Weather 09 10

WeatherWeather

AtmosphereAtmosphere

CharacteristicsCharacteristics

The Earth’s atmosphere is a mixture of The Earth’s atmosphere is a mixture of gases, dust and water vapor. The gases, dust and water vapor. The atmosphere is divided into layers based on atmosphere is divided into layers based on temperature changes. The lowest layer is temperature changes. The lowest layer is called the troposphere, it is where weather called the troposphere, it is where weather occurs. The temperature and pressure occurs. The temperature and pressure decreases as the altitude increases.decreases as the altitude increases.

AtmosphereAtmosphere

HeatingHeatingThe Earth is heated by the energy from the Sun.The Earth is heated by the energy from the Sun.

The amount of solar radiation an area receives The amount of solar radiation an area receives is due to the angle the sunlight strikes the is due to the angle the sunlight strikes the surface. Areas near the equator are heated surface. Areas near the equator are heated more than the poles.more than the poles.

30% reflected 50% reaches surface

20% absorbed by atmosphere

Spreads out

concentrated

WindWindWhen the air is heated it When the air is heated it

rises and is replaced rises and is replaced by cooler air. by cooler air.

Three convection cells Three convection cells are formed in the are formed in the Northern hemisphere.Northern hemisphere.

The rotation of the Earth The rotation of the Earth causes the winds in causes the winds in the cells to “turn” the cells to “turn” causing winds to blow causing winds to blow in one main direction in one main direction depending on latitude.depending on latitude.

Water CycleWater Cycle

HumidityHumidityHumidity is the amount of water vapor in the air. Humidity is the amount of water vapor in the air.

Relative humidity is the ratio of the actual Relative humidity is the ratio of the actual amount of water vapor in the air to the amount amount of water vapor in the air to the amount of water the air can hold at a specific of water the air can hold at a specific temperature. temperature.

The warmer the air the more moisture it can The warmer the air the more moisture it can hold. hold.

As warm air rises it cools and the relative As warm air rises it cools and the relative humidity increases until it reaches 100%, then humidity increases until it reaches 100%, then clouds will form. Precipitation may occur at this clouds will form. Precipitation may occur at this time.time.

Humidity & PrecipitationHumidity & PrecipitationHumidityHumidity is measured using a is measured using a

hygrometer or a sling psychrometer. hygrometer or a sling psychrometer. Relative humidity is always given as a Relative humidity is always given as a percent (%)percent (%)

PrecipitationPrecipitation is measured with a rain is measured with a rain gauge and a ruler.gauge and a ruler.

Weather, Climate, and Weather, Climate, and TemperatureTemperature

Weather is the condition of the Weather is the condition of the atmosphere at the present time.atmosphere at the present time.

Climate is the overall average Climate is the overall average temperature and precipitation for a temperature and precipitation for a region.region.

ThermometersThermometers (digital, liquid, or metal (digital, liquid, or metal coil) are used to measure temperature. coil) are used to measure temperature.

Air PressureAir Pressure

Air pressure is the weight of the atmosphere Air pressure is the weight of the atmosphere all around an object.all around an object.

When the air pressure increases it means a When the air pressure increases it means a high pressure system is moving towards high pressure system is moving towards you, thus fair weather. you, thus fair weather.

When the barometer is falling it means a low When the barometer is falling it means a low

pressure system is moving in and it will pressure system is moving in and it will soon rain/snow or be cloudy. soon rain/snow or be cloudy.

BarometerBarometerA digital, dial, or liquid barometer is A digital, dial, or liquid barometer is

used to measure air pressure.used to measure air pressure.

On most barometers you must take On most barometers you must take two readings to tell if the air pressure two readings to tell if the air pressure is increasing or decreasing. Air is increasing or decreasing. Air pressure is difficult to detect without pressure is difficult to detect without an instrument.an instrument.

Wind Speed & Wind Wind Speed & Wind DirectionDirection

Wind SpeedWind Speed is measured with an is measured with an anemometer, which can be digital or anemometer, which can be digital or mechanical.mechanical.

Wind DirectionWind Direction – the direction the wind – the direction the wind is is comingcoming fromfrom. (measured using: . (measured using: weather vane, windsock) weather vane, windsock)

Weather MapsWeather Maps

Weather maps are used to show Weather maps are used to show existing conditions and predict existing conditions and predict changes.changes.

FrontsFronts

Where cold and warm air meet.Where cold and warm air meet.

Warm Front Cold Front

Severe WeatherSevere Weather

WatchWatch – conditions could produces – conditions could produces severe weathersevere weather

WarningWarning – severe weather is occurring – severe weather is occurring or is expected to occuror is expected to occur

ThunderstormsThunderstorms

Warm moist air rises creating a low pressure Warm moist air rises creating a low pressure area. The raising air cools until it reaches the area. The raising air cools until it reaches the Dew Point (100% R.H.) Warm air weighs less Dew Point (100% R.H.) Warm air weighs less than cold air, moist air weighs less than dry than cold air, moist air weighs less than dry air.air.

Thunderstorms have areas of strong updrafts Thunderstorms have areas of strong updrafts and strong downdrafts. Hail is formed when and strong downdrafts. Hail is formed when the tops of the large thunderhead clouds are the tops of the large thunderhead clouds are below freezing. The hail falls, gets coated below freezing. The hail falls, gets coated with water, is caught in the updraft and is with water, is caught in the updraft and is refrozen when it reaches the top.refrozen when it reaches the top.

6 and 1/8 inch hailstone6 and 1/8 inch hailstone

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Largest hailstone in U.S. history: 7 in. Largest hailstone in U.S. history: 7 in. diameterdiameter

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LightningLightning

Lightning is a static discharge from Lightning is a static discharge from clouds to ground, ground to cloud, or clouds to ground, ground to cloud, or cloud to cloud.cloud to cloud.

TornadoesTornadoes

• Wind speed to 300 mphWind speed to 300 mph

• Occurs in spring/early summerOccurs in spring/early summer

• Called a funnel cloud if it does not touch the Called a funnel cloud if it does not touch the ground.ground.

• Most common in Texas, Kansas, and OklahomaMost common in Texas, Kansas, and Oklahoma

HurricanesHurricanes

• Wind speed up to 150 mphWind speed up to 150 mph

• Occurs in late summerOccurs in late summer

• Called Typhoons in the PacificCalled Typhoons in the Pacific

• Low pressure area 400 miles wide that rotatesLow pressure area 400 miles wide that rotates

• The eye is calm, fastest winds are just outside the The eye is calm, fastest winds are just outside the eyeeye