Weather Earth Science Chapter 16. Chapter 16-1 Objectives: Explain how solar heating and water vapor in the atmosphere affect weather. Discuss how clouds.

Weather

Earth Science Chapter 16

Chapter 16-1 Objectives: Explain how solar heating and water vapor

in the atmosphere affect weather. Discuss how clouds form and how they are

classified. Describe how rain, hail, sleet and snow

develop.

Meteorology Meteorologists are people who study the

weather. A> Weather is the specific daily condition

of the Earth’s atmosphere. The atmospheric factors that interact to

cause weather are air pressure, wind, temperature, and moisture.

Heating the atmosphere The Sun’s heat evaporates water and it also

heats the air directly and indirectly. Temperature is the measure of air molecule

movement. a. The Sun energizes molecules to move more

rapidly…temperatures are high and it feels warm.

When less energy reaches air molecules = cold

Wind = air mass moving in a specific direction

The temperature of air affects air pressure. As the Sun heats air, the air expands, becomes less dense, rises, and has low air pressure.

Cooler air is denser and sinks, causing high atmospheric pressure.

Wind is air that is moving from an area of high pressure to an area of low pressure.

Wind speed can be measured with an anemometer.

Humidity Water vapor, or moisture, in the air is called

humidity. The amount of moisture varies from place to place and time to time. Warmer air can hold more water vapor.

Relative humidity is the percentage of moisture the air holds relative to the amount it could hold at a specific temperature.

When the relative humidity is 100 percent, the air is saturated.

Dew When air cools, it can’t hold as much water

vapor, so the vapor condenses into a liquid or forms ice crystals.

The dew point is the temperature at which air is saturated and condensation forms.

Clouds B> Clouds form as warm air is forced

upward and cools. Then the water vapor condenses into tiny droplets that stay suspended in the air. The shape and height of clouds vary with

temperature, pressure and water vapor in air. Three shapes…

Types of Clouds

Stratus Cumulus Cirrus Cloud Types

Cloud height prefixes Cirro = high Alto = middle Strato = low

Nimbus clouds are very dark and so full of water that sunlight can’t penetrate them. Cumulonimbus clouds

are thunderstorm clouds. High winds can flatten

the top of the cloud into an anvil-like shape.

When we see cumulonimbus clouds, we may have heavy rain, snow, hail, lightning and even tornadoes.

Stratus Clouds Smooth, gray clouds that cover

the whole sky and block out the sun are called stratus clouds. They form at an altitude of about 2.5 kilometers.

Light rain and drizzle are associated with stratus clouds. Nimbostratus clouds bring rain and snow.

When stratus clouds form near the ground, the result is fog.

Cirrus Clouds Feathery or fibrous

clouds are called cirrus clouds. Cirrus clouds form at very high altitudes.

Cirrus clouds are usually made of ice crystals.

Precipitation Water vapor that condenses and

forms clouds can fall to the Earth as rain, sleet, snow or hail, as determined by air temperature. Water that falls from the atmosphere to the Earth is called precipitation.

Sleet When falling snow or rain

passes through an extremely cold layer of air, they sometimes freeze into small ice pellets called sleet. Sleet reaches the Earth only in winter.

Snow Snow forms when water vapor

changes directly into a solid. Snowflakes are flat six-sided ice crystals that have beautiful shapes. Because they sometimes clump together, it is hard to see the separate crystals. No two snowflakes are exactly alike.

Hail Hail is one of the most

damaging forms of precipitation forms in cumulonimbus clouds. Hailstones are small balls of ice ranging from 5-75 mm in diameter.

Hailstones are formed when water droplets hit ice pellets in a cloud and freeze.

http://www.youtube.com/watch?v=wZr8jXo1Uso

Chapter 16-2 Weather PatternsObjectives: Describe how weather is associated with

fronts and high and low pressure systems. Explain how tornadoes develop from

thunderstorms. Discuss the dangers of severe weather.

A. Because air and moisture move in the atmosphere, weather constantly changes.

Air masses are large bodies of air that form over the same area and take on the properties of that part of Earth’s surface.

Stormy weather is associated with low pressure.

Fair weather is associated with high pressure.

Air pressure is measured with a barometer.

B. FrontsWhen two air masses that have different

properties meet, they do not mix easily. A boundary forms between the two air masses. This boundary is called a front.

The weather at a front is usually unsettled and produces clouds, precipitation and storms.

There are four types of fronts:

Cold Front A cold front forms when

a mass of colder air meets and pushes under a mass of warm air. The cold air mass forces its way underneath the warm air mass and pushes it upward. Violent storms are associated with a cold front. Fair, cool weather usually follows.

