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82-660: The Caribbean Current is a warm ocean current that transports significant amounts of water and flows northwestward through the Caribbean from the east along the coast of South America and into the Gulf of Mexico. The current results from the flow of the Atlantic South Equatorial Current as it flows north along the coast of Brazil. As the current turns north through the Yucatán Channel , it

164-493: A change in daily floral and animal events can be observed, the season is changing. In this sense, ecological seasons are defined in absolute terms, unlike calendar-based methods in which the seasons are relative. If specific conditions associated with a particular ecological season do not normally occur in a particular region, then that area cannot be said to experience that season on a regular basis. Six ecological seasons can be distinguished without fixed calendar-based dates like

246-399: A decisive role in influencing the climates of regions through which they flow. Ocean currents are important in the study of marine debris . Upwellings and cold ocean water currents flowing from polar and sub-polar regions bring in nutrients that support plankton growth, which are crucial prey items for several key species in marine ecosystems . Ocean currents are also important in

328-404: A four-season model to demarcate the warmest and coldest seasons, which are further separated by two intermediate seasons. Calendar-based reckoning defines the seasons in relative rather than absolute terms, so the coldest quarter-year is considered winter even if floral activity is regularly observed during it, despite the traditional association of flowers with spring and summer. The major exception

410-569: A much colder northern Europe and greater sea-level rise along the U.S. East Coast." In addition to water surface temperatures, the wind systems are a crucial determinant of ocean currents. Wind wave systems influence oceanic heat exchange, the condition of the sea surface, and can alter ocean currents. In the North Atlantic, equatorial Pacific, and Southern Ocean, increased wind speeds as well as significant wave heights have been attributed to climate change and natural processes combined. In

492-628: A number of both modern and historical definitions of the seasons. The Northern Hemisphere experiences most direct sunlight during May, June, and July (thus the traditional celebration of Midsummer in June), as the hemisphere faces the Sun. For the Southern Hemisphere it is instead in November, December, and January. It is Earth's axial tilt that causes the Sun to be higher in the sky during

574-453: A result, influence the biological composition of oceans. Due to the patchiness of the natural ecological world, dispersal is a species survival mechanism for various organisms. With strengthened boundary currents moving toward the poles, it is expected that some marine species will be redirected to the poles and greater depths. The strengthening or weakening of typical dispersal pathways by increased temperatures are expected to not only impact

656-418: A significant role in influencing climate, and shifts in climate in turn impact ocean currents. Over the last century, reconstructed sea surface temperature data reveal that western boundary currents are heating at double the rate of the global average. These observations indicate that the western boundary currents are likely intensifying due to this change in temperature, and may continue to grow stronger in

738-532: A six-season model for temperate climate regions which are not tied to any fixed calendar dates: prevernal , vernal , estival , serotinal , autumnal , and hibernal . Many tropical regions have two seasons: the rainy / wet / monsoon season and the dry season . Some have a third cool , mild , or harmattan season . "Seasons" can also be dictated by the timing of important ecological events such as hurricane season , tornado season , and wildfire season . Some examples of historical importance are

820-487: A wind-driven current which flows clockwise uninterrupted around Antarctica. The ACC connects all the ocean basins together, and also provides a link between the atmosphere and the deep ocean due to the way water upwells and downwells on either side of it. Ocean currents are patterns of water movement that influence climate zones and weather patterns around the world. They are primarily driven by winds and by seawater density, although many other factors influence them – including

902-787: Is 1 November ( Samhain , the Celtic origin of Halloween ); spring starts 1 February (Celtic Imbolc ); summer begins 1 May ( Beltane , the Celtic origin of May Day ); the first day of autumn is 1 August (Celtic Lughnasadh ). The traditional calendar in China has 4 seasons based on 24 periods, twelve of which are called zhōngqi and twelve of which are known as jiéqi . These periods are collectively known in English as "solar terms" or "solar breaths". The four seasons chūn ( 春 ), xià ( 夏 ), qiū ( 秋 ), and dōng ( 冬 )—translated as "spring", "summer", "autumn", and "winter" —each center on

