64-495: The Campbell Islands (or Campbell Island Group ) are a group of subantarctic islands, belonging to New Zealand. They lie about 600 km south of Stewart Island . The islands have a total area of 113 km (44 sq mi), consisting of one big island, Campbell Island , and several small islets , notably Dent Island , Isle de Jeanette Marie, Folly Island (or Folly Islands), Jacquemart Island , and Monowai Island (also known as Lion Rock). Ecologically, they are part of
128-463: A carbon sink , absorbing atmospheric carbon dioxide and storing it in solution. If the SAMW temperature increases as a result of climate change , the SAMW will have less capacity to store dissolved carbon dioxide. Research using a computerized climate system model suggests that if atmospheric carbon dioxide concentration were to increase to 860 ppm by the year 2100 (roughly double today's concentration),
192-459: A breeding site for several species of seabirds, as well as the endemic Campbell teal and Campbell snipe . The seabirds are southern rockhopper and yellow-eyed penguins , Antipodean , southern royal , light-mantled , black-browed , Campbell and grey-headed albatrosses , northern giant and white-chinned petrels , and the Campbell shag . Subantarctic The subantarctic zone
256-450: A cold or warm front if the conditions aloft change. Stationary fronts are marked on weather maps with alternating red half-circles and blue spikes pointing opposite to each other, indicating no significant movement. When stationary fronts become smaller in scale and stabilizes in temperature, degenerating to a narrow zone where wind direction changes significantly over a relatively short distance, they become known as shearlines. A shearline
320-414: A high pressure area, implying fair or clear weather. An L on the other hand may represent low pressure, which frequently accompanies precipitation and storms . Low pressure also creates surface winds deriving from high pressure zones and vice versa. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on
384-404: A label of outflow boundary . Fronts are the principal cause of significant weather. Convective precipitation (showers, thundershowers, heavy rain and related unstable weather) is caused by air being lifted and condensing into clouds by the movement of the cold front or cold occlusion under a mass of warmer, moist air. If the temperature differences of the two air masses involved are large and
448-725: A pattern where the upper level jet splits apart into two streams, with the resultant Mesoscale Convective System (MCS) forming at the point of the upper level split in the wind pattern running southeast into the warm sector parallel to low-level thickness lines. When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise. Even weaker and less organized areas of thunderstorms lead to locally cooler air and higher pressures, and outflow boundaries exist ahead of this type of activity, which can act as foci for additional thunderstorm activity later in
512-416: A recent time period. The glaciers of Laurens Peninsula, whose maximum elevation is only 500 m above sea level, are smaller and shorter than most of the other Heard Island glaciers, and therefore much more sensitive to temperature effects. Accordingly, their total area has decreased by over 30 percent. Jacka Glacier on the east coast of Laurens Peninsula has also demonstrated marked recession since 1955. In
576-409: A return visit in early 1980. Retreat of Heard Island glaciers is most dramatic on the eastern section of the island, where the termini of former tidewater glaciers are now located inland. Glaciers on the northern and western coasts have narrowed significantly, while the area of glaciers and ice caps on Laurens Peninsula have shrunk by 30% – 65%. During the time period between 1947 and 1988,
640-406: A sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cold air mass receding from the warm front and plows under both air masses. In a warm occlusion, the cold air mass overtaking the warm front is warmer than the cold air mass receding from the warm front and rides over the colder air while lifting
704-602: A unique environment, noted for its very high marine productivity , especially for antarctic krill . Because of this, all lands and waters situated south of the Antarctic Convergence are considered to belong to the Antarctic from a climatological , biological and hydrological standpoint. However, the text of the Antarctic Treaty , article VI ("Area covered by Treaty") states: "The provisions of
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#1732794145904768-749: Is a region in the Southern Hemisphere , located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator . The subantarctic region includes many islands in the southern parts of the Atlantic , Indian , and Pacific oceans, especially those situated north of the Antarctic Convergence . Subantarctic glaciers are, by definition, located on islands within
832-610: Is a boundary separating air masses for which several characteristics differ, such as air density , wind , temperature , and humidity . Disturbed and unstable weather due to these differences often arises along the boundary. For instance, cold fronts can bring bands of thunderstorms and cumulonimbus precipitation or be preceded by squall lines , while warm fronts are usually preceded by stratiform precipitation and fog . In summer, subtler humidity gradients known as dry lines can trigger severe weather . Some fronts produce no precipitation and little cloudiness, although there
