My Science School

 

 

Can sand dunes move?

Sand dunes can move slowly, causing deserts to spread over more fertile land. Continuous winds blow the sand to form crescent-shaped dunes. Sand from the top of the dune is blown farther away, and it gradually collects to form a new dune.

Picture credit: google

 

 

 

 

How can people live in extreme climates?

Over millions of years, the human body has altered to suit the climate of the regions we inhabit. In general the hotter the region, the darker the skin of its inhabitants. Also, many people from Asia have a fold of skin in their eyelid to protect them from strong sunlight. People living in hot climates do not need a fat layer to keep warm, so they are usually slim. The Inuits of the Arctic, however, are mostly shorter and stockier to help conserve heat. 

Picture credit: google

 

 

 

 

 

Which are the wettest places on the Earth?

Tropical rainforests are among the wettest places in the world. In general, most rainfall occurs on the sides of hills and mountains. The wettest place of all is Cherrapunji, in Assam, India. It faces the full force of the monsoon winds that sweep in from the Indian Ocean in July. Their warm, damp air rises in the Himalayan foothills, causing torrential rain. Mount Wai-‘ale-‘ale in Hawaii has the wet days each year. It rains on 350 days on average, and the annual rainfall is the highest recorded anywhere.

Picture credit: google

 

What is permafrost?

Permafrost is a layer of ice and frozen soil that never thaws. It lies beneath nearly one-quarter of the Earth’s surface, throughout Alaska, Canada and Russia. Sometimes the soil in these places is frozen to a depth of up to 1,500 m. The surface layers may melt enough in summer for plants to grow, but the soil beneath is permanently frozen.

Picture credit: google

 

 

 

 

 

Are there places where nothing can live?

Hot volcanic lava is probably the only place on the Earth’s surface where there is no life at all. Living things have evolved to survive in the harshest environments. Tiny bacteria can be found everywhere on the Earth, even buried in thick ice at the poles or in the very deepest parts of the ocean. 

Picture credit: google

 

 

Where are the most extreme temperatures found?

Libya and the Antarctic have recorded the most extreme temperatures. The hottest shade temperature was in Libya in 1922, when the temperature in the Sahara desert reached 58 °C. Temperatures nearly as high as this were recorded in Death Valley in the USA in 1913. The coldest ever recorded temperature was in Antarctica in 1983, when Russian scientists measured a temperature low of - 89.2°C.

Picture credit: google

 

 

 

 

 

The desert process

Deserts were once green and fertile areas, until a climate change altered them permanently. Just a small reduction in rainfall causes plants to die off. Without plant roots to bind and nourish the soil, the land gradually becomes barren. Soon the animals move away, and only desert remains. Very few deserts are completely barren, and plants and animals have evolved to live in the driest conditions, conserving their body water so they do not need to rely on rainfall.

Picture credit: google

 

 

Are there cold deserts?

Antarctica is the biggest cold desert in the world. All of its water is locked up in ice and snow, so nothing can grow. The Gobi desert in Mongolia and western China is also very cold in the winter, when temperatures drop below freezing. However, it is hot in the summer.

Picture credit: google

 

 

 

 

What is a mirage?

Mirages form in hot deserts, where the air is so hot it bends and distorts light rays. The shimmering images that a mirage produces have often tricked travellers in deserts. People think that they can see a town or oasis on the horizon, but in reality there is none. 

Picture credit: google

Where is the world’s driest place?

The world’s driest place is the Atacama Desert in Chile. It is a narrow strip between the Andes and the Pacific, where the first rain for 400 years fell in 1971. Like other hot deserts, the Atacama lies in a region where air pressure is constantly high, with little air movement or cloud. Rainfall is very low in other deserts. Near Cairo, Egypt, annual rainfall averages about 28 mm each year, while in Bahrain, on the edge of the Arabian Desert, there is as much as 81 mm of rainfall. The rain may come in a single heavy storm, and some years there is no rainfall at all. 

Picture credit: google

 

 

 

How much of the world is covered by desert?

About one-third of the world’s land surface is covered by desert. Desserts are found wherever there is too little water to allow much plant life to grow. This lack of vegetation leaves large areas of soil exposed. The largest desert in the world is the Sahara in Africa. It has an area of about 9 million sq km. 

Picture credit: google

What are ‘highs’ and ‘lows’?

