https://courses.washington.edu/tesc243/jamaica/index_files/page0004.htm
https://en.wikipedia.org/wiki/Karst
Saturday, March 18, 2017
Friday, March 17, 2017
Mass Movement (General, Incomplete) (integrated)
Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a mass, largely under the force of gravity, but frequently affected by water and water content as in submarine environments and mudflows.[1] Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to years. Mass wasting occurs on both terrestrial and submarine slopes
When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. The slope material's strength and cohesion and the amount of internal friction between material help maintain the slope's stability and are known collectively as the slope's shear strength. The steepest angle that a cohesionless slope can maintain without losing its stability is known as its angle of repose. When a slope made of loose material possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it.
Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may also occur at very high speed, such as in rockslides or landslides, with disastrous consequences, both immediate and delayed, e.g., resulting from the formation of landslide dams.
Factors that change the potential of mass wasting include: change in slope angle, weakening of material by weathering, increased water content; changes in vegetation cover, and overloading.
Types of mass movement[edit]
Types of mass movement are distinguished based on how the soil, regolith or rock moves downslope as a whole.
Creeps[edit]
Soil creep is a long term process. The combination of small movements of soil or rock in different directions over time are directed by gravity gradually downslope. The steeper the slope, the faster the creep. The creep makes trees and shrubs curve to maintain their perpendicularity, and they can trigger landslides if they lose their root footing. The surface soil can migrate under the influence of cycles of freezing and thawing, or hot and cold temperatures, inching its way towards the bottom of the slope forming terracettes. This happens at a rate that is not noticeable to the naked eye.
Landslides[edit]
A landslide, also called a landslip, is a rapid movement of a large mass of earth and rocks down a hill or a mountainside. Little or no flowage of the materials occurs on a given slope until heavy rain and resultant lubrication by the same rainwater facilitate the movement of the materials, causing a landslide to occur. The common forms of landslides are slump, debris slide, rock slide, rock fall, debris fall and avalanche.
Flows[edit]
Movement of soil and regolith that more resembles fluid behavior is called a flow. These include avalanches, mudflows, debris flows, earth flow, lahars and sturzstroms. Water, air and ice are often involved in enabling fluidlike motion of the material.
Slump[edit]
A slipping of coherent rock material along the curved surface of a decline. Slumps involve a mass of soil or other material sliding along a curved surface (shaped like a spoon). It forms a small, crescent-shaped cliff, or abrupt scarp at the top end of the slope. There can be more than one scarp down the slope.
Falls[edit]
A fall, including rockfall, occurs where regolith cascades down a slope, but is not of sufficient volume or viscosity to behave as a flow. Falls are promoted in rocks which are characterised by presence of vertical cracks. Falls can result from undercutting by running water as well as from undercutting by waves. They usually occur at very steep slopes such as a cliff face. The rock material may be loosened by earthquakes, rain, plant-root wedging, and expanding ice, among other things. The accumulation of rock material that has fallen and resides at the base of the structure is known as talus.
Triggers of mass wasting[edit]
Soil and regolith remain on a hillslope only while the gravitational forces are unable to overcome the frictional forces keeping the material in place (see slope stability). Factors that reduce the frictional resistance relative to the downslope forces, and thus initiate slope movement, can include:
- earthquakes
- increased overburden from structures
- increased soil moisture
- reduction of roots holding the soil to bedrock
- undercutting of the slope by excavation or erosion
- weathering by frost heave
- bioturbation
- volcanic edifice over-steepening
The importance of water in mass wasting[edit]
Water can increase or decrease the stability of a slope depending on the amount present. Small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry. If too much water is present the water may act to increase the pore pressure, reducing friction, and accelerating the erosion process and resulting in different types of mass wasting (i.e. mudflows, landslides, etc.). A good example of this is to think of a sand castle. Water must be mixed with sand in order for the castle to keep its shape. If too much water is added the sand washes away, if not enough water is added the sand falls and cannot keep its shape. Water also increases the mass of the soil, this is important because an increase in mass means that there will be an increase in velocity if mass wasting is triggered.
