Adropsonde is an expendableweather reconnaissance device created by theNational Center for Atmospheric Research (NCAR), designed to be dropped from anaircraft at altitude over water to measure (and therefore track) storm conditions as the device falls to the surface. The sonde contains aGPS receiver, along withpressure,temperature, andhumidity (PTH)sensors to captureatmospheric profiles andthermodynamicdata. It typically relays this data to a computer in the aircraft by radio transmission.
Dropsonde instruments are typically the only current method to measure the winds and barometric pressure through the atmosphere and down to the sea surface within the core of tropical cyclones far from land-based weather radar. The data obtained is usually fed via radio into supercomputers fornumerical weather prediction, enabling forecasters to better predict the effects and intensity, based on computer-generated models using data gathered from previous storms under similar conditions. This helps meteorologists to more reliably establish a storm's potential damage, based on those factors.
Since the early 1970s,[1]United States Air Force ReservesHurricane Hunters of the53rd Weather Reconnaissance Squadron based atKeesler Air Force Base inBiloxi, Mississippi, have employed dropsondes while flying over the ocean to obtain meteorological data on the structure ofhurricanes deemed to be of possible concern to coastal and inland locations in the northern Atlantic ocean, northeastern Pacific ocean, and theGulf of Mexico. During a typical hurricane season, Hurricane Hunters deploys 1,000 to 1,500 sondes on training and storm missions.
Aircraft reconnaissance missions are also sometimes requested to investigate the broader atmospheric structure over the ocean when cyclones may pose a significant threat to the United States. These interests include not only potential hurricanes, but also possible snow events (likenor'easters) or significanttornado outbreaks. The dropsondes are used to supplement the large gaps over oceans within the global network ofdaily radiosonde launches. Typically satellite data provides an estimate of conditions in such areas, but the increased precision of sondes can improve forecasts, particularly of the storm path.
Dropsondes may also be employed during meteorological research projects.
The sonde is a lightweight system designed to be operated by one person and is launched through a chute installed in the measuring aircraft. The device's descent is slowed and stabilized by a small square-coneparachute, allowing for more readings to be taken before it reaches the ocean surface. The parachute is designed to immediately deploy after release so as to reduce or eliminate anypendulum effect, and the device typically drops for three to five minutes. The sonde has a casing of stiff cardboard to protect electronics and form a more stable aerodynamic profile.
To obtain data in a tropical cyclone, an aircraft (in the US, operated either byNOAA or theU.S. Air Force) flies into the system. A series of dropsondes are typically released as the plane passes through the storm, typically launched with greatest frequency near the center of the storm, including into theeyewall andeye (center), if one exists. Most drops are performed at a flight level of around 10,000 feet (approx. 3,000 meters).
The dropsonde sends back coded data, which includes:
Also included in the report is information on the aircraft, the mission, the dropsonde itself, and other remarks.
Adriftsonde is a high altitude, durableweather balloon holding a transmitter and a bank (35 in the first models) of miniature dropsonde capsules which can then be dropped at automatic intervals or remotely. The water-bottle-sized transmitters in the dropsondes have enough power to send information to the balloon during their parachute-controlled fall. The balloon carries a larger transmitter powerful enough to relay readings to a satellite. The single-use sensor packages cost US$300 to $400 each.[2]
After being introduced in April 2007, around a thousand a year are expected to be used to track winds in hurricane breeding grounds off of West Africa, which are outside the operating region ofhurricane hunter planes.[2]
