SCIENCE: 2010

Wednesday, July 28, 2010

PESTICIDES ON POLLUTION

The chemical substances used to kill the pests are known as pesticides. A pest is a living organism which destroys plants, foods or animals. Fungus, insects, rodents and various plants are the major pests. The pests reduce the crop yield significantly. The pests interface the life of many plants and animals. They also degrade the food quality of harvested food and grains. Herbicides, fungicides, insectides and rodenticides are common pesticides.
The pests are the organism which may damage the economic and physical well being of human. A variety of unwanted, and even harmful insects, weeds, micro-organism (bacteria, fungi), rodents nematodes and other organisms come under the categories of pests. Without pest control food production could decrease.
Pesticides are those substances which are used to kill, control or repel pests. Depending upon the type of target organism, the pesticides are classified as Fungicides (for fungi), Herbicides (for weeds), Insectides (for insects), Nematocides (for nematodes), Bactericides (for bacteria), Rodenticides (for rodents).
Chemical pesticides are toxic chemicals used for killing pests. On the basis of chemical composition, chemical pesticides are grouped into:
1. Organochlorides: The pesticides which contain organic chlorides are DDT, BHC, Aldrin ,Deildrin, chlordane, toxaphene, etc
2. Organophospates: The pesticides which contain organic phosphates like parathion, malathion,diazion, phenothane guthion,etc.
3. Carbamates: These pesticides are pyrethrins, baygon, temik, zectran, Carbaryl, Aldicarb, Carbofuran etc.
4.Pesticides of plant origin are pyrethroids from Chrysanthemum flower, nicotine from tobacco leaf and other like neem plant, Artemisia leaf, etc.
Insecticides and rodenticides are Zinc phosphide, Arsenic compounds, Thallium sulphate, etc. Nematicides are aliphatic halogen compounds, organophosphates and carbamates. Herbicides are phenoxy acids (2-4D and 2, 4, 5-T), Paraquat, Diquat and Triazoles. Fungicides are HCN, ethylene oxide, acetaldehyde and methyl bromide.
]
MODES OF ACTION:
Insecticides are either nervous or respiratory poisons. The Organochlorides are nervous poisons. They either inside the insects body either through the integument (cuticle) or spiracles. If the pesticides are in solution or absorbed form, they are taken orally and reach the nerve fibres where they inhibit NA+, K+ and Mg++ ATPase (Adenosine- triphosphate enzyme) activity in the nerve endings (synapsis) of insects. The poisons mostly affect the sensory or motor nerve fibres as well as motor cortex, thus results nerve paralysis and ultimately the insect pests die.
Some pesticides are respiratory poisons. They enter through spiracles. They cause nausea, vomiting and nervousness leading to death due to respiratory arrest.
Herbicides attack the photolysis of water (photosynthesis II) and evolution of O2 in the process, regulates growth and also affects the translocation of organic solutes.

Effects of pesticides:
a. Polluting the environment: Although pesticides save about 10% of the world food supply from the pests but these cause serious environmental and health threats to the various organisms. The organochlorides have longer life-time, therefore, persist and accumulate in environment. The pesticides are generally non-biodegradables, therefore, get incorporated into the food chain and ultimately deposited in the fatty tissue of different animals including man.
b. Kills board spectrum of organisms: The use of pesticides in the farms, gardens may also kill the useful organisms such as natural enemies (predators, parasites and pathogens) of the pests as well as earthworms and detrivores in the soil. Nitrogen fixing bacteria are also destroyed by the use of pesticides.

Tuesday, July 20, 2010

ACID RAIN

Short desdription about acid rain
Along with some chief air pollutants like aluminium, cadmium, lead, zinc and arsenic, oxides of sulphur and nitrogen lead to the formation of acid rain which causes acid rain or black rain.
Unpolluted or normal rain has a Ph of 5.6; the acidity is due to the presence of CO2 in air. But acid rain has Ph value of 4 to4.5 which is mainly due to SO2 (Oxides of sulphur) and oxides of nitrogen present in atmosphere. Problem of acid rain the world started only after the industrial revolution and after the extensive use of fossil fuels.
Acid precipitation or acid rain is a process of deposition of acid gases (SO2, nitrogen oxide) from the atmosphere on land in the form of precipitation or rain. It thus increases H-ion concentration of precipitation. During acid rain fall acidic gases mix with water vapors forming the respective acids.

CAUSES OF ACID RAIN:

The incomplete combustion of hydrocarbons is very harmful. It gives the effect of black snow covering the hill tops.
Oxides of sulphur and nitrogen (SO2, NO, NO2) are the main air pollutants produced mainly by the combustion of fossil fuels for power generation. In the industrial area the concentration of SO2 may reach to that extent that it damages the plants and some objects forming sulphuric acid. The sulphur

dioxide present in the atmosphere reacts with water and forms sulphuric acid which later falls as acid rain.
In the atmosphere, SO2, NO2 do not remain in gaseous state for a long time ratehr they react with moisture to form respective acids (H2SO4 and HNO3) which then dissolve in wter vapour in the atmosphere and fall on the earth as acid rain or may remain in atmosphere in the form of clouds or fogs. These acidic oxides may even undergo physical and chemical transformations to produce toxic agents. About 60-70% of acids in the atmosphere are derived by the oxidation and hydrolysis of SO2 and H2S and rest 30-40% from various nitrogen compounds and other compounds.

EFFECT &CONSEQUENCE OF ACID RAIN:

Effect on biochemical cycle: The major impact of acid rain is on the nitrogen and sulphur cycle (biogeochemical cycle). Nitrogen cycle in the atmosphere is more sensitive to acidification than the other major nutrient cycles. PH level of soil and water affects the survival of Rhizobium bacteria and free living bacteria. It also affects dentrification and volatilization of ammonia.
Effects on aquatic and terrestial flora and fauna: The acid rain raises the acidity of water of pond and lakes. This acidification kills many bacteria, cynobacteria, algae, zooplanktons, etc. thus disrupting the ecological balance. Acid rain is responsible for top-drying of the forest trees. Calcium and Potassium nutrients also leach away from soil by acids. Soil acidity affects the activity of soil organisms. There is a direct effect of acid on fish. The acid mobilizes metal like aluminium (Al) from the surrounding soil which then enters into lakes by run off. When combined with high acidity, Al becomes toxic to fishes. Other heavy metals like Zn, Cd, Pb, Mg, Cu, etc also become toxic if acidified.
Health hazards: Acid rain is responsible for health hazards like cough, irritation of throat, bronchitis, asthma, diarrhoea and other respiratory and cardiac problems.
Corrodes the metals: Buildings, monuments, statue, bridges, fences, railways, etc are corroded by the acid rains.
Drifting action: Sometimes oxides are produced at one place and carried elsewhere where precipitation occurs and acids are formed. Drifted SO2 and NO2 cause acid rain in some big cities.

