Friday, March 20, 2009
"Thundersnow" Facts: Mysterious Storms Explained
Christine Dell'AmoreNational Geographic News
March 3, 2009
The late-winter snowstorm that blanketed much of the eastern U.S. on Sunday and Monday packed some serious sound and fury—emphasis on sound.
Along with the snow clouds, a rare and little-known phenomenon known as thundersnow rumbled over parts of Georgia and South Carolina.
Thundersnow—when thunder and lighting occur during a snowstorm—most often appears in late winter or early spring, experts say.
That's because the ingredients for thundersnow—a mass of cold air on top of warm, plus moist air closer to the ground—often come together during that time.
What Causes Thundersnow
Thundersnow starts out like a summer thunderstorm, Market said. The sun heats the ground and pushes masses of warm, moist air upward, creating unstable air columns.
As it rises, the moisture condenses to form clouds, which are jostled by internal turbulence.
The "tricky part" for making thundersnow, Market said, is creating that atmospheric instability in the wintertime.
For thundersnow to occur, the air layer closer to the ground has to be warmer than the layers above, but still cold enough to create snow—a very precise circumstance.
In the recent southern U.S. thundersnow storms, for instance, the atmosphere became unstable enough that thunderstorms with rain developed. Those storms then moved north where the air was below freezing, said Howard Silverman, a National Weather Service senior forecaster in Sterling, Virginia.
The thundersnow events were also coupled with "pretty decent snowfall rates," at the rapid clip of more than two inches (five centimeters) an hour, Silverman said.
Heavier snowfall is usually linked to thundersnow, both experts agreed.
The University of Missouri's Market has done research showing that most of the time 6 inches (15 centimeters) of snow will accumulate within a 70-mile (113-kilometer) radius of a thundersnow event.
(Related news: "Volcanic Lightning Sparked by 'Dirty Thunderstorms,' Study Finds.")
How to See Thundersnow
Experiencing thundersnow requires being in the right place at the right time, said University of Missouri atmospheric scientist Patrick Market, who has received funding from the National Geographic Society's Expeditions Council. (The National Geographic Society owns National Geographic News.)
Even then, he said, you probably won't see anything but white.
"In a really nice thundersnow event, the sky [simply] gets bright. You don't see a lightning bolt. There's nothing for a second or two, and then you hear a rumble of thunder."
The best spots for catching thundersnow in person are Wolf Creek Pass, Colorado, and the eastern shores of Lake Ontario, Market said—two hot spots that he has pinpointed in his research.
Thundersnow can also occur along coasts, experts say, because that's where moisture from warm water can easily evaporate into the colder, drier air above.
(Watch an interactive animation of a thunderstorm.)
Thundersnow to Aid Weather Forecasts?
Market and colleagues track thundersnow storms in the field. After the researchers identify a winter storm, they release weather balloons, which are meant to reveal how the atmosphere becomes unstable.
By collecting data on pressure, temperature, humidity, and wind speed and direction—the five key factors meteorologists use to make predictions—Market and colleagues hope their thundersnow studies can help make future weather forecasts more accurate.
Tuesday, March 17, 2009
Q. What are the different patterns of rural settlement?
1. These type of settlements have two parallel rows of houses facing each other.
2. These linear settlements are mainly situated along the roads and streams.
3. These type of settlements are common in coastal Kerala, Manipur, Bala Ghat, Mandala and Raigrah districts of Madhya Pradesh and Chhattisgarh.
4. Linear settlements are also common feature of Nagaland.
5.Fishing villages in the coastal areas also look like linear cluster.
1. Radial pattern of rural settlement develops at a place where several roads converge on a nodal position.
2. The housing development clings to these roads and appear to be radiating from the nodal point.
1. A village acquires a star-like pattern when streets radiate from a common centre.
2. Expansion of these villages due to population growth leads to the formation of a double radial pattern.
3. This type of pattern is more common in Tamil Nadu and Upper Ganga Plain.
Cross-shape or Rectangular Pattern
1. Such villages develop at the meeting place of two roads.
2. The streets are either parallel or perpendicular to each other and the settlement takes a rectangular shape.
3. These type of settlements are more common in the Northern Plain especially in the Ganga-Yamuna Doab.
4. These settlements arealso found in Tamil Nadu, Karnataka,Andhra Pradesh and thestates of South India.
T-shapePattern: Villages and towns confined between two rivers at their junction or confluences or between bifurcations of two roads eventually result in aT-shape pattern.
1. When the houses are constructed along the bank of a pond or a lake, the settlement take the shape ofcircle and is known as circular pattern.
2. These type of settlements are mainly found in Upper Ganga-Yamuna Doab, Trans-Yamuna Region and in parts of Madhya Pradesh, Gujarat and Maharashtra.
