Chapter 12 – ‘Weather’
Study Guide
True or False???
In the water cycle, water vapor enters the atmosphere by evaporation from the oceans and other bodies of water and leaves by condensation. TRUE!!!
What is evaporation?
Answer: Evaporation is the process by which molecules of liquid water escape into the air after becoming water vapor.
What is condensation?
Answer: Condensation is the process by which water vapor becomes liquid water.
How is water vapor added to the air by living things?
Answer: Water enters the roots of plants, rises to the leaves, and is released into the air as water vapor. Animals also release water vapor into the air every time they exhale.
What is humidity?
Answer: Humidity is a measure of the amount of water vapor in the air.
What is relative humidity?
Answer: Relative humidity is the percentage of water vapor that is actually in the air compared to the maximum amount of water vapor the air can hold at a particular temperature.
True or False???
Air with a relative humidity of 100 percent is said to be saturated (filled with the most moisture it can hold). TRUE!!!
What instrument is used to measure relative humidity?
Answer: A psychrometer is used to measure relative humidity. It has two thermometers, a wet-bulb thermometer and a dry-bulb thermometer. The relative humidity is found by comparing the temperatures of the wet-bulb and dry-bulb thermometers.
How do clouds form?
Answer: Clouds form when water vapor in the air condenses to form liquid water or ice crystals.
What is the dew point?
Answer: The temperature at which condensation begins is called the dew point.
What happens to water vapor if the dew point is above freezing?
Answer: The water vapor forms droplets.
What happens to water vapor if the dew point is below freezing?
Answer: The water vapor may change directly into ice crystals.
In order for water vapor to condense and form clouds, what must be present in the atmosphere so that the water has a surface on which to condense?
Answer: Tiny particles (salt crystals, dust from soil, or smoke) must be present.
What are the three main types of clouds?
Answer:
1) Cirrus—These wispy, feathery clouds come from a word meaning “a curl.” They form at high altitudes, usually above 6 km, and at low temperatures. They are made of ice crystals and indicate fair weather.
2) Cumulus---These clouds look like cotton. The word cumulus means “heap” in Latin. They form less than 2 km above the ground, but they may extend upward as much as 18 km. Short cumulus clouds usually indicate fair weather. Towering clouds with flat tops, or cumulonimbus clouds, often produce thunderstorms! The suffix -nimbus means “rain.”
3) Stratus---Clouds that form in flat layers are known as stratus clouds, from the Latin word strato, meaning “spread out.” They usually cover all or most of the sky and are a dull, gray color. As they thicken, they may produce drizzle, rain, or snow. Then, they are called nimbostratus clouds.
What is fog?
Answer: Clouds that form near the ground are called fog. Fog can form when the ground cools at night after a humid day.
What do cirrocumulus clouds look like, and what do they indicate?
Answer: They look like cotton balls, and indicate that a storm is on its way.
What are the two main types of clouds that form between 2 and 6 km above Earth’s surface? (Hint: They begin with the prefix alto-.) Both of these clouds indicate precipitation (rain, freezing rain, snow, sleet, hail). They are “medium-level” clouds that are higher than regular cumulus and stratus clouds, but lower than cirrus clouds.
1) altocumulus
2) altostratus
What is the most common kind of precipitation?
Answer: Rain
How is rain measured?
Answer: An open-ended tube that collects rain is called a rain gauge. The amount of rain is measured by dipping a ruler into the water or by reading a scale.
How is snow measured?
Answer: Snow is measured in two ways: by using a simple measuring stick or by melting collected snow and measuring the depth of water it produces.
What are five common types of precipitation?
1) rain
2) sleet
3) freezing rain
4) snow
5) hail
How does freezing rain form?
Answer: Raindrops fall as liquid water but freeze when they touch a cold surface.
How do snowflakes form?
Answer: A snowflake forms when water vapor in a cloud is converted directly into ice crystals.
How does sleet form?
Answer: Raindrops fall through a layer of air that is below 0 degrees Celcius (the freezing point of water), and freeze into solid particles of ice. Ice particles smaller than 5 millimeters in diameter are called sleet.
How does hail form?
Answer: Hail forms only inside of cumulonimbus clouds during thunderstorms. Hailstones start out as ice pellets inside a cold region of a cloud. Strong updrafts (winds) carry the hailstone up through the cold region many times. Each time the hailstone goes through the cold region, a new layer of ice forms around it. Eventually it gets heavy enough to fall to the ground. A hailstone is a round pellet of ice larger than 5 millimeters in diameter!
What is a flood?
Answer: A flood is an overflowing of water in a normally dry area.
What causes floods?
Answer: Floods occur when the volume of water in a river increases so much that the river overflows its channel.
What is a drought?
Answer: A drought is a long period of scarce rainfall or dry weather.
What causes a drought?
Answer: Droughts are usually caused by dry weather systems that remain in one place for weeks or months at a time.
What is an air mass?
Answer: An air mass is a huge body of air in the lower atmosphere that has similar temperature, humidity, and air pressure at any given height.
What are the four major types of air masses that influence the weather in North America?
Answer: 1) tropical-warm air masses form in the tropics and have low air pressure
2) polar-cold air masses form north of 50 degrees north latitude and south of 50 degrees south latitude and have high air pressure
3) maritime-air masses that form over oceans
4) continental-air masses that form over land
What are three ways that air masses move?
Answer: 1) prevailing westerlies-major wind belts over the continental United
States that generally push air masses from west to east
2) jet streams-bands of high-speed winds about 10 km above Earth’s surface, blowing from west to east
3) front-the boundary where the air masses meet
What are the main types of fronts?
