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EAS 202 > 10: Tornadoes > Flashcards

10: Tornadoes Flashcards

1
Q

what is a tornado, produced by, visible due to, and lifetime

A
  • violently rotating column of air in contact with ground and produced by a severe thunderstorm
  • made visible by condensed water droplets
  • funnel cloud formed by localized lowering of cloud base
  • most violent of weather systems
  • small and short lived
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2
Q

path lengthm width, speed, and lifetime of two types of tornadoes

A
  1. weak tornado
    * length:1.6km
    * width: 100m
    * lifetime: few minutes
    * speed: <180km/hr
  2. Violent tornado
    * length:160 km
    * width: 1000m
    * lifetime: up to 2 hours
    * speed: up to 500km/hr
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3
Q

which part of the world has the most tornadoes worldwoide and what is it called

A
  • central USA
  • tornado alley: north south corridor stretching from texas thorugh oklahoma, kansas and south dakota
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4
Q

where does canada rank in tornadoes

A
  • Canadian prairies ranks second behind US
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5
Q

odds of tornado in 100 thunderstorms

A
  • 1 of 100 thunderstorms there is a tornado
  • 1 of 100 tornadoes are strong and 1 of 1000 are violent
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6
Q

what is the tornado scale called

A

fujita tornado intensity scale

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7
Q

what is the fujita tornado intensity scale

A
  • in this order: f scale, category, km/hr
    0 weak 65-118
    1 weak 119-181
    2 strong 182-253
    3 strong 254-332
    4 violent 333-419
    5 violent 420-514
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8
Q

what makes a tornado stronger and where are they formed

A
  • a stronger vertical wind shear
  • form in supercells
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9
Q

clouds that sign a tornado formation

A

mammatus clouds

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10
Q

environment that develops supercells and how it develops

A
  • develop sin an environment with horizontal wind that has strong shear in both speed and direction
  • sher in windspeed causes air to rotate about a horizontal axis in a rolling motion
  • consists of one updraft and down downdraft
  • updraft tilts horizontal rotation into rotation around vertical axis (which creates rotation in the updraft aka mesocyclone)
  • horizontal extent of mesocyclone is 3-10km
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11
Q

what is a funnel cloud

A
  • cloud that extends to the surface and when it touches down it converts to a tornado
  • most tornadoes occur about 10-20 mins after rotating wall clouds become noticeable
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12
Q

characteristics of the wall cloud

A
  • circular lowered portion of the rain free base of the supercell
  • usually associated with a mesocycone
  • wall cloud about 3km in diameter and is in the region of the strongest updraft
  • most wall clouds do not produce a tornado
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13
Q

things radar image shows

A
  • radar reflectivity image depicts a hook echo in the south east side
  • hook echo shows rainfall as it is drawn around the mesocyclone
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14
Q

F0 - F5 Fujita Scale Descriptions

A

F0: light damage
F1: moderate damage
F2: considerable
F3: extreme
F4: devastating
F5: incredible

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15
Q

5 other torando like phenomena

A
  1. gustnado
  2. dust devil
  3. fire whirls
  4. steam devils
  5. waterspout
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16
Q

what is a gustnado

A
  • smaller tornado
  • small vertical swirl associated with a gust front or downburst
  • not connected with a cloud base
17
Q

what is a dust devil

A
  • also known as whirwind
  • resembles a tornado but they form under clear skies
  • form when a strong updraft is formed near the ground on a hot day (dust goes up)
18
Q

what is a fire whirl

A
  • small tornado near intense surface heat source. Ex: near wildfires
  • not considered tornadoes except in the rare case where they connect to a pyrocumulus or other cumulus cloud
19
Q

what is a steam devil

A

small tornado that involves steam or smoke

20
Q

components of tornado airflow and what does it lead to

A
  • 3 components: rotational motion (azimuthal velocity), radial inflow (radial velocity), upward motion (vertical velocity)
  • combo of all 3 leads to inward and upward spiral
  • objects are destroyed by tornadoes mostlu by drag force and not by suction
21
Q

draw pic of of 3 velocities

A

image 20

22
Q

what is a suction vortex and what is it a result of

A
  • secondary vortex that is associated with the main tornado
  • made when you combine tornado velocities (Vtotal): radial (Vr), suctionial (Vs), translational (Vt)
  • Vt: movement horizontally
  • Vr: rotation
  • Vs: rotation in main vortex rotation
  • image 21
23
Q

speed/velocity ds of suction vortex rotation

A
  • image 22
  • velocity at bottom is faster: 340km/h
  • velocity at top is slower: 140 km/h
24
Q

what is rotation quantified by

A
  • azimuthal velocity (V) and radius (R)
  • time period of full rotation (T)in seconds
  • frequency of rotation (F) in 1/sec or Hz
25
Q

formula for F and F of tornado typically

A
  • F of tornado usually <1Hz (merry go round)
    F = V/2piR (circumference of circle)
26
Q

what is vorticity and the formula

A
  • rotation in a fluid
  • Vorticity = 4piF
  • vorticity is a vector and the vector is defined using the right hand rule (thumbs up –> vortex lines are parllel to the vorticity
  • so if vortex line are vertical from ground to sky the spin is counterclockwise
  • image 23
27
Q

what are vortex lines and how they affect funnel direction

A
  • vortex lines need to be perpendicular to the ground to produce circulation
  • can be distorted by the airflow causing the funnel to bend
28
Q

how does vorticity arise in a fluid

A
  1. Spin: like solid body rotation
  2. Shear: unique to a fluid; one region of fluid slides over another region
29
Q

how is horizontal vorticity and what can it be converted to

A
  • horizontal vorticity is created by wind shear in the atmospheric boundary layer
  • can be converted into vertical vorticity when the updraft tilts the vortex lines
  • vertical vorticity is necessary for a tornado
  • image 24
30
Q
A
30
Q

two counter rotating vortices is made by what and what it creates

A
  • updraft creates two counter rotating vortices
  • if there is a downdraft there are multiple vortex tubes due to storm splitting
  • image 25
31
Q

conservation of angular momentum affect on tornadoes and formula

A
  • smaller radius means faster
  • V1R1 = V2R2
32
Q

how to increase vorticity

A
  • by convergence (radial inflow) using conservation of angular momentum (smaller radius)
  • inflow is caused by cyclostrophic balance
33
Q

Cyclostrophic balance and formula

A
  • inward and outward force balances
  • steady rotation requires inward pressure gradient force (P) balances outward centrifugal force (C)
  • requires low pressure centre on the axis of rotation
  • P = C = V^2/R
34
Q

what height does cyclostrophic balance occur and its purpose

A
  • occurs at heights >50m above the surface in a tornado
  • cyclostrophic balance minimizes radial flow and maintains low pressure in the centre, maintaining funnel cloud
35
Q

what happens to cyclostrophic balance near the groundz

A
  • friction near the ground reduces the angular velocity
  • outward centrifugal force is lower and inward pressure gradient force remains the same
  • unbalance pressure gradient force pulls the flow radially inward near the surface
  • think of stiring ur tea and the tea leaves go in the middle
36
Q

how does the mid level rotation in a thunderestorm get to the surface

A
  • dynamic pipe effect:
  • cyclostrophic balance in rotating mid level air prevents radial inflow so it acts like the wall of a vacuum - produces low pressure at centre
  • below this level, air is sucked in towards low pressure centre and begins to rotate faster, producing cyclostrophic balance at lower levels too
  • rotation works its way down to the surface

EAS 202 (14 decks)

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