Additional Material:
Detailed Document (48 pages) on Mass Movement:
https://www.google.com.sg/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwji0qqilu_SAhVFwI8KHddoALoQFggeMAE&url=http%3A%2F%2Fgis.ess.washington.edu%2Fgrg%2Fcourses10_11%2Fess326%2Ftextbook%2FChapter_5_Revised.doc&usg=AFQjCNHkPjkrqaYAZtLOmzrQzpdW7AqMNg&sig2=ATfkpeelnAJfNJN8Gs-nZwThursday, March 16, 2017
(Unformatted) El Nino Phenomenon: Walker Circulation & El Nino Southern Oscillation (integrated)
Concept:
At the end of every year, the cold, northward strong Peruvian current is replaced by a warm, southward weak countercurrent. This occurrence was orginally named 'El Nino', after Christ as it usually appeared during the Christmas season. The warm weak southward countercurrents typically last for a few weeks before it is replaced by the cold strong northward Peruvian current. However, this weak warm southward countercurrent becomes stronger every 3 to 7 years, and along with this current is the accumulation of warm surafce water in the Eastern Pacific. Scientists these days use the term 'El Nino' specifically referring to the episodes of ocean warming that occurs every few years only.
The first observation of something related would be by Sir Gilbert Walker, who noticed an irregular oscillation between atomspheric pressure in Darwin, northern Australia, and Tahiti, a central Pacific equatorial Island. Tahiti usually has higher atmospheric pressure than Darwin, but every time, towards the end of the year, where El Nino occurs, the barometric pressure drops over large portions of the South eastern Pacific, whereas in the Western Pacific, near Indonesia and Northern Australia, the pressure increases. Then, when the currents change, the pressure difference between the two regions change back to normal, with the Eastern Pacific having higher pressure while the Western Pacific turned to having lower pressure.
From Wikipedia:
El Niño /ɛl ˈniːnjoʊ/ (Spanish pronunciation: [el ˈniɲo]) is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America. El Niño Southern Oscillation refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, SST, of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. The cool phase of ENSO is called "La Niña" with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. The ENSO cycle, both El Niño and La Niña, cause global changes of both temperatures and rainfall.[2][3]
Originally the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time.[7] However, over time the term has evolved and now refers to the warm and negative phase of the El Niño Southern Oscillation and is the warming of the ocean surface or above-average sea surface temperatures in either the central and eastern tropical Pacific Ocean.[8][9] This warming causes a shift in the atmospheric circulation with rainfall becoming reduced over Indonesia and Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean.[10] The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.[9]
Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.[24] The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode".[25]
At the end of every year, the cold, northward strong Peruvian current is replaced by a warm, southward weak countercurrent. This occurrence was orginally named 'El Nino', after Christ as it usually appeared during the Christmas season. The warm weak southward countercurrents typically last for a few weeks before it is replaced by the cold strong northward Peruvian current. However, this weak warm southward countercurrent becomes stronger every 3 to 7 years, and along with this current is the accumulation of warm surafce water in the Eastern Pacific. Scientists these days use the term 'El Nino' specifically referring to the episodes of ocean warming that occurs every few years only.
The first observation of something related would be by Sir Gilbert Walker, who noticed an irregular oscillation between atomspheric pressure in Darwin, northern Australia, and Tahiti, a central Pacific equatorial Island. Tahiti usually has higher atmospheric pressure than Darwin, but every time, towards the end of the year, where El Nino occurs, the barometric pressure drops over large portions of the South eastern Pacific, whereas in the Western Pacific, near Indonesia and Northern Australia, the pressure increases. Then, when the currents change, the pressure difference between the two regions change back to normal, with the Eastern Pacific having higher pressure while the Western Pacific turned to having lower pressure.