896-763: Is a geographic zone, the Subantarctic Zone (SAZ). South of the SAZ is the Subantarctic Front (SAF). South of the SAF is another marine zone, called the Polar Frontal Zone (PFZ). The SAZ and the PFZ together form the subantarctic region. The southernmost boundary of the PFZ (and hence, the southern border of the subantarctic region) is the Antarctic Convergence, located approximately 200 kilometers south of
960-601: Is a special type of weather map which provides a top view of weather elements over a geographical area at a specified time based on information from ground-based weather stations. Weather maps are created by detecting, plotting and tracing the values of relevant quantities such as sea-level pressure , temperature , and cloud cover onto a geographical map to help find synoptic scale features such as weather fronts. Surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation , or other important information. For example, an H may represent
1024-523: Is also well documented. Many subantarctic glaciers are also in retreat. Mass balance is significantly negative on many glaciers on Kergeulen Island, Heard Island, South Georgia and Bouvet Island. Heard Island is a heavily glacierized, subantarctic volcanic island located in the Southern Ocean , roughly 4000 kilometers southwest of Australia . 80% of the island is covered in ice, with glaciers descending from 2400 meters to sea level . Due to
1088-498: Is characterized by tundra, permafrost , and volcanoes . These islands are situated close to or south of the Antarctic Convergence, but north of 60° S latitude (the continental limit according to the Antarctic Treaty). Therefore, although some are located south of the Antarctic Convergence, they should still be considered as subantarctic islands by virtue of their location north of 60° S. At between 60° – 69° south of
1152-772: Is debatable whether these islands should be considered as such because their climate and geography differs significantly from other subantarctic islands. At between 52° – 57° south of the Equator, the Campbell Island Group , Heard Island and McDonald Islands , Bouvet Island , the South Georgia Group , Macquarie Island , and the South Sandwich Islands are also located in the Furious Fifties. The geography of these islands
1216-453: Is depicted as a line of red dots and dashes. Stationary fronts may bring light snow or rain for a long period of time. A similar phenomenon to a weather front is the dry line , which is the boundary between air masses with significant moisture differences instead of temperature. When the westerlies increase on the north side of surface highs, areas of lowered pressure will form downwind of north–south oriented mountain chains, leading to
1280-486: Is estimated to have decreased by roughly 29% between 1947 and 2004. This degree of loss of glacier mass is consistent with the measured increase in temperature of +0.9 °C over that time span. The coastal ice cliffs of Brown Glacier and Stephenson Glacier, which in 1954 were over 50 feet (15 m) high, had disappeared by 1963 when the glaciers terminated as much as 100 yards (91 m) inland. Baudissin Glacier on
1344-488: Is formed with a cold front. A weaker form of the dry line seen more commonly is the lee trough, which displays weaker differences in moisture . When moisture pools along the boundary during the warm season, it can be the focus of diurnal thunderstorms . The dry line may occur anywhere on earth in regions intermediate between desert areas and warm seas. The southern plains west of the Mississippi River in
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#17327941459041408-446: Is invariably a wind shift . Cold fronts generally move from west to east, whereas warm fronts move poleward , although any direction is possible. Occluded fronts are a hybrid merge of the two, and stationary fronts are stalled in their motion. Cold fronts and cold occlusions move faster than warm fronts and warm occlusions because the dense air behind them can lift as well as push the warmer air. Mountains and bodies of water can affect
1472-429: Is more dense than warm air, lifting as well as pushing the warm air preceding the boundary. The lifting motion often creates a narrow line of showers and thunderstorms if enough humidity is present as the lifted moist warm air condenses. The concept of colder, dense air "wedging" under the less dense warmer air is too simplistic, as the upward motion is really part of a maintenance process for geostrophic balance on
1536-436: Is most common behind cold fronts that move into mountainous areas. It may sometimes occur in advance of warm fronts moving northward to the east of mountainous terrain. However, precipitation along warm fronts is relatively steady, as in light rain or drizzle. Fog, sometimes extensive and dense, often occurs in pre-warm-frontal areas. Although, not all fronts produce precipitation or even clouds because moisture must be present in
1600-626: Is that portion of the global ocean circulation that is driven by global density gradients created by surface heat and evaporation . Several distinct water masses converge in the immediate vicinity of the APF or Antarctic Convergence (in particular the Subantarctic Surface Water (Subantarctic Mode Water or SAMW), Antarctic Surface Water , and the Antarctic Intermediate Water ). This convergence creates
1664-408: Is weaker, bringing smaller changes in temperature and moisture, as well as limited rainfall. A cold front is located along and on the bounds of the warm side of a tightly packed temperature gradient. On surface analysis charts, this temperature gradient is visible in isotherms and can sometimes also be identified using isobars since cold fronts often align with a surface trough . On weather maps,