Air pressure varies across different parts of the Earth’s surface, and this difference causes winds. Air moves from an area of high pressure, or an anticyclone, to an area of low pressure, or a depression. Depressions are usually associated with worsening weather conditions and rain. These changes in air pressure can be measured by an instrument called a barometer. In a mercury barometer the air pressure pushes down on the mercury, which is forced up the barometer to give an accurate reading. 

Picture credit: google

 

 

 

Why do we get thunder and lightning?

Lightning is a huge spark of electricity that is produced in a cloud. Thunder is the loud noise made by the lightning as it rips through the air.

During thunderstorms, enormous electrical charges build up inside a cloud. Eventually the charges seem to flow down to the ground when lightning strikes. In fact, the electrical charges flow up from the ground and down from the cloud at the same time. The tremendous heat generated by the lightning causes the explosive noise of thunder. Lightning frequently strikes in the same place repeatedly, and along the same path through the air. It can also strike between two clouds.

Picture credit: google

 

Thunderbolts

A lightning strike discharges about 100 million volts of electricity, and heats the air in its path to more than 33,000°C.The lightning strike travels at 299,792 km per second, which is almost the speed of light. A strike between a cloud and the ground may be 14 km long, and a strike between clouds can be over 140 km long.

Ball lightning is a small fiery ball which occasionally appears during thunderstorms. There is no accepted scientific explanation for it. 

Picture credit: google

 

 

How can forecasters predict the weather?

Meteorologists use a wide range of instruments and techniques to help them track changes in the weather and to predict future weather conditions. Weather forecasters have used simple instruments such as thermometers, rain gauges, barometers and wind gauges for many years, but the advent of satellite photography has transformed weather forecasting. Weather satellites can track the movements of clouds, and show the positions of high and low pressure areas and weather fronts. Radar measures the size, speed and direction of storms, so accurate warnings of severe weather can be given. With the use of computers, increasingly accurate forecasting is now possible.

Picture credit: google

What causes mist and fog?

Tiny water droplets condensing from moist air cause both mist and fog. They can occur at ground level. The air can only hold a limited amount of water vapour. If the air suddenly cools, its capacity to hold water is reduced, resulting in mist or fog. When fog occurs visibility can be affected. Mist is less dense. It commonly occurs on calm, clear nights when heat rises, forming a thin layer of mist close to the ground. 

Picture credit: google

 

 

 

How are hailstones formed?

Hail is produced when particles of ice bounce up and down inside a cloud. In cold temperatures, water droplets inside a cloud will freeze into small pellets of ice. As these begin to fall, they may meet warm air rising, which carries them back up into the cloud. There they cool once more, and the process is repeated. As more and more water freezes onto their surface, the ice pellets gradually grow in size. Eventually they become so heavy that they fall to the ground as hailstones. Some hailstones are as big as a clenched fist and can do serious damage to buildings and livestock. 

Picture credit: google

 

 

 

 

 

What is a monsoon?

A monsoon is a season of very heavy rain falling in tropical countries. They are most common near the Equator, when seasonal winds spring up, carrying moist air in from the sea. Important crops such as rice depend entirely on the monsoon to provide the right growing conditions. If the monsoon rains fail, famine commonly follows.

 

Picture credit: google

 

 

 

 

 

 

What is smog?

Smog is a serious form of air pollution that can cause breathing problems. The term smog was first used to describe a type of air pollution in London, when smoke from coal fires combined with fog to produce dense yellow clouds that sometimes persisted for days. The term now describes the hazy fog that is caused mainly by vehicle exhausts and smoke from factories. It builds up when there is little air movement, and can happen when a layer of warm air traps cooler air near the ground, preventing the smog from being blown away. Cities in bowls or sheltered valleys are particularly liable to this condition. 

Picture credit: google

 

 

 

 

 

Who studies the weather?

People called meteorologists study the world’s weather and the changes in the atmosphere that produce our weather. They observe and analyze the weather, and try to understand the processes that lead to changing weather conditions. The study of weather is known as meteorology. 

Picture credit: google

 

 

 

Why does rain fall?

Water evaporates from the Earth’s surface, condenses into water droplets and falls back down to the ground as rain. Heat from the Sun causes water to evaporate from the land, from rivers and lakes and from the sea. The water vapour rises with the warm air, and eventually reaches high altitudes where it cools and condenses into water droplets, forming clouds. The droplets grow larger until they are too heavy to stay in the cloud and they fall as rain. Rain usually falls from the largest and darkest clouds, which contain the most water vapour. 

Picture credit: google