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984-657: Is a 7% variation in sunlight received. Orbital eccentricity can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; research shows that the Earth as a whole is actually slightly warmer when farther from the sun. This is because the Northern Hemisphere has more land than the Southern, and land warms more readily than sea. Any noticeable intensification of southern winters and summers due to Earth's elliptical orbit

1066-425: Is also known as the ocean's conveyor belt. Where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling . The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content , factors which together determine the density of seawater. The thermohaline circulation is a part of the large-scale ocean circulation that

1148-585: Is contradictory. These are mainly a matter of custom and not generally proclaimed by governments north or south of the equator for civil purposes. Meteorological seasons are reckoned by temperature, with summer being the hottest quarter of the year and winter the coldest quarter of the year. In 1780 the Societas Meteorologica Palatina (which became defunct in 1795), an early international organization for meteorology, defined seasons as groupings of three whole months as identified by

1230-418: Is defined as when the mean daily temperature permanently rises above 0 °C. The beginning of summer is defined as when the temperature permanently rises above +10 °C, autumn as when the temperature permanently falls below +10 °C, and winter as when the temperature permanently falls below 0 °C. In Finland, "permanently" is defined as when the mean daily averaged temperature remains above or below

1312-537: Is driven by global density gradients created by surface heat and freshwater fluxes . Wind -driven surface currents (such as the Gulf Stream ) travel polewards from the equatorial Atlantic Ocean , cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water ). This dense water then flows into the ocean basins . While the bulk of it upwells in the Southern Ocean ,

1394-461: Is in the tropics where, as already noted, the winter season is not observed. The four seasons have been in use since at least Roman times, as in Rerum rusticarum of Varro Varro says that spring, summer, autumn, and winter start on the 23rd day of the sun's passage through Aquarius, Taurus, Leo, and Scorpio, respectively. Nine years before he wrote, Julius Caesar had reformed the calendar, so Varro

1476-634: Is mitigated by the abundance of water in the Southern Hemisphere. Seasonal weather fluctuations (changes) also depend on factors such as proximity to oceans or other large bodies of water, currents in those oceans, El Niño /ENSO and other oceanic cycles, and prevailing winds . In the temperate and polar regions , seasons are marked by changes in the amount of sunlight , which in turn often causes cycles of dormancy in plants and hibernation in animals. These effects vary with latitude and with proximity to bodies of water. For example,

1558-781: Is renamed the Yucatán Current . The Caribbean Current water comes from the Atlantic Ocean via the North Equatorial, North Brazil, and Guiana Currents. The circulation of the Columbia-Panama Gyre flows counter-clockwise to the Caribbean Current. This article about a specific ocean current is a stub . You can help Misplaced Pages by expanding it . Ocean current Ocean currents flow for great distances and together they create

1640-482: The Atlantic meridional overturning circulation (AMOC) is in danger of collapsing due to climate change, which would have extreme impacts on the climate of northern Europe and more widely, although this topic is controversial and remains an active area of research. The "State of the cryosphere" report, dedicates significant space to AMOC, saying it may be enroute to collapse because of ice melt and water warming. In

1722-506: The East Australian Current , global warming has also been accredited to increased wind stress curl , which intensifies these currents, and may even indirectly increase sea levels, due to the additional warming created by stronger currents. As ocean circulation changes due to climate, typical distribution patterns are also changing. The dispersal patterns of marine organisms depend on oceanographic conditions, which as

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1804-645: The Gulf Stream , which, together with its extension the North Atlantic Drift , makes northwest Europe much more temperate for its high latitude than other areas at the same latitude. Another example is Lima, Peru , whose cooler subtropical climate contrasts with that of its surrounding tropical latitudes because of the Humboldt Current . The largest ocean current is the Antarctic Circumpolar Current (ACC),

1886-633: The Midwestern United States and parts of eastern Europe . The actual dates for each season vary by climate region and can shift from one year to the next. Average dates listed here are for mild and cool temperate climate zones in the Northern Hemisphere: Indigenous people in polar, temperate and tropical climates of northern Eurasia, the Americas, Africa, Oceania, and Australia have traditionally defined

