Inflow (meteorology)
Encyclopedia
Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology
, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere
into storm
systems. Extratropical cyclones are fed by inflow focused along their cold front
and warm front
s. Tropical cyclones require a large inflow of warmth and moisture from warm oceans in order to develop significantly, mainly within the lowest 1 kilometre (0.621372736649807 mi) of the atmosphere. Once the flow of warm and moist air is cut off from thunderstorms and their associated tornado
es, normally by the thunderstorm's own rain-cooled outflow boundary
, the storms begin to dissipate. Rear inflow jets behind squall line
s act to erode the broad rain
shield behind the squall line, and accelerate its forward motion.
Cool air, carried to the ground by thunderstorm downdraft, cuts off the inflow of the thunderstorm, destroying its updraft and causing its dissipation. Tornadoes, which form within stronger thunderstorms, grow until they reach their mature stage. This is when the rear flank downdraft of the thunderstorm, fed by rain-cooled air, begins to wrap around the tornado, cutting off the inflow of warm air which previously fed the tornado. When thunderstorms are able to organize into squall lines, a feature known as a rear inflow jet develops to the south of the mid-level circulation associated with its northern bookend vortex, leading to an erosion of rain
within the broad rain shield behind the squall line, and this can lead to acceleration of the squall line itself.
While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure
more than a few millibars (0.10 inch of mercury
). Inflow of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest 1 kilometres (3,280.8 ft) of the atmosphere.
Polar front theory is attributed to Jacob Bjerknes
, and was derived from a coastal network of observation sites in Norway
during World War I
. This theory proposed that the main inflow into a cyclone
was concentrated along two lines of convergence, one ahead (or east) of the low and another trailing equatorward (south in the Northern Hemisphere and north in the Southern Hemisphere) and behind (or west) of the low. The convergence line ahead of the low became known as either the steering line or the warm front
. The trailing convergence zone was referred to as the squall line
or cold front
. Areas of clouds and rainfall appeared to be focused along these convergence zones. A conveyor belt, also referred to as the warm conveyor belt, is a term describing the flow of a stream of warm moist air originating within the warm sector (or generally equatorward) of an extratropical cyclone in advance of the cold front which slopes up above and poleward (north in the Northern Hemisphere and south in the Southern Hemisphere) of the surface warm front. The concept of the conveyor belt originated in 1969.
The left edge of the conveyor belt is sharp due to higher density air moving in from the west forcing a sharp slope to the cold front. An area of stratiform precipitation develops poleward of the warm front along the conveyor belt. Active precipitation poleward of the warm front implies potential for greater development of the cyclone. A portion of this conveyor belt turns to the right (left in the Southern Hemisphere), aligning with the upper level westerly flow. However, the western portion of this belt wraps around the northwest (southwest in the Southern Hemisphere) side of the cyclone, which can contain moderate to heavy precipitation. If the air mass is cold enough, the precipitation falls in the form of heavy snow. Theory from the 1980s talked about the presence of a cold conveyor belt originating north of the warm front and flowing along a clockwise path (in the northern hemisphere) into the main belt of the westerlies aloft, but there has been conflicting evidence as to whether or not this phenomenon actually exists.
Meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
into storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
systems. Extratropical cyclones are fed by inflow focused along their cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
and warm front
Warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...
s. Tropical cyclones require a large inflow of warmth and moisture from warm oceans in order to develop significantly, mainly within the lowest 1 kilometre (0.621372736649807 mi) of the atmosphere. Once the flow of warm and moist air is cut off from thunderstorms and their associated tornado
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
es, normally by the thunderstorm's own rain-cooled outflow boundary
Outflow boundary
An outflow boundary, also known as a gust front, is a storm-scale or mesoscale boundary separating thunderstorm-cooled air from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature and a related pressure jump...
, the storms begin to dissipate. Rear inflow jets behind squall line
Squall line
A squall line is a line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts....
s act to erode the broad rain
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
shield behind the squall line, and accelerate its forward motion.
Thunderstorms
Cool air, carried to the ground by thunderstorm downdraft, cuts off the inflow of the thunderstorm, destroying its updraft and causing its dissipation. Tornadoes, which form within stronger thunderstorms, grow until they reach their mature stage. This is when the rear flank downdraft of the thunderstorm, fed by rain-cooled air, begins to wrap around the tornado, cutting off the inflow of warm air which previously fed the tornado. When thunderstorms are able to organize into squall lines, a feature known as a rear inflow jet develops to the south of the mid-level circulation associated with its northern bookend vortex, leading to an erosion of rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
within the broad rain shield behind the squall line, and this can lead to acceleration of the squall line itself.
Tropical cyclones
While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
more than a few millibars (0.10 inch of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
). Inflow of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest 1 kilometres (3,280.8 ft) of the atmosphere.
Extratropical cyclones
Jacob Bjerknes
Jacob Aall Bonnevie Bjerknes was a Norwegian-American meteorologist. -Background:Jacob Aall Bonnevie Bjerknes was born in Stockholm, Sweden. His father was the Norwegian meteorologist Vilhelm Bjerknes, one of the pioneers of modern weather forecasting. His paternal grandfather was noted...
, and was derived from a coastal network of observation sites in Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
. This theory proposed that the main inflow into a cyclone
Cyclone
In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...
was concentrated along two lines of convergence, one ahead (or east) of the low and another trailing equatorward (south in the Northern Hemisphere and north in the Southern Hemisphere) and behind (or west) of the low. The convergence line ahead of the low became known as either the steering line or the warm front
Warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...
. The trailing convergence zone was referred to as the squall line
Squall line
A squall line is a line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts....
or cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
. Areas of clouds and rainfall appeared to be focused along these convergence zones. A conveyor belt, also referred to as the warm conveyor belt, is a term describing the flow of a stream of warm moist air originating within the warm sector (or generally equatorward) of an extratropical cyclone in advance of the cold front which slopes up above and poleward (north in the Northern Hemisphere and south in the Southern Hemisphere) of the surface warm front. The concept of the conveyor belt originated in 1969.
The left edge of the conveyor belt is sharp due to higher density air moving in from the west forcing a sharp slope to the cold front. An area of stratiform precipitation develops poleward of the warm front along the conveyor belt. Active precipitation poleward of the warm front implies potential for greater development of the cyclone. A portion of this conveyor belt turns to the right (left in the Southern Hemisphere), aligning with the upper level westerly flow. However, the western portion of this belt wraps around the northwest (southwest in the Southern Hemisphere) side of the cyclone, which can contain moderate to heavy precipitation. If the air mass is cold enough, the precipitation falls in the form of heavy snow. Theory from the 1980s talked about the presence of a cold conveyor belt originating north of the warm front and flowing along a clockwise path (in the northern hemisphere) into the main belt of the westerlies aloft, but there has been conflicting evidence as to whether or not this phenomenon actually exists.