A dropsonde is an expendable

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmo ...

reconnaissance device created by the

National Center for Atmospheric Research The US National Center for Atmospheric Research (NCAR ) is a US federally funded research and development center (FFRDC) managed by the nonprofit University Corporation for Atmospheric Research (UCAR) and funded by the National Science Foundat ...

(NCAR), designed to be dropped from an

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

at altitude over water to measure (and therefore track) storm conditions as the device falls to the surface. The sonde contains a GPS receiver, along with

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

, and

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

(PTH)

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

s to capture

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

profiles and

thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of th ...

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

. It typically relays this data to a computer in the aircraft by radio transmission.

Usage

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 for

numerical weather prediction Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to weather forecasting, predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of comput ...

, 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, United States Air Force Reserves Hurricane Hunters of the 53rd Weather Reconnaissance Squadron based at Keesler Air Force Base in

Biloxi, Mississippi Biloxi ( ; ) is a city in Harrison County, Mississippi, United States. It lies on the Gulf Coast of the United States, Gulf Coast in southern Mississippi, bordering the city of Gulfport, Mississippi, Gulfport to its west. The adjacent cities ar ...

, have employed dropsondes while flying over the ocean to obtain meteorological data on the structure of

hurricanes A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

deemed to be of possible concern to coastal and inland locations in the northern Atlantic ocean, northeastern Pacific ocean, and the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

. 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 (like

nor'easters A nor'easter (also northeaster; see below) is a large-scale extratropical cyclone in the western North Atlantic Ocean. The name derives from the direction of the winds that blow from the northeast. Typically, such storms originate as a low-p ...

) or significant

tornado outbreak A tornado outbreak is the occurrence of multiple tornadoes spawned by the same Synoptic scale meteorology, synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least ...

s. The dropsondes are used to supplement the large gaps over oceans within the global network of daily 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.

Device and launch details

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-cone

parachute A parachute is a device designed to slow an object's descent through an atmosphere by creating Drag (physics), drag or aerodynamic Lift (force), lift. It is primarily used to safely support people exiting aircraft at height, but also serves va ...

, 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 any

pendulum A pendulum is a device made of a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate i ...

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 by

NOAA The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with forecasting weather, monitoring oceanic and atmospheric conditions, charting the seas, conducting deep-sea exploratio ...

or the U.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 the eyewall and eye (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: # The date and time of the drop. Time is always in UTC. # Location of the drop, indicated by the

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...

, and Marsden square. # The height, temperature, dewpoint depression,

wind speed In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind spe ...

, and

wind direction Wind direction is generally reported by the direction from which the wind originates. For example, a ''north'' or ''northerly'' wind blows from the north to the south; the exceptions are onshore winds (blowing onto the shore from the water) and ...

recorded at any standard isobaric surfaces encountered as the dropsonde descends, which are from the set of: 1000, 925, 850, 700, 500, 400, 300, 250 hectopascals (hPa), and at the sea surface. # The temperature and dewpoint depression at all other atmospheric pressure deemed significant due to important changes or values in the atmospheric conditions found # Air pressure, temperature, dewpoint depression, wind speed and wind direction of the tropopause. Also included in the report is information on the aircraft, the mission, the dropsonde itself, and other remarks.

Driftsondes

A driftsonde is a high altitude, durable

weather balloon A weather balloon, also known as a sounding balloon, is a balloon (specifically a type of high-altitude balloon) that carries instruments to the stratosphere to send back information on atmospheric pressure, temperature, humidity and wind spe ...

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. 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 of hurricane hunter planes.

References

External links

Data from Expendable Probes (NOAA site)

NCAR GPS Dropsonde System (AVAPS)

Vaisala Dropsonde RD94

{{Meteorological equipment Meteorological instrumentation and equipment Atmospheric sounding

Usage

Device and launch details

Driftsondes

See also

References

External links