1968-642: The Paracel Islands and parts of the Tibetan plateau ) may be said to have summer all year round or winter all year round. Astronomical timing as the basis for designating the temperate seasons dates back at least to the Julian Calendar used by the ancient Romans. As mentioned above, Varro wrote that spring, summer, autumn, and winter start on the 23rd day of the sun's passage through Aquarius, Taurus, Leo, and Scorpio, respectively, and that (in

2050-654: The South Pole is in the middle of the continent of Antarctica and therefore a considerable distance from the moderating influence of the southern oceans. The North Pole is in the Arctic Ocean , and thus its temperature extremes are buffered by the water. The result is that the South Pole is consistently colder during the southern winter than the North Pole during the northern winter. The seasonal cycle in

2132-630: The elliptical nature of the orbit of the Earth, as discovered by Johannes Kepler . From the March equinox it currently takes 92.75 days until the June solstice, then 93.65 days until the September equinox, 89.85 days until the December solstice and finally 88.99 days until the March equinox. Thus the time from the March equinox to the September equinox is 7.56 days longer than from the September equinox to

2214-401: The global conveyor belt , which plays a dominant role in determining the climate of many of Earth's regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is

2296-581: The middle of the respective seasons. Because of seasonal lag due to thermal absorption and release by the oceans, regions with a continental climate , which predominate in the Northern Hemisphere , often consider these four dates to be the start of the seasons as in the diagram, with the cross-quarter days considered seasonal midpoints. The length of these seasons is not uniform because of Earth's elliptical orbit and its different speeds along that orbit . Most calendar-based partitions use

2378-408: The northern and southern hemispheres always experience opposite seasons. This is because during summer or winter , one part of the planet is more directly exposed to the rays of the Sun than the other, and this exposure alternates as the Earth revolves in its orbit. For approximately half of the year (from around March   20 to around September   22), the Northern Hemisphere tips toward

2460-533: The southern hemisphere . In addition, the areas of surface ocean currents move somewhat with the seasons ; this is most notable in equatorial currents. Deep ocean basins generally have a non-symmetric surface current, in that the eastern equator-ward flowing branch is broad and diffuse whereas the pole-ward flowing western boundary current is relatively narrow. Large scale currents are driven by gradients in water density , which in turn depend on variations in temperature and salinity. This thermohaline circulation

2542-512: The ( proleptic ) Gregorian calendar agrees with the Julian calendar in the third century of the Christian era , rather than in the fourth. Currently, the most common equinox and solstice dates are March 20, June 21, September 22 or 23, and December 21; the four-year average slowly shifts to earlier times as a century progresses. This shift is a full day in about 128 years (compensated mainly by

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2624-460: The Elder , in his Natural History , mentions the two equinoxes and the two solstices and gives the lengths of the intervals (values which were fairly correct in his day but are no longer very correct because the perihelion has moved from December into January). He then defines the seasons of autumn, winter, spring, and summer as starting half-way through these intervals. He gives "the eighth day to

2706-494: The Gregorian calendar. According to this definition, for temperate areas in the northern hemisphere, spring begins on 1 March, summer on 1 June, autumn on 1 September, and winter on 1 December. For the southern hemisphere temperate zone, spring begins on 1 September, summer on 1 December, autumn on 1 March, and winter on 1 June. In Australasia the meteorological terms for seasons apply to

2788-531: The ICZ migrates to a position south of the Equator. In meteorological terms, the solstices (the maximum and minimum insolation ) do not fall in the middles of summer and winter. The heights of these seasons occur up to 7 weeks later because of seasonal lag . Seasons, though, are not always defined in meteorological terms. In astronomical reckoning by hours of daylight alone, the solstices and equinoxes are in

2870-470: The Julian Calendar) these days were February 7, May 9, August 11, and November 10. He points out that the lengths are not equal, being 91 (in non-leap years), 94, 91, and 89 days for spring, summer, autumn, and winter, respectively. The midpoints of these seasons were March 24 or 25, June 25, September 25 or 26, and December 24 or 25, which are near to the equinoxes and solstices of his day. Pliny

