Storm
A storm is any disturbed state of an environment or astronomical bodys atmosphere especially affecting its surface, and strongly implying severe weather. Heavy snowfall can allow special recreational activities to take place which would not be possible otherwise, the English word comes from Proto-Germanic *sturmaz meaning noise, tumult. Storms are created when a center of low pressure develops with a system of high pressure surrounding it and this combination of opposing forces can create winds and result in the formation of storm clouds, such as the cumulonimbus. Small localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller disturbances such as dust devils, There are many varieties and names for storms, Ice storm — Ice storms are one of the most dangerous forms of winter storms. When surface temperatures are below freezing, but a layer of above-freezing air remains aloft, rain can fall into the freezing layer. In general,8 millimetres of accumulation is all that is required, especially in combination with breezy conditions, Ice storms make unheated road surfaces too slick to drive upon.
Ice storms can vary in range from hours to days and can cripple small towns. Blizzard — There are varying definitions for blizzards, both time and by location. In general, a blizzard is accompanied by winds, heavy snow. Snow storms, especially ones with a liquid equivalent and breezy conditions, can down tree limbs, cut off power. Ocean Storm — Storm conditions out at sea are defined as having sustained winds of 48 knots or greater, usually just referred to as a storm, these systems can sink vessels of all types and sizes. Firestorm — Firestorms are conflagrations which attain such intensity that they create and it is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires. The Peshtigo Fire is one example of a firestorm, Firestorms can be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden. Nuclear detonations generate firestorms if high winds are not present, dust devil — a small, localized updraft of rising air.
Wind storm— A storm marked by high wind with little or no precipitation, windstorm damage often opens the door for massive amounts of water and debris to cause further damage to a structure. European windstorms and derechos are two type of windstorms, high wind is the cause of sandstorms in dry climates. Squall — sudden onset of wind increase of at least 16 knots or greater sustained for at least one minute, gale — An extratropical storm with sustained winds between 34-48 knots. Thunderstorm — A thunderstorm is a type of storm that generates lightning and it is normally accompanied by heavy precipitation
Ice storm
An ice storm is a type of winter storm characterized by freezing rain, known as a glaze event or, in some parts of the United States, as a silver thaw. The U. S. National Weather Service defines an ice storm as a storm results in the accumulation of at least 0. 25-inch of ice on exposed surfaces. From 1982 to 1994, ice storms were more common than blizzards and they are generally not violent storms but instead are commonly perceived as gentle rains occurring at temperatures just below freezing. The formation of ice begins with a layer of above-freezing air above a layer of sub-freezing temperatures closer to the surface, frozen precipitation melts to rain while falling into the warm air layer, and begins to refreeze in the cold layer below. If the precipitate refreezes while still in the air, it will land on the ground as sleet, the liquid droplets can continue to fall without freezing, passing through the cold air just above the surface. This thin layer of air cools the rain to a temperature below freezing, the drops themselves do not freeze, a phenomenon called supercooling.
When the supercooled drops strike ground or anything else below 0 °C, while meteorologists can predict when and where an ice storm will occur, some storms still occur with little or no warning. In the United States, most ice storms are in the part of the country. An ice storm in February 1994 resulted in ice accumulation as far south as Mississippi. More timber was damaged than that caused by Hurricane Camille, an ice storm in eastern Washington in November 1996 directly followed heavy snowfall. The combined weight of the snow and 25 to 37 millimeters of ice caused damage and was considered the most severe ice storm in the Spokane area since 1940. The freezing rain from an ice storm covers everything with heavy, in addition to hazardous driving or walking conditions, branches or even whole trees may break from the weight of ice. Falling branches can block roads, tear down power and telephone lines, even without falling trees and tree branches, the weight of the ice itself can easily snap power lines and break and bring down power/utility poles, even electricity pylons with steel frames.
