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WEATHER is THE physical condition or state of the atmosphere at any given time. It is what is happening in the atmosphere at any time or over any short period of time. If there were no atmosphere, there would be no weather. The principal elements of weather are temperature, pressure, winds, moisture, and precipitation. Thus, weather of any place is the sum total of its temperature, pressure, winds, moisture, and precipitation conditions for a short period of a day or a week. Temperature expresses intensity of heat. Unequal distribution of temperature over the Earth's surface causes differences in atmospheric pressure, which causes winds. Moisture is present in the atmosphere as water vapor, often condensed into clouds. It may be precipitated in the form of rain, hail, sleet, or snow. The capacity of air to gather and retain water vapor is largely dependent on its temperature. The higher the temperature, the greater the capacity of air to hold moisture. On cooling, the air is not able to retain all the moisture it gathers while warm. This leads to condensation and precipitation.

Weather is not synonymous with climate. Weather changes from day to day, whereas climate is something more stable, commonly defined as the average weather. Climate is the composite weather conditions over a considerable period of time. Weather conditions can change suddenly. Today may be warm and sunny, tomorrow may be cool and cloudy. Weather conditions include clouds, rain, snow, sleet, hail, fog, mist, sunshine, wind, temperature, and thunderstorms. Weather is driven by the heat stored in the Earth's atmosphere, which comes from solar energy. When heat is moved around the Earth's surface and in the atmosphere because of differences in temperature between places, this makes winds. Winds form part of larger weather systems, the most powerful of which is the hurricane. Other weather features like the thunderstorm also develop because of the movement of heat in the atmosphere. Some thunderstorms result in tornadoes. The Earth's water cycle plays an important role in the development of many weather features such as dew, fog, clouds, and rain.

Weather can be described using terms such as wet or fine, warm or cold, windy or calm. The science of studying weather is called meteorology. Meteorologists measure temperature, rainfall, air pressure, humidity, sunshine, and cloudiness, and they make predictions and forecasts about what the weather will do in the future. This is important for giving people advance notice of severe weather such as floods and hurricanes. Temperature is measured with a mercury thermometer in degrees Celsius. Temperature is the hotness or coldness of an object. Rainfall

Thunderclouds contain a great amount of energy, and the currents of air are strong enough to split apart the raindrops that are forming. This builds up an electric charge, released as lightning. The sound of thunder is the effect of the lightning strike on the air.

is usually measured by collecting what falls in rain gauges and is expressed as a depth of water that has fallen, in millimeters. Wind can be observed with a weather vane, but to measure its speed, more technical equipment is needed. Alternatively, the Beaufort scale can be used to make a judgment of the strength of the wind by observing how it affects objects outdoors, such as trees. The relative humidity and dew point temperature of the air can be determined by making measurements with a hygrometer and reading a table of numbers.

The purpose of a weather map is to give a graphical or pictorial image of weather to a meteorologist. As a forecasting tool, weather maps allow a meteorologist to see what is happening in the atmosphere at virtually any location on earth. Complex three-dimensional models of weather systems can be made by collecting weather data at multiple levels in the atmosphere. Computers then compile that information to produce the pictures that weather scientists analyze.

In the early days of meteorology, these pictures were all drawn by hand.

WEATHER PREDICTION AND FORECASTING

Weather affects virtually everyone daily. Human beings live largely at the mercy of the weather. It influences our daily lives and choices and has an enormous effect on corporate revenues and earnings. Weather can be predicted to some degree by observing the state of the sky and the wind. Weather is measured, and forecasts are usually released and used to make important decisions about travels, timing, and so on. Weather forecasts can save lives, reduce damages to property, reduce damages to crops, and tell the public and the global community about expected weather conditions. A forecast is basically predicting how the present state of the atmosphere will change with time. This involves plotting weather information on special charts. Weather radar and satellites are now also used to help pre dict the weather. Weather forecasters measure the weather so they can forecast it. Temperature, rainfall, wind, clouds, sunshine, and air pressure are measured all over the country, and the information is plotted on special charts. These weather charts have been used by forecasters for many years to predict what the weather will do over the next few days. Weather presenters often show simplified charts on television. Sophisticated equipment is used to help forecast the weather: weather radar can help to show where it is raining over a country, whereas satellites are used to reveal cloud cover and the development of large weather systems. Procedures for collecting and taking the observations are determined by the World Meteorological Organization.