Monday, July 19, 2010

Ozone layer

What is ozone layer?
Ozone layer discovered in 1913 by the French physicists Charles Fabry and Henri Buisson refers to “the Earth’s atmospheric layer having high concentration of ozone (O3) which absorbs 97-99% sun high frequency ultraviolet ray potentially harming the life on the earth.” It is situated in the lower portion of stratosphere at a height of13-20 km above the earth surface and thickness varying seasonally and geographically which contains 90% ozone of earth atmosphere.
ORIGIN OF OZONE
Ozone is an irritating, corrosive, colorless gas with a smell something like burning electrical wiring which can be easily produced by any high-voltage electrical arc (spark plugs, Van de Graaff generators, Tesla coils, arc welders). British meterologist G.M.B.Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could measure syratospheric ozone from the ground explored its properties Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The "Dobson unit", a convenient measure of the columnar density of ozone overhead, is named in his honour.
Formation of ozone layer
Ozone is created naturally in the stratosphere by the combining of atomic oxygen (O) with molecular oxygen (O2) which appears as layer known as Ozone layer. This process is activated by sunlight. Ozone is destroyed naturally by the absorption of ultraviolet radiation,
O + O>>> O2 ( in the presence of UV)
O2 + O>>> O3
O3 + UV >>> O2 + O
and by the collision of ozone with other atmospheric atoms and molecules.
O3 + O >>> 2O2

O3 + O3 >>> 3O2

Ozone layer depletion:
There are certain chemicals which are emitted and are inert in normal chemical and physical reactions but when they get accumulated in greater amounts at high altitudes cause great damage to the protective ozone envolve. These harmful ozone depleting chemicals (CFCs) come from industries of refrigerator, air conditioning, liquid fuel producing plants etc. Ozone layer depletion is the process of destruction or using up of ozone (O3) in the stratosphere by different pollutants making the ozone layer thinner.” Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total volume of ozone in Earth's stratosphere since the late 1970s and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period.
Causes of ozone layer depletion:
About 80% of ozone layer depletion is through Chloro Fluro Carbon (CFCs). The CFCs are highly stable and non-reactive substances. Different types of CFCs (CFCl3, CF2Cl2, CF3Cl) are extensively used as coolers, in air conditioners, refrigerators, cleaning solvents and aerosol propellants. They are also released by aircrafts, satellites, industries, nitrogen fertilizer plants and from combustion of fossil fuels. CFCs release their chlorine atoms to form chlorine monoxide, which reacts with ozone to form chlorine again. The free chlorine reacts continuously with ozone depleting the ozone layer.
CF2Cl2 ultra violet radiation CF2Cl + Cl
O3 + Cl O2 + OCl
OCl O + Cl
O3+O 2O2

It has been estimated that 1 molecule of CFCs can destroyed 1 lakh molecule of ozone.

global warming

What is Global warming ?

Global warming is a global phenomenon which can be defined as the huge dramatic changes, unpredictable unusual weather condition with increase in average temperature of the earth including surface air and oceans over time due primarily to human influences.”The temperature of the earth has been increased by 1degree Fahrenheit in the last 100 years” which was propounded during industrial revolution when emission of carbon dioxide and other greenhouse gases in the atmosphere increased. The main cause of global warming is human generated CO2. If this process is continued then the pattern of weather and temperature will not be simmilar as now.Philippines will be one of the most severely affected areas, with its archipelagic formation and strategic locations as time hits the pearl of the orient by climatic and environment condition in coming years.
Now a day’s global warming has become a greatest” environment issue” in the present context we can watch news update commercials, different talk show in different channel. There are different advertisement program advocacy campaigns about the global warming or greenhouse effect which we can experience now a day.
It was first suggested in 1863 that changes in the composition of the atmosphere due to pollution could lead to climate change. According to the first actual calculations of the effect of greenhouse warming made by Swedish scientist Svante Arrhenius in 1896 estimated that a doubling of carbon dioxide [in the atmosphere] would increase the global average temperature by 4 ° C to 6 ° C. By the middle of 1980 there was wide appreciation of global warming and its consequence to the planet. The United Nations Framework Convention on Climate Change (UNFCCC) developed The Kyoto Protocol as an international agreement to reduce greenhouse gas emissions worldwide. The Protocol was entered into force in February 2005, and signed by countries committed to reducing CO2 emissions and 5 other greenhouse gases. Up to now 141 countries have ratified the agreement but neither united state of America nor Australia has been participated. In 1988 United nation established The Intergovernmental Panel on Climate Change (IPCC), a scientific body for the purpose of evaluating the risk of climatic changes. During the 20th century, the sea levels rose by 17 cm (6.7 inches) and 18 to 59 cm (7 to 23 inches) during the 20th century and 21th century respectively. During the time period between 1920 and 2005 snow cover in the Northern Hemisphere declined by 4%. Eastern Arctic Archipelago decreased by 15% between 1969 and 2004.
The indication of global warming is rise in sea level, decrease snowfall, change in weather rise in temperature and so on.
The causes of global warming:
The cause of global warming is mainly of two types
1. Natural causes
2. man made causes
Natural causes includes exploding of sunspots, solar output variations or solar activities, volcanic eruptions and changes in the Earth's orbit. Considering these natural causes, many scientists are of the opinion that the Earth will have to experience global warming, even without the influence of industrial and human activities.
Man made causes includes excess amount of GHG ;burning of fossil fuels which released CO2, ozone and other gases which traps the solar energy.leading to increase in temperature. Power plants generate the highest GHG, while automobiles rank second. Another man-made cause of global warming is Deforestation; with a decline in the number of trees, the amount of carbon dioxide getting absorbed will be less.Due to human civilization excessive amount of CO2 is being deposited in the atmosphere through furnances of power plants, automobiles, factories, burning of charcoal or fossil fuels, etc. To some extent an increase in CO2 level in atmosphere increases the rate of photosynthesis but further increase pollute the air and water. There are some gases also which cause the global warming like CO, SO2, NO2, methane and CFCS.
Effect of global warming
Many consequences of global warming once controversial or thought to be unlikely are now being observed. Arctic shrinkage and Arctic methane release, alongside large reductions in the Greenland and West Antarctic Ice Sheets, accelerated global warming due to carbon cycle feedbacks in the terrestrial biosphere, and releases of terrestrial carbon from permafrost regions and methane from hydrates in coastal sediments are accelerating, leading to expectations of runaway climate change.
EFFECT & CONQUENCE OF GLOBAL WARMING
The effect of global warming on the environment and human life are numerous and varied, One of the main effects of global warming is the climatic change, which is evident from the melting of glaciers, rising of sea level, changing pattern of precipitation and drying of cloud forests. Eventually, the potential risks of global warming includes species extinction, ecological imbalance, disturbed food chain and web, coastal flooding, shrinkage of rainforest, increased drought, extreme weather condition, increased health hazard and change or decreasse in crop yield. The rise in temperature of the earth's atmosphere results increase in sea level due to melting of polar ice-caps, more hurricanes and cyclones nearby the oceans, evaporation of water form the farms, thus reduce the crop yield. The melting of glaciers causes rising in sea level causing flood. Sea level is expected to rise 18 to 59 cm (7.1 to 23.2 inches) by the end of the 21st century. High temperature also causes the concentration of ozone in the lower atmosphere. Ozone is a harmful pollutant and causes respiratory disease. Researchers have found that the risk of extinction for mountain birds due to global warming is greatest for species that occupy a narrow range of altitude. In fact, a species vertical distribution is a better predictor of extinction risk than the extent of temperature change they experience, the researchers report. A threat to animal and plant life even in biodiversity hot spots once thought is less likely to suffer from climate change due to global warming, according to a new study. With these potential threats, there have been many issues regarding the responsibilities that should be taken up against global warming.

Mitosis

Mitosis, process in which a cell’s nucleus replicates and divides in preparation for division of the cell. Mitosis results in two cells that are genetically identical, a necessary condition for the normal functioning of virtually all cells. Mitosis is vital for growth; for repair and replacement of damaged or worn out cells; and for asexual reproduction, or reproduction without eggs and sperm.

All multicellular animals, plants, fungi, and protists, which begin life as single cells, carry out mitosis to develop into complex organisms containing billions of cells. Mitosis continues in full-grown organisms as a means of maintaining the organism—replacing dying skin cells, for example, or repairing damaged muscle cells. In the cells of the adult human body, mitosis occurs about 25 million times per second. Multicellular organisms such as sea stars, sea anemones, fungi, and certain plants rely on mitosis for asexual reproduction at particular stages in their life cycles, and mitosis is the sole mode of reproduction for many single-celled organisms.

INTERPHASE

The life cycle of eukaryotic cells, or cells containing a nucleus, is a continuous process typically divided into three phases for ease of understanding: interphase, mitosis, and cytokinesis. Interphase includes three stages, referred to as G₁, S and G₂. In G₁, a newly formed cell synthesizes materials needed for cell growth. In the S stage, deoxyribonucleic acid (DNA), the genetic material of the cell, is replicated. At this stage, DNA consists of long, thin strands called chromatin. As each strand is replicated, it is linked to its duplicate by a structure known as a centromere. When the S stage is complete, the cell enters a brief stage known as G_2, when specialized enzymes correct any errors in the newly synthesized DNA, and proteins involved with the next phase, mitosis, are synthesized.