Warm Front A warm front forms

when a mass of warmer air overtakes a colder air mass and moves over it. Rain and showers usually accompany a warm front. Hot, humid weather usually follows.

Occluded Front A cold front travels faster than

a warm front. When a cold front overtakes a warm front, an occluded front forms. As the warm air is pushed upward, the cold air meets cool air. An occluded front may also occur when cool air overtakes a cold front and warm air is pushed upward. An occluded front produces less extreme weather than a cold or warm front.

Stationary Front When a warm air

mass meets a cold air mass and no movement occurs, a stationary front forms. Rain may fall in an area for many days when a stationary front is in place.

C. Severe Weather A storm is a violent disturbance in the

atmosphere. It is marked by sudden changes in air pressure and rapid air movements. Some storms may cover a huge area, whereas others cover only a small area.

1. Thunderstorms Occur inside warm, moist air masses and at

fronts. Warm, moist air is forced rapidly upwards

where it cools and condenses. Strong updrafts of warm air and sinking,

rain-cooled air cause strong winds.

2. Lightning Movement of air inside storm

clouds can cause parts of cloud to have be oppositely charged.

Current flows between the oppositely charged regions, forming a lightning bolt.

Lightning, an electrical discharge, striking the ground is the leading cause of forest fires.

Lightning

3. Thunder When lightning superheats the air,

it expands rapidly and then contracts. This sudden expansion and contraction of the air results in sound waves, or thunder.

4. Tornado A tornado is whirling, funnel-shaped

cloud. Tornadoes often form from a type of cumulonimbus cloud called a wall cloud. They are usually formed from severe thunderstorms.

The air pressure at the bottom of the funnel of swirling air is extremely low. When this low-pressure area touches the ground, it acts like a giant vacuum cleaner.

A tornado over water is called a water spout. They can travel 95 km per hour.

Tornadoes 101

Fujita Scale The Fujita scale ranks

tornadoes according to how much damage they cause.

Only 1% is classified as an F5.

Cyclones and Anticyclones Air pressure has a great effect on the

weather. An area of low pressure that contains rising warm air is called a cyclone. In a cyclone, cooler air moves in to take the place of the warm air and spiral around and into the center of the cyclone.

As the winds blow into a low pressure area, they swirl counterclockwise direction in the Northern Hemisphere. Cyclones usually cause rainy, stormy weather.

The weather caused by high pressure systems, called anticyclones, is usually clear, dry and fair.

5. Hurricane A hurricane is a powerful cyclone

that forms over tropical oceans. Hurricanes that form over the western Pacific Ocean are called typhoons. In the Indian Ocean they are called cyclones.

Hurricanes that affect the United States move from the Eastern Atlantic near Africa to the north west striking the East Coast, usually between Florida and North Carolina.

Hurricanes 101

Formation of Hurricanes Warm, moist air begins

to rise rapidly. Cooler air moves in and the air begins to spin.

As the air pressure in the center drops more air is drawn into the spinning system. The system begins to spin faster.

Damage of a Hurricane The high waves and strong winds

of a hurricane often cause great damage, especially in coastal areas. Heavy rain may also cause serious flooding.

Meteorologists can track the path of a hurricane and issue watches or warnings. A typical hurricane lasts for about 9 days. Some may last 3 or 4 weeks.

6. Blizzard A blizzard is a winter storm with strong

winds, cold temps, and low visibility that lasts more than three hours.

Severe Weather Safety When severe weather threatens, the

National Weather Service will issue a watch or a warning.

During a watch conditions are favorable for severe weather to develop. Stay tuned to a radio or television for updates/instructions.

During a warning, severe conditions already exist; you should immediate action.

Chapter 16-3 Objectives: Explain how data are collected for weather

maps and forecasts. Identify the symbols used in a weather

map.

Weather Forecasts Meteorologists study and predict weather. Weather data from 300 local stations are

used by the National Weather Service to prepare daily weather maps. The information is recorded in the form of numbers and symbols.

Symbols are used to show wind speed and direction, cloud cover, precipitation, position and direction of fronts and areas of high and low pressure.

How to Read a Weather Map

1. Station Models show weather conditions at a specific location.

Meteorologists interpret weather information from local weather observers, balloons, satellites, and weather stations around the world.

When meteorologists gather data it is recorded on a map using a combination of symbols forming a station model.

Isotherms

Isotherms are lines that connect locations with the same temperature. The number on the end of an isotherm indicates the temperature at all point along the isotherm.

Isobars Isobars are lines that join places

on a weather map that have the same air pressure.

The number at the end of an isobar represents the air pressure recorded at each observation.

The air pressure can be given in millibars, inches of mercury or both.

Frontal Movement In North America, weather fronts usually

moved from west to east. Why?