This can leave people without power for anywhere from days to a month. According to most meteorologists, just one quarter of an inch of ice accumulation can add about 500 pounds of weight per line span, damage from ice storms is easily capable of shutting down entire metropolitan areas. Additionally, the loss of power during ice storms has indirectly caused numerous illnesses, at lower levels, CO poisoning causes symptoms such as nausea, dizziness and headache, but high levels can cause unconsciousness, heart failure, and death. The relatively high incidence of CO poisoning during ice storms occurs due to the use of methods of heating and cooking during prolonged power outages. Gas generators and propane barbecues, and kerosene heaters contribute to CO poisoning when they operate in confined locations, CO is produced when appliances burn fuel without enough oxygen present, such as basements and other indoor locations
Waterspout
A waterspout is an intense columnar vortex that occurs over a body of water. Some are connected to a cumulus cloud, some to a cumuliform cloud. In the common form, it is a tornado over water. While it is weaker than most of its land counterparts. Most waterspouts do not suck up water, they are small, although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands. Waterspouts exist on a microscale, where their environment is less than two kilometers in width, the cloud from which they develop can be as innocuous as a moderate cumulus, or as great as a supercell. While some waterspouts are strong and tornadic in nature, most are much weaker, weak tornadoes, known as landspouts, have been shown to develop in a similar manner. More than one waterspout can occur in the vicinity at the same time. As many as nine simultaneous waterspouts have been reported on Lake Michigan, waterspouts that are not associated with a rotating updraft of a supercell thunderstorm are known as non-tornadic or fair-weather waterspouts, and are by far the most common type.
Fair-weather waterspouts occur in waters and are associated with dark, flat-bottomed. Waterspouts of this type rapidly develop and dissipate, having life cycles shorter than 20 minutes and they usually rate no higher than EF0 on the Enhanced Fujita scale, generally exhibiting winds of less than 30 m/s. They are most frequently seen in tropical and sub-tropical climates, with upwards of 400 per year observed in the Florida Keys, fair-weather waterspouts are very similar in both appearance and mechanics to landspouts, and largely behave as such if they move ashore. A tornado which travels from land to a body of water would be considered a tornadic waterspout, however, in some areas, such as the Adriatic and Ionian seas, tornadic waterspouts can make up half of the total number. A winter waterspout, known as a devil, an icespout, an ice devil. The term winter waterspout is used to differentiate between the warm season waterspout and this rare winter season event. Very little is known about this phenomenon and only six known pictures of this event exist to date, four of which were taken in Ontario, there are a couple of critical criteria for the formation of a winter waterspout.
Very cold temperatures need to be present over a body of water enough to produce fog resembling steam above the waters surface. Like the more efficient lake-effect snow events, winds focusing down the axis of long lakes enhance wind convergence and they are not restricted to saltwater, many have been reported on lakes and rivers including the Great Lakes and the St. Lawrence River
Firestorm
A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires and wildfires, although the word has been used to describe certain large fires, the phenomenons determining characteristic is a fire with its own storm-force winds from every point of the compass. The Black Saturday bushfires and the Great Peshtigo Fire are possible examples of forest fires with some portion of combustion due to a firestorm. A firestorm is created as a result of the effect as the heat of the original fire draws in more and more of the surrounding air. This draft can be increased if a low-level jet stream exists over or near the fire. As the updraft mushrooms, strong inwardly-directed gusty winds develop around the fire and this would seem to prevent the firestorm from spreading on the wind, but the tremendous turbulence created may cause the strong surface inflow winds to change direction erratically.
A firestorm may develop into a mesocyclone and induce true tornadoes/fire whirls and this occurred with the 2002 Durango fire, and probably with the much greater Peshtigo Fire. The greater draft of a firestorm draws in greater quantities of oxygen, the intense heat of a firestorm manifests largely as radiated heat, which may ignite flammable material at a distance ahead of the fire itself. This serves to expand the area and the intensity of the firestorm, the very high temperatures ignite anything that might possibly burn, until the firestorm runs low on fuel. Thus the fire front is essentially stationary and the spread of fire is prevented by the in-rushing wind. At Hiroshima, this inrushing to feed the fire is said to have prevented the firestorm perimeter from expanding, large wildfire conflagrations are distinct from firestorms if they have moving fire fronts which are driven by the ambient wind and do not develop their own wind system like true firestorms. In Australia, the prevalence of eucalyptus trees that have oil in their leaves results in forest fires that are noted for their extremely tall, hence the bush fires appear more as a firestorm than a simple forest fire.
