments Upper-air measurements began in 1749 with temperature measurements made with kites by Dr. Alexander Wilson of Glasgow, Scotland. In 1894, routine meteorological kites were launched from the Blue Hill Observatory in Milton, Massachusetts. Kites, balloons, aircraft, rockets have, and are, used as platforms for making in-situ measurements of the upper air.

Early Balloon platforms 1905 1906

Early Kite platforms 1906 ~1920

Early Airplane platforms 1934 ~ 1935

Early Airplane platforms 1934 ~ 1935

Balloon types Ceiling Balloons: Used to measure the height to a cloud base. 10 gram balloons (weight of balloon) of natural rubber or neoprene Filled with helium or hydrogen to obtain a specified rate of ascent. Empirical formula is: w = rate of ascent (ft/min) L = free lift or lifting force = F - W (grams) W = weight of balloon and attachments (grams) F = Buoyant Force (grams) = weight of volume of air it displaces = rair g V

The buoyant force is equal to the weight of the air displaced by the balloon which is equal to the balloon’s volume X density of the air X gravity. The net force acting on the balloon is then: To increase the upward net force, we can either increase the volume of displaced air, reduce the mass (molecular weight) of gas in the balloon, or decrease the weight of the balloon and its attachments.

Bursting altitude is about 10,000 feet for these balloons. By timing the balloon until it disappears into the cloud and multiplying “w” by the time, the height of the cloud layer base is determined. Bursting altitude is about 10,000 feet for these balloons. The color used depends on the sky conditions. White Balloons: clear sky, not cumulus or cirrus Red or orange: scattered to broken clouds Black and blue: overcast sky Nighttime: requires light source.

Pilot Balloons Used to determine winds aloft. 20 gm to 100 gm balloon. Balloon is filled to a specified ascent rate. Tracked by one or two theodolites.

Theodolite Ascent rate is used to determine height for each minute. Elevation angles and azimuth angles are used to determine the wind speed and direction for each height.

Single Theodolite

Double theodolite Do not need to assume a constant ascent rate. Baseline should be perpendicular to the flight of the balloon - not always provided. Measurements from each theodolite need to be taken at the same time.

Radiosonde/Rawinsonde Balloons 100, 200, 350, 500, 600, 1100 and 1200 gm neoprene balloons Rate of ascent ~1000 ft./min. ~320 m/min. Burst altitude ~110,000 feet (1 hour 50 min.) for larger balloons, 30,000 ft. for smaller.

Jimsphere Named after Dr. Jim Scoggins Made of mylar with 938 cones The cones rough the surface which prevents formation of vortices and increases drag on the balloon. Balloon is more stable, quickly assuming the speed of the wind in a changing wind environment without zigzagging in the air. Easily tracked by high precision radar. Produced by Orbital Sciences Corporation

ROBIN Balloon Rocket Balloon Instrument Balloon released from rocket at apogee with instrument package to slowly descend. Corner reflector built into the balloon for tracking by radar.

Global Horizontal Sounding Technique Constant Density Balloon Can drop dropsondes • Measure temp., wind, Made of mylar particles, radiation, ozone Float between 30 and 10 mb (80,000 - 100,000 ft)

Ultra-long Duration Balloons Can stay aloft up to three weeks. NASA supports ~25 launches per year

Tetroon Balloons New Designs: Tetrahedron balloon. Created to better withstand high altitude pressure extremes. Straight seals on balloon are stronger than curved seals. NOAA design. Utilizes GPS for position and level determinations. Constant level (pressure) Early design: Could not compensate for radiation and precipitation produced changes in level. Use as a standard radiosonde balloon.

ACE-1: Made of mylar. Internal ballast and release valve allows for adjustments to keep balloon near a constant pressure level.

Superpressure Smart Balloon ACE-2: Spherical balloon, not a tetroon. Stronger outer shell. New design internal ballast. Two-way communication with ground to allow interactive control.

Basic Assumptions on balloon ascent 1. Balloon exerts no compressive force on the contained gas. 2. Temperatures inside equals those outside. 3. Balloon is always spherical. 4. No loss of gas from balloon.

Errors in assumption of rate of ascent 1. Loss of gas: Lift decreases 2. Volume change: Due to heating / cooling of the neoprene As balloon warms, it will rise faster 3. Stability: Vertical fluctuations in the atmosphere cause more rapid or more slower ascent. Changes level of constant pressure balloons also. 4. Ice, rain, snow, frost: reduce lift of balloon by adding weight.

Radiosonde Instruments Classification by platform Ordinary: Rises on a balloon Dropsonde: Dropped from an aircraft, rocket, or another balloon. Balloonsonde: Constant-level balloon

Classification by Converter type Chronometric: Switch between sensors by clock, or electronic, or wind driven mechanism. Codesonde: Morse-code characters are transmitted as sensors move levers which make contact with a disk on which are grooves that cause the Morse-code characters to be transmitted; much like a phonograph disk. Range of characters (values) is limited.

Variable Radio Frequency: Electric or wind driven switch rotates between contacts for pressure, temperature, humidity whose sensors vary the capacitance in the circuit which modulates the carrier wave frequency which is in the radio frequency range. Variable Audio Frequency: Switch (usually a baroswitch) alternates between contacts for pressure, temperature, humidity, reference. Sensor signal modulates a carrier wave frequency with the modulating frequency being in the audio frequency range.

Radiosonde Commutator bar Alternating silver and insulating strips Allows switching between temperature, humidity, reference signals Pressure determined by which silver or insulating strip the contact arm is on Temperature transmitted at every insulating segment Humidity at every silver strip. Every 5th silver strip sends a reference signal.

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