Answer: 1) cold fronts-clouds and heavy precipitation occur by these fronts
2) warm fronts-clouds and many days of precipitation occur
3) stationary fronts-clouds and many days of precipitation occur
4) occluded fronts-warm air is occluded (cut off)-clouds and precipitation occur
What is a cyclone?
Answer: A cyclone is a swirling center of low air pressure. The word cyclone is from a Greek word meaning “wheel.”
True or False???
Cyclones and decreasing air pressure are associated with clouds, wind, and precipitation. TRUE!!!
What is an anticyclone?
Answer: Anticyclones are high-pressure centers of dry air. It is the opposite of a cyclone.
True or False???
The descending air in an anticyclone generally causes dry, clear weather. TRUE!!!
What is a storm?
Answer: A storm is a violent disturbance in the atmosphere.
What are four types of severe storms?
Answer:
1) winter storms
2) thunderstorms
3) hurricanes
4) tornadoes
How do thunderstorms form?
Answer: Thunderstorms form in large cumulonimbus clouds, also known as thunderheads. They are small storms often accompanied by heavy precipitation and frequent thunder and lightning.
What is lightning?
Answer: Lightning is a sudden spark, or electrical discharge, as areas of positive and negative electrical charges build up in the storm clouds.
What causes thunder?
Answer: A lightning bolt can heat the air near it to as much as 30,000 degrees Celcius, much hotter than the sun’s surface. The rapidly heated air expands explosively. Thunder is the sound of the explosion.
True or False???
Because light travels faster than sound, you see lightning before you hear thunder!
TRUE!!!
What are some dangers associated with thunderstorms?
Answer: Heavy rains can cause flooding. Lightning can strike the ground and cause tree trunks to shatter or forest fires to start. Lightning can cause harm to people or animals.
What is a flash flood?
Answer: A flash flood is a sudden, violent flood that occurs shortly after a storm.
What is a hurricane?
Answer: A hurricane is a tropical cyclone with winds of 119 km/hour or higher.
How does a hurricane that strikes the United States form?
Answer: Usually these hurricanes form in the Atlantic Ocean north of the equator in August, September, and October. A hurricane begins over warm ocean water as a low-pressure area, or tropical disturbance. As it grows in size and strength, it becomes a tropical storm, which may then become a hurricane.
What is the center of a hurricane called, and give a brief description of it.
Answer: At the center of a hurricane is a ring of clouds, called the eyewall, that encloses a quiet “eye.” The weather changes suddenly within the eye—air is calm and the sky may clear. After the eye passes, the storm resumes.
What is a storm surge?
Answer: A storm surge is a “dome” of water that sweeps across the coast where the hurricane lands. Storm surges can cause great damage, washing away beaches, destroying coastal buildings, and eroding the coastline.
What is a tornado?
Answer: A tornado is a rapidly-whirling, funnel-shaped cloud that reaches down from a thunderstorm to touch Earth’s surface.
How do tornadoes form?
Answer: Tornadoes most commonly develop in thick cumulonimbus clouds---the same clouds that bring thunderstorms.
How are tornadoes measured?
Answer: The scale for ranking the impact of a tornado was named after Dr. T. Theodore Fujita, who is a scientist who devised the original scale. The scale is as follows:
EF (Enhanced Fujita) Types of damage:
EF0---branches broken off of trees
EF1---mobile homes overturned
EF2---trees uprooted
EF3---roofs and walls torn down
EF4---houses leveled (destroyed)
EF5---houses carried away
How can you stay safe in the various storms?
Answer:
1) Winter Storm---If you are caught in a snowstorm, try to find shelter from the wind in order to stay dry and warm.
2) Thunderstorm---Stay indoors. Avoid places where lightning may strike. Also, avoid objects that can conduct electricity, such as metal objects and bodies of water.
3) Hurricane---If you hear a hurricane warning and are told to evacuate (leave for another location), do so immediately.
4) Tornado---The safest place to be during a tornado is in a storm shelter or a basement. If you do not have a storm shelter or basement, move to the middle of the ground floor. Stay away from windows and doors, and lie under a sturdy piece of furniture. If you are outside, lie flat in a ditch.
What is a meteorologist?
Answer: A meteorologist is a scientist who studies and tries to predict the weather.
How do meteorologists predict the weather?
Answer: Meteorologists use maps, charts, computers, and other technology to analyze weather data and to prepare weather forecasts.
What are some ways that meteorologists can predict weather through the use of technology?
Answer:
1) automated weather stations
2) weather satellites
3) weather balloons
4) computer forecasts
What is a weather map?
Answer: A weather map is a “snapshot” of conditions at a particular time over a huge area.
What are two types of weather maps?
Answer:
1) Weather Service Maps---data from many local weather stations all over the country are assembled into weather maps at the National Weather Service.
2) Newspaper Weather Maps---these maps are simplified versions of maps produced by the National Weather Service.
IMPORTANT TO KNOW: Standard symbols on weather maps show fronts, areas of high and low pressure, types of precipitation, and temperatures.
Is it possible to predict the weather a month in advance?
Answer: No, it is not possible due to the “butterfly effect.” A small change in the weather today can mean a larger change in the weather a week later. The name “butterfly effect” refers to a scientist’s suggestion that even the flapping of a butterfly’s wings causes a tiny disturbance in the atmosphere. A tiny disturbance might cause a larger disturbance that could-eventually-grow into a large storm.