Q. What is the meaning of settlement? or
Varanasi and Madurai are two examples of Ancient cities.
Q. What are the two different types of Human settlements classified on the basis of size and function? or
1. Urban settlements:
i. These types of settlement are nodal in character and have secondary and tertiary activities.
ii. The chief occupation of the people of urban areas is non-agricultural i.e.industry, trade and services.
iii. The major function of an urban area are trades and commerce, transport and communication, mining and manufacturing, defence, administration, cultural and recreational activities.
iv. Population density is high and the settlement size is large.
i. These settlements are chiefly concerned with primary activities such as agriculture, mining, fishing, forestry etc.
ii. Most of the people of rural settlement are engaged in agricultural work.
iii. The major function of rural settlement is agriculture and each settlement specializes in various activities.
iv. Population density is small and the settlement size is small.
Settlement is classified into urban and rural, but there is no consensus:
i. Population size is small in rural settlement than urban settlements but it is not a universally applied because many villages of India and China have population exceeding that of some towns of Western Europe and United States.
ii. People living in villages pursued agriculture or other primary activities, but presently in developed countries, large sections of urban populations prefer to live in villages even though they work in the city.
iii. Petrol pumps are considered as a rural function in the United States while it is an urban function in India.
iv. Facilities available in the villages of developed countries may be considered rare in villages of developing and less developed countries.
Ans. Settlements can also be classified on the basis of shape and pattern into:
A. Compact settlements:-
i. In these settlement houses are built very close to each other.
ii. Such settlements are found in river valleys and fertile plains.
iii. The people are closely tied and share common occupations.
B. Dispersed settlements:-
i. In these settlements houses are built far apart from each other.
ii. These settlements consist of one or two houses and cultural feature such as a church or a temple binds the settlement together.
iii. Such settlements are found over hills, plateau and highlands.
Q. What are rural settlements?
Ans. Rural settlements are most closely and directly related to land. They are dominated by primary activities such as agriculture, animal husbandry, fishing etc. The settlements size is relatively small.
Q. Explain the factors which influence the location of rural settlements.
Ans. Rural settlements are influenced by following factors:
i. Water Supply: Usually rural settlements are located near water bodies such as rivers, lakes, and springs where water can be easily obtained. The need for water drives people to settle in islands surrounded by swamps or low lying river banks. Water supply is main factor because water is used for drinking, cooking and washing, rivers and lakes can be used to irrigate farm land, water bodies also have fish which can be caught for diet and navigable rivers and lakes can be used for transportation.
ii. Land: People choose to settle near fertile lands suitable for agriculture. Early settlers chose plain areas with fertile soils. In Europe villages are found near gently sloping land, in south East Asia villages are near low lying river valleys and coastal plains suited for wet rice cultivation.
iii. Upland: Villages are located on uplands which is not prone to flooding. Thus, in low lying river basins people chose to settle on terraces and levees which are “dry points”. In tropical countries people build their houses on stilts near marshy lands to protect themselves from flood, insects and animal pests.
iv. Building Material: The availability of building materials- wood, stone near settlements is another factor. Early villages were built in forests where wood was plentiful. In African Savanna’s mud bricks are used as building materials and the Eskimos, in Polar Regions, use ice blocks to construct igloos.
v. Defence: During the times of political instability, war, aggression of neighbouring groups villages were built on defensive hills and islands. In Nigeria, villages are built on upstanding rocks; in India most of the forts are located on hills.
Q. Describe the different types of rural settlements patterns.
Patterns of rural settlements is influenced by the site of the village, the surrounding topography and terrain.
i. On the basis of setting : The main types are
a. Plain villages,
b. Plateau villages,
c. Coastal villages,
d. Forest villages and
e. Desert villages.
ii. On the basis of functions : There may be
a. Farming villages,
b. Fishermen’s villages,
c. Lumberjack villages,
d. Pastoral villages etc.
iii. On the basis of forms or shapes of the settlements : These may be a number of geometrical forms and shapes such as:
a. Linear pattern : In such settlements houses are located along a road, railway line, river, canal edge of a valley or along a levee.
b. Rectangular pattern : Such patterns of rural settlements are found in plain areas or wide inter-montane valleys. The roads are rectangular and cut each other at right angles.
c. Circular pattern : Circular villages develop around lakes, tanks and sometimes the village is planned in such a way that the central part remains open and is used for keeping the animals to protect them from wild animals.
d. Star like pattern : Where several roads converge, star shaped settlements develop by the houses built along the roads.
e. T-shaped, Y-shaped, Cross-shaped or cruciform settlements : T –shaped settlements develop at tri-junctions of the roads.
Y–shaped settlements emerge as the places where two roads converge on the third one and houses are built along these roads. Cruciform settlements develop on the cross-roads and houses extend in all the four direction.
f. Double village : These settlements extend on both sides of a river where there is a bridge or a ferry.
ponsible for different types of settlements are:
Q.Describe the major problems of rural settlements in developing countries.