Sometimes, emission of gases from swamps has a similar effect. For instance, methane explosions enforced the Peshtigo Fire, for example, the black rain that began to fall at ~20 minutes after the atomic bombing of Hiroshima produced in total 5–10 cm of black soot-filled rain in a 1–3 hour period. Moreover, if the conditions are right, a large pyrocumulus can grow into a pyrocumulonimbus and produce lightning, apart from city and forest fires, pyrocumulus clouds can be produced by volcanic eruptions due to the comparable amounts of hot buoyant material formed. The same underlying combustion physics can apply to structures such as cities during war or natural disaster. Firestorms are thought to have part of the mechanism of large urban fires, such as accompanied the 1906 San Francisco earthquake. Firestorms were created by the raids of World War II in cities like Hamburg
Tropical cyclone
Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane, typhoon /taɪˈfuːn/, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface and this energy source differs from that of mid-latitude cyclonic storms, such as noreasters and European windstorms, which are fueled primarily by horizontal temperature contrasts. The strong rotating winds of a tropical cyclone are a result of the conservation of momentum imparted by the Earths rotation as air flows inwards toward the axis of rotation. As a result, they form within 5° of the equator. Tropical cyclones are typically between 100 and 2,000 km in diameter, Tropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas.
Cyclone refers to their nature, with wind blowing counterclockwise in the Northern Hemisphere. The opposite direction of circulation is due to the Coriolis effect, in addition to strong winds and rain, tropical cyclones are capable of generating high waves, damaging storm surge, and tornadoes. They typically weaken rapidly over land where they are cut off from their energy source. For this reason, coastal regions are vulnerable to damage from a tropical cyclone as compared to inland regions. Heavy rains, can cause significant flooding inland, though their effects on human populations are often devastating, tropical cyclones can relieve drought conditions. They carry heat away from the tropics and transport it toward temperate latitudes. Tropical cyclones are areas of low pressure in the troposphere. On Earth, the pressures recorded at the centers of tropical cyclones are among the lowest ever observed at sea level, the environment near the center of tropical cyclones is warmer than the surroundings at all altitudes, thus they are characterized as warm core systems.
The near-surface wind field of a cyclone is characterized by air rotating rapidly around a center of circulation while flowing radially inwards. At the outer edge of the storm, air may be nearly calm, due to the Earths rotation, as air flows radially inward, it begins to rotate cyclonically in order to conserve angular momentum. At an inner radius, air begins to ascend to the top of the troposphere and this radius is typically coincident with the inner radius of the eyewall, and has the strongest near-surface winds of the storm, consequently, it is known as the radius of maximum winds. Once aloft, air flows away from the center, producing a shield of cirrus clouds
Tropics
The tropics are a region of the Earth surrounding the equator. The tropics are referred to as the zone and the torrid zone. The tropics include all the areas on the Earth where the Sun is at a point directly overhead at least once during the solar year. The tropics are distinguished from the climatic and biomatic regions of Earth, which are the middle latitudes. Tropical is sometimes used in a sense for a tropical climate to mean warm to hot and moist year-round. Many tropical areas have a dry and wet season, the wet season, rainy season or green season, is the time of year, ranging from one or more months, when most of the average annual rainfall in a region falls. Areas with wet seasons are disseminated across portions of the tropics and subtropics, under the Köppen climate classification, for tropical climates, a wet season month is defined as a month where average precipitation is 60 millimetres or more. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is distributed through the year.
When the wet season occurs during the season, or summer, precipitation falls mainly during the late afternoon. The wet season is a time when air quality improves, freshwater quality improves and vegetation grows significantly, floods cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients diminish and erosion increases, the incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for the wetter regime, the previous dry season leads to food shortages into the wet season, as the crops have yet to mature. Regions within the tropics may well not have a tropical climate, there are alpine tundra and snow-capped peaks, including Mauna Kea, Mount Kilimanjaro, and the Andes as far south as the northernmost parts of Chile and Argentina. Under the Köppen climate classification, much of the area within the tropics is classed not as tropical but as dry including the Sahara Desert.
