10: Tornadoes Flashcards
what is a tornado, produced by, visible due to, and lifetime
- 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
path lengthm width, speed, and lifetime of two types of tornadoes
- weak tornado
* length:1.6km
* width: 100m
* lifetime: few minutes
* speed: <180km/hr - Violent tornado
* length:160 km
* width: 1000m
* lifetime: up to 2 hours
* speed: up to 500km/hr
which part of the world has the most tornadoes worldwoide and what is it called
- central USA
- tornado alley: north south corridor stretching from texas thorugh oklahoma, kansas and south dakota
where does canada rank in tornadoes
- Canadian prairies ranks second behind US
odds of tornado in 100 thunderstorms
- 1 of 100 thunderstorms there is a tornado
- 1 of 100 tornadoes are strong and 1 of 1000 are violent
what is the tornado scale called
fujita tornado intensity scale
what is the fujita tornado intensity scale
- 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
what makes a tornado stronger and where are they formed
- a stronger vertical wind shear
- form in supercells
clouds that sign a tornado formation
mammatus clouds
environment that develops supercells and how it develops
- 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
what is a funnel cloud
- 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
characteristics of the wall cloud
- 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
things radar image shows
- radar reflectivity image depicts a hook echo in the south east side
- hook echo shows rainfall as it is drawn around the mesocyclone
F0 - F5 Fujita Scale Descriptions
F0: light damage
F1: moderate damage
F2: considerable
F3: extreme
F4: devastating
F5: incredible
5 other torando like phenomena
- gustnado
- dust devil
- fire whirls
- steam devils
- waterspout
what is a gustnado
- smaller tornado
- small vertical swirl associated with a gust front or downburst
- not connected with a cloud base
what is a dust devil
- 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)
what is a fire whirl
- 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
what is a steam devil
small tornado that involves steam or smoke
components of tornado airflow and what does it lead to
- 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
draw pic of of 3 velocities
image 20
what is a suction vortex and what is it a result of
- 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
speed/velocity ds of suction vortex rotation
- image 22
- velocity at bottom is faster: 340km/h
- velocity at top is slower: 140 km/h
what is rotation quantified by
- azimuthal velocity (V) and radius (R)
- time period of full rotation (T)in seconds
- frequency of rotation (F) in 1/sec or Hz
formula for F and F of tornado typically
- F of tornado usually <1Hz (merry go round)
F = V/2piR (circumference of circle)
what is vorticity and the formula
- 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
what are vortex lines and how they affect funnel direction
- vortex lines need to be perpendicular to the ground to produce circulation
- can be distorted by the airflow causing the funnel to bend
how does vorticity arise in a fluid
- Spin: like solid body rotation
- Shear: unique to a fluid; one region of fluid slides over another region
how is horizontal vorticity and what can it be converted to
- 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
two counter rotating vortices is made by what and what it creates
- updraft creates two counter rotating vortices
- if there is a downdraft there are multiple vortex tubes due to storm splitting
- image 25
conservation of angular momentum affect on tornadoes and formula
- smaller radius means faster
- V1R1 = V2R2
how to increase vorticity
- by convergence (radial inflow) using conservation of angular momentum (smaller radius)
- inflow is caused by cyclostrophic balance
Cyclostrophic balance and formula
- 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
what height does cyclostrophic balance occur and its purpose
- 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
what happens to cyclostrophic balance near the groundz
- 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
how does the mid level rotation in a thunderestorm get to the surface
- 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