Major problem of rural settlements are:
i. Rural settlements in the developing countries have poor infrastructure facilities.
ii. Supply of water to rural settlements in developing countries is not adequate. People in villages, particularly in mountainous and arid areas have to walk long distances to fetch drinking water.
iii. Water borne diseases such as cholera and jaundice are common problem because of lack of safe drinking water and unhygienic conditions.
iv. Villages are adversely affected by the conditions of drought and flood. This in turn affects the crop cultivation.
v. The absence of toilet and garbage disposal facilities cause health related problems.
vi. The houses made up of mud, wood and thatch get damaged during heavy rains and floods.
vii. Most houses have no proper ventilation.
viii. Unmetalled roads and lack of modern communication network causes difficulties in providing emergency services during floods.
ix. It is also difficult to provide adequate health and educational infrastructure for large rural population. The problem is particularly serious where houses are scattered over a large area.
ourtyard. This has the influence of their temples.
Urban settlements are classified on the basis of its size of the population, occupational structure and administration.
1. Population size: - in India a settlement having population more than 5000 persons is called urban. In Japan it is 30000 persons whereas in Sweden it is 250 persons. The cut off figure depends on the density of population in the country.
2. Occupational structure: - besides population size, occupation is also taken as the criteria. In India, if more than 75 percent of workforce is engaged in nonagricultural activities then the settlement is called as urban. Other countries have their own criteria for e.g. in Italy it is 50 percent.
3. Administrative structure: - in India a settlement is classified as urban if it has a municipality, cantonment board or a notified area. In Brazil any administrative centre is termed as urban.
Q. Explain the role of site and situation in determining the location and expansion of towns.
Ans. Location of urban centres is influenced by their function. Site refers to the actual piece of ground on which the settlement is built. Situation refers to the location of the settlement in relation to the surrounding areas.
i. Strategic towns require sites offering natural defence;
ii. Mining towns require the presence of economically valuable minerals;
iii. Industrial towns generally need local energy supplies or raw materials;
iv. Tourist centres require attractive scenery, or a marine beach, a spring with medicinal water or historical relics,
v. Ports require a harbour.
vi. Availability of water, building materials and fertile land also plays an important role in locating urban settlements.
vii. The urban centres which are located close to an important trade route have experienced rapid development.
Q. State any four important functions of urban centres.
Ans. Dominant functions of urban areas are:
i. The earlier functions of towns were related to administration, trade, industry, defence and religious.
ii. Today, towns perform multiple functions such as, recreational, residential, transport, mining, manufacturing and most recently activities related to information technology.
iii. Some towns are known for their functions for example, Sheffield as an industrial city, London as a port city, Chandigarh as an administrative city.
iv. Large cities have a rather greater diversity of functions.
1. Administrative Towns: - National capitals, which have headquarters of the administrative offices of Central Government, are called administrative towns, such as new Delhi, Canberra, Moscow, and Washington.
2. Defence Towns: - Centres of military activities are known as defence towns. They are of three types: Fort towns, Garrison towns and Naval bases. Jodhpur is a fort town; Mhow is a garrison town; and Kochi is a naval base.
3. Cultural Towns: - towns famous for religious, educational or recreational functions are called cultural towns. Places of pilgrimage, such as Jerusalem, Mecca, Jagannath Puri and Varanasi etc. are considered as religious towns. There are also recreational towns such as Las Vegas in the USA.
4. Industrial Towns: - Mining and manufacturing regions. Dhanbad and Khetri are examples of mining towns. Towns which have developed due to setting up of industries such as Jameshdpur are called industrial towns.
5. Trading and Commercial Towns: - Many old towns were famous as trade centres such as Lahore in Pakistan, Baghdad in Iraq and Agra in India. Some towns have developed as transport towns such as Rotterdam in the Netherlands, Aden in Yemen and Mumbai in India are port towns.
Ans. Depending on the size and the services available and functions rendered, urban centres are designated as town, city, million city, conurbation, and megalopolis.
i. Town: Population size in town is higher than the village. Functions such as, manufacturing, retail and wholesale trade, and professional services exist in towns.
ii. City: A city may be regarded as a leading town. Cities are much larger than towns and have a greater number of economic functions. They tend to have transport terminals, major financial institutions and regional administrative offices. When the population crosses the one million mark it is designated as a million city.
iii. Conurbation: The term conurbation was coined by Patrick Geddes in 1915 and applied to a large area of urban development that resulted from the merging of originally separate towns or cities. Greater London, Greater Mumbai, Manchester, Chicago and Tokyo are examples.
iv. Megalopolis: This Greek word meaning “great city”, was popularised by Jean Gottman (1957) and signifies ‘super- metropolitan’ region extending, as union of conurbations. The urban landscape stretching from Boston in the north to south of Washington in U.S.A. is the best known example of a megalopolis.
