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Intro to Weather and Climate (MEA 130) > Chapter 10 - Test Four > Flashcards

Chapter 10 - Test Four Flashcards

1
Q

Storms comprised of cumulonimbus clouds that contain:

A

Lightning and thunder

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2
Q

Thunderstorms

A

Can produce gusty winds, torrential rains, hail and tornadoes.

They form when warm, moist air (mT) rises in an unstable environment.

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3
Q

Various mechanisms can trigger the upward movement of thunderstorms:

A
  • Convection (unequal heating of earth’s surface)
  • Cold Fronts
  • Topographic lifting
  • Sea-breeze induced lifting
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4
Q

The globe experiences 45,000 thunderstorms / day (Fig. 10.2), most in:

A
  • Lower (more tropical) latitudes

- Over land masses

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5
Q

The US experiences 100,000 thunderstorms every year (Fig 10.3)

A
  • More in southeast (mT air)
  • max. in FL (sea breeze convergence Fig. 4.21)
  • less on west coast, New England (mP air)
  • North Carolina averages 40-50
  • Raleigh: 42
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6
Q

Air-Mass Thunderstorms

A

Scattered, individual storms that develop within unstable mT air masses.

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7
Q

Air-Mass Thunderstorms characteristics:

A
  • Small (10s of kms in diameter)
  • short lived (1- 2 hours)
  • Non- severe
  • Most occur in spring and summer
  • Most occur in the afternoon
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8
Q

Thunderstorm Stages of Development

A

A three-stage model was developed in the 1940’s after numerous thunderstorm related airplane crashes prompted field studies in Florida.

Cumulus, Mature, and Dissipating Stage.

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9
Q

Cumulus Stage

A

Warm, moist air rises, expands, cools and condenses, forming thencumulus cloud. Condensation releases Latent Heat Energy, warming the cloud making it less dense than surrounding air
- Allows continue rising and growth

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10
Q

Cumulus Stage Characteristics:

A
  • 5-10 km height
  • updrafts only
  • no precipitation
  • no lightning/thunder
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11
Q

Mature Stage

A

Cumulonimbus cloud grows well above freezing level, allowing cloud droplets to grow larger thru both Bergeron and Collision/Coalescence processes, until too large to be supported by updrafts.
- Rain starts to fall- creating a cool dense downdraft

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12
Q

Mature Stage Characteristics:

A
  • 10-15 km height
  • Anvil cloud spreads out at tropopause
  • Updrafts and downdrafts
  • Intense precipitation
  • Frequent lightning/thunder
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13
Q

Dissipating Stage

A

Begins when downdrafts begin to dominate updrafts, cutting off the release of Latent Heat Energy, which is the “fuel” of the thunderstorm.
- The storm literally collapses on itself

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14
Q

Dissipating Stage Characteristics:

A
  • Still 15 km height
  • Downdrafts only
  • Precipitation decreases, stops
  • Lightning/thunder decreases, stops
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15
Q

A single Air Mass Thunderstorm generally goes thru all ____ stages within several hours.

A

three

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16
Q

Surprisingly, ____ of the water vapor that is condensed in a thunderstorm actually reaches the ground as rain. The remaining 80% Is carried off as cloud that eventually evaporates.

A

less than 20 percent

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17
Q

Hail

A

Produced by very strong up/down drafts (up to 100 mph) within Cb clouds

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18
Q

Hail stones grow by colliding and coalescing with:

A

Super cooled liquid water droplets in the upper portions of the Cb cloud that freeze instantaneously
&
Regular liquid water droplets
in the lower portions of the Cb cloud
that freeze more slowly only after the
hail ascends back into the upper portions
of the Cb

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19
Q

A cross section of a hailstone reveals its life-cycle much like the cross section of a tree:

A

Clear sections result from slow freezing (air escapes: no bubbles): occurs in lower part of Cb
&
Opaque sections result from instant freezing (air can’t escape: bubbles): occurs in upper part of Cb

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20
Q

Hail Stone Facts

A 
A golf ball sized hailstone requires: 
-	1 billion collisions! 
-	1 hour “hang time”
Largest ever found fell in 2003:
- 	Weight: 1.7 ibs
-	Diameter: 7 inches
Causes billions of $ damage yearly
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21
Q

NC ranks #____ nationally in damage

A

2

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22
Q

Severe Thunderstorms are defined by National Weather Service as a thunderstorm with:

A

Hail ≥ 0.75” in diameter (nickel sized), Wind gusts ≥ 50 knots (58 mph), Tornadoes

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23
Q

Only 10% thunderstorms become severe, so annually, the US experiences roughly:

A

10,000 severe thunderstorms.