2952-471: The Kalends of January" (December 25) as the date of the winter solstice, though actually it occurred on the 22nd or 23rd at that time. Nowadays the astronomical timing has winter starting at the winter solstice, spring at the spring equinox, and so on. This is used worldwide, although some countries like Australia, New Zealand, Pakistan and Russia prefer to use meteorological reckoning. The precise timing of

3034-403: The March equinox. The times of the equinoxes and solstices are not fixed with respect to the modern Gregorian calendar, but fall about six hours later every year, amounting to one full day in four years. They are reset by the occurrence of a leap year. The Gregorian calendar is designed to keep the March equinox no later than 21 March as accurately as is practical. The calendar equinox (used in

3116-539: The Sami people in Scandinavia. Many indigenous people who no longer live directly off the land in traditional often nomadic styles, now observe modern methods of seasonal reckoning according to what is customary in their particular country or region. The North American Cree and possibly other Algonquian speaking peoples used or still use a 6-season system. The extra two seasons denoting the freezing and breaking up of

3198-633: The Sun, with the maximum amount occurring on about June   21. For the other half of the year, the same happens, but in the Southern Hemisphere instead of the Northern, with the maximum around December   21. The two instants when the Sun is directly overhead at the Equator are the equinoxes . Also at that moment, both the North Pole and the South Pole of the Earth are just on the terminator , and hence day and night are equally divided between

3280-516: The ancient Egyptian seasons— flood , growth , and low water —which were previously defined by the former annual flooding of the Nile in Egypt . Seasons often hold special significance for agrarian societies, whose lives revolve around planting and harvest times, and the change of seasons is often attended by ritual . The definition of seasons is also cultural. In India, from ancient times to

3362-452: The average temperature difference between summer and winter in location — will also change over time because the Earth's axial tilt fluctuates between 22.1 and 24.5 degrees. Smaller irregularities in the times are caused by perturbations of the Moon and the other planets. Solar timing is based on insolation in which the solstices and equinoxes are seen as the midpoints of the seasons. This was

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3444-646: The calculation of Easter) is 21 March, the same date as in the Easter tables current at the time of the Council of Nicaea in AD 325. The calendar is therefore framed to prevent the astronomical equinox wandering onto 22 March. From Nicaea to the date of the reform, the years 500, 600, 700, 900, 1000, 1100, 1300, 1400, and 1500, which would not have been leap years in the Gregorian calendar, amount to nine extra days, but astronomers directed that ten days be removed. Because of this,

3526-609: The case with the seasons described by the Roman scholar Varro (see above). It was the method for reckoning seasons in medieval Europe, especially by the Celts , and is still ceremonially observed in Ireland and some East Asian countries. Summer is defined as the quarter of the year with the greatest insolation and winter as the quarter with the least. The solar seasons change at the cross-quarter days, which are about 3–4 weeks earlier than

3608-434: The century "leap year" rules of the Gregorian calendar); as 2000 was a leap year, the current shift has been progressing since the beginning of the last century, when equinoxes and solstices were relatively late. This also means that in many years of the twentieth century, the dates March 21, June 22, September 23, and December 22 were much more common, so older books teach (and older people may still remember) these dates. All

3690-407: The circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is imprecisely used to refer to the meridional overturning circulation , (MOC). Since the 2000s an international program called Argo has been mapping the temperature and salinity structure of

3772-554: The cost and emissions of shipping vessels. Ocean currents can also impact the fishing industry , examples of this include the Tsugaru , Oyashio and Kuroshio currents all of which influence the western North Pacific temperature, which has been shown to be a habitat predictor for the Skipjack tuna . It has also been shown that it is not just local currents that can affect a country's economy, but neighboring currents can influence

3854-500: The defined limit for seven consecutive days. (In Sweden the number of days ranges from 5 to 7 depending on the season.) This implies two things: The India Meteorological Department (IMD) designates four climatological seasons: In China, a common temperature-based reckoning holds that it is winter for the period when temperatures are below 10°C on average and summer for the period when temperatures are above 22°C on average. This means that areas with relatively extreme climates (such as