Q. Write a short notes on evolution of towns in India?
Towns florished since prehistoric times in India. Even at the time of Indus valley civilisation, towns like Harappa and Mohanjodaro were in existence. The following period has witnessed evolution of towns. It continued with periodic ups and downs until the arrival of Europeans in India in the eighteenth century On the basis of their evolution in different periods, Indian towns may be classified as: 1) Ancient Towns 2) Medieval towns and 3) Modern towns.
A minimum population of 5000 persons. At least 75% of male working population engaged in non agricultural pursuits. A density of population of at least 400 persons per sq. km. Statutory Towns Census Towns Atown and its adjoining urban outgrowths, Two or more contiguous towns with or without their outgrowths, Acity and one or more adjoining towns with their outgrowths together forming a contiguous spread. Most towns and cities are overgrown villages. People are even more rural in their habits and attitude which reflects their socio-economic outlook. Several cities have slums caused by migration of rural people without much improvement in infrastructure. Many cities have distinct marks of earlier rulers and old functions. Functional segregation is distinctly rudimentary and cannot be compared with western cities. Social segregation of population is based either on caste, religion, income or occupation.
PROBLEMS OF URBANISATION
Q. What is urbanization? What are the five major problems associated with urban settlements in developing countries? OR Describe the five problems faced by developing countries due to high urbanization.
Urbanization: - is the process of change from rural to urban population. Most cities in developing countries are unplanned.
Major problems of urban areas in developing countries are:
1. Economic Problems :
a. Over urbanization or the uncontrolled urbanization in developing countries is due to large-scale in-migration of rural people.
b. Decreasing employment opportunities in the rural as well as smaller urban areas has caused large scale rural to urban migration.
c. The huge migrant population in urban areas creates stagnation and generates a pool of unskilled and semi-skilled labour force.
d. Urban areas suffer from shortage of housing, transport, health and civic amenities.
e. A large number of people live in substandard housing i.e. slums and squatter settlements or on the streets.
f. Illegal settlements called squatter settlement are growing as fast as the city.
2. Socio-cultural Problems : Cities in the developing countries suffer from several social ills.
a. Inadequate social infrastructure and basic facilities is due to lack of financial resources and over-population in the cities.
b. The available educational and health facilities remain beyond the reach of the urban poor.
c. Cities suffer from poor health conditions.
d. Lack of employment and education tends to aggravate the crime rates.
e. Male selective migration to the urban areas distorts the sex ratio in these cities.
3. Environmental Problems :
a. The large urban population in developing countries uses and disposes off a huge quantity of water and all types of waste materials.
b. Many cities of the developing countries do not provide the minimum required quantity of drinkable water and water for domestic and industrial uses.
c. An improper sewerage system creates unhealthy conditions.
d. Massive use of traditional fuel in the domestic as well as the industrial sector severely pollutes the air.
e. The domestic and industrial wastes are either let into the general sewerages or dumped without treatment at unspecified locations.
f. Huge concrete structures of buildings create heat in the city environment.
A major problem of urban areas is the large-scale immigration of rural people. It is due to high population growth than the generation of employment and economic opportunities in rural areas.
i. It is urgent to eradicate rural poverty
ii. Improve the quality of living conditions as well as create employment and educational opportunities in rural areas.
iii. Balance must be created between rural and urban areas in their different economic, social and environmental conditions.
The classification of towns and cities on the basis of their population by the census of India is as follows:
% of total Urban Population
% Growth 1991-2001
1,00,000 and more
Less then 5000
These towns are also calledcantonment towns. A
A courtyard is a typical feature of the Indian houses. Every house in villages has separate space for storing agricultural produce for draught and dairy animals. Roofs according to weather conditions isanother feature and arebuilt accordingly. The building material for the construction of houses is procured from local sources such as mud, thatch, bamboo, pieces of stones, wood or unburnt bricks. Cultural values play an important role in determining the direction of the main entrance. The internal layout plan and the architecture reflects the ethnic values of the community. Burnt bricks, cement and concrete are being used by rich people.
1. Compact settlements are normally found in highly productive alluvial plains.
1. Dispersed settlements are normally found in mountainous high lands ridges, forested areas, deserts and semi-deserts.
2. Main occupation is agriculture.
2. Main occupation is cattle-rearing, lumbering etc.
3. The houses are located adjacent to each other and form a compact block. They are comparatively small in size and provide less living space.
3. The houses are located at a distance from each other. They are comparatively bigger and provide more living space.
4. Fields in compact settlements are small.
4. Fields in dispersed settlements are large.
5. Streets are generally dirty due to lack of sanitation.
5. Dispersed settlements are normally neat and clean.