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24
Q

Severe thunderstorms can also produce:

A

Flash Flooding (Box 10.1)

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25
Q

Flash Flooding

A

Localized floods of great volume, but short duration.

- Number 1 (storm related) killer in the United States

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26
Q

Severe thunderstorms also form in warm, moist, unstable air, but need an additional “ingredient”:

A

Strong Vertical Wind Sheer

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27
Q

Strong Vertical Wind Sheer

A

Defined as a rapid change in wind speed and/or direction wrt height.

28
Q

Wind Sheer allows the thunderstorm to tilt vertically, which prevents the downdrafts from “____” the updrafts

A

killing

29
Q

Strong Vertical Wind Sheer tilt allows the updrafts to continue to grow…

A

resulting in additional Latent Heat energy release - allowing the storm to become stronger hence severe characteristics

30
Q

Characteristics as a result of Strong Vertical Wind Sheer:

A
  • 15-20 km height
  • Intense rain, large hail
  • Continuous lightning/thunder
  • Gust fronts, roll clouds (fig 10.7)
  • Overshooting tops
31
Q

Supercell Thunderstorms

A

Only 2-3% of thunderstorms reach “Supercell” status
Characteristics:
- > 20 km height
- Mesocyclone/ Tornadoes

32
Q

Squall Line

A

Relatively narrow, long (up to 500 kms) line of thunderstorms that form along or ahead of cold fronts in mT air

33
Q

Mesoscale Convective Complexes (MCCs)

A 
Extremely large (1000 km diameter), long lived
(12-36 hours) complex of many thunderstorms working in concert to maintain favorable environment
34
Q

Microbursts

A

An intense concentration of downdraft winds that results in:

  • Winds exceeding 100 mph
  • Extensive straight line wind damage
35
Q

The combination of downburst and gust fronts has been responsible for numerous ____ disasters.

A

airline

36
Q

Lightning is an electrical discharge that occurs within thunderstorms:

A
  • 80%: cloud-to-cloud/ within cloud (Sheet Lightning)

- 20%: Ground-to-cloud (most dangerous)

37
Q

In order for lightning to occur a charge separation must occur within / near the cumulonimbus (Cb) cloud; results in:

A

separate regions of opposite electrical charge (+, - ions)

38
Q

Although the source of charge separation within lightning is debatable; it results in:

A

+ Positive ions accumulating in the upper part of the Cb

- Negative ions accumulating in the lower portion of the Cb

39
Q

Because “opposites attract” the negative ions at the base of the Cb attract positive ions on the ground under the cloud

A

These positive ions accumulate around tall objects (trees, building, etc.)

40
Q

When the charge separation gets too large, the insulating property of the atmosphere is surpassed, resulting in the electrical discharge called:

A

The Lightning Stroke

41
Q

The Lightning Stroke

A

When the negative charge at the base of the Cb becomes excessive, a flow of negative ions rushes toward the ground, ionizing the air

  • This flow, which is invisible, is called the:
    Stepped Leader
42
Q

As the stepped leader approaches the ground, a flow of positive ions rushes up to meet it, when they meet a tremendous visible electrical
discharge occurs, called the:

A

Return stroke

43
Q

This Return Stroke neutralizes the charge separation.

A
  • It is typically several miles long

- But, only about 1 inch in diameter!

44
Q

Thunder

A

Lightning causes the air to instantly heat to 33,000ºC:

- Results in an explosive expansion of air creating a shockwave resulting in thunder

45
Q

Because light travels at 3 x 10 8 m/s we see lightning immediately; sound; however, travels much slower (3 x 10 2 m/s) so the thunder lags.

A

We can use this difference in speed to estimate the distance that
lightning occurs from a location.