MITOSIS

Mitosis occurs in five steps: prophase, prometaphase, metaphase, anaphase, and telophase . In prophase the replicated, linked DNA strands slowly wrap around proteins that in turn coil and condense into two short, thick, rodlike structures called chromatids, attached by the centromere. Two structures called centrioles, both located on one side of the nucleus, separate and move toward opposite poles of the cell. As the centrioles move apart, they begin to radiate thin, hollow, proteins called microtubules. The microtubules arrange themselves in the shape of a football, or spindle, that spans the cell, with the widest part at the center of the cell and the narrower ends at opposite poles.

Prometaphase is marked by the disintegration of the nuclear membrane. As the spindle forms, the nuclear membrane breaks down into tiny sacs or vesicles that are dispersed in the cytoplasm. The spindle fibers attach to the chromatids near the centromeres, and tug and push the chromatids so that they line up in the equatorial plane of the cell halfway between the poles. Like two individuals standing back to back at the equator, one chromatid faces one pole of the cell, and its linked partner faces the opposite pole.

In metaphase, exactly half of the chromatids face one pole, and the other half face the other pole. This equilibrium position is called the metaphase plate.

Anaphase begins when the centromeres split, separating the identical chromatids into single chromosomes, which then move along the spindle fibers to opposite poles of the cell. At the end of anaphase, two identical groups of single chromosomes congregate at opposite poles of the cell.

In telophase, the final stage of mitosis, a new nuclear membrane forms around each new group of chromosomes. The spindle fibers break down and the newly formed chromosomes begin to unwind. If viewed under a light microscope, the chromosomes appear to fade away. They exist, however, in the form of chromatin, the extended, thin strands of DNA too fine to be seen except with electron microscopes. Mitosis accomplishes replication and division of the nucleus, but the cell has yet to divide.

CYTOKINESIS

The final phase of the cell cycle is known as cytokinesis. The timing of cytokinesis varies depending on the cell type. It can begin in anaphase and finish in telophase; or it can follow telophase. In cytokinesis, the cell’s cytoplasm separates in half, with each half containing one nucleus. Animals and plants accomplish cytokinesis in slightly different ways. In animals, the cell membrane pinches in, creating a cleavage furrow, until the mother cell is pinched in half. In plants, cellulose and other materials that make up the cell wall are transported to the midline of the cell and a new cell wall is constructed. The process of DNA replication, the precise alignment of the chromosomes in mitosis, and the successful separation of identical chromatids in anaphase results in two new cells that are genetically identical. The new cells enter interphase, and the cell cycle begins again.

CONTROL OF CELL DIVISION

In multicellular organisms, cell division must be carefully regulated to ensure that growth of the organism is coordinated, replacement of dead cells takes place in an orderly fashion, and repair of injured cells is initiated when needed. Cell division must also be halted when growth and repair are completed. Cell division is controlled by a variety of factors. One of the most important controls is carried out by molecules called growth factors.

Growth factors first come into play late in the G₁stage of interphase. Cells cannot pass from G₁to the S stage unless growth factors bind to the plasma membrane. The binding of growth factors triggers a cascade of biochemical activity that propels the cell into the S stage. If the cell does not enter the S stage, it exits from the cell cycle into the G₀ stage, a period of normal metabolic activity where other control mechanisms prevent it from dividing. Most of the cells in the adult human body remain in the G₀ stage throughout life. Certain cells, such as bone, muscle, or liver cells, can return to the cell cycle and divide if they are injured. Injuries release growth factors that override the controls over the non-dividing state.

Once a cell is committed to dividing, still other growth factors ensure that steps in mitosis are carried out accurately. At the end of the G₂ stage, mitotic (or maturation) promoting factor (MPF) triggers prophase, and enzymes condense DNA into chromosomes, break down the nuclear membrane, and form the spindle. A complex interplay of other growth factors carries the cell through the remaining steps of mitosis and cytokinesis.

Scientists have identified over 50 different growth factors. Some are very specific, and react only with certain cells. Nerve growth factor, for example, stimulates the growth of nerve cells during embryonic development, but has no effect on other cells. Others, such as epidermal growth factor, control division in a variety of cells. Understanding the production of growth factors and their precise mode of activity pose significant research challenges. As scientists learn more about the mechanisms for normal cell division, they gain insight into the causes of the unregulated cell growth that leads to cancer.

Mitosis

INTERPHASE

MITOSIS

In metaphase, exactly half of the chromatids face one pole, and the other half face the other pole. This equilibrium position is called the metaphase plate.

CYTOKINESIS

CONTROL OF CELL DIVISION

Meiosis

Meiosis, process of cell division in which the cell’s genetic information, contained in chromosomes, is mixed and divided into sex cells with half the normal number of chromosomes. The sex cells can later combine to form offspring with the full number of chromosomes. The random sorting of chromosomes during meiosis assures that each new sex cell, and therefore each new offspring, has a unique genetic inheritance.

Meiosis differs from normal cell division, or mitosis, in that it involves two consecutive cell divisions instead of one and the genetic material contained in chromosomes is not copied during the second meiotic division. Whereas mitosis produces identical daughter cells, meiosis randomly mixes the chromosomes, resulting in unique combinations of chromosomes in each daughter cell.

To illustrate the steps of meiosis, consider a corn plant cell with 10 pairs of chromosomes. The normal number of chromosomes, or diploid number, for corn is 20. In order for the diploid corn cell to reproduce, it must undergo meiosis to produce cells with half the normal number of chromosomes, called the haploid number. Each haploid corn cell contains only 10 chromosomes.

Prior to meiosis, the corn cell undergoes interphase, in which it synthesizes materials needed for cell growth and prepares for cell division. During this stage the cell’s genetic information, in the form of deoxyribonucleic acid (DNA), is replicated. Each of the two consecutive cell divisions consists of four stages: prophase, metaphase, anaphase, and telophase.

In prophase I each long DNA strand wraps around proteins that in turn coil and condense to form a chromosome. Since the DNA was copied during interphase, each chromosome condenses to form two identical chromatids, joined at a centromere. A corn cell has 20 chromosomes at this stage, each with two identical chromatids, making a total of 40 chromatids.

Chromosomes exist in pairs; one is inherited from the mother (maternal) and one from the father (paternal). When the chromosomes duplicate, two maternal and two paternal chromatids are produced. These two pairs of chromatids gather together in groups of four called tetrads. Each corn cell contains 10 tetrads. While grouped together in tetrads, sections of the chromatids from the maternal pair may randomly exchange, or cross over, with sections of the paternal chromatid pair. Called genetic recombination, this process is the first of two ways that meiosis mixes genetic information during sexual reproduction.

Also in prophase I, two structures called centrioles, both located on one side of the nucleus, separate and move toward opposite sides of the cell. As the centrioles move apart, they radiate thin hollow structures called spindle fibers. The membrane around the nucleus of the cell breaks down, marking the beginning of the next stage.

During metaphase I, the spindle fibers attach to the chromatids near the centrioles. The spindle fibers move the tetrads so that they line up in a plane halfway between two centrioles.

Anaphase I begins when the spindle fibers pull the tetrads apart, pulling the maternal and paternal chromosomes toward opposite sides of the cell. The first meiotic division concludes with telophase I, when the two new groups of chromosomes reach opposite sides of the cell. A nuclear membrane may form around the two new groups of chromosomes and a division of cell cytoplasm forms two new daughter cells.

Each daughter corn cell receives 10 chromosomes made up of a random mixture of maternal and paternal chromosomes. This second mixing of genetic information is called independent assortment. Genetic recombination and independent assortment make it possible for parents to have many offspring who are all different from each other.