There are a variety of forecasting techniques. The easiest of the techniques is called persistence. In this technique, tomorrow's weather is said to be same as today's weather. Local factors that should be considered when forecasting include clouds and snow. Clouds during the day will decrease the maximum temperature expected. Without the clouds, higher maximum temperatures would be obtained. With snow, the surface stays colder during the day, as less short-wave radiation is absorbed. During the night, radiational cooling effectively cools the surface. If there is some wind, the wind could create mechanical turbulence, which will mix down warmer air to the surface. Hence, winds keep the minimum nighttime temperature warmer than in calm conditions. By looking at cloud movement at different levels, one can infer the type of temperature advection that may be occurring, and therefore atmospheric stability.

Synoptic weather analysis and forecasting began after the telegraph made instantaneous long-distance communications possible after 1850. The invention of radio allowed the extension of the weather observation net over the oceans, and this was one of its first important uses. Every ship became a weather station, radioing reports at regular intervals to a central office. This great advance occurred by 1915, and weather prediction was of great service in Would War I. Significant theoretical advances were made during the middle of the 20th century, especially in the properties of the upper atmosphere, elucidated by such indirect methods as sound propagation and meteor trails.

THE SUN, THE AIR, AND THE WEATHER

The state of the air is important in weather studies. The elements of weather are air temperature, precipitation, cloud cover and sunshine, wind speed and direction, and air pressure. The air in the atmosphere is a mixture of gases consisting of nitrogen, oxygen, water vapor, carbon (IV) oxide, and some rare gases. The amount of water vapor is very important, as it gives us clouds and rain. Clouds are seen in the sky every day. They come in all shapes and sizes and bring with them all sorts of weather. A cloud is simply a visible mass of tiny water droplets that have formed because the air has become too cold at that height to store all its water as invisible vapor. This usually happens when warmer air near the ground is cooled down by rising higher in the atmosphere.

Different types of clouds can be described as they are viewed from the ground, using different terms. A cloud's name generally reflects the height at which it forms, as well as its general shape. The three main types of clouds are cirrus, cumulus, and stratus. Cirrus clouds are wispy in appearance and resemble horsetails. They are formed almost entirely of tiny ice crystals. Cumulus clouds look like fluffy balls of cotton wool. These can sometimes grow much larger, becoming cumulonimbus clouds, which bring heavy bursts of rain during thunderstorms. Cumulus clouds are clouds of vertical development and may grow upward dramatically under certain circumstances. Another type of cumulus cloud is the altocumulus cloud, which sometimes resembles fish scales. They sometimes have dark, shadowed undersides. Stratus clouds are layer clouds that form near the ground and make the weather very grey and dreary, and sometimes rainy. Stratus clouds form flat layers or uniform sheets. Only a fine drizzle can form from stratus clouds because there is no vertical development.

Air usually contains some water in the form of moisture called dew. The water is hardly seen, as it is like a gas. Humid air contains more moisture than dry air, but when the temperature of air falls, its ability to hold moisture decreases. If the temperature drops low enough, air can become saturated, even if it was originally much drier at the warmer temperature. At this point, excess moisture begins to condense, forming small water droplets on the ground called dew. As an air mass cools, it can hold less and less water vapor. If it cools down enough, it reaches a point at which the water vapor present in the air mass represents the amount needed to saturate an air mass at the lower temperature. The temperature at which saturation occurs is the dew point. The dew point depends on the amount of water vapor in the air. In winter, the temperature may fall below freezing. If dew has formed on the ground, it will freeze, forming white crystals called frost.