From Wikipedia:
El Niño /ɛl ˈniːnjoʊ/ (Spanish pronunciation: [el ˈniɲo]) is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America. El Niño Southern Oscillation refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, SST, of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. The cool phase of ENSO is called "La Niña" with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. The ENSO cycle, both El Niño and La Niña, cause global changes of both temperatures and rainfall.[2][3]
Originally the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time.[7] However, over time the term has evolved and now refers to the warm and negative phase of the El Niño Southern Oscillation and is the warming of the ocean surface or above-average sea surface temperatures in either the central and eastern tropical Pacific Ocean.[8][9] This warming causes a shift in the atmospheric circulation with rainfall becoming reduced over Indonesia and Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean.[10] The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.[9]
Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.[24] The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode".[25]
Effects on the global climate[edit]
El Nino affects the global climate and disrupts normal weather patterns, which as a result can lead to intense storms in some places and droughts in others.[60][61]
Tropical cyclones[edit]
Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies.[62] Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E, which would favor the Japanese archipelago.[63]
Within the Atlantic Ocean vertical wind shear is increased, which inhibits tropical cyclone genesis and intensification, by causing the westerly winds in the atmosphere to be stronger.[64] The atmosphere over the Atlantic Ocean can also be drier and more stable during El Niño events, which can also inhibit tropical cyclone genesis and intensification.[64] (Recall: Air is drier means unsaturated and thus conditional stability due to environmental lapse rate being between the dry adiabatic lapse rate and the moist adiabatic lapse rate. Additionally, air may also be absolutely stable because the environmental lapse rate is below the moist adiabatic lapse rate.) Within the Eastern Pacific basin: El Niño events contribute to decreased easterly vertical wind shear and favours above-normal hurricane activity.[65] However, the impacts of the ENSO state in this region can vary and are strongly influenced by background climate patterns.[65] The Western Pacific basin experiences a change in the location of where tropical cyclones form during El Niño events, without a major change in how many develop each year.[64]As a result of this change Micronesia is more likely to be affected by several tropical cyclones, while China has a decreased risk of being affected by several tropical cyclones.[citation needed] A change in the location of where tropical cyclones form also occurs within the Southern Pacific Ocean between 135°E and 120°W, with tropical cyclones more likely to occur within the Southern Pacific basin than the Australian region.[10][64] As a result of this change tropical cyclones are 50% less likely to make landfall on Queensland, while the risk of a tropical cyclone is elevated for island nations like Niue, French Polynesia, Tonga, Tuvalu and the Cook Islands.[10][66][67]
Remote influence on tropical Atlantic Ocean[edit]
A study of climate records has shown that El Niño events in the equatorial Pacific are generally associated with a warm tropical North Atlantic in the following spring and summer.[68] About half of El Niño events persist sufficiently into the spring months for the Western Hemisphere Warm Pool to become unusually large in summer.[69] Occasionally, El Niño's effect on the Atlantic Walker circulation over South America strengthens the easterly trade winds in the western equatorial Atlantic region. As a result, an unusual cooling may occur in the eastern equatorial Atlantic in spring and summer following El Niño peaks in winter.[70] Cases of El Niño-type events in both oceans simultaneously have been linked to severe famines related to the extended failure of monsoon rains.[22]
Antarctica[edit]
Many ENSO linkages exist in the high southern latitudes around Antarctica.[71] Specifically, El Niño conditions result in high-pressure anomalies over the Amundsen and Bellingshausen Seas, causing reduced sea ice and increased poleward heat fluxes in these sectors, as well as the Ross Sea. The Weddell Sea, conversely, tends to become colder with more sea ice during El Niño. The exact opposite heating and atmospheric pressure anomalies occur during La Niña.[72] This pattern of variability is known as the Antarctic dipole mode, although the Antarctic response to ENSO forcing is not ubiquitous.[72]
Regional impacts[edit]
