ST L3: Lightning/ From Heat to Motion

Question 1

What is incandesce?

Answer 1

The glow in the air caused by heat (warmer than the surface of the sun!) from electrical discharge (lightning).

Question 2

What is lightning?

Answer 2

Electrical discharge through air that heats the air to temperatures warmer than the surface of the sun. Th path of air instantly heated by lightning explosively expands to create a shock wave, which changes into the sound waves of thunder further from the lightning bolt.

Question 3

Describe how lightning in a thunderstorm occurs.

Answer 3

Positive and negative electrical charge separates within the cloud.

Question 4

Where does negative charge build up? Positive charge?

Answer 4

lower level in the cloud. positive charge builds up near the top of the cloud.

Question 5

What is voltage? How does this relate to lightning?

Answer 5

Electrical force caused by buildup of negative charge. Electrical force becomes so strong an electrical breakdown occurs, resulting in lightning flashes.

Question 6

How does the cloud return to equilibrium?

Answer 6

Lightning transfers the charge.

Question 7

Describe the process of how lightning strikes the Earth.

Answer 7

Lightning begins with an electrical breakdown in the cloud. Breakdown causes electrical discharge called a downward propagating leader. Just before reaching ground, many small upward leaders rise to meet it. At least one of the upward leaders connect with the downward propagating leader. When they meet, the charge from the cloud transfers to the ground.

Question 8

How fast is lightning?

Answer 8

Moves at hundreds of miles per second.

Question 9

What is a return stroke? How hot is it? How fast?

Answer 9

Sudden, super fast transfer of charge from the cloud to the ground. It produces temperatures exceeding fifty thousand degrees F in a fraction of a second. Hotter than any other natural phenomenon on Earth.

Question 10

How is a shock wave produced?

Answer 10

Air expanding explosively. We hear it as thunder.

Question 11

Describe what happens once lightning finds a path to the ground.

Answer 11

Once lightning finds a path to the ground, it forms a channel through the air. Makes it easier for addition return strokes to transfer remaining charge from the cloud.

Question 12

How many return strokes usually involved in lightning we see?

Answer 12

3 or 4, sometimes more.

Question 13

Why do we see lightning strokes flicker?

Answer 13

More charge is being transferred to the ground following the same channel.

Question 14

How much % of cloud-to-ground lightning is positively charged?

Answer 14

10%

Question 15

Which flashes are generally more powerful? What does that entail?

Answer 15

positive flashes. they have higher chance of starting fires and damaging electrical power lines.

Question 16

How can cloud-to-ground strikes be further classified?

Answer 16

by whether negative or positive charge moves to the ground

Question 17

Where do negative strikes form?

Answer 17

Cloud base. They are more numerous.

Question 18

Where do positive strikes form?

Answer 18

Thunderstorm anvil. Positive strikes are less frequent, often much stronger, and most likely to start wild fires. (In Canada, 10-25% of cloud-to-ground lightning is positive)

Question 19

How do electrical charges build up in the thunderstorms?

Answer 19

From freezing and collision of cloud droplets and ice crystals. When the electrical potential (charge difference) between cloud and ground become great enough, the air ionizes. Air becomes conductor instead of insulator along the ionized path. Stepped leader nearing ground causes ground streamers of electrons rise from tall trees, poles, buildings to meet stepped leader.

Question 20

What are graupeln?

Answer 20

ice crystals

Question 21

How great of a breakdown potential is needed to ionize air?

Answer 21

3 billion volts.

Question 22

What is a stepped leader?

Answer 22

Path of ionized air rapidly stepping down from the cloud.

Question 23

What occurs once the stepped leader connects to the ground streamers?

Answer 23

Electrons flow in a massive current called a return stroke (we see the return stroke).

Question 24

How strong is the current of return stroke?

Answer 24

(2 000 to 200 000 amperes)

Question 25

What tears the ionized path apart?

Answer 25

wind

Question 26

List the types of lightning.