In the second meiotic division the cell moves directly into prophase II, skipping the interphase replication of DNA. Each corn cell begins the second division with 10 chromosomes. Once again the centrioles radiate spindle fibers as they move to opposite sides of the cell. During metaphase II, the chromosomes line up along the plane in the center of the cell, and in anaphase II the pairs of chromatids are pulled apart, each moving toward opposite ends of the cell.

Telophase II completes meiosis. The spindle fibers disappear and a new nuclear membrane forms around each new group of chromosomes to form four haploid cells. The original diploid corn cell with 20 chromosomes has undergone meiosis to form four haploid daughter cells, each containing 10 chromatids. It is now possible for two haploid sex cells to join during fertilization to form one egg cell with the normal diploid number of chromatids. After fusion and DNA replication, two haploid corn cells will yield one diploid egg cell with 10 pairs of chromosomes.

In humans meiosis occurs only in the reproductive organs, the testes in males and the ovaries in females. In males, each of the meiotic divisions result in four equally sized haploid cells that mature into functional sperm cells. In females, the meiotic divisions are uneven, resulting in three tiny cells called polar bodies and one large egg that can be fertilized.

Atmospheric layer

The atmosphere of the is composed of different kinds of layer. it consists of 5 kinds of layer. It is thickest near the surface and thins out with height until it eventually merges with space. The types of ozone are as follows:

Troposphere:

it is the first atmospheric layer of the earth which contains around 80% of the mass of the total atmosphere. Although the heights of each layer can vary due to changing weather and climate conditions, the Troposphere extends up to 20 km above sea level. The content of water vapor and temperature rapidly decreases with altitude in the troposphere.The troposphere contains 99 % of the water vapor in the atmosphere whose concentration vary with latitude which absorbs solar energy and thermal radiation from the planet's surface and plays a major role in regulating air temperature. They are greatest above the tropics, where they may be as high as 3 %, and decrease toward the polar regions. The fraction of the gases which makes up the atmosphere are found in the troposphere as being a lower layer and as a result of pull of gravity.All weather phenomena occur within the troposphere, although turbulence may extend into the lower portion of the stratosphere. Troposphere means "region of mixing" and is so named because of vigorous convective air currents within the layer.The upper boundary of the layer is known as the tropopause,which ranges in height from 5 miles (8 km) near the poles up to 11 miles (18 km) above the equator. Its height also varies with the seasons; highest in the summer and lowest in the winter.

Stratosphere:

The Latin word, 'stratus' meaning 'spreading out' has given birth to the word, 'stratosphere. The stratosphere is the second major strata of air in the atmosphere which extends above the tropopause to an altitude of about 30 miles (50 km) above the planet's surface. It consists of ozone layer which is located between 15 to 35 km above the surface of the Earth. The ozone layer consists of large amount of ozone gas. it absorbs the sun ultraviolet radiation coming directly to the earth surface and saves from harmful effect. Ozone plays the major role in regulating the thermal regime of the stratosphere, as water vapor content within the layer is very low.The air temperature remains relatively constant up to an altitude of 15 miles (25 km)and then increases gradually to up to the stratopause. As air temperature in the stratosphere increases with altitude, it does not cause convection and has a stabilizing effect on atmospheric conditions in the region. Temperature increases with ozone concentration. Absorption of ultraviolet radiation by ozone molecules converts solar energy into kinetic energy , resulting in heating of the stratosphere. The ozone layer is at an altitude between 10-15 miles (15-25 km). Approximately 90 % of the ozone in the atmosphere resides in the stratosphere. Ozone concentration in the this region is about 10 parts per million by volume (ppmv) as compared to approximately 0.04 ppmv in the troposphere. Ozone absorbs the bulk of solar ultraviolet radiation in wavelengths from 290 nm - 320 nm (UV-B radiation). These wavelengths are harmful to life because they can be absorbed by the nucleic acid in cells. Increased penetration of ultraviolet radiation to the planet's surface would damage plant life and have harmful environmental consequences. Appreciably large amounts of solar ultraviolet radiation would result in a host of biological effects, such as a dramatic increase in cancers.

Mesophere:

The word mesosphere (from the Greek words mesos = middle and sphaira = ball) which is third layer of the earth just below Thermosphere and above Stratosphere layer, staring from the ground, from about 45-50 Km (28-32 miles) to 80-85 Km (50-53 miles) of height. The temperature of mesophere decreases with increase in height.The anomalous propagation of sound refers to the downward refraction of an oblique sound wave an explosion, the refraction occurring in the region of increasing temperature with height in the lower mesosphere. The temperature in this layer be as low as 200K( -73° C, -99° F), varying according to latitude and season. Millions of meteors burn up daily in the mesosphere, as a result of collisions with the gas particles contained there, leading to a high concentration of iron and metal atoms. The collisions almost always create enough heat to burn the falling objects long before they reach the ground. Thus the mesosphere protects the Earth from a barrage of would-be meteorites. mesosphere and stratosphere is regarded as the middle layer and from thermosphere it is regarded as the upper layer. the mesosphere and thermosphere is separated by the mesopause, at an altitude of about 80 km. which lies near the turbopause .

Thermosphere:

The word thermo refers to heat. It is the fourth layer of atmosphere as well as the biggest layer above the mesosphere and below exosphere. It extent from about 85-640 km above the earth . At these altitude, the residual atmospheric gases sort into strata according to molecular mass. Temperature in this layer increases with increase in altitude and can reach up to 1200C at a time due to absorption of highly energetic solar radiation by the small amount of residual oxygen present. However, even though the temperature is high one would not feel hot in the thermosphere as it is near the vacuum of deep space due to low density of gas atoms there.

Exosphere

Exosphere is the last layer of earth atmosphere. The exosphere (from the Greek word exo = out or outside) is the uppermost layer of the atmosphere. Its lower boundary at the edge of the thermosphere is estimated to be 500 km to 1,000 km above the Earth's surface, and its upper boundary at about 10,000 km. It is only from the exosphere that atmospheric gases can, to any appreciable extent, escape into outer space. The main gases in the exosphere are the lightest ones, mainly hydrogen and helium, with some atomic oxygen near the exobase (the lowest altitude of the exosphere). The few particles of gas here can reach 2,500° C (4,500° F) during the day. The atmosphere in this layer is sufficiently rarified for satellites to orbit the Earth, although they still receive some atmospheric drag. The exact altitude at which the exosphere ends and space begins is not well-defined, and attempting to attach a specific value to it is not particularly useful.

Fossil fuel

SHORT DESCRIPTION ABOUT FOSSIL FUEL

From the word fossil fuels, fossil fuel are the fuels formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust over millions of years. This biogenic theory was first introduced by Georg Agricola in 1556 and later by Mikhail Lomonosov in the 18th century. Fossil fuels are non renewable sources, simply put, the remains of prehistoric plants and animals that have, over time, been reduced to simple hydrocarbons either in liquid or solid forms after millions of years. Fossil fuels are responsible for providing energy needed worldwide in household and industrial purpose in this century. The utilization of fossil fuels has fueled industrial development and largely supplanted water driven mills an

d wood or peat burning for heat. They are used in transportation, in electricity production, in powering homes and industries, and in the production of plastics and other derivatives. They are produced as a result of the decomposition of the remains of different organic matters, buried for several millions of years under anaerobic conditions. Fossil fuels are the carbon rich remains of ancient vegetation and other organisms that have endured intense heat and pressure inside the earth over periods of millions of years. Severe heat and pressure over time convert these organic remains into fossil fuels, which collect in reservoirs that are sought after by oil focused companies. Some fossil fuel contains pure carbon whereas some contains carbon in the form of hydrocarbon. Though the use of fossil fuel increased during the 19th century, it was discovered by mankind thousands of years ago. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years. Fossil fuels range from volatile materials with low carbon: hydrogen ratios like methane, to liquid petroleum to non-volatile materials composed of almost pure carbon, like anthracite coal. According to the estimation made by the Energy Information Administration in 2007 primary sources of energy consisted of petroleum 36.0%, coal 27.4%, and natural gas 23.0%, amounting to an 86.4% share for fossil fuels in primary energy consumption in the world. Non-fossil sources in 2006 included hydroelectric 6.3%, nuclear 8.5%, and (geothermal, solar, tide, wind, wood, waste) amounting 0.9 percent. World energy consumption is growing about 2.3% per year.

