Follow this link to skip to the main content
Hurricanes: Science and Society
Glossary - A
The movement (typically horizontal) of air (or water) that causes changes in the physical properties of the air (or water) such as temperature and moisture. Commonly used with temperatures. Source: NOAA-NWS SRH.
Official information issued by tropical cyclone warning centers describing all tropical cyclone watches and warnings in effect, along with details concerning tropical cyclone locations, intensity and movement, and precautions that should be taken. Advisories are also issued to describe: (a) tropical cyclones prior to issuance of watches and warnings and (b) subtropical cyclones. Source NOAA-NHC.
aerosol particles
A particle of matter, solid or liquid, larger than a molecule but small enough to remain suspended in the atmosphere (up to 100 pico-m diameter). Natural origins include salt particles from sea spray and clay particles as a result of weathering of rocks. Aerosols can also originate as a result of the activity of man and in this case are often considered pollutants. Source: NOAA-NWS ERH.
air parcel
An imaginary small body of air that is used to explain the behavior of air. A parcel is large enough to contain a very great number of molecules, but small enough so that the properties assigned to it are approximately uniform throughout. Source: NOAA-NWS ERH.
Airborne eXpendable BathyThermographs (AXBTs)
An expendable instrument that is dropped from an aircraft and used to measure the profile of temperature in the water column. The probe consists of a thermistor in a weighted, streamlined case. It falls freely at a fixed, known rate so that the elapsed time can be converted to depth. It is connected by a thin, freely unwinding wire to a small buoy with a radio transmitter through which the data are transmitted to the aircraft, which continues its flight. (c) 1999, American Meteorological Society. Used with permission.
Height expressed as the distance above a reference point, which is normally sea level or ground level.Source: NOAA-NWS ERH.
An instrument that measures wind speed. Source: NOAA-NWS ERH.
Without oxygen
A pollutant source caused or produced by humans. Source: NOAA-NWS.
Rotation that is clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere. It is the opposite of cyclonic. Source: Canadian Hurricane Centre.
The region within the Arctic Circle, or, loosely, northern regions in general, characterized by very low temperatures. Source: NOAA-NWS.
area of low pressure
A region where the atmospheric pressure is lower in relation to the surrounding area. Since air always moves from areas of high pressure to areas of low pressure, air from these adjacent areas of higher pressure will move toward the low-pressure area to equalize the pressure. This inflow of air toward the low will be affected by the rotation of the Earth (see Coriolis force) and will cause the air to spiral inward in a counterclockwise direction in the northern hemisphere (clockwise direction in the Southern Hemisphere). An area of low pressure is marked as L on a weather map and is usually accompanied by precipitation, extensive cloudiness, and moderate winds.
Atlantic basin
The s-shaped basin in which the Atlantic Ocean occupies, extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. It is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest (Panama Canal), the Indian Ocean in the southeast, and the Southern Ocean in the south. The equator subdivides the basin into the North Atlantic Ocean and South Atlantic Ocean.
Atlantic Multidecadal Oscillation (AMO)
A natural oscillation of the North Atlantic sea surface temperature (SST) between warm and cool phases. The SST difference between these warm and cool phases is about 0.5°C and the period of the oscillation is roughly 20-40 years (the period is variable, but is a few decades long).
Atlantic Ocean
The second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres (41.1 million square miles), it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek mythology, making the Atlantic the "Sea of Atlas". The oldest known mention of this name is contained in The Histories of Herodotus around 450 BCE (I 202); see also: Atlas Mountains. Another name historically used was the ancient term Ethiopic Ocean, derived from Ethiopia, whose name was sometimes used as a synonym for all of Africa and thus for the ocean. Before Europeans discovered other oceans, the term "ocean" itself was to them synonymous with the waters beyond Western Europe that we now know as the Atlantic and which the Greeks had believed to be a gigantic river encircling the world; see Oceanus. The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. A component of the all-encompassing World Ocean, it is connected in the north to the Arctic Ocean (which is sometimes considered a sea of the Atlantic), to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. (Alternatively, in lieu of it connecting to the Southern Ocean, the Atlantic may be reckoned to extend southward to Antarctica.) The equator subdivides it into the North Atlantic Ocean and South Atlantic Ocean.
The mass of air surrounding the Earth that acts as a buffer between the Earth and the sun. It is mainly composed of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases. The atmosphere is described as a series of distinct layers: troposphere (lowest), stratosphere, mesosphere, thermosphere, and exosphere (highest).
atmospheric dynamics
The study of those motions of the atmosphere that are associated with weather and climate. In atmospheric dynamics, the fluid is regarded as a continuous medium, and the fundamental laws of fluid mechanics and thermodynamics are expressed in terms of partial differential equations involving the fluid velocity, density, pressure, and temperature. Source: (c) 1999, American Meteorological Society. Used with permission.
atmospheric pressure
(also called air pressure or barometric pressure) Generally, the pressure asserted by the mass of the column of air directly above any specific point. Source: NOAA-NWS ERH.