The Nature of StormsChapter 13

Thunderstorms Severe Weather Tropical Storms Recurring Weather

Thunderstorms The conditions that must be met for them to form how thunderstorms are often classifiedThe two types of thunderstorms as well as the mechanisms that cause themStages of thunderstorms

ExperimentCloud in a bottle

Materials:•2 litre bottle•Water•Matches

Purpose: This will help with the understanding of what conditions must be met in order for a storm to form as well as how they form

Procedure:Step 1: first you put a little bit of water in the bottom of the two litre bottle.

Step 2: then you light the cardboard on fire and drop it in the drop of the bottle fastening the lid on quickly after. Swish the water around gently if the smoke is showing.

Step 3: you then squeeze the bottle very tightly and the release the bottle. Repeat this step a few times and observe what’s occurs

Observations: -when you put the cardboard that was on fire in the bottle it should stay relatively clear inside but become a little bit foggy due to the smoke. -When you squeezed the bottle the air inside should have became clear-When you released the bottle a cloud should have formed

Conclusion: Why does this happen? It is not the smoke that causes this cloud to form. It is due to the moisture from the bottom of the bottle being condensed as the change in pressure causes the air to rise.

What does this tell us about the formation of storms?

Thunderstorms

Must Have Abundant Moisture

• the moisture condenses, releasing latent heat which keeps the cloud warmer than the air around it which maintains the upward motion of the cloud.

There Must be a Mechanism

• Something must lift the air so that the moisture can condense.

Atmosphere Must be Unstable

• this means that the air must continue to cool with the increasing altitude for the cloud to stay warmer than the surrounding air (air can only rise if its warmer than the air around it)

How Thunderstorms Form

Unstable Atmosphere

Mechanisms•A mechanism is what lifts the air up so that the moisture can condense•Storms are also often classified by the mechanisms that caused the air to rise

Un equal Heating of Earth’s surface Within one Air Mass

Advancing Cold Fronts

-The thunderstorm created is called an air-mass thunderstorm-The unequal heating reaches is peak during the afternoon-An example would be the difference in temperature of air over water and over land

-Create frontal thunderstorms-Cold air pushes warm air rapidly up the steep cold-front boundary

Two Types of Mechanisms

Cumulus Stage

-Air starts to rise almost vertically upward-Updrafts are created which transports moisture to upper regions of the cloud-Moisture condenses into visible droplets and eventually fall to Earth as precipitation.

Mature Stage

-as the precipitation falls it cools the air around it-the cool air is more dense than surrounding air causing it to sink rapidly-this creates downdrafts

Dissipation Stage

-downdrafts are the thunderstorms ending because the thunderstorm can only exist if there is warm air at Earth’s surface-the downdrafts will linger until the cloud runs out of rain drops

Tropical Cyclone What are they and how do they occurFormation of tropical cyclonesStages Classifying Hurricanes Surges

What are Tropical Cyclones and How do They Occur?

Definition: large, rotating, low pressure systems

Step 2: the Coriolis effect causes the air to turn counterclockwise in the northern hemisphere, this is what causes the cyclonic rotation in a tropical cyclone. As air approaches the center of the storm, it rises and begins to rotate faster. Air pressure in the center continues to decrease. this process will continue as long as warm air is being fed into the center of the storm.

Step 1: Water evaporates from the ocean surface and stores latent heat. When the air starts to rise the latent heat is released and water vapor forms clouds and rain. The rising air creates an area of low pressure at the ocean surface.

How: Tropical Cyclones thrive on the enormous amount of energy in warm tropical oceans.

When: Tropical cyclones take place during the summer and fall seasons Where: in the tropics.

Formation of Tropical Cyclones

~ Hurricanes occur mostly at the end of summer, beginning of fall, when Earth’s oceans contain the most stored heat energy.

An abundant supply of very warm ocean water and some sort of disturbance to lift the warm air up.

Tropical cyclones need two basic conditions

These conditions occur in every Tropical oceans except two:

South Atlantic Ocean and the Pacific Ocean west of the South American coast.

They do not occur in these locations because the water in these two oceans is somewhat cooler and have a lack of disturbances.

~ Near Caribbean Sea, the Gulf of Mexico, and up the western coast of Mexico, they are called Hurricanes. Some places they are also known as Typhoons .

Storm surges Normally occur on the right side of the eye.

Storm Surges ~ A storm surge takes place when hurricane-forced winds drive ocean water towards the coastal areas.

~storm surges can sometimes reach 6 m above sea level. This can cause serious damage.

Hurricane Hazards~ When hurricanes do damage it is normally because of the violent winds. Winds up to 60 km/h can stretch 400km from the center of the hurricane.

Classifying Hurricanes~The Saffir-Simpson hurricane scale, classifies hurricanes on air pressure in the center, wind speed, and potential to damage.

~ The scale ranges from category 1 with wind speeds up to (120km/h) to category 5 with wind speeds up to (250km/h)

~ Once a hurricane reaches category 3 status, it is considered to be a major hurricane.

Second stageTropical depression- is when a disturbance over a tropical ocean acquires a cyclonic circulation around a center of low pressure. ~ The system is called a tropical storm when wind speeds around the low pressure center of a tropical depression are above 65 km/h. ~ If the air pressure continues to drop and winds go above 120km/h, the storm is considered a Hurricane. ~ Once winds reach these speeds the calm center of a storm called an eye develops. ~Surrounding the eye of the hurricane is the eyewall which contains the strongest winds.

Stages of Tropical cyclones

First stage~ A Tropical disturbance, which causes air in a developing tropical cyclone to rise. ~only a small percentage of tropical disturbances turn into hurricanes.

~ A hurricane will continue until it, moves over land and no longer has access to the warm ocean surface, or when the storm moves over colder water.

Severe WeatherThe cause of severe thunderstormsThe five main hazards of thunderstorms

What makes a thunderstorm become severe?

- The increasing instability of the air is what makes a thunderstorm severe.-The temperature difference between the upper and lower levels of the cloud cause the air to become unstable-The more unstable the air the stronger the updrafts and downdrafts