TYPES OF FOSSIL FUELS:

Fossil fuels include the term petroleum, coal and natural gas and Orimulsion has been recently recognized as the fourth fossil fuel.Let study about this fossil fuels in short:

Petroleum:
Petroleum, or crude oil, is the most extensively used fossil fuel. Due to its value to mankind, it is also known as "black gold." The word petroleum comes from the Latin words "petro" (meaning rock) and "leum" (meaning oil).

Petroleum mainly is used to fuel jets and automobiles. It also is used to generate electricity, and its derivatives are utilized in the medicine and plastic industries. As demand for oil is still increasing, the average worldwide rate of oil field depletion is believed to be around 2.5 percent per year, according to Richard Heinberg, an eminent ecology writer. The widespread use of petroleum also has contributed to air and water pollution.

Coal:

Coal is the most abundant fossil fuel resource. It provides about one-quarter of the total energy the world uses, and 40 percent of the electricity generated worldwide is powered by coal. The steel industry also is greatly dependent upon this fossil fuel. Like other depleting sources of global energy, coal reserves are also on a steep decline. Moreover, coal is a greenhouse gas nightmare.

Natural gas: Natural gas is made out of methane, which is a simple chemical compound made up of carbon and hydrogen atoms. Natural gas is a fossil fuel by-product of petroleum. Once discarded as a waste, it is now in wide demand as one of the clean fossil fuels. Natural gas burns with clean flame. Natural gas forms mainly from the remains of plankton, or a type of small water organisms including algae.

Orimulson:
Orimulsion became the "fourth fossil fuel" in the mid-1980s. It is derived from the bitumen that occurs naturally in large reserves in the Orinoco oil belt in Venezuela. It is estimated that there are more than 1.2 trillion barrels of bitumen available in reserves, an amount greater than 50 percent of the world's estimated oil reserves.

Orimulsion has achieved growing recognition as an economically viable fuel for power generation. In countries such as Canada, Denmark, Japan, Italy, Lithuania and China, it is used as a commercial boiler fuel in power plants. Orimulsion is the cost-effective choice when compared to other fossil fuels used to generate electricity.

FORMATION OF FOSSIL FUEL:

The theory of formation of fossil fuels from fossilized organic was put forward by a Russian scientist, Mikhail Lomonosov, in the year 1757. According to this theory fossil fuels were formed by the anaerobic decomposition of remains of dead and decay of plant and animal life in millions of years ago, under high pressure and temperature. The organic matter, mixed with mud and got buried under heavy layers of sediment over geological time and as a result of high heat and pressure the organic molecules associated with these organisms forms a group of chemicals known as kerogens which are then transformed into hydrocarbons by the process of catagenesis . Fuels consists of wide range of organic, or hydrocarbon, compounds. The melting point, density, viscoity,boiling point,etc of fuel is characteristics by the specific mixture of hydrocarbons. Oil and natural gas are formed within sedimentary rocks that contain organic matter originating from small marine life such as phytoplankton, algae and bacteria. Most oil and natural gas around the world is found in layers that were deposited during the Cenozoic era about 50 million years ago. Coal forms within sedimentary rocks that contain organic matter originating from plant life such as trees and bushes. Most of the world’s coal is found in layers of sediment that were deposited during the Carboniferous period, when plant life was emerging and vast swamps covered most of the Earth’s land.

BURNING OF FOSSIL FUELS:

Burning of the fossil fuels is the major cause of climatic change which has become a major

issue. The burning of fossil fuel causes
Global warming: According to the research made by journal science half the carbon dioxide released into the atmosphere by the burning of fossil fuels is actually winding up the oceans, and that's threatening the health of the oceans and the diverse organisms living there. Burning of fossil fuels and global warming are interlinked with each other. The CO2 does not only affect the air quality but also oceans, too, are heavily impacted by the release of carbon dioxide. Due to cause of global warming the oceans temperature is rising. The rise in ocean temperature causes ocean to absorb less carbon dioxide and more carbon dioxide remains at the atmosphere which forms cycle of global warming.

Acid rain: Burning of fossil fuel releases nitrogen oxide, sulphur oxide in the atmosphere. Acid rain is a process of deposition of acid gases (SO2, nitrogen oxide) from the atmosphere on land in the form of precipitation or rain. Acid rain causes lakes, streams acidity causing threat to aquatic life.

Health hazard: Pollutants such as carbon monoxide, nitrogen oxide, sulfur oxide and hydrocarbons are generated from fossil fuel combustion. According to the Union of Concerned Scientists, carbon monoxide exposure can cause headaches and may aggravate stress in people with heart conditions. Exposure to nitrogen oxide can result in bronchitis, pneumonia and irritation in the lungs. Hydrocarbons emitted to from vehicular exhausts reacts with nitrogen oxides the presence of heat and sunlight to form ozone. Prolonged exposure to ozone can result in permanent lung damage.

Depletion of Natural Resources: Industrial manufacturing, transportation and agriculture uses fossil fuel as main source of energy. As fossil fuel is non-renewable source of energy the burning of fossil fuels causes a decline in the world's natural reserve.

ADVANTAGES AND DISADVANTAGES OF FOSSIL FUEL:
Man’s fuel needs, since the olden times, have been met through the use of fossil fuels. Since 1900, the world’s consumption of fossil fuels has nearly doubled every 20 years. Fossil fuels are responsible for providing energy needed worldwide in household and industrial purpose in this century.
Advantages of fossil fuel:
1. All fossil fuels originally derive their energy from the sun; thus all fossil fuels are essentially solar power.
2. Power plants construction which works on fossil fuels is easy.
3. Fossil fuels can be transported through pipe as fossil fuels are transported in gaseous or liquid form.
4. Petroleum is used in large quantity by fuels vehicle.
5. Fossil fuels are easier to extract and process, hence are cheaper than the non-conventional forms of energy.
6. Fossils fuels can generate huge amount electricity in a single
7. Widely and easily distributed all over the world.
8. Power stations that make use of fossil fuel can be constructed in almost any location. This is possible as long as large quantities of fuel can be easily brought to the power plants.
9. Comparatively inexpensive due to large reserves and easy accessibility.
Disadvantages of fossil fuel:
1. Leakage of some fossil fuels, such as natural gas, crude oil can lead to severe hazards. Hence, transportation of these fuels is very risky.
2. They are Nonrenewable (in the sense that once used it is no longer available as the current use of that word violates laws of thermodynamics)
3. Use of crude oil causes pollution and poses environmental hazards such as oil spills when oil tankers, for instance, experience leaks or drown deep under the sea. Crude oil contains toxic chemicals which cause air pollutants when combusted.
4. Prices for fossil fuels are rising, because certain lobbying factions do not want the USA to harvest its own vast oil-, coal-, and natural gas stores.
5. Power stations that utilize coal need large amounts of fuel. In other words, they not only need truckloads but train loads of coal on a regular basis to continue operating and generating electricity. This only means that coal-fired power plants should have reserves of coal in a large area near the plant’s location.

Sunday, July 18, 2010

Animal Behavior

INTRODUCTION
Animal Behavior, the way different kinds of animals behave, which has fascinated inquiring minds since at least the time of Plato and Aristotle. Particularly intriguing has been the ability of simple creatures to perform complicated tasks—weave a web, build a nest, sing a song, find a home, or capture food—at just the right time with little or no instruction. Such behavior can be viewed from two quite different perspectives, discussed below: Either animals learn everything they do (from “nurture”), or they know what to do instinctively (from “nature”). Neither extreme has proven to be correct.