3936-410: The direction of the axis, known as axial precession , takes place over the course of 26,000 years, and therefore is not noticeable to modern human civilization. The seasons result from the Earth's axis of rotation being tilted with respect to its orbital plane by an angle of approximately 23.4 degrees . (This tilt is also known as "obliquity of the ecliptic ".) Regardless of the time of year,

4018-570: The dispersal and distribution of many organisms, inclusing those with pelagic egg or larval stages. An example is the life-cycle of the European Eel . Terrestrial species, for example tortoises and lizards, can be carried on floating debris by currents to colonise new terrestrial areas and islands . The continued rise of atmospheric temperatures is anticipated to have various effects on the strength of surface ocean currents, wind-driven circulation and dispersal patterns. Ocean currents play

4100-432: The ice on rivers and lakes. The Noongar people of South-West Western Australia recognise maar-keyen bonar, or six seasons. Each season's arrival is heralded not by a calendar date, but by environmental factors such as changing winds, flowering plants, temperature and migration patterns and lasts approximately two standard calendar months. The seasons also correlate to aspects of the human condition, intrinsically linking

4182-509: The large scale prevailing winds drive major persistent ocean currents, and seasonal or occasional winds drive currents of similar persistence to the winds that drive them, and the Coriolis effect plays a major role in their development. The Ekman spiral velocity distribution results in the currents flowing at an angle to the driving winds, and they develop typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in

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4264-482: The lives of the people to the world that surrounds them and also dictating their movements, as with each season, various parts of country would be visited which were particularly abundant or safe from the elements. In the tropics, where seasonal dates also vary, it is more common to speak of the rainy (or wet, or monsoon ) season versus the dry season . For example, in Nicaragua the dry season (November to April)

4346-536: The meteorological and astronomical seasons. Oceanic regions tend to experience the beginning of the hibernal season up to a month later than continental climates . Conversely, prevernal and vernal seasons begin up to a month earlier near oceanic and coastal areas. For example, prevernal crocus blooms typically appear as early as February in coastal areas of British Columbia , the British Isles , but generally do not appear until March or April in locations like

4428-534: The meteorological seasons and 6–7 weeks earlier than seasons starting at equinoxes and solstices. Thus, the day of greatest insolation is designated "midsummer" as noted in William Shakespeare 's play A Midsummer Night's Dream , which is set on the summer solstice. On the Celtic calendar , the start of the seasons corresponds to four Pagan agricultural festivals - the traditional first day of winter

4510-462: The near future. There is evidence that surface warming due to anthropogenic climate change has accelerated upper ocean currents in 77% of the global ocean. Specifically, increased vertical stratification due to surface warming intensifies upper ocean currents, while changes in horizontal density gradients caused by differential warming across different ocean regions results in the acceleration of surface zonal currents . There are suggestions that

4592-532: The number of seasons between summer and winter can number from one to three. The dates are fixed at even intervals of months. In the Hindu calendar of tropical and subtropical India, there are six seasons or Ritu that are calendar-based in the sense of having fixed dates: Vasanta (spring), Grishma (summer), Varsha ( monsoon ), Sharada (autumn), Hemanta (early winter), and Shishira (prevernal or late winter). The six seasons are ascribed to two months each of

4674-515: The ocean with a fleet of automated platforms that float with the ocean currents. The information gathered will help explain the role the oceans play in the earth's climate. Ocean currents affect temperatures throughout the world. For example, the ocean current that brings warm water up the north Atlantic to northwest Europe also cumulatively and slowly blocks ice from forming along the seashores, which would also block ships from entering and exiting inland waterways and seaports, hence ocean currents play

4756-656: The oceans. Ocean temperature and motion fields can be separated into three distinct layers: mixed (surface) layer, upper ocean (above the thermocline), and deep ocean. Ocean currents are measured in units of sverdrup (Sv) , where 1 Sv is equivalent to a volume flow rate of 1,000,000 m (35,000,000 cu ft) per second. There are two main types of currents, surface currents and deep water currents. Generally surface currents are driven by wind systems and deep water currents are driven by differences in water density due to variations in water temperature and salinity . Surface oceanic currents are driven by wind currents,