Tropical plants and animals are those native to the tropics. Tropical ecosystems may consist of rainforests, dry forests, spiny forests, desert. There are often significant areas of biodiversity, and species present, particularly in rainforests. In biogeography, the tropics are divided into Paleotropics and Neotropics, they are sometimes referred to as the Pantropic
Microburst
A microburst is a small downdraft that moves in a way opposite to a tornado. Microbursts are found in strong thunderstorms, there are two types of microbursts within a thunderstorm, wet microbursts and dry microbursts. They go through three stages in their cycle, the downburst and cushion stages, a microburst can be particularly dangerous to aircraft, especially during landing, due to the wind shear caused by its gust front. A microburst often has high winds that can knock over fully grown trees and they usually last from a couple of seconds to several minutes. Fujita coined the term macroburst for downbursts larger than 4 km, a distinction can be made between a wet microburst which consists of precipitation and a dry microburst which typically consists of virga. Microbursts are recognized as capable of generating wind speeds higher than 75 m/s, Microbursts have been called air bombs. When rain falls below the base or is mixed with dry air, it begins to evaporate. The cool air descends and accelerates as it approaches the ground, when the cool air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst.
High winds spread out in type of pattern showing little or no curvature are known as straight-line winds. Wet microbursts are downbursts accompanied by significant precipitation at the surface which are warmer than their environment and these downbursts rely more on the drag of precipitation for downward acceleration of parcels than negative buoyancy which tend to drive dry microbursts. As a result, higher mixing ratios are necessary for these downbursts to form, melting of ice, particularly hail, appears to play an important role in downburst formation, especially in the lowest 1 km above ground level. These factors, among others, make forecasting wet microbursts a difficult task, the evolution of downbursts is broken down into three stages, the contact stage, the outburst stage, and the cushion stage. The virtual temperature correction usually is small and to a good approximation. In some storms this term has an effect on updrafts but there is not much reason to believe it has much of an impact on downdrafts.
The second term is the effect of buoyancy on vertical motion, clearly, in the case of microbursts, one expects to find that B is negative meaning the parcel is cooler than its environment. This cooling typically takes place as a result of phase changes, precipitation particles that are small, but are in great quantity, promote a maximum contribution to cooling and, hence, to creation of negative buoyancy. The major contribution to this process is from evaporation, the last term is the effect of water loading. Whereas evaporation is promoted by large numbers of small droplets, it requires a few large drops to contribute substantially to the downward acceleration of air parcels
European windstorm
European windstorm is a name given to the strongest extratropical cyclones which occur across the continent of Europe. They form as cyclonic windstorms associated with areas of low atmospheric pressure and they are most common in the autumn and winter months. On average, the month when most windstorms form is January, the seasonal average is 4.6 windstorms. However, when they track further south they can affect almost any country in Europe and these phenomena vary in terms of physical mechanisms, atmospheric structure, spatial extent, severity level and location relative to cyclone and fronts. On average these storms cause economic damage €1.9 billion per year and they rank as the second highest cause of global natural catastrophe insurance loss. Up to the half of the 19th century, European windstorms were named after the person who spotted them. Usually, they would be named either by the year, the date, however, a storm may still be named differently in different countries. 2011 storm Dagmar in Norway and Sweden is known as Patrick in Germany, an alternative Scottish naming system arose in 2011 via social media/Twitter which resulted in the humorous naming of Hurricane Bawbag and Hurricane Fannybaws.
Such usage of the term Hurricane is not without precedent, as the 1968 Scotland storm was referred to as Hurricane Low Q, the UK Met Office and Irish forecasting service Met Éireann held discussions about developing a common naming system for Atlantic storms. An independent forecaster, the European Windstorm Centre, has its own naming list, the university subsequently started to name every area of high or low pressure within its weather forecasts, from a list of 260 male and 260 female names submitted by its students. The female names were assigned to areas of low pressure while male names were assigned to areas of high pressure, the DWD subsequently banned the usage of the names by their offices during July 1991, after complaints had poured in about the naming system. However, the order was leaked to the German press agency, Deutsche Presse-Agentur, Germanys ZDF television channel subsequently ran a phone in poll on 17 July 1991 and claimed that 72% of the 40,000 responses favored keeping the names.