NURTURE: THE BEHAVIORISTS
Until recently the dominant United States school in behavioral theory has been behaviorism, whose best-known figures are J. B. Watson and B. F. Skinner. Strict behaviorists hold that all behavior, even breathing and the circulation of blood, according to Watson, is learned; they believe that animals are, in effect, born as blank slates upon which chance and experience are to write their messages. Through conditioning, they believe, an animal’s behavior is formed. Behaviorists recognize two sorts of conditioning: classical and operant.
In the late 19th century the Russian physiologist Ivan Pavlov discovered classical conditioning while studying digestion. He found that dogs automatically salivate at the sight of food—an unconditioned response to an unconditioned stimulus, to use his terminology. If Pavlov always rang a bell when he offered food, the dogs began slowly to associate this irrelevant (conditioned) stimulus with the food. Eventually the sound of the bell alone could elicit salivation. Hence, the dogs had learned to associate a certain cue with food. Behaviorists see salivation as a simple reflex behavior, something like the knee-jerk reflex doctors trigger when they tap a patient’s knee with a hammer.
The other category, operant conditioning, works on the principle of punishment or reward. In operant conditioning a rat, for example, is taught to press a bar for food by first being rewarded for facing the correct end of the cage, next being rewarded only when it stands next to the bar, then only when it touches the bar with its body, and so on, until the behavior is shaped to suit the task. Behaviorists believe that this sort of trial-and-error learning, combined with the associative learning of Pavlov, can serve to link any number of reflexes and simple responses into complex chains that depend on whatever cues nature provides. To an extreme behaviorist, then, animals must learn all the behavioral patterns that they need to know.

Lava

INTRODUCTION
Lava, molten or partially molten rock that erupts at the earth’s surface. When lava comes to the surface, it is red-hot, reaching temperatures as high as 1200° C (2200° F). Some lava can be as thick and viscous as toothpaste, while other lava can be as thin and fluid as warm syrup and flow rapidly down the sides of a volcano. Molten rock that has not yet erupted is called magma. Once lava hardens it forms igneous rock. Volcanoes build up where lava erupts from a central vent. Flood basalt forms where lava erupts from huge fissures. The eruption of lava is the principal mechanism whereby new crust is produced (see Plate Tectonics). Since lava is generated at depth, its chemical and physical characteristics provide indirect information about the chemical composition and physical properties of the rocks 50 to 150 km (30 to 90 mi) below the surface.

TYPES OF LAVA
Most lava, on cooling, forms silicate rocks—rocks that contain silicon and oxygen. Lava is classified according to which silicate rocks it forms: basalt, rhyolite, or andesite. Basaltic lava is dark in color and rich in magnesium and iron, but poor in silicon. Rhyolitic lava is light colored and poor in magnesium and iron, but rich in silicon. Andesitic lava is intermediate in composition between basaltic and rhyolitic lava. While color is often sufficient to classify lava informally, formal identification requires chemical analysis in a laboratory. If silica (silicon dioxide) makes up more than 65 percent of the weight of the lava, then the lava is rhyolitic. If the silica content is between 65 percent and 50 percent by weight, then the lava is andesitic. If the silica content is less than 50 percent by weight, then the lava is basaltic.
Classification by Composition.
Many other physical properties, in addition to color, follow the distinctions between basaltic, andesitic, and rhyolitic lava. For example, basaltic lava has a low viscosity, meaning it is thin and runny. Basaltic lava flows easily and spreads out. Rhyolitic lava has a high viscosity and oozes slowly like toothpaste. The viscosity of andesitic lava is intermediate between basaltic and rhyolitic lava. Similarly, basaltic lava tends to erupt at higher temperatures, typically around 1000° to 1200° C (1800° to 2200° F), while rhyolitic lava tends to erupt at temperatures of 800° to 1000° C (1500° to 1800° F). Dissolved gases make up between 1 percent and 9 percent of magma. These gases come out of solution and form gas bubbles as the magma nears the surface. Rhyolitic lava tends to contain the most gas and basaltic lava tends to contain the least.

Lava Flows
When lava flows out of a central vent, it forms a volcano. Basaltic lava is thin and fluid so it quickly spreads out and forms gently sloping volcanoes with slopes of about 5°. The flattest slopes are nearest the top vent, where the lava is hottest and most fluid. These volcanoes are called because from a distance, they look like giant shields lying on the ground. Mauna Kea and Mauna Loa, on the island of Hawaii, are classic examples of shield volcanoes. Andesitic lava is more viscous and does not travel as far, so it forms steeper volcanoes. Rhyolitic lava is so viscous it does not flow away from the vent. Instead, it forms a cap or dome over the vent.
Sometimes, huge amounts of basaltic lava flow from long cracks or fissures in the earth. These basaltic lava flows, known as flood basalts, can cover more than 100,000 sq km (40,000 sq mi) to a depth of more than 100 m (300 ft). The Columbia River plateau in the states of Washington, Oregon, and Idaho was formed by repeated fissure eruptions. The accumulated basalt deposits are more than 4,000 m (13,000 ft) thick in places and cover more than 200,000 sq km (80,000 sq mi). The Parana of Brazil and Paraguay covers an area four times as large. Flood basalts occur on every continent. When basaltic lava cools, it shrinks. In thick sheets of basaltic lava, this shrinking can produce shrinkage cracks that often occur in a hexagonal pattern and create hexagonal columns of rock, a process known as columnar jointing. Two well-known examples of columnar jointing are the Giant’s Causeway on the coast of Northern Ireland and Devil’s Tower in northeastern Wyoming.
Basaltic lava flows and rocks are classified according to their texture. Pahoehoe flows have smooth, ropy-looking surfaces. They form when the semicooled, semihard surface of a lava flow is twisted and wrinkled by the flow of hot fluid lava beneath it. Fluid lava can drain away from beneath hardened pahoehoe surfaces to form empty lava tubes and lava caves. Other basaltic lava flows, known as aa flows, have the appearance of jagged rubble. Very fast-cooling lava can form volcanic glass, such as obsidian. Vesicular basalt, or scoria, is a solidified froth formed when bubbles of gas trapped in the basaltic lava rise to the surface and cool. Some gas-rich andesitic or rhyolitic lava produces rock, called pumice, that has so many gas bubbles that it will float in water.
Pillow lava is made up of interconnected pillow-shaped and pillow-sized blocks of basalt. It forms when lava erupts underwater. The surface of the lava solidifies rapidly on contact with the water, forming a pillow-shaped object. Pressure of erupting lava beneath the pillow causes the lava to break through the surface and flow out into the water, forming another pillow. Repetition of this process gives rise to piles of pillows. Pillow basalts cover much of the ocean floor.
Pyroclastic Eruptions
Pyroclasts are fragments of hot lava or rock shot into the air when gas-rich lava erupts. Gases easily dissolve in liquids under pressure and come out of solution when the pressure is released. Magma deep underground is under many tons of pressure from the overlying rock. As the magma rises, the pressure from the overlying rocks drops because less weight is pressing down on the magma. Just as the rapid release of bubbles can force a fountain of soda to be ejected from a shaken soda bottle, the rapid release of gas can propel the explosive release of lava.
Pyroclasts come in a wide range of sizes, shapes, and textures. Pieces smaller than peas are called ash. Cinders are pea sized to walnut sized, and anything larger are lava bombs.
Cinders and bombs tend to fall to earth fairly close to where they are ejected, but in very strong eruptions they can travel farther. Lava bombs as large as 100 tons have been found 10 km (6 mi) from the volcano that ejected them. When cinders and bombs accumulate around a volcanic vent, they form a cinder cone. Although the fragments of lava cool rapidly during their brief flight through the air, they are usually still hot and sticky when they land. The sticky cinders weld together to form a rock called tuff.
Ash, because it is so much smaller than cinders, can stay suspended in the air for hours or weeks and travel great distances. The ash from the 1980 eruption of Mount Saint Helens in the state of Washington circled the earth twice.
Many volcanoes have both lava eruptions and pyroclastic eruptions. The resulting volcano is composed of alternating layers of lava and pyroclastic material. These volcanoes are called composite volcanoes or stratovolcanoes. With slopes of 15° to 20°, they are steeper than the gently sloped shield volcanoes. Many stratovolcanoes, such as the picturesque Mount Fuji in Japan, have convex slopes that get steeper closer to the top.
Pyroclastic materials that accumulate on the steep upper slopes of stratovolcanoes often slide down the mountain in huge landslides. If the volcano is still erupting and the loose pyroclastic material is still hot, the resulting slide is called a pyroclastic flow or nuée ardente (French for “glowing cloud”). The flow contains trapped hot gases that suspend the ash and cinders, enabling the flow to travel at great speed. Such flows have temperatures of 800° C (1500° F) and often travel in excess of 150 km/h (100 mph). One such pyroclastic flow killed 30,000 people in the city of Saint-Pierre on the Caribbean island of Martinique in 1902. Only one person in the whole town survived. He was in a basement jail cell.
Loose accumulations of pyroclastic material on steep slopes pose a danger long after the eruption is over. Heavy rains or melting snows can turn the material into mud and set off a catastrophic mudflow called a lahar. In 1985 a small pyroclastic eruption on Nevado del Ruiz, a volcano in Colombia, melted snowfields near the summit. The melted snow, mixed with new and old pyroclastic material, rushed down the mountain as a wall of mud 40 m (140 ft) tall. One hour later, it smashed into the town of Armero 55 km (35 mi) away, killing 23,000 people.
Explosive Eruptions
Rhyolitic lava, because it is so viscous, and because it contains so much gas, is prone to cataclysmic eruption. The small amount of lava that does emerge from the vent is too thick to spread. Instead it forms a dome that often caps the vent and prevents the further release of lava or gas. Gas and pressure can build up inside the volcano until the mountaintop blows apart. Such an eruption occurred on Mount Saint Helens in 1980, blowing off the top 400 m (1,300 ft) of the mountain.
Other catastrophic eruptions, called phreatic explosions, occur when rising magma reaches underground water. The water rapidly turns to steam which powers the explosion. One of the most destructive phreatic explosions of recorded history was the 1883 explosion of Krakatau, in the strait between the Indonesian islands of Java and Sumatra. It destroyed most of the island of Krakatau. The island was uninhabited, so no one died in the actual explosion. However, the explosion caused tsunamis (giant ocean waves) that reached an estimated height of 30 m (100 ft) and hit the nearby islands of Sumatra and Java, destroying 295 coastal towns and killing about 34,000 people. The noise from the explosion was heard nearly 2,000 km (1,200 mi) away in Australia.