4838-471: The oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of

4920-449: The polar and temperate zones of one hemisphere is opposite to that of the other. When it is summer in the Northern Hemisphere, it is winter in the Southern, and vice versa. The tropical and (to a lesser degree) subtropical regions see little annual fluctuation of sunlight and temperature due to Earth's moderate 23.4-degree tilt being insufficient to appreciably affect the strength of the sun's rays annually. The slight differences between

5002-428: The present day, six seasons or Ritu based on south Asian religious or cultural calendars are recognised and identified for purposes such as agriculture and trade. The Earth's orbit exhibits approximate axial parallelism , maintaining its direction toward Polaris (the "North Star") year-round. This is one of the primary reasons for the Earth's seasons, as illustrated by the diagram to the right. Minor variation in

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5084-472: The respective solstice or equinox. Astronomically, the seasons are said to begin on Lichun ( 立春 , "the start of spring") on about 4 February, Lixia ( 立夏 ) on about 6 May, Liqiu ( 立秋 ) on about 8 August, and Lidong ( 立冬 ) on about 8 November. This system forms the basis of other such systems in East Asian lunisolar calendars. Some calendars in south Asia use a six-season partition where

5166-478: The result of the axial parallelism of Earth's tilted orbit around the Sun . In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate , and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are

5248-604: The result of the variation in Earth's distance to the Sun because of its elliptical orbit . In fact, Earth reaches perihelion (the point in its orbit closest to the Sun) in January, and it reaches aphelion (the point farthest from the Sun) in July, so the slight contribution of orbital eccentricity opposes the temperature trends of the seasons in the Northern Hemisphere. In general, the effect of orbital eccentricity on Earth's seasons

5330-582: The same latitude North America's weather was colder. A good example of this is the Agulhas Current (down along eastern Africa), which long prevented sailors from reaching India. In recent times, around-the-world sailing competitors make good use of surface currents to build and maintain speed. Ocean currents can also be used for marine power generation , with areas of Japan, Florida and Hawaii being considered for test projects. The utilization of currents today can still impact global trade, it can reduce

5412-450: The same time, the Antarctic Circumpolar Current (ACC) is also slowing down and is expected to lose 20% of it power by the year 2050, "with widespread impacts on ocean circulation and climate". UNESCO mentions that the report in the first time "notes a growing scientific consensus that melting Greenland and Antarctic ice sheets, among other factors, may be slowing important ocean currents at both poles, with potentially dire consequences for

5494-411: The seasons ecologically by observing the activity of the plants, animals and weather around them. Each separate tribal group traditionally observes different seasons determined according to local criteria that can vary from the hibernation of polar bears on the arctic tundras to the growing seasons of plants in the tropical rainforests. In Australia, some tribes have up to eight seasons in a year, as do

5576-450: The seasons is determined by the exact times of the sun reaching the tropics of Cancer and Capricorn for the solstices and the times of the sun's transit over the equator for the equinoxes , or a traditional date close to these times. The following diagram shows the relation between the line of solstice and the line of apsides of Earth's elliptical orbit. The orbital ellipse (with eccentricity exaggerated for effect) goes through each of

5658-424: The shape and configuration of the ocean basin they flow through. The two basic types of currents – surface and deep-water currents – help define the character and flow of ocean waters across the planet. Ocean currents are driven by the wind, by the gravitational pull of the moon in the form of tides , and by the effects of variations in water density. Ocean dynamics define and describe the motion of water within

5740-483: The six Earth images, which are sequentially the perihelion (periapsis—nearest point to the sun) on anywhere from 2 January to 5 January, the point of March equinox on 19, 20 or 21 March, the point of June solstice on 20 or 21 June, the aphelion (apoapsis—farthest point from the sun) on anywhere from 3 July to 6 July, the September equinox on 22 or 23 September, and the December solstice on 21 or 22 December. These "astronomical" seasons are not of equal length, because of