This made the DWD pause and think about the naming system, during 1998 a debate started about if it was discrimination to name areas of high pressure with male names and the areas of low pressure with female names. The issue was resolved by alternating male and female names each year. The naming comes with the chance that the system will be notable. The money raised by this is used by the department to maintain weather observations at the Free University. Several European languages use cognates of the word huracán to indicate particularly strong winds occurring in Europe. The term hurricane as applied to these storms is not in reference to the structurally different tropical cyclone of the same name, in English, use of term hurricane to refer to European windstorms is mostly discouraged, as these storms do not display the structure of tropical storms
Graupel
Graupel, called soft hail or snow pellets, is precipitation that forms when supercooled droplets of water are collected and freeze on falling snowflakes, forming 2–5 mm balls of rime. The term graupel comes from the German language, the METAR code for graupel is GS. Under some atmospheric conditions, snow crystals may encounter supercooled water droplets and these droplets, which have a diameter of about 10 µm, can exist in the liquid state at temperatures as low as −40 °C, far below the normal freezing point. Contact between a crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystal. This process of growth is known as accretion. Crystals that exhibit frozen droplets on their surfaces are referred to as rimed. When this process continues so that the shape of the snow crystal is no longer identifiable. Graupel was formerly referred to by meteorologists as soft hail, graupel is easily distinguishable from hail in both the shape and strength of the pellet and the circumstances in which it falls.
Ice from hail is formed in hard, relatively uniform layers, graupel forms fragile, oblong shapes and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets. Graupel is fragile enough that it will fall apart when touched. However, observations of snow crystals with a scanning electron microscope clearly show cloud droplets measuring up to 50 µm on the surface of the crystals. The rime has been observed on all four forms of snow crystals, including plates, columns. As the riming process continues, the mass of frozen, accumulated cloud droplets obscures the form of the snow crystal. Graupel commonly forms in high-altitude climates and is denser and more granular than ordinary snow, due to its rimed exterior. Macroscopically, graupel resembles small beads of polystyrene, the combination of density and low viscosity makes fresh layers of graupel unstable on slopes, and layers of 20–30 cm present a high risk of dangerous slab avalanches. In addition, thinner layers of graupel falling at low temperatures can act as ball bearings below subsequent falls of more stable snow.
Graupel tends to compact and stabilise approximately one or two days after falling, depending on the temperature and the properties of the graupel, merriam-Webster Online Dictionary, accessed September 12,2006. The Weather Channel, accessed September 12,2006, national Snow and Ice Data Center, accessed September 12,2006
Snowsquall
A snowsquall is a sudden moderately heavy snow fall with blowing snow and strong, gusty surface winds. It is often referred to as a whiteout and is similar to a blizzard but is localized in time or in location, there are two primary types of snowsqualls, lake effect and frontal. When arctic air moves over large expanses of open waters in winter. Whiteout conditions will affect narrow corridors from shores to inland areas aligned along the wind direction. This will be enhanced when the air mass is uplifted by higher elevations. The name originates from the Great Lakes area of North America, regions in lee of oceans, such as the Canadian Maritimes could experience such snowsqualls. The areas affected by lake-effect snow are called snowbelts and deposition rate of many inches of snow per hour are common in these situations, extremely cold air over still warm water in early winter can even produce thundersnow, snow showers accompanied by lightning and thunder. A frontal snowsquall is an intense frontal convective line, when temperature is near freezing at the surface, the strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow.
