The variation with depth of motions associated with variation of density with depth. The baroclinic component of the velocity is the total minus the barotropic component. In a baroclinic state, neutral surfaces are inclined to surfaces of constant pressure. The baroclinic torque vector is proportional to the vector cross product and is responsible for generating vertical shears associated with baroclinic flow. Source: (c) 1999, American Meteorological Society. Used with permission.

An instrument for measuring atmospheric pressure. Source: NOAA-NWS ERH.

The actual pressure value indicated by a pressure sensor. Source: NOAA-NWS SRH. (Also see atmospheric pressure.)

A computer model that treats the atmosphere (or any fluid) as being barotropic. In a barotropic atmosphere, temperature and pressure surfaces are coincident, i.e., temperature is uniform (no temperature gradient) on a constant pressure surface. Barotropic systems are characterized by a lack of wind shear. Source: NOAA-NWS ERH.

An elongate accumulation of sand that is separated from the mainland by open water in the form of estuaries, bays, or lagoons. These primarily sandy islands are now in great demand for both residential and recreational development. Beaches on the seaward side of barrier islands are the principal location for beach nourishment. Source: NOAA-CSC.

The water depth relative to sea level. Depth values may be either negative or positive, but should all be understood to be negative. Depths are almost always derived indirectly by measuring the time required for a signal to travel from a transmitter, to the bottom, and back to a receiver. This travel time is then converted to a depth based on a variety of estimations of the signal speed through the water column. Signal speed varies with salinity and temperature. Source: USGS.

A scale that indicates the wind speed using the effect wind has on certain familiar objects. Source: NOAA-NWS ERH.

A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores in the eastern part of the North Atlantic, during which time it may be referred to as the Azores High. Source: NOAA-NWS SRH.

A subjectively-smoothed representation of the location of a tropical cyclone and intensity over its lifetime. The best track contains the latitude, longitude, maximum sustained surface winds, and minimum sea-level pressure of the cyclone at 6-hour intervals. Best track positions and intensities, which are based on a post-storm assessment of all available data, may differ from values contained in storm advisories. They also generally will not reflect the erratic motion implied by connecting individual center fix positions. Source NOAA-NHC.

The drift of a tropical cyclone through the large-scale background wind in which it is embedded. The drift is caused by the advection of the background potential vorticity field by the storm circulation. Beta drift generally causes tropical cyclones to move poleward and westward relative to the motion they would have if the background potential vorticity field were unperturbed by the storms. This drift speed is generally around 1–2 m/s. Source: (c) 1999, American Meteorological Society. Used with permission.

The mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community.

Pertaining to waters with a salt concentration between that of pure ocean water and freshwater (ie, bay water). Source: NOAA.

Standards and guidelines for construction of buildings to ensure a minimum level of safety for the occupants. Source: Canadian Hurricane Centre.