Observations of El Niño events since 1950, show that impacts associated with El Niño events depend on what season it is.[73] However, while certain events and impacts are expected to occur during events, it is not certain or guaranteed that they will occur.[73] The impacts that generally do occur during most El Niño events include below-average rainfall over Indonesia and northern South America, while above average rainfall occurs in southeastern South America, eastern equatorial Africa, and the southern United States.[73]
Australia and the Southern Pacific[edit]
During El Niño events, the shift in rainfall away from the Western Pacific, can mean that rainfall across Australia is reduced.[10] Over the southern part of the continent, warmer than average temperatures can be recorded as weather systems are more mobile and fewer blocking areas of high pressure occur.[10] The onset of the Indo-Australian Monsoon in tropical Australia is delayed by two to six weeks, which as a consequence means that rainfall is reduced over the northern tropics.[10] The risk of a significant bushfire season in south-eastern Australia is higher following an El Niño event, especially when it is combined with a positive Indian Ocean Dipole event.[10] During an El Niño event, New Zealand tends to experience stronger or more frequent westerly winds during their summer, which leads to an elevated risk of drier than normal conditions along the east coast.[74] There is more rain than usual though on New Zealand's West Coast, because of the barrier effect of the North Island mountain ranges and the Southern Alps.[74]
Fiji generally experiences drier than normal conditions during an El Niño, which can lead to drought becoming established over the Islands.[75] However, the main impacts on the island nation is felt about a year after the event becomes established.[75] Within the Samoan Islands, below average rainfall and higher than normal temperatures are recorded during El Niño events, which can lead to droughts and forest fires on the islands.[76] Other impacts include a decrease in the sea level, possibility of coral bleaching in the marine environment and an increased risk of a tropical cyclone affecting Samoa.[76]
Africa[edit]
In Africa, East Africa — including Kenya, Tanzania, and the White Nile basin — experiences, in the long rains from March to May, wetter-than-normal conditions. Conditions are also drier than normal from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana.
Asia[edit]
As warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.[77]
Europe[edit]
El Niño's effects on Europe are controversial, complex and difficult to analyse, as it is one of several factors that influence the weather over the continent and other factors can overwhelm the signal.[78][79]
North America[edit]
Over North America, the main temperature and precipitation impacts of El Niño, generally occur in the six months between October and March.[80][81] In particular the majority of Canada generally has a milder than normal winters and springs, with the exception of eastern Canada where no significant impacts occur.[82] Within the United States, the impacts generally observed during the six-month period include; wetter-than-average conditions along the Gulf Coast between Texas and Florida, while drier conditions are observed in Hawaii, the Ohio Valley, Pacific Northwest and the Rocky Mountains.[80] Over California and the South-Western United States, there is a weak relationship between El Nino and above-average precipitation, as it strongly depends on the strength of the El Niño event amongst other factors.[80]
The synoptic condition for the Tehuantepecer is associated with high-pressure system forming in Sierra Madre of Mexico in the wake of an advancing cold front, which causes winds to accelerate through the Isthmus of Tehuantepec. Tehuantepecers primarily occur during the cold season months for the region in the wake of cold fronts, between October and February, with a summer maximum in July caused by the westward extension of the Azores High. Wind magnitude is greater during El Niño years than during La Niña years, due to the more frequent cold frontal incursions during El Niño winters.[83] Its effects can last from a few hours to six days.[84]
South America[edit]
Because El Niño's warm pool feeds thunderstorms above, it creates increased rainfall across the east-central and eastern Pacific Ocean, including several portions of the South American west coast. The effects of El Niño in South America are direct and stronger than in North America. An El Niño is associated with warm and very wet weather months in April–October along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme.[85] The effects during the months of February, March, and April may become critical. Along the west coast of South America, El Niño reduces the upwelling of cold, nutrient-rich water that sustains large fish populations, which in turn sustain abundant sea birds, whose droppings support the fertilizer industry. The reduction in upwelling leads to fish kills off the shore of Peru.[86]