Hurricane

INTRODUCTION
Hurricane, name given to violent storms that originate over the tropical or subtropical waters of the Atlantic Ocean, Caribbean Sea, Gulf of Mexico, or North Pacific Ocean east of the International Date Line. Such storms over the North Pacific west of the International Date Line are called typhoons; those elsewhere are known as tropical cyclones, which is the general name for all such storms including hurricanes and typhoons. These storms can cause great damage to property and loss of human life due to high winds, flooding, and large waves crashing against shorelines. The deadliest natural disaster in United States history was caused by a hurricane that struck Galveston, Texas, in 1900. The costliest and most destructive natural disaster in U.S. history was caused by the storm surge and winds created by Hurricane Katrina along the Louisiana, Mississippi, and Alabama coasts. The hurricane’s storm surge burst some levees protecting New Orleans, flooding the city and forcing a complete evacuation. See also Tropical Storm; Cyclone.
HOW HURRICANES FORM
Tropical cyclones form and grow over warm ocean water, drawing their energy from latent heat. Latent heat is the energy released when water vapor in rising hot, humid air condenses into clouds and rain. As warmed air rises, more air flows into the area where the air is rising, creating wind. The Earth’s rotation causes the wind to follow a curved path over the ocean (the Coriolis effect), which helps give tropical cyclones their circular appearance.
Hurricanes and tropical cyclones form, maintain their strength, and grow only when they are over ocean water that is approximately 27°C (80°F). Such warmth causes large amounts of water to evaporate, making the air very humid. This warm water requirement accounts for the existence of tropical cyclone seasons, which occur generally during a hemisphere’s summer and autumn. Because water is slow to warm up and cool down, oceans do not become warm enough for tropical cyclones to occur in the spring.
Oceans can become warm enough in the summer for hurricanes to develop, and the oceans also retain summer heat through the fall. As a result, the hurricane season in the Atlantic Basin, which comprises the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico, runs from June 1 through November 30. At least 25 out-of-season storms, however, have occurred from 1887 through 2003, and 9 of these strengthened into hurricanes for at least a few hours.
Hurricanes weaken and die out when cut off from warm, humid air as they move over cooler water or land but can remain dangerous as they weaken. Hurricanes and other tropical cyclones begin as disorganized clusters of showers and thunderstorms. When one of these clusters becomes organized with its winds making a complete circle around a center, it is called a tropical depression.
When a depression’s sustained winds reach 63 km/h (39 mph) or more, it becomes a tropical storm and is given a name. By definition, a tropical storm becomes a hurricane when winds reach 119 km/h (74 mph) or more.
For a tropical depression to grow into a hurricane, winds from just above the surface of the ocean to more than 12,000 m (40,000 ft) in altitude must be blowing from roughly the same direction and at the same speed. Winds that blow in opposite directions create wind shear—different wind speeds or direction at upper and lower altitudes—that can prevent a storm from growing.
CHARACTERISTICS OF HURRICANES
A hurricane consists of bands of thunderstorms that spiral toward the low-pressure center, or “eye” of the storm. Winds also spiral in toward the center, speeding up as they approach the eye. Large thunderstorms create an “eye wall” around the center where winds are the strongest. Winds in the eye itself are nearly calm, and the sky is often clear. Air pressures in the eye at the surface range from around 982 hectopascals (29 inches of mercury) in a weak hurricane to lower than 914 hectopascals (27 inches of mercury) in the strongest storms. (Hectopascals are the metric unit of air pressure and are the same as millibars, a term used by many weather forecasters in the United States. Hectopascals is the preferred term in scientific journals and is being used more often in public forecasts in nations that use the metric system.)
In a large, strong storm, hurricane-force winds may be felt over an area with a diameter of more than 100 km (60 m). The diameter of the area affected by gale winds and torrential rain can extend another 200 km (120 m) or more outward from the eye of the storm. The diameter of the eye may be less than 16 km (10 m) in a strong hurricane to more than 48 km (30 m) in a weak storm. The smaller the diameter of the eye, the stronger the hurricane winds will be. A hurricane’s strength is rated from Category 1, which has winds of at least 119 km/h (74 mph), to Category 5, which has winds of more than 249 km/h (155 mph). These categories, known as the Saffir-Simpson hurricane scale, were developed in the 1970s.
In the tropics, hurricanes move generally east to west, steered by global-scale winds. Hurricanes, typhoons, and cyclones usually “recurve” in the direction of either the South Pole in the Southern Hemisphere or the North Pole in the Northern Hemisphere. Eventually the storms move toward the east in the middle latitudes, but not all storms recurve. Hurricanes travel at varying rates. In the lower latitudes the rate usually ranges from 8 to 32 km/h (5 to 20 mph), and in the higher latitudes it may increase to as much as 80 km/h (50 mph).
In addition to generating large waves that travel out in all directions, hurricane winds pile up water. This piling up of water is known as a storm surge, and it can raise the sea level more than 6 m (20 ft) when the storm hits land.
HURRICANE DEVASTATION
The deadliest natural disaster in United States history was the 1900 Galveston, Texas, hurricane, which killed an estimated 8,000 people. The storm surge accounted for most of the deaths. The costliest natural disaster in U.S. history was caused by the storm surge created by Hurricane Katrina in 2005. The hurricane’s storm surge burst levees protecting New Orleans, Louisiana, flooding the city and forcing a complete evacuation. The worst tropical storm disaster since the 20th century began was a 1970 cyclone that struck East Pakistan (now Bangladesh) when a storm surge killed an estimated 300,000 people.
Since the last third of the 20th century, floods and landslides from heavy rain were the leading cause of hurricane and tropical storm deaths. In October 1998 Hurricane Mitch’s torrential rain caused floods and landslides that killed more than 9,000 people with another 9,000 missing and presumed dead in Central America, according to the U.S. National Hurricane Center. Although the hurricane death toll steadily declined in the United States during the 20th century and at the start of the 21st century, the costs of damage soared as coastal populations grew and the value of property outstripped population growth. Before Hurricane Katrina, the costliest U.S. natural disaster was Hurricane Andrew, which hit the Miami, Florida, metropolitan area in 1992, causing $26.5 billion in damages, including both insured and uninsured losses. Some estimates of Hurricane Katrina’s damages ran as high as $125 billion. In addition, federal relief efforts were expected to cost tens of billions of dollars.
HOW HURRICANES ARE DETECTED AND MONITORED
Since 1943 U.S. military and civilian aircraft have been flying into hurricanes to measure wind velocities and directions, the location and size of the eye, air pressures, and temperatures in different parts of the storm. A coordinated system of tracking hurricanes was developed in the mid-1950s, and steady improvements have been made over the years. In addition to reports from aircraft, geosynchronous weather satellites (since 1966) and ocean buoys that automatically record and transmit data such as wave heights and wind speeds furnish information to the National Hurricane Center in Miami, Florida.