1728-474: The trowal , the projection on the Earth's surface of the tongue of warm air aloft formed during the occlusion process of the depression or storm. Occluded fronts are indicated on a weather map by a purple line with alternating half-circles and triangles pointing in direction of travel. The trowal is indicated by a series of blue and red junction lines. The warm sector is a near-surface air mass in between
1792-685: The Antarctic Polar Front (APF). The subantarctic Front, found between 48°S and 58°S in the Indian and Pacific Ocean and between 42°S and 48°S in the Atlantic Ocean, defines the northern boundary of the Antarctic Circumpolar Current (or ACC). The ACC is the most important ocean current in the Southern Ocean , and the only current that flows completely around the Earth. Flowing eastward through
1856-650: The Antipodes Subantarctic Islands tundra ecoregion . The islands are one of five subantarctic island groups collectively designated as a World Heritage Site by UNESCO. The islands are relatively flat; due to tectonic pressure, however, there are mountains in the centre of each island. A sea stack at the southern tip of Jacquemart Island is – with the exception of the country's Antarctic claims – New Zealand's southernmost point. The following table includes named islands according to Land Information New Zealand . Since its discovery in 1810,
1920-864: The Kerguelen Islands , the Antipodes Islands , and the Auckland Islands . The geography of these islands is characterized by tundra, with some trees on the Snares Islands and the Auckland Islands. These islands are all located near the Antarctic Convergence (with the Kerguelen Islands south of the Convergence) and are properly considered to be subantarctic islands. At between 51° – 56° south of
1984-488: The New Zealand Department of Conservation (DOC) spread 120 tonnes of rodenticide -laced bait across the island over one month. Repeated monitoring has found no signs of rats since. This operation became a template for rat eradication on other islands around the world. The Campbell Islands have been identified as an Important Bird Area (IBA) by BirdLife International because of its significance as
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2048-593: The United States are a particularly favored location. The dry line normally moves eastward during the day and westward at night. A dry line is depicted on National Weather Service (NWS) surface analyses as an orange line with scallops facing into the moist sector. Dry lines are one of the few surface fronts where the pips indicated do not necessarily reflect the direction of motion. Organized areas of thunderstorm activity not only reinforce pre-existing frontal zones, but can outrun actively existing cold fronts in
2112-414: The warm front and the cold front , usually found on the equatorward side of an extratropical cyclone . With its warm and humid characteristics, this air is susceptive to convective instability and can sustain thunderstorms , especially if lifted by the advancing cold front. A stationary front is a non-moving (or stalled) boundary between two air masses, neither of which is strong enough to replace
2176-550: The Brown Glacier, in an effort to determine whether glacial retreat is rapid or punctuated. Using a portable echo sounder , the team took measurements of the volume of the glacier. Monitoring of climatic conditions continued, with an emphasis on the impact of Foehn winds on glacier mass balance. Based on the findings of that expedition, the rate of loss of glacier ice on Heard Island appears to be accelerating. Between 2000 and 2003, repeat GPS surface surveys revealed that
2240-546: The Equator, in the region often referred to as the Shrieking Sixties , the South Orkney Islands , South Shetland Islands , Balleny Islands , Scott Island , and Peter I Island are all properly considered to be Antarctic islands for the following three reasons: In light of the above considerations, the following should be considered to be subantarctic islands : This is a list of glaciers in
2304-663: The Equator, the Falkland Islands , Isla de los Estados , Ildefonso Islands , Diego Ramírez Islands , and other islands associated with Tierra del Fuego and Cape Horn , lie north of the Antarctic Convergence in the region often referred to as the Furious Fifties . Unlike other subantarctic islands, these islands have trees , temperate grasslands (mostly tussac grass ), and even arable land . They also lack tundra and permanent snow and ice at their lowest elevations. Despite their more southerly location, it
2368-709: The SAMW will decrease in density and salinity. The resulting reductions in the subduction and transport capacity of SAMW and AAIW water masses could potentially decrease the absorption and storage of CO 2 in the Southern Ocean. The Antarctic realm and Antarctic Floristic Kingdom include most of the subantarctic islands native biota , with many endemic genera and species of flora and fauna . The physical landscape and biota communities of Heard Island and McDonald Islands are constantly changing due to volcanism , strong winds and waves, and climate change . Volcanic activity has been observed in this area since
2432-606: The air mass which is being lifted. Fronts are generally guided by winds aloft , but do not move as quickly. Cold fronts and occluded fronts in the Northern Hemisphere usually travel from the northwest to southeast, while warm fronts move more poleward with time. In the Northern Hemisphere a warm front moves from southwest to northeast. In the Southern Hemisphere, the reverse is true; a cold or occluded front usually moves from southwest to northeast, and