When the temperature of air close to the ground falls low enough, dew will form. If a larger layer of air is cooled, the condensation of excess moisture in the air forms a mist of tiny water droplets known as fog. Fog is common in the autumn and winter and usually forms when there is little or no wind to disturb it. It is also more common in hollows and valleys, where the air tends to be a little colder because it is heavier and sinks down into these places. Fog is least likely on hilltops, unless low clouds have descended to cover them.

The major driving force behind the weather is the sun. Energy from the sun is stored in the atmosphere as heat. When this heat is moved around, it makes the weather. The equator is much hotter than the poles because it receives much stronger sunlight. There is more heat stored in the atmosphere nearer the equator. Heat, however, likes to flow from warm to cold temperatures. More heat is also stored nearer the ground. This makes the air lighter than that above it, and it rises. When air rises, its temperature falls, which makes weather features such as clouds and rain.

SEVERE WEATHER

The greater part of Europe often experiences bad weather, particularly in winter. Bad weather usually comes in from the Atlantic Ocean with weather systems called depressions—regions of low pressure, strong winds, and rain. In the tropics, bad weather is much less common, but when it strikes, it can be devastating. Large tropical storms, which usually develop toward the end of summer, are called hurricanes. The most common place for hurricanes to form is in the Caribbean. Here, seawater temperature is high because the sunlight is strong, and a lot of heat is stored there. Under the right conditions, a storm will develop, which, with sufficient energy, will become a hurricane. Viewed from a satellite, a hurricane appears almost circular, with clouds spiralling out from a small center. On the ground, the weather in the center may be fairly calm, with clear skies, but as the hurricane moves over, the weather can become very nasty, with winds of over 100 mi. (161 km.) per hour that are strong enough to tear roofs off houses.

Heavy rain, dark black clouds, and lightning are evidence of a thunderstorm. Thunderstorms are not nearly as strong as hurricanes, but they can be damaging, particularly if large hailstones fall out from their clouds. Thunderclouds are known scientifically as cumulonimbus clouds. Thunderstorms are more common in summer because they need a lot of energy to form. The energy comes from the heating of the ground and the surface air by the sun. If this heating is strong enough, air heated near the ground will rise up a long way into the atmosphere because it is lighter than the air around it. Warmer air is lighter than colder air. As the air rises up, it becomes colder. Moisture in the air begins to condense out as clouds, in the same way as fog forms on a calm, cool night. In thunderclouds, however, the energy is much greater, and the currents of air are strong enough to split apart the raindrops that are forming. This builds up an electric charge, which, when released, is seen as lightning. The sound of thunder is the effect of the lightning strike on the surrounding air. When rain or hail begins to fall from a thundercloud, it is usually very heavy, but it generally lasts no more than 30 minutes. Sometimes, however, the death of one thunderstorm may lead to the development of another, and the bad weather may continue for several hours.

A rapidly spiralling column of air is called a tornado. Large thunderstorms develop because there is an awful lot of energy stored in the atmosphere. Some large thunderstorms give birth to tornadoes. The tornado is usually very small in comparison to the thunderstorm, but it can wreak terrible havoc across the small area over which it moves. At a distance, a tornado is seen as a rapidly rotating funnel or spout of air, usually colored grey because of clouds and earth debris caught up inside it. The strongest tornadoes can have wind speeds of over 250 mi. (402 km.) per hour— and sometimes over 300 mi. (483 km.) per hour.

Most water on earth is in the oceans. A little, however, is contained by air in the atmosphere. The water in the atmosphere is usually not seen except when it rains, as it is in the form of moisture or vapor. Water enters the atmosphere by evaporating from the surface of the oceans, lakes, and other liquid water bodies. At higher levels in the atmosphere, the air is colder,

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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