Chapter 19 Flashcards
(22 cards)
Tornado
A violent rotating column of air that extends from cloud to ground
How many tornados are reported in the u.s. per year?
~1000 reported in U.S. per year
What percentage of the worlds tornados occur in the U.S.?
75%
What are the wind speeds that tornados can get to?
65mph to 200mph
What is tornado alley?
Area of most frequent tornado occurrence in the United States.
How extensive in tornado alley?
Extends from Texas to Illinois
What is the Fujita Scale?
Scale of tornado intensity, based on damage caused by a tornado, that gives estimates of wind speeds.
What is the most common intensity of tornados?
EF1
What is the least common intensity of tornados?
EF5
Why are tornados most common from April through June?
Thermal contrast between polar tropical air masses is strong - jet stream around.
What time of day are tornados most common?
Tornados from most often in late afternoon or early evening, slightly after the peak surface warming.
3 Steps in creating a supercell type tornado?
- A cylinder of horizontally rotating air is pulled into an updraft to form mid-level mesocyclone. This starts the supercell
- Another cylinder of horizontaly rotating air.
- Tornado born in three possable ways,
After the first two steps of creating a supercell tornado, what are the three ways a tornado can be born?
- Bottem up
- Top down or dynamic pipe effect
- Vortex breakdown
Bottom up?
A horizontally rotating cylinder that forms along rear flank downdraft is pulled into updraft, streached out, and this forms a tornado
Top-Down or dynamic pipe effect?
Rotating and rising air is constricted as it enters low-level mesocyclone. This forms a ‘pipe’, that grows down to ground
Vortex breakdown?
Within the mesocyclone. Extreme low pressures in center of mesocyclone can lead to decending air. A tornado can be generated in shear between this air and the rotating, ascending air that surrounds it.
Mesocyclone?
The rotating circulation in a supercell thunderstorm that is associated with the updraft.
Mesocyclone Occlusion
Where the foward flank updraft and rear flank updraft meet.
How does Vortex breakdown lead to tornado formation in a supercell?
A process similar to vortex breakdown in an existing tornado can occur in the mesocyclone updraft of a supercell thunderstorm.
Occlusion Downdraft?
The central downdraft that can form in the mesocyclone
How do we know when a Tornado is forming?
Storm spotters, Police Reports, Reports from the public, Doppler Radar.
Hook Echo?
Area of weaker reflectivity near mesocyclone updraft.