Answer 26

``` cloud-to-ground lightning upward-moving lightning (or ground-to-cloud) intracloud lightning cloud-to-air lightning anvil crawler lightning bead lightning/chain lightning ```

Question 27

Describe upward-moving/ground-to-cloud lightning

Answer 27

Often has strange smooth and fluid channel. Extremely rare type of lightning before Industrial Revolution. Tall man-made structures trigger the discharge.

Question 28

Before the Industrial Revolution, how did upward-moving lightning occur?

Answer 28

From mountain peaks

Question 29

What helps trigger upward-moving lightning these days?

Answer 29

Tall man-made structures, increasing skyscrapers and radio antennae make upward-moving lightning more common.

Question 30

Where do most lightning discharges occur? What is this type of lightning called?

Answer 30

Only in clouds. | It is called intracloud lightning. Sometimes, it leaps out into air. Called cloud-to-air lightning.

Question 31

What is bead lightning or chain lightning?

Answer 31

When main lightning channel begins to cool, sometimes decays in glowing fragments. This string of dots is the bead or chain lightning.

Question 32

What is ribbon lightning?

Answer 32

Parallel successive flashes or strokes offset from each other. Occurs when strong winds blow the flashing channel (lightning sailing).

Question 33

Where is lightning mainly found in North America

Answer 33

Southeast US. (where most thunderstorms occur) Florida has highest lightning strikes. Known as lightning alley.

Question 34

How do thunderstorms get triggered in Alberta? In Ontario near the Great Lakes?

Answer 34

Alberta(most frequent lightning): updrafts of air along the Rockies Ontario (highest lightning density): lake-breeze fronts

Question 35

What is lightning flash density?

Answer 35

Flash density is the number of flashes per square kilometre per year

Question 36

How to be safe when lightning is present?

Answer 36

a. Monitor weather conditions b. Follow 30/30 rule c. Stay indoors

Question 37

What is the 30/30 rule for lightning?

Answer 37

If 30 seconds or less between the flash is seen and a bang is heard, then move indoors and stay there until 30 minutes after last lightning or thunder.

Question 38

Where are safe indoor places during lightning storms?

Answer 38

fully enclosed metal vehicle with the windows rolled up; Metal cars/vehicles (with windows up) and aircraft are safe because the lightning flows on the outside of the skin of the vehicle, leaving the people inside unharmed. Modern composite (fiber glass) aircraft contain an embedded mesh of wires for the purpose of safely conducting the lightning electricity away from people and sensitive instruments substantial permanent building

Question 39

When indoors, what should you do during lightning event?

Answer 39

Don't touch electrical appliances like wired phones. (cordless and cell phones are OK) Don't touch any plumbing connected by metal pipes. Stay away from windows

Question 40

When outdoors, what to do during lightning event?

Answer 40

Avoid unsafe areas like small structures, huts, rain shelters, nearby metallic objects (pole, trees, water, hill top, etc.) If you feel the hair standing up on your head or arms, there is a good chance that you are about to be struck by lightning in the next second or so. Move immediately so that you are not the highest point. if caught in the open and cannot find a safe place, in desperation do the "Lightning-Safety Crouch" with feet together, hands over ears

Question 41

What is a "bolt from the blue?"

Answer 41

When lightning shoots out of the side of a storm and hits the ground ten miles away from the storm.

Question 42

What to do if someone is struck by lightning?

Answer 42

Try to revive them with CPR.

Question 43

How many deaths does lightning cause a year on average? How many injuries per year? Where do most of the casualties occur?

Answer 43

93 deaths, 300 injuries. Most take place outdoors during the summer, mainly in the afternoon and early evening.

Question 44

How many cloud-to-ground strikes per year?

Answer 44

8 million. Causes 6-12 deaths every year.

Question 45

When are lightning storms most frequent in the US?

Answer 45

Mid to late summer, when there are more thunderstorms.

Question 46

How far away is the lightning?

Answer 46

Count the number of seconds between when you see the lightning and hear the thunder. Divide that number by 3 to estimate the range in kilometers to the lightning. For Example: a 9 second difference means the lightning is 3 km away.

