Atmosphere and Weather

    The definition of weather is simple: the state of the atmosphere at any given time and place. It can be learned about easily by simple direct observation, but there are also many scientific ways to study this science with complicated instruments. The earth's atmosphere is a mixture of mainly nitrogen and oxygen that thins out with height. The ozone layer, which protects life on earth from ultra violet radiation, is threatened greatly by both nitric acid and CFC's, which include the freons used both in aerosol spray cans and refrigerators. The atmosphere is divided into different layers based on temperature; for example the ionosphere is made up of ionized air. Radiation, convection, and conduction are the three ways in which heat moves in the earth's atmosphere. Most solar radiation is absorbed on earth's surface, which heats the air above, making a balanced heat budget. The greenhouse effect is like that of a greenhouse, trapping heat in the earth's atmosphere. An increase of carbon dioxide and other greenhouse gases may cause global warming. On clear nights temperature inversions occur when the ground and air just above it cool faster than the air higher up. The reason for climates being warmer at lower altitudes is because the sun is more directly overhead. Interestingly, the warmest month is the moth after the maximum sunlight, as the coldest month is the month after the minimum sunlight. Celsius and Fahrenheit are the two commonly used temperature scales, which are based on the principle that materials expand when heated. Isotherms shift more dramatically over land than water with the seasons.
 

Precipitation, Condensation, Evaporation

    When water molecules evaporate (leave the Earth's surface), energy is required for it to change its state to a liquid. When this energy is absorbed from its surroundings, the water becomes cooler, then allows the energy back in. Condensation (when water vapor transforms into liquid water) occurs in cold water because warm water can hold more moisture at a time. Frost forms on the ground when the ground temperature drops below freezing, and dew forms when the temperature drops below dew point. Fog and clouds are condensation of water vapor around tiny particles called condensation nuclei. The main types of clouds are cirrus, which are high, feathery ice clouds; cumulus, which are fluffy with flat bases; and stratus, which are low, layered clouds. Rising air cools at the dry adiabatic lapse rate with condensation. Cumuli form clouds form when the air currents rise from the heated ground and form from the buoyant tops of clouds. stratiform clouds are formed when the air in the cloud is not buoyant and lifting cools the air. Precipitation in warm clouds grow from drop collisions. In cold clouds, ice crystals grow from the collisions and by using water vapor from the evaporating super cooled drops. Precipitation tends to fall where the air rises, producing condensation. This happens when clouds go over mountains and when surface air converges. Acid rain comes from the sulfate and nitrate particles, which mix with water to form sulfuric or nitric acid.
 

Winds and Atmospheric Pressure

    The cause of air pressure is it's weight in the atmosphere, which is measured in barometers (a measuring instrument: the two kinds are mercury and aneroid). The pressure changes from time to time, due to things like temperature change and humidity.  Air flows differently depending on whether the pressure is high or low.  A sea breeze occurs when there is an uneven heating of land and water.  Global wind and pressure belts are caused by Earth's rotation and the uneven heating between its hemispheres.  There is low air pressure on continents in the summer, while there is high air pressure at the seas.  Winds tend to blow more from the sea.  In the winter the pattern reverses.  Monsoons (changing winds) are a result of these reversing winds.  Jet streams are strong winds at heights of 6-12 kilometers.  The Coriolis effect turns winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.  Winds are defined depending on their speed and blowing direction.  Low air pressure belts and air that is rising lie at the equator and at 60 degrees.  Belts of the surface and high air pressure that are sinking lie at the 30 degrees and the poles.
 

Fronts and Air Masses

    Areas with the same temperatures and humidity are known as air masses.  The air must stay in the same place for a long time to form.  Air masses are named according to the climate of their regions.  The weather of a moving air mass can be determined by humidity and how warm or cold the temperature is beneath its surface.  Temperature, humidity and wind in an air mass are measured by a Rawinsonde, which is a balloon carried package of instruments.  Measurements are made twice during the day, at noon and midnight, Greenwich, England time at many weather stations throughout the world. The boundaries between air masses that aren't alike are called fronts.  There are four kinds: stationary, warm, cold, occluded.  The less dense air of a front is on top, with the more dense air on bottom.  Condensation and precipitation can be caused by rising air in the lows.  Mid latitude lows are formed through the waves in the polar front.  The location of a low center and the kinds of passing fronts determine the sequence of clouds and precipitation. Precipitation which mainly takes place near surface fronts, is water which falls to the Earth's surface after the cloud droplets become heavy enough. Cumuli form clouds are found on cold frontal surfaces, while stratiform clouds are found on warm frontal surfaces.  Fair weather is caused by sinking of air in highs.
 

Storms and Weather Forecasts

     Thunderstorms occur solitary and in groups when humid air rises through unstable air. When this happens, you usually get an electrical discharge from the clouds called lightning. Thunder is then created from the "sudden expansion of air in the lightning channel." If storms like these are strong, then they can create tornadoes. Tornadoes are a mass of whirling winds that are shaped like a funnel. Their violent winds can reach up to 500 kilometres per hour.
    Hurricanes are severe storms with devastating winds that can die out over land or cold water. They have a central eye where the winds circle and rotate around, and are very intense. They can be tracked with satellites, various types of aircraft, and radar. Hurricane warnings, though not as bad as tornado warnings, are given at the last minute. The are usually issued when the hurricane is less than 24 hours offshore.
    Tools that we have today, such as radar, satellites, and computers, can be the key to predicting weather and staying on top of what's going to happen. Daily temperatures, cloud pictures, humidity, and wind can be all detected via satellite, and radars are used to track severe weather and storms. Precipitation areas can also be spotted by radar, which can help predict flooding.
 

Climate and Climate Change

    The climate, the overall description of the weather experience in a region, of earth is determined by numerous factors. These include altitude, latitude, topography, the amount of heat received from the sun, ocean currents, prevailing winds, and the distance from large bodies of water.
    Many different things can affect an area's temperature. Ocean currents, mountains, precipitation, and greenhouse gases all can change the temperature. Mountains can hold the cold air out and make cities in those areas much warmer during the winter. Precipitation in tropical areas makes the air humid and warm, but precipitation in a cooler climate, especially with wind, can cause the temperature to drop considerably. Greenhouse gases, which come from natural causes and human activities, cause the atmosphere and the climate to heat up.
    Global climate change us determined by the earth's energy budget. Global climate change can also determine local climate change if it varies along with factors that only determine local climate. Long-term climate change depends greatly on geologic processes.
 

Other Weather links:

Educational Site for All Ages: http://www.nssl.noaa.gov/edu/
For Any Weather Related Terms not Understood on This Page:  http://www.weather.com/glossary/
Weather Forecasting: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fcst/home.rxml
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