Weather Systems © Lisa Michalek

Energy in the Atmosphere  The sun is the major source of energy for Earth.  Stars, including our sun, give off electromagnetic energy over the wide range of wavelengths that make up the electromagnetic spectrum. Earth’s atmosphere filters out most of the short-wave radiation. Earth’s atmosphere filters out most of the short-wave radiation. Most of the output from the sun that reaches the surface of Earth is in the narrow band that we perceive as visible light. Most of the output from the sun that reaches the surface of Earth is in the narrow band that we perceive as visible light.  Earth also radiates electromagnetic energy, mostly in the infrared (heat) part of the spectrum.

Electromagnetic Spectrum

Evaporation  Of the solar radiation that reaches Earth, about ¾ evaporates water from the oceans. Evaporation is the change of state from liquid to gas or vapor. Evaporation is the change of state from liquid to gas or vapor. Evaporation adds energy and matter to the atmosphere.Evaporation adds energy and matter to the atmosphere. Decreases when water is covered or cooled.Decreases when water is covered or cooled. Increases when water is uncovered, heated, and when wind blows over it.Increases when water is uncovered, heated, and when wind blows over it.

Three Stages of Water  Ice, liquid water, water vapor.  Energy that is absorbed or released during a change in state is called latent (hidden) heat, a form of potential energy. It is latent energy because it does not cause a change in temperature. It is latent energy because it does not cause a change in temperature.

Heat of Fusion  When the temperature of the ice reaches 0°C, it begins to melt. As the ice changes to liquid, it absorbs 80 calories per gram. As the ice changes to liquid, it absorbs 80 calories per gram. The heat of fusion (the energy needed to melt one gram of ice is 80 cal/g). The heat of fusion (the energy needed to melt one gram of ice is 80 cal/g). The temperature of the ice does not change until all the ice has melted. The temperature of the ice does not change until all the ice has melted.

Heat of Vaporization  When the temperature of the liquid water reaches 100°C, the boiling point of water, liquid water changes to water vapor.  The energy necessary to change one gram of a substance from the liquid to the vapor state is called the heat of vaporization. The heat of vaporization of water is 540 cal/g. The heat of vaporization of water is 540 cal/g. The gram of water absorbs 540 calories of latent heat as it changes to vapor. The gram of water absorbs 540 calories of latent heat as it changes to vapor.  After all the liquid water becomes vapor, the temperature begins to rise again.

Latent Heat Energy  The specific heat of water vapor is 0.5 cal/g°C.  If the water vapor is cooled to 100°C, it will condense and release the 540 calories of latent heat it absorbed.  As the cooling continues, the water will release the heat it absorbed while it was heated.  It also releases the 80 calories per gram that was needed to melt the original ice.

Synoptic Weather Maps  A weather map that shows a variety of atmospheric field quantities.  May show information about temperature, air pressure, precipitation, and other weather conditions at a particular time and over a large geographic area.

Weather Station Symbols

Air Masses  The leading edges of air masses.  When a front passes, precipitation often accompanies the changes in temperature, humidity, and atmospheric pressure.  The character of an air mass depends on its geographic origin.

Weather Fronts  Fronts are shown by lines that separate two air masses.  Symbols along the fronts indicate the direction the fronts are moving and what kind of front they are.  Stationary fronts are boundaries between air masses that are not moving.  Occluded fronts result from warm air being pushed above the surface of Earth by cooler air closing in from both sides.

Front Symbols

Natural Hazards  Thunderstorms Most occur in the summer when the air is warm and moist. Most occur in the summer when the air is warm and moist. Advancing cold fronts may push the warm air upward, causing the formation of giant cumulus clouds, and heavy precipitation. Advancing cold fronts may push the warm air upward, causing the formation of giant cumulus clouds, and heavy precipitation. Lightning, damaging hail, and tornadoes are possible. Lightning, damaging hail, and tornadoes are possible. Lightning strikes, flash floods and tornadoes spawned by thunderstorms cause about 100 fatalities per year in the US.Lightning strikes, flash floods and tornadoes spawned by thunderstorms cause about 100 fatalities per year in the US.

Natural Hazards  Tornadoes Most common in the spring and early summer over the central US. Most common in the spring and early summer over the central US. Are usually less than 0.3 miles (0.5 km) in diameter and usually last for 10 min or less. Are usually less than 0.3 miles (0.5 km) in diameter and usually last for 10 min or less. Winds have been measured by radar in excess of 300 mi/hr. Winds have been measured by radar in excess of 300 mi/hr.

Natural Hazards  Hurricanes Tropical depressions, areas of low pressure that usually develop in the late summer and early autumn in the Atlantic Ocean between South America and Africa. Tropical depressions, areas of low pressure that usually develop in the late summer and early autumn in the Atlantic Ocean between South America and Africa. When winds exceed 74 mi/hr the designation is changed from tropical storm to a hurricane. When winds exceed 74 mi/hr the designation is changed from tropical storm to a hurricane.

Tropical Storm Formation

Tropical Storm Categories Category Wind Speed (mph) Damage at Landfall Storm Surge (feet) Minimal Moderate Extensive Extreme Over 155Catastrophic19+