Sound takes ~ 5 seconds to travel one mile

Example: 20 seconds / 5 = 4 miles away

46
Q

Typically, thunder can only be heard if lightning is within 10-12 miles. This leads to the term “____ lightning”, which is no different than normal lightning.

A

heat

47
Q

Lightning is the # 2 (Storm related) killer in the U.S. Annually, lightning:

A
  • Kills roughly 100 people (NC ranks#3)
  • Starts 10,000 fires
  • Causes $5 Billion in damage (homes, forests)
48
Q

Tornadoes

A

An intense rotating column (or vortex) of air extending from the base of a Cb whose circulation has reached the ground

  • Extremely low barometric pressure (900 mb)
  • Extremely strong winds
  • Also called twisters, cyclones
  • some are single vortex, others multiple vortices (Fig.10.19)
    • Only 1 % of thunderstorms produce tornadoes
49
Q

Tornado Development

A

Doppler Rader cannot dictate a tornado

50
Q

Mesocyclone:

A

vertical cylinder of rotating air within a thunderstorm

- Detectable only by Doppler Rader

51
Q

Wall Cloud:

A

Portion of the mesocyclone that is observed beneath the Cb as an area of rotating clouds
- This is where the funnel will appear

52
Q

Funnel Cloud:

A

Cone shape cloud rotating beneath wall cloud

- Comprised of condensation only

53
Q

Tornado:

A

Circulation has reached the surface

  • Debris gets pulled into the circulation
  • Roughly ½ of mesocycones will produce a tornado
  • A tornadic thunderstorm can go through all four stages within 30 minutes
54
Q

Tornado Climatology

A

The vast majority of the world’s tornadoes occurs in the US

  • 1200 annually (figs. 10.21)
  • Many occur in “Tornado alley” , which stretches from Texas to Nebraska
55
Q

North Carolina averages ____ tornadoes per year

A

10-20

56
Q

Most US tornadoes occur during spring and early summer (Fig. 10.21)

A
  • Following the clash between cP air and mT air
57
Q

Most US tornadoes occur during the afternoon and early evening

A
  • Diurnal heating increases instability, likelihood of thunderstorms, hence tornadoes.
58
Q

Profile of a Tornado

A

General Characteristics Average Extreme

Diameter: 500 - 2000 feet 1 mile
Movement Speed: 30 mph 70 mph
Movement Direction: from sw to ne any
Lifetime: Minutes hours
Distance: 10-15 miles 100 miles
Wind speed: 100-200 mph 300 mph

59
Q

Tornado Destruction is measured by the

A

Fujita Intensity Scale

  • intensity scale developed in the 1960’s
  • based on observed damage
60
Q

Fujita Intensity Scale

A

Fujita Scale Description %
F0, F1 weak tornadoes 63 F2, F3 Strong tornadoes 35
F4, F5 Violent Tornadoes less than 2

61
Q

70% of tornado deaths are associated with the rare ____

A

F4/F5s

62
Q

Noted Tornado Outbreaks

A

1925 Tri-State Tornado (Fig. 10.23)
1974 Super outbreak (Box 10.4, Fig. 10.E)
2011 Worst Tornado year in US history

63
Q

Noted NC Tornadoes

A

1984 Over 40 fatalities, 800 injuries in eastern NC
1988 Several fatalities , 160 injuries in Raleigh
2011 Over 20 fatalities (4 in Raleigh), 30 tornadoes

64
Q

Tornado Forecasting

The Storm Prediction Center in Oklahoma issues:

A

Tornado Watches for the entire US, which are designed to alert the public to the fact that conditions are favorable for the development of tornadoes.

65
Q

Watch “Boxes” are typically issued for:

A
  • Large areas (25,000 square miles)

- Relatively long time period (4-6 hours).

66
Q

The local National Weather Service Offices (ours is at Centennial Campus) issue:

A

Tornado Warnings only after a tornado has been spotted or indicated on Doppler RADAR.

67
Q

Warnings are typically issued for:

A
  • Small areas (i.e. counties)

- Short time period (30-60 minutes)

Intro to Weather and Climate (MEA 130) (9 decks)

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