The local fishing industry along the affected coastline can suffer during long-lasting El Niño events. The world's largest fishery collapsed due to overfishing during the 1972 El Niño Peruvian anchoveta reduction. During the 1982–83 event, jack mackerel and anchoveta populations were reduced, scallops increased in warmer water, but hake followed cooler water down the continental slope, while shrimp and sardines moved southward, so some catches decreased while others increased.[87] Horse mackerel have increased in the region during warm events. Shifting locations and types of fish due to changing conditions provide challenges for fishing industries. Peruvian sardines have moved during El Niño events to Chilean areas. Other conditions provide further complications, such as the government of Chile in 1991 creating restrictions on the fishing areas for self-employed fishermen and industrial fleets.[citation needed]
The ENSO variability may contribute to the great success of small, fast-growing species along the Peruvian coast, as periods of low population removes predators in the area. Similar effects benefit migratory birds that travel each spring from predator-rich tropical areas to distant winter-stressed nesting areas.[citation needed]
Southern Brazil and northern Argentina also experience wetter than normal conditions, but mainly during the spring and early summer. Central Chile receives a mild winter with large rainfall, and the Peruvian-Bolivian Altiplano is sometimes exposed to unusual winter snowfall events. Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America.[citation needed]
Wednesday, March 15, 2017
Tropical Cyclone Genesis, Maintenance, & intensification (integrated)
Tropical Cyclones
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere.[1] Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.[2]
⭄ There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear.[3]
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere.[1] Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.[2]
⭄ There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear.[3]
Sunday, March 12, 2017
Atmospheric Circulation (integrated)
Global Atmospheric Circulation
Atmospheric circulation is the large-scale movement of air, and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.
⇰ The Earth's weather is a consequence of its illumination by the Sun, and the laws of thermodynamics. There are differences in shortwave solar radiation received and longwave terrestrial radiation emitted for the earth at the equatorial and the polar regions (specifically, the torrid zones and the friggid zones).
⇰ The atmospheric circulation can be viewed as a heat engine driven by the Sun's energy, and whose energy sink, ultimately, is the blackness of space. The work produced by that engine causes the motion of the masses of air and in that process it redistributes the energy absorbed by the Earth's surface near the tropics to space and incidentally to the latitudes nearer the poles.
Atmospheric circulation is the large-scale movement of air, and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.
⇰ The Earth's weather is a consequence of its illumination by the Sun, and the laws of thermodynamics. There are differences in shortwave solar radiation received and longwave terrestrial radiation emitted for the earth at the equatorial and the polar regions (specifically, the torrid zones and the friggid zones).
⇰ The atmospheric circulation can be viewed as a heat engine driven by the Sun's energy, and whose energy sink, ultimately, is the blackness of space. The work produced by that engine causes the motion of the masses of air and in that process it redistributes the energy absorbed by the Earth's surface near the tropics to space and incidentally to the latitudes nearer the poles.
Saturday, March 11, 2017
Tropical Climatic Zones (integrated)
Climate Classification
The variations in interactions between planet earth and the spheres (atmosphere, biosphere, hydrosphere, geosphere) give each location certain distinct climatic characteristics. In order to conveniently analyse them, there is a need to classify them. This would simplify all the climatic types into a few groups, each with their own unique climatic character.
The variations in interactions between planet earth and the spheres (atmosphere, biosphere, hydrosphere, geosphere) give each location certain distinct climatic characteristics. In order to conveniently analyse them, there is a need to classify them. This would simplify all the climatic types into a few groups, each with their own unique climatic character.
Friday, March 10, 2017
The Science of Climate Change (integrated)
Climate Change
➽ Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time.
➽ Climate change is caused by natural factors such as biotic processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain anthropogenic activities have also been identified as significant causes of recent climate change.
➽ Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time.
➽ Climate change is caused by natural factors such as biotic processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain anthropogenic activities have also been identified as significant causes of recent climate change.
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