A subtropical front is a surface water mass boundary or front, which is a narrow zone of transition between air masses of contrasting density, air masses of different temperatures or different water vapour concentrates. It is also characterized by an unforeseen change in wind direction, and speed across its surface between water systems, which are based on

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

and

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

. The subtropical separates the more saline subtropical waters from the fresher sub-Antarctic waters.Graham, Robert M., and Agatha M. Boer. "The dynamical subtropical front." Journal of Geophysical Research: Oceans 118.10 (2013): 5676-5685.

Subtropical frontal zone

A subtropical frontal zone (STFZ) is a large seasonal cycle located on the eastern side of basins. It is made up of fronts of multiple weak sea surface temperature (SST), aligned northwest–southeast, spread over a large latitudinal span. On the far eastern side of basins, the subtropical frontal zone becomes narrower and temperature gradients stronger, but still much weaker than across the dynamical subtropical frontal zone. A dynamical frontal zone sits at the southern limit of the saline subtropical waters on the western sides of basins. There are no water mass boundaries or fronts in correlation with the sea surface temperature at the subtropical frontal zone at the surface or beneath. The structure of a subtropical frontal zone results in the formation of a positive

wind stress In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a f ...

curl, which is the

shear stress Shear stress, often denoted by (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. ''Normal stress'', on the ot ...

exerted by

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...

on the

surface A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...

of water. The areas of most positive wind stress curl are characterized by very weak sea surface temperature incline, and are likely consistent to regions of

mode water Mode water is defined as a particular type of water mass, which is nearly vertically homogeneous. Its vertical homogeneity is caused by the deep vertical convection in winter. The first term to describe this phenomenon is ''18° water'', which wa ...

Northern subtropical front

The Northern subtropical front is found in the Pacific Ocean between 25° and 30° north latitude.

North Atlantic subtropical fronts

The North Atlantic subtropical fronts possess the characteristics of seasonal variability. Highest front occurrences are during early spring in the western region. Less front probability occurs in late spring to early summer in the eastern region. The strengths of the fronts differ with seasons, building strength when moving southward during the winter and spring, and weakening when moving northward during the summer.

North Pacific subtropical fronts

The North Pacific subtropical fronts are occupied by wind driven submesoscale subduction. Due to the constant

thermohaline Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to tempe ...

circulation fronts, cold air flows near the surface and bottom of the ocean. There are alternating fluxes throughout the year, that is influenced by jet streams which causes temperatures in these areas to differ.

Southern subtropical front

The Southern subtropical front is caused by warm, salty subtropical waters and Antarctic waters, found in all three

ocean basins In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, ocean basins are large  geologic basins that are below sea level. Most commonly the ocean is divided into basins foll ...

. A commonly used criterion found is that the salinity at a depth of 100m drops below 34.9 practical salinity units.

South Atlantic subtropical frontal zone

A characteristic of the South Atlantic subtropical frontal zone, between 15°W and 5°E, is the conversion from subtropical to sub-polar waters. As a result, this coerces the

South Atlantic Current The South Atlantic Current is an eastward ocean current, fed by the Brazil Current. That fraction of it which reaches the African coast feeds the Benguela Current. It is continuous with the northern edge of the Antarctic Circumpolar Current. Th ...

flow and is surrounded by a distinct front.D. Smythe-Wright, P. Chapman, C.Duncombe Rae, L.V. Shannon, S.M. Boswell
Characteristics of the South Atlantic subtropical frontal zone between 15°W and 5°E
Deep-Sea Research Part I: Oceanographic Research Papers, Volume 45, Issue 1, January 1998, Pages 167-192, ISSN 0967-0637.

References

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External links

Southern Subtropical Front
Physical oceanography