The National Hurricane Center is part of the U.S. National Weather Service and is the main forecast center for storms that originate over the Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico, and the northeastern Pacific Ocean west to longitude 140° west. The Hawaiian Hurricane Center at the Honolulu National Weather Service office handles storms from longitude 140° west to longitude 180° west. Hurricanes rarely hit Hawaii. The centers of only two hurricanes moved ashore there from 1950 through 2003, although three others came close enough to cause wind or wave damage. Hurricane Iniki in September 1992 was by far the worst, killing six people and doing an estimated $2.3 billion in damages.
In the past, hurricanes often hit land without being detected beforehand. Today, weather satellites ensure that this never happens. As a storm begins to threaten land, forecasters call on military or civilian aircraft for detailed storm data that satellites cannot supply. When a storm comes within about 160 km (100 m) of land, weather radar images also become available. Forecasters use several computer models, which combine observational data from all around the world and mathematical equations, to make forecasts. But since forecasts from different models often disagree, they are merely tools to help humans make predictions.
HOW HURRICANES ARE NAMED
The National Hurricane Center began officially naming tropical storms and hurricanes in 1950, although some forecasters had been informally naming storms since the 19th century. The World Meteorological Organization’s (WMO) Western Hemisphere Hurricane Committee selects hurricane names, using alternating men’s and women’s names in English, Spanish, and French in alphabetical order. Names of deadly storms or those that cause great damage are retired. Otherwise, names remain on six rotating, yearly lists, with each list being used again six years after its last use. WMO committees also select tropical cyclone names used elsewhere in the world.
HURRICANE PREPAREDNESS
The National Hurricane Center issues a hurricane watch for areas where a hurricane could hit in about 36 hours or less. The center issues a hurricane warning when hurricane-force winds of 119 km/h (74 mph) are expected in 24 hours or less. The Hurricane Center issues watches and warnings for the United States and works closely with the weather services of other nations, which issue their own watches and warnings.
Residents of areas where hurricanes can strike, which includes the entire U.S. Atlantic and Gulf of Mexico coasts from Maine to the Mexican border, should begin preparing before the hurricane season starts. They need to learn whether they live in an area that storm surge could flood, and if so, need to decide where to go if ordered to evacuate. All homeowners should ensure they have covers to fit all windows and doors that are not impact resistant. A survival kit with a two-week supply of prescription medications, nonperishable food, and water should be prepared.
When a hurricane watch is issued, those in the affected area should make sure window covers and emergency kits are ready, and install the window covers that are most difficult to put in place. They should also fill vehicles with fuel and withdraw emergency cash before power failures close service stations and automated teller machines (ATMs). Finally, they should follow storm reports and listen for directions from local emergency management officials.
When a hurricane warning is issued, residents should quickly finish installing window and door protection panels. Those who are evacuating should be sure to take their emergency kits and important papers and notify friends and family where they are going. Evacuees should leave as soon as possible after turning off the main circuit breaker and the outside gas and water shut-off valves for their houses.
During a hurricane, everyone should stay indoors and away from doors and windows, even if they have protective covers. If debris begins striking the house, those inside should seek refuge in an interior bathroom, closet, or under a stairwell. People should not go outdoors when the wind dies down because the storm’s eye could be passing over and winds could quickly begin blowing again at full speed. Wait until radio announcements say that the hurricane has passed before going outside.
The danger is not over when a hurricane passes. In recent years in the United States, poststorm accidents have killed as many or more people than hurricane wind, storm surge, or flooding. Poststorm dangers include accidents at intersections without working traffic lights, downed power lines, fires caused by candles, falls from roofs, and injuries to those unskilled in using equipment such as chain saws.
HURRICANES, GLOBAL WARMING, AND CYCLES
Some evidence is emerging that hurricanes could be growing slightly stronger, possibly as a result of global warming. But most scientists who study hurricanes say that growing coastal populations and higher coastal property values, not global warming, account for the increasing costliness and loss of life caused by hurricanes.
Long-term records do not provide enough information to conclude whether the global total of tropical cyclones increased during the 20th century. But detailed records of Atlantic, Caribbean, and Gulf of Mexico hurricanes show that the numbers of storms increase and decrease in cycles. The cycles are most noticeable for “major” hurricanes in Categories 3, 4, and 5 with wind speeds faster than 177 km/h (110 mph). The years 1944 through 1969 were active with an average of 2.7 major hurricanes a year. A quiet period, with an average of 1.5 major hurricanes a year, began in 1970 and lasted through 1994. Another active period that began in 1995 saw 32 major hurricanes through the 2003 season, an average of 3.55 per year.
The 2005 hurricane season set records for the greatest number of tropical storms (26), the most hurricanes (14), and the most Category 5 hurricanes (3). Seven major hurricanes—that is, Category 3 or higher—occurred in 2005. For the first time since the National Hurricane Center began naming storms, letters from the Greek alphabet were used after the center exhausted its original list of 21 names. The last storm in the 2005 season, Tropical Storm Epsilon, formed just before the official end of the hurricane season on November 30 and was upgraded to a hurricane on December 2. Another notable hurricane event occurred in 2004 when Hurricane Catarina became the first recorded South Atlantic hurricane in history. The National Oceanic and Atmospheric Administration (NOAA), which oversees the National Hurricane Center, attributed the active 2005 hurricane season to a multidecadal cycle in which warmer-than-average sea-surface temperatures and low wind shear enhanced hurricane activity.
Many hurricane researchers think the cycles are related to changes in Atlantic Ocean temperatures that last decades. From the late 19th century through the 1980s about one-third of the major hurricanes that formed in the Atlantic hit the United States, which means around ten such hurricanes could have been expected to hit from 1995 through 2003. Yet for reasons atmospheric scientists do not understand, only three such hurricanes hit the United States from 1995 through 2003. That pattern changed in 2004, when three major hurricanes hit the United States. In 2005 four of the season’s seven major hurricanes—Dennis, Katrina, Rita, and Wilma—hit the United States.
Researchers who study hurricanes and climate say that the computer models used to predict global climate changes do not look at weather in the detail needed to forecast whether a warmer world would increase the number or strength of hurricanes. On the other hand, scientists have no reason to expect fewer or weaker hurricanes to form than has occurred in the past. They also have no reason to think that many storms will miss the United States as they did in the 1990s and early 2000s. This means that no matter how global climate change affects hurricanes, increased population along the coasts places more people and property in harm’s way.