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Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor to ice as the water vapor reaches the freezing point. In temperate climates, it most commonly appears on surfaces near the ground as fragile white crystals; in cold climates, it occurs in a greater variety of forms. The propagation of crystal formation occurs by the process of nucleation.
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole.
Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures define different dates as the start of winter, and some use a definition based on weather.
In meteorology, a cyclone is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
The subarctic climate is a continental climate with long, cold winters, and short, warm to cool summers. It is found on large landmasses, often away from the moderating effects of an ocean, generally at latitudes from 50°N to 70°N, poleward of the humid continental climates. Subarctic or boreal climates are the source regions for the cold air that affects temperate latitudes to the south in winter. These climates represent Köppen climate classification Dfc, Dwc, Dsc, Dfd, Dwd and Dsd.
Larches are deciduous conifers in the genus Larix, of the family Pinaceae. Growing from 20 to 45 metres tall, they are native to the cooler regions of the northern hemisphere, where they are found in lowland forests in the high latitudes, and high in mountains further south. Larches are among the dominant plants in the boreal forests of Siberia and Canada. Although they are conifers, larches are deciduous trees that lose their needles in the autumn.
Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June and December.
The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from 23°26′10.4″ (or 23.43622°) to approximately 35° north and south. The horse latitudes lie within this range.
Podocarpaceae is a large family of mainly Southern Hemisphere conifers, known in English as podocarps, comprising about 156 species of evergreen trees and shrubs. It contains 19 genera if Phyllocladus is included and Manoao and Sundacarpus are recognized.
The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions. The tree line is sometimes distinguished from a lower timberline, which is the line below which trees form a forest with a closed canopy.
The Restionaceae, also called restiads and restios, are a family of flowering plants native to the Southern Hemisphere; they vary from a few centimeters to 3 meters in height. Following the APG IV (2016): the family now includes the former families Anarthriaceae, Centrolepidaceae and Lyginiaceae, and as such includes 51 genera with 572 known species. Based on evidence from fossil pollen, the Restionaceae likely originated more than 65 million years ago during the Late Cretaceous period, when the southern continents were still part of Gondwana.
Antarctic flora are a distinct community of vascular plants which evolved millions of years ago on the supercontinent of Gondwana. Presently, species of Antarctica flora reside on several now separated areas of the Southern Hemisphere, including southern South America, southernmost Africa, New Zealand, Australia, and New Caledonia. Joseph Dalton Hooker was the first to notice similarities in the flora and speculated that Antarctica had served as either a source or a transitional point, and that land masses now separated might formerly have been adjacent.
The trifoliate orange, Citrus trifoliata, is a member of the family Rutaceae. Whether the trifoliate oranges should be considered to belong to their own genus, Poncirus, or be included in the genus Citrus is debated. The species is unusual among citrus for having deciduous, compound leaves and pubescent (downy) fruit.
Hardiness of plants describes their ability to survive adverse growing conditions. It is usually limited to discussions of climatic adversity. Thus a plant's ability to tolerate cold, heat, drought, flooding, or wind are typically considered measurements of hardiness. Hardiness of plants is defined by their native extent's geographic location: longitude, latitude and elevation. These attributes are often simplified to a hardiness zone. In temperate latitudes, the term most often describes resistance to cold, or "cold-hardiness", and is generally measured by the lowest temperature a plant can withstand.
A humid continental climate is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by four distinct seasons and large seasonal temperature differences, with warm to hot summers and cold winters. Precipitation is usually distributed throughout the year but often does have dry seasons. The definition of this climate regarding temperature is as follows: the mean temperature of the coldest month must be below 0 °C (32.0 °F) or −3 °C (26.6 °F) depending on the isotherm, and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F). In addition, the location in question must not be semi-arid or arid. The cooler Dfb, Dwb, and Dsb subtypes are also known as hemiboreal climates.
Nothofagus cunninghamii, commonly known as myrtle beech or Tasmanian myrtle, is the dominant species of cool temperate rainforests in Tasmania and Southern Victoria. It has low fire resistance and grows best in partial shade conditions.
The Grevilleoideae are a subfamily of the plant family Proteaceae. Mainly restricted to the Southern Hemisphere, it contains around 46 genera and about 950 species. Genera include Banksia, Grevillea, and Macadamia.
Autumn leaf color is a phenomenon that affects the normal green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of yellow, orange, red, purple, and brown. The phenomenon is commonly called autumn colours or autumn foliage in British English and fall colors, fall foliage, or simply foliage in American English.
Solanum commersonii is a species of wild potato in the family Solanaceae. It is native to southern Brazil, Uruguay, and northeastern Argentina, and has been introduced to Mauritius. It is being extensively studied for its resistance to root knot nematode, soft rot, blackleg, bacterial wilt, verticillium wilt, Potato virus X, tobacco etch virus, common scab, and late blight, and for its frost tolerance and ability to cold acclimate, in an effort to improve the domestic potato Solanum tuberosum.
Peter Bannister was an English-born New Zealand botanist and academic.
References
- ↑ Bannister, Peter (2007). "Godley review: A touch of frost? Cold hardiness of plants in the southern hemisphere". New Zealand Journal of Botany : 1–33. doi: 10.1080/00288250709509700 .
- ↑ Feild, Taylor S.; Brodribb, Tim; Holbrook, N. Michele (2002). "Hardly a relict: Freezing and the evolution of vesselless wood in Winteraceae". Evolution . 56 (3): 464–478. doi:10.1111/j.0014-3820.2002.tb01359.x. PMID 11989678. S2CID 31376453.
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