Transcript AOS 100: Weather and Climate

AOS 100: Weather and
Climate
Instructor: Nick Bassill
Class TA: Courtney Obergfell
Miscellaneous
• Homework due by the end of weather
discussion
• Extra Credit Offer:
- If you’re interested in an extra credit project, email me with a topic you’re considering, and
we’ll figure it out from there
Review of November 12th: Thunderstorms
Continued
• Air-mass thunderstorms (which are nonsevere thunderstorms) have updrafts
which are eventually cut off by the
thunderstorm’s own downdrafts
• Severe thunderstorms have strong wind
shear, which tilts the updrafts and
downdrafts so that this problem doesn’t
occur
• This allows severe thunderstorms to last
longer, and become more intense
Review Continued
•
For our purposes, we can consider two
types of severe weather:
(1) A squall line is mostly linear continuous
line of thunderstorms associated with
speed wind shear, and they often
produce strong straight line winds
(2) Supercells are smaller storms associated
with directional wind shear, and often
cause tornados and large hail
Review Continued: Doppler RADAR
• Doppler RADAR makes use of the “Doppler
Effect” to determine whether objects are
traveling towards or away from the radar site
• Doppler RADAR measures the change in
wavelength of the incoming signal (compared
with the signal that was sent out)
• This allows meteorologists to locate areas where
air is moving towards the radar with adjacent air
moving away from the radar
• This usually indicates a tornado might be
present or forming
A Supercell
A Supercell
Reflectivity:
Velocity:
We call this
feature a
“velocity
couplet”, and it
often signifies a
tornado
From: http://kkd.ou.edu/METR%202603/supercell%20velocity.jpg
Classic Supercell
Classic Supercell
Classic Supercell – using doppler radar
Tornadoes
• Tornadoes are caused by the creation of a
rotating updraft
A Supercell (with tornado)
A Supercell (with tornado)
Fig. 14-46, p. 402
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Tornado
Wall Cloud
Tornado Damage
Supercell Setup
• Supercells form at near
the surface cold front
• As you move upward in
the atmosphere, the
winds “veer”
• Oftentimes, very fast
winds occur at upper
levels
• These two factors help
to increase the wind
shear
A Squall Line
• Dry air coming in behind the storm causes rain to evaporate,
quickly cooling the air
• This makes the air very dense, causing it to sink rapidly to
the surface, which leads to strong straight-line winds
Approaching Squall Line
Cold Air
Incoming Dry Air
Squall Line Motion
Cold Air
A Squall Line
• Dry air coming in behind the storm causes rain to evaporate,
quickly cooling the air
• This makes the air very dense, causing it to sink rapidly to
the surface, which leads to strong straight-line winds