5822-489: The solstices and the equinoxes cause seasonal shifts along a rainy low-pressure belt called the Intertropical Convergence Zone (ICZ). As a result, the amount of precipitation tends to vary more dramatically than the average temperature. When the ICZ is north of the Equator, the northern tropics experience their wet season while the southern tropics have their dry season. This pattern reverses when

5904-492: The summer months , which increases the solar flux . Due to seasonal lag , June, July, and August are the warmest months in the Northern Hemisphere while December, January, and February are the warmest months in the Southern Hemisphere. In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring , summer , autumn ( fall ), and winter . Ecologists often use

5986-413: The survival of native marine species due to inability to replenish their meta populations but also may increase the prevalence of invasive species . In Japanese corals and macroalgae, the unusual dispersal pattern of organisms toward the poles may destabilize native species. Knowledge of surface ocean currents is essential in reducing costs of shipping, since traveling with them reduces fuel costs. In

6068-413: The temperate zone that occupies all of New Zealand , New South Wales , Victoria , Tasmania , the south-eastern corner of South Australia and the south-west of Western Australia, and the south east Queensland areas south of Brisbane . In Sweden and Finland, meteorologists and news outlets use the concept of thermal seasons, which are defined based on mean daily temperatures. The beginning of spring

6150-524: The times are given in UTC (roughly speaking, the time at Greenwich , ignoring British Summer Time ). People living farther to the east (Asia and Australia), whose local times are in advance, see the astronomical seasons apparently start later; for example, in Tonga (UTC+13), an equinox occurred on September 24, 1999, a date on which the equinox will not fall again until 2103. On the other hand, people living far to

6232-554: The twelve months in the Hindu calendar. The rough correspondences are: The Bengali Calendar is similar but differs in start and end times. It has the following seasons or ritu: The Odia Calendar is similar but differs in start and end times. The Tamil calendar follows a similar pattern of six seasons Ecologically speaking, a season is a period of the year in which only certain types of floral and animal events happen (e.g.: flowers bloom—spring; hedgehogs hibernate—winter). So, if

6314-464: The two hemispheres. Around the March equinox , the Northern Hemisphere will be experiencing spring as the hours of daylight increase, and the Southern Hemisphere is experiencing autumn as daylight hours shorten. The effect of axial tilt is observable as the change in day length and the altitude of the Sun at solar noon (the Sun's culmination ) during the year . The low angle of the Sun during

6396-786: The viability of local fishing industries. Currents of the Arctic Ocean Currents of the Atlantic Ocean Currents of the Indian Ocean Currents of the Pacific Ocean Currents of the Southern Ocean Oceanic gyres Season A season is a division of the year based on changes in weather , ecology , and the number of daylight hours in a given region. On Earth , seasons are

6478-470: The west (America), whose clocks run behind UTC, may experience an equinox as early as March 19. Over thousands of years, the Earth's axial tilt and orbital eccentricity vary (see Milankovitch cycles ). The equinoxes and solstices move westward relative to the stars while the perihelion and aphelion move eastward. Thus, ten thousand years from now Earth's northern winter will occur at aphelion and northern summer at perihelion. The severity of seasonal change —

6560-527: The wind powered sailing-ship era, knowledge of wind patterns and ocean currents was even more essential. Using ocean currents to help their ships into harbor and using currents such as the gulf stream to get back home. The lack of understanding of ocean currents during that time period is hypothesized to be one of the contributing factors to exploration failure. The Gulf Stream and the Canary current keep western European countries warmer and less variable, while at

6642-470: The winter months means that incoming rays of solar radiation are spread over a larger area of the Earth's surface, so the light received is more indirect and of lower intensity. Between this effect and the shorter daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres. Compared to axial parallelism and axial tilt, other factors contribute little to seasonal temperature changes. The seasons are not

6724-408: Was able to assign the dates of February 7, May 9, August 11, and November 10 to the start of spring, summer, autumn, and winter. As noted, a variety of dates and even exact times are used in different countries or regions to mark changes of the calendar seasons. These observances are often declared "official" within their respective areas by the local or national media, even when the weather or climate

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