2496-478: The day. These features are often depicted in the warm season across the United States on surface analyses and lie within surface troughs. If outflow boundaries or squall lines form over arid regions, a haboob may result. Squall lines are depicted on NWS surface analyses as an alternating pattern of two red dots and a dash labelled SQLN or squal line , while outflow boundaries are depicted as troughs with
2560-516: The early 1950s, Jacka Glacier had receded only slightly from its position in the late 1920s, but by 1997 it had receded about 700 m back from the coastline. Possible causes of glacier recession on Heard Island include: The Australian Antarctic Division conducted an expedition to Heard Island during the austral summer of 2003–04. A small team of scientists spent two months on the island, conducting studies on avian and terrestrial biology and glaciology. Glaciologists conducted further research on
2624-460: The flora and fauna have been under threat from mammals introduced by humans. Cats ( Felis catus ) and Norway rats ( Rattus novegicus ) prey on native birds, and much of the vegetation was destroyed by sheep ( Ovis aries ) and cattle ( Bos taurus ). Restoration of the island began in 1970 with the removal of the feral cattle and sheep; subsequently the island's vegetation recovered, becoming denser. In 2001, four helicopters, under instruction from
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2688-433: The formation of a lee trough. Near the surface during daylight hours, warm moist air is denser than dry air of greater temperature, and thus the warm moist air wedges under the drier air like a cold front. At higher altitudes, the warm moist air is less dense than the cooler dry air and the boundary slope reverses. In the vicinity of the reversal aloft, severe weather is possible, especially when an occlusion or triple point
2752-492: The ice formations above 5,000 feet (1,500 m) on the southwestern slopes of Big Ben , possibly as a result of volcanic activity . By 1963, major recession was obvious below 2,000 feet (610 m) on almost all glaciers, and minor recession was evident as high as 5,000 feet (1,500 m). Retreat of glacier fronts across Heard Island is evident when comparing aerial photographs taken in December 1947 with those taken on
2816-752: The mid-1980s, with fresh lava flows on the southwest flanks of Heard Island. Satellite imagery shows that McDonald Island increased in size from about 1 to 2.5 square kilometers between 1994 and 2004, as a result of volcanic activity. In addition to new land being produced by volcanism, global warming of the climate is causing the retreat of glaciers on the islands ( see section below ). These combined processes produce new ice-free terrestrial and freshwater ecoregions , such as moraines and lagoons , which are now available for colonization by plants and animals. Heard Island has vast colonies of penguins and petrels , and large harems of land-based marine predators such as elephant seals and fur seals . Due to
2880-655: The movement and properties of fronts, other than atmospheric conditions. When the density contrast has diminished between the air masses, for instance after flowing out over a uniformly warm ocean, the front can degenerate into a mere line which separates regions of differing wind velocity known as a shear line . This is most common over the open ocean. The Bergeron classification is the most widely accepted form of air mass classification. Air mass classifications are indicated by three letters: Fronts separate air masses of different types or origins, and are located along troughs of lower pressure . A surface weather analysis
2944-467: The north coast has lost at least 100 vertical feet (30 vertical m), and Vahsel Glacier on the west coast has lost at least 200 vertical feet (61 vertical m). Winston Glacier , which retreated approximately one mile (1.6 km) between 1947 and 1963, appears to be a very sensitive indicator of glacier change on the island. The young moraines flanking Winston Lagoon show that Winston Glacier has lost at least 300 vertical feet (91 vertical m) of ice within
3008-539: The other. They tend to remain essentially in the same area for extended periods of time, especially with parallel winds directions; They usually move in waves but not persistently. There is normally a broad temperature gradient behind the boundary with more widely spaced isotherm packing. A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts either dissipate after several days or devolve into shear lines, but they can transform into
3072-744: The present Treaty shall apply to the area south of 60° South latitude ". Therefore, Antarctica is defined from a political standpoint as all land and ice shelves south of 60°S latitude. At between about 46° – 50° south of the Equator, in the region often referred to as the Roaring Forties , are the Crozet Islands , the Prince Edward Islands , Wager Island , the Bounty Islands , the Snares Islands ,
3136-489: The rate of loss of ice in both the ablation zone and the accumulation zone of Brown Glacier was more than double average rate measured from 1947 to 2003. The increase in the rate of ice loss suggests that the glaciers of Heard Island are reacting to ongoing climate change, rather than approaching dynamic equilibrium . The retreat of Heard Island's glaciers is expected to continue for the foreseeable future. Download coordinates as: Weather front A weather front
3200-525: The rotating Earth in response to frontogenesis . Warm fronts are at the leading edge of a homogeneous advancing warm air mass, which is located on the equatorward edge of the gradient in isotherms, and lie within broader troughs of low pressure than cold fronts. A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to lift from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds appearing ahead of