This type of snowsquall generally lasts less than 30 minutes at any point along its path and this is similar to a line of thunderstorms in the summer but the tops of the clouds are only 5,000 to 10,000 feet, often difficult to see on radar. Forecasting these types of events is equivalent to summer severe weather forecast for squall lines, presence of a frontal trough with wind shift. However, the dome behind the trough is at 850 mbar instead of a higher level. In cases where there is an amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning. Both types of snowsqualls are very dangerous for motorists and airplanes or generally any traveler unfortunate enough to get stuck in one, the change in conditions is very sudden, and slippery conditions and abrupt loss of visibility due to whiteouts often cause multiple-vehicle collisions. In the case of lake effect snow, heavy amounts of snow can accumulate in short periods of time, possibly causing road closures, for instance, on January 9,2015, a localized, heavy snow squall caused a 193-vehicle pile-up on I-94 highway near Galesburg, Michigan
Extratropical cyclone
Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms and tornadoes. These types of cyclones are defined as large scale low pressure systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, the term cyclone applies to numerous types of low pressure areas, one of which is the extratropical cyclone. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics and they are termed mid-latitude cyclones if they form within those latitudes, or post-tropical cyclones if a tropical cyclone has intruded into the mid latitudes. Weather forecasters and the public often describe them simply as depressions or lows. Terms like frontal cyclone, frontal depression, frontal low, extratropical low, non-tropical low, Extratropical cyclones are classified mainly as baroclinic, because they form along zones of temperature and dewpoint gradient known as frontal zones.
They can become barotropic late in their cycle, when the distribution of heat around the cyclone becomes fairly uniform with its radius. Extratropical cyclones form anywhere within the regions of the Earth. A study of extratropical cyclones in the Southern Hemisphere shows that between the 30th and 70th parallels, there are an average of 37 cyclones in existence during any 6-hour period, a separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter. Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, cyclogenesis, or low pressure formation, occurs along frontal zones near a favorable quadrant of a maximum in the upper level jetstream known as a jet streak. The favorable quadrants are usually at the rear and left front quadrants. The divergence causes air to rush out from the top of the air column and this in turn forces convergence in the low-level wind field and increased upward motion within the column.
The increased upward motion causes atmospheric pressure at ground level to lower and this is because the upward air motion counteracts gravity, lessening the weight of the atmosphere in that location. The lowered pressure strengthens the cyclone, as the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as the air ahead of the system is denser. Later, the cyclones occlude as the portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal. Eventually, the cyclone will become cold and begin to weaken. Atmospheric pressure can fall very rapidly when there are upper level forces on the system
Season
A season is a division of the year marked by changes in weather and hours of daylight. Seasons result from the orbit of the Earth around the Sun. During May and July, the northern hemisphere is exposed to direct sunlight because the hemisphere faces the sun. The same is true of the hemisphere in November, December. It is the tilt of the Earth that causes the Sun to be higher in the sky during the months which increases the solar flux. However, due to lag, June and August are the hottest months in the northern hemisphere and December, January. In temperate and subpolar regions, four calendar-based seasons are recognized, summer, autumn or fall. Ecologists often use a model for temperate climate regions, vernal, serotinal, autumnal. Many tropical regions have two seasons, the rainy, wet, or monsoon season and the dry season, some have a third cool, mild, or harmattan season. Seasons often held special significance for agrarian societies, whose lives revolved around planting and harvest times, in some parts of the world, some other seasons capture the timing of important ecological events such as hurricane season, tornado season, and wildfire season.
The most historically important of these are the three seasons—flood and low water—which were previously defined by the annual flooding of the Nile in Egypt. The seasons result from the Earths axis of rotation being tilted with respect to its orbital plane by an angle of approximately 23.5 degrees, regardless of the time of year, the northern and southern hemispheres always experience opposite seasons. This is because during summer or winter, one part of the planet is directly exposed to the rays of the Sun than the other. For approximately half of the year, the northern hemisphere tips toward the Sun, 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 the northern and southern hemispheres.
Around the March equinox, the northern hemisphere will be experiencing spring as the hours of daylight increase, the effect of axial tilt is observable as the change in day length and altitude of the Sun at noon during a year. Between this effect and the daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres
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This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "article name needed". Cyclopædia, or an Universal Dictionary of Arts and Sciences (first ed.). James and John Knapton, et al.
This article incorporates text from a publication now in the 
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