Question 47

What does buoyancy do? What is it the dominant process of?

Answer 47

creates vertical motions (up and down drafts). dominant process in thunderstorms.

Question 48

What does pressure do? What is it the dominant process of?

Answer 48

creates horizontal motions/winds. | dominant process of cyclones.

Question 49

What are important for hurricanes?

Answer 49

buoyancy and pressure.

Question 50

What makes a storm organized?

Answer 50

If they tend to perpetuate themselves with positive feedback (drawing in fuel by converting temperature into motion)

Question 51

____ creates winds

Answer 51

forces. It causes air parcels to accelerate in the direction of the force.

Question 52

What is an air parcel?

Answer 52

An object that is a blob of air, about the size of a toy balloon. When air parcel moves, there is nothing more than wind. (horizontal or vertical)

Question 53

______ alters buoyancy to drive vertical winds.

Answer 53

Temperature

Question 54

Warm air wants to ___, thereby creating ___. Cold air wants to ___, thereby creating ____.

Answer 54

rise; updrafts; sink; down drafts

Question 55

Which type of air is denser?

Answer 55

Colder air. Results in downward buoyancy force, while warmer air is less dense and results in an upward buoyancy force.

Question 56

______ alters pressure to drive horizontal winds.

Answer 56

temperature

Question 57

A pressure difference across a horizontal distance creates a horizontal ______ force that can accelerate air parcels to create winds.

Answer 57

pressure-gradient

Question 58

What is a pressure-gradient force?

Answer 58

A change of pressure between one air parcel and its neighbour.

Question 59

As the hurricane develops, its center (____) becomes a ring of _____. ______ in these storms makes the core _____ relative to the outside

Answer 59

core; thunderstorms; Condensation; warmer

Question 60

The horizontal pressure gradient at the top of the hurricane creates outward ____ winds. These winds remove air molecules from the ____. Fewer molecules in the core causes ____ pressure at the surface (as shown in the figure below), because pressure is the ____ of all the overlying air. This low pressure at the bottom of the core creates a ____ ____ that sucks in air. This gives the ____ ____ into the bottom of a hurricane. This inflow ____ in more fuel (warm humid air), making the hurricane stronger.

Answer 60

spiraling; core lower; weight; pressure gradient; spiral inflow; advects

Question 61

Pressure decreases with height in the atmosphere in what manner?

Answer 61

Exponential. Rate of decrease with height depending on how densely packed the air molecules are.

Question 62

Pressure decreases more gradually with height in which kind of air? Why?

Answer 62

Warmer air, because the warm-air column takes up more vertical space.

Question 63

What concept ties the vertical and horizontal motions (winds) together? Describe the concept

Answer 63

the concept of continuity. the air molecules tend to spread themselves smoothly and evenly, and don't leave any gaps (i.e., they don't leave a vacuum), and don't get bunched together. the air is continuous

Question 64

the vertical motion generated initially by buoyancy within the parcel will generate a _____ motion in the air just outside and under the parcel.

Answer 64

horizontal

Question 65

the ____moving air creates gaps or bunched-up air molecules slightly off to the sides of the rising air parcel, which drive other vertical motions

Answer 65

horizontally

Question 66

the air parcel is rising because of its ____, and there is a ____ of the surrounding environmental air out of the way above the parcel, and filling back in under the parcel (Figure ST.61e). In real life, this circulation develops smoothly and continuously as the warm parcel begins to rise, and creates only ____ pressure changes, not a complete ____.

Answer 66

buoyancy; circulation; small; vacuum

Question 67

air parcels that are forced horizontally will cause ____ circulations to move the surrounding air out of the way and to deposit it back behind the air parcel. Thus, vertical and horizontal motions are linked, by the effect of ____.

Answer 67

vertical; continuity

Question 68

____ create winds. Temperature alters ____, to create vertical winds. Temperature alters ____, to drive horizontal winds. Continuity links vertical and horizontal winds into ____.

Answer 68

Forces; buoyancy; pressure; circulations