Weather SystemsWeather Systems

Energy in the AtmosphereEnergy in the Atmosphere The sun is the major source of energy for EarthThe sun is the major source of energy for Earth Stars, including our sun, give off electromagnetic Stars, including our sun, give off electromagnetic

energy over the wide range of wavelengths that energy over the wide range of wavelengths that make up the make up the electromagnetic spectrumelectromagnetic spectrum Earth’s atmosphere filters out most of the short-wave Earth’s atmosphere filters out most of the short-wave

radiationradiation Most of the output from the sun that reaches the surface Most of the output from the sun that reaches the surface

of Earth is in the narrow band that we perceive as visible of Earth is in the narrow band that we perceive as visible lightlight

Earth also radiates electromagnetic energy, mostly Earth also radiates electromagnetic energy, mostly in the infrared (heat) part of the spectrumin the infrared (heat) part of the spectrum

Electromagnetic SpectrumElectromagnetic Spectrum

EvaporationEvaporation

Of the solar radiation that Of the solar radiation that reaches Earth, about ¾ reaches Earth, about ¾ evaporates water from the evaporates water from the oceansoceans Evaporation is the change of state from Evaporation is the change of state from liquidliquid to to

gasgas or or vaporvapor• Evaporation adds energy and matter to the Evaporation adds energy and matter to the

atmosphereatmosphere• DecreasesDecreases when water is covered or cooled when water is covered or cooled• IncreasesIncreases when water is uncovered, heated, and when when water is uncovered, heated, and when

wind blows over itwind blows over it

Three Stages of WaterThree Stages of Water Ice, liquid water, water vaporIce, liquid water, water vapor Energy that is absorbed or released during a Energy that is absorbed or released during a

change in state is called latent (hidden) heat, change in state is called latent (hidden) heat, a form of potential energya form of potential energy It is latent energy It is latent energy

because it does because it does not cause a change not cause a change in temperaturein temperature

Heat of FusionHeat of Fusion When the temperature of the ice reaches When the temperature of the ice reaches

0°C, it begins to melt0°C, it begins to melt As the ice changes to liquid, it absorbs 80 As the ice changes to liquid, it absorbs 80

calories per gramcalories per gram The The heat of fusionheat of fusion (the energy needed to melt (the energy needed to melt

one gram of one gram of ice is ice is 80 cal/g80 cal/g))

The temperature of The temperature of the ice does not the ice does not change until all the change until all the ice has meltedice has melted

Heat of VaporizationHeat of Vaporization When the temperature of the liquid water reaches When the temperature of the liquid water reaches

100°C, the boiling point of water, liquid water 100°C, the boiling point of water, liquid water changes to water vaporchanges to water vapor

The energy necessary to change one gram of a The energy necessary to change one gram of a substance from the liquid to the vapor state is substance from the liquid to the vapor state is called the called the heat of vaporizationheat of vaporization The heat of vaporization The heat of vaporization

of water is of water is 540 cal/g540 cal/g The gram of water absorbs The gram of water absorbs

540 calories of latent heat 540 calories of latent heat as it changes to vaporas it changes to vapor

After all the liquid water After all the liquid water becomes vapor, the becomes vapor, the temperature begins to temperature begins to rise againrise again

Latent Heat EnergyLatent Heat Energy The specific heat of water vapor is 0.5 cal/g·°CThe specific heat of water vapor is 0.5 cal/g·°C If the water vapor is cooled to 100°C, it will If the water vapor is cooled to 100°C, it will

condense and release the 540 calories of condense and release the 540 calories of latent heat it absorbedlatent heat it absorbed

As the cooling continues, the water will release As the cooling continues, the water will release the heat it absorbed the heat it absorbed while it was heatedwhile it was heated

It also releases the 80 It also releases the 80 calories per gram that calories per gram that was needed to melt was needed to melt the original icethe original ice

Synoptic Weather MapsSynoptic Weather Maps A weather map that shows a variety of A weather map that shows a variety of

atmospheric field quantitiesatmospheric field quantities May show information about temperature, air May show information about temperature, air

pressure, precipitation, and other weather pressure, precipitation, and other weather conditions at a conditions at a particular time and particular time and over a large over a large geographic areageographic area

Weather Station SymbolsWeather Station Symbols

Weather Station SymbolsWeather Station Symbols

Air MassesAir Masses The leading edges of air massesThe leading edges of air masses When a front passes, precipitation often When a front passes, precipitation often

accompanies the changes in temperature, accompanies the changes in temperature, humidity, and atmospheric pressurehumidity, and atmospheric pressure

The character of an The character of an air mass depends on air mass depends on its geographic originits geographic origin

Weather FrontsWeather Fronts

Fronts are shown by lines that separate Fronts are shown by lines that separate two air massestwo air masses

Symbols along the fronts indicate the Symbols along the fronts indicate the direction the fronts are moving and what direction the fronts are moving and what kind of front they arekind of front they are

StationaryStationary fronts are boundaries between fronts are boundaries between air masses that are not movingair masses that are not moving

OccludedOccluded fronts result from warm air being fronts result from warm air being pushed above the surface of Earth by pushed above the surface of Earth by cooler air closing in from both sidescooler air closing in from both sides

Front SymbolsFront Symbols

Natural HazardsNatural Hazards ThunderstormsThunderstorms

Most occur in the summer when the air is warm Most occur in the summer when the air is warm and moistand moist

Advancing cold fronts may push the warm air Advancing cold fronts may push the warm air upward, causing the formation of giant cumulus upward, causing the formation of giant cumulus clouds, and heavy precipitationclouds, and heavy precipitation

Lightning, damaging hail, and Lightning, damaging hail, and tornadoes are possibletornadoes are possible• Lightning strikes, flash floods Lightning strikes, flash floods

and tornadoes spawned by and tornadoes spawned by thunderstorms cause about thunderstorms cause about 100 fatalities per year in the US100 fatalities per year in the US

Natural HazardsNatural Hazards TornadoesTornadoes

Most common in the spring and early summer Most common in the spring and early summer over the central USover the central US

Are usually less than 0.3 miles (0.5 km) in Are usually less than 0.3 miles (0.5 km) in diameter and usually diameter and usually last for 10 min or lesslast for 10 min or less

Winds have been Winds have been measured by radar in measured by radar in excess of 300 mi/hr excess of 300 mi/hr

Natural HazardsNatural Hazards

HurricanesHurricanes Tropical depressions, areas of low pressure that Tropical depressions, areas of low pressure that

usually develop in the late summer and early usually develop in the late summer and early autumn in the Atlantic Ocean between South autumn in the Atlantic Ocean between South America and AfricaAmerica and Africa

When winds exceed When winds exceed 74 mi/hr the designation 74 mi/hr the designation is changed from tropical is changed from tropical storm to a hurricanestorm to a hurricane

Tropical Storm FormationTropical Storm Formation

Tropical Storm CategoriesTropical Storm Categories

CategoryWind Speed

(mph)Damage at

LandfallStorm Surge

(feet)

1 74-95 Minimal 4-5

2 96-110 Moderate 6-8

3 111-130 Extensive 9-12

4 131-155 Extreme 13-18

5 Over 155 Catastrophic 19+