3264-971: The southern hemisphere. With respect to glaciers of the Andes mountains in South America , abundant evidence has been collected from ongoing research at Nevado del Ruiz in Colombia , Quelccaya Ice Cap and Qori Kalis Glacier in Peru , Zongo , Chacaltaya and Charquini glaciers in Bolivia , the Aconcagua River Basin in the central Chilean Andes , and the Northern Patagonian and Southern Patagonian ice fields . Retreat of glaciers in New Zealand and Antarctica
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#17327941459043328-507: The southern portions of the Atlantic, Indian, and Pacific Oceans, the ACC links these three otherwise separate oceanic basins . Extending from the sea surface to depths of 2000–4000 meters, and with a width of as great as 2000 kilometers, the ACC transports more water than any other ocean current. The ACC carries up to 150 Sverdrups (150 million cubic meters per second), equivalent to 150 times
3392-439: The steep topography of Heard Island, most of its glaciers are relatively thin (averaging only about 55 meters in depth). The presence of glaciers on Heard Island provides an excellent opportunity to measure the rate of glacial retreat as an indicator of climate change. Available records show no apparent change in glacier mass balance between 1874 and 1929. Between 1949 and 1954, marked changes were observed to have occurred in
3456-538: The subantarctic . This list includes one snow field ( Murray Snowfield ). Snow fields are not glaciers in the strict sense of the word, but they are commonly found at the accumulation zone or head of a glacier. For the purposes of this list, Antarctica is defined as any latitude further south than 60° (the continental limit according to the Antarctic Treaty). Together, the Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) act as
3520-529: The subantarctic region. All glaciers located on the continent of Antarctica are by definition considered to be Antarctic glaciers . The subantarctic region comprises two geographic zones and three distinct fronts . The northernmost boundary of the subantarctic region is the rather ill-defined Subtropical Front (STF), also referred to as the Subtropical Convergence. To the south of the STF
3584-417: The surface location of a warm front is marked with a red line of semicircles pointing in the direction the air mass is travelling. An occluded front is formed when a cold front overtakes a warm front, and usually forms around mature low-pressure areas, including cyclones. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point. It lies within
3648-410: The surface position of the cold front is marked by a blue line with triangles pointing in the direction where cold air travels and it is placed at the leading edge of the cooler air mass. Cold fronts often bring rain, and sometimes heavy thunderstorms as well. Cold fronts can produce sharper and more intense changes in weather and move at a rate that is up to twice as fast as warm fronts, since cold air
3712-487: The total area of Heard Island's glaciers decreased by 11%, from 288 km (roughly 79% of the total area of Heard Island) to only 257 km . A visit to the island in the spring of 2000 found that the Stephenson , Brown and Baudissin glaciers, among others, had retreated even further. The terminus of Brown Glacier has retreated approximately 1.1 kilometres since 1950. The total ice-covered area of Brown Glacier
3776-433: The turbulence is extreme because of wind shear and the presence of a strong jet stream , " roll clouds " and tornadoes may occur. In the warm season , lee troughs, breezes, outflow boundaries and occlusions can lead to convection if enough moisture is available. Orographic precipitation is precipitation created through the lifting action of air due to air masses moving over terrain such as mountains and hills, which
3840-510: The very high numbers of seabirds and marine mammals on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of species including corals , sponges , barnacles and echinoderms . This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest. Glaciers are currently retreating at significant rates throughout
3904-442: The volume of water flowing in all the world's rivers. The ACC and the global thermohaline circulation strongly influence regional and global climate as well as underwater biodiversity . Another factor that contributes to the climate of the subantarctic region, though to a much lesser extent than the thermohaline circulation, is the formation of Antarctic Bottom Water (ABW) by halothermal dynamics . The halothermal circulation
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#17327941459043968-425: The warm air. A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is also associated with a drying of the air mass. Within the occlusion of the front, a circulation of air brings warm air upward and sends drafts of cold air downward, or vice versa depending on the type of occlusion the front is experiencing. Precipitations and clouds are associated with
4032-410: The warm front are mostly stratiform , and rainfall more gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may still continue. On weather maps,
4096-403: The weather map. In addition, areas of precipitation help determine the frontal type and location. There are two different meanings used within meteorology to describe weather around a frontal zone. The term " anafront " describes boundaries which show instability, meaning air rises rapidly along and over the boundary to cause significant weather changes and heavy precipitation . A " katafront "
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