Open Cell Convection

Open Cell Convection
What is it?
• Three-dimensional convective circulation
• Occurs when cold air moves over warmer
• Hexagonal rings of convective clouds
surrounding clear air.
• Cross section view:
• Thought to be an atmospheric analogue to
Rayleigh-Benard convection, a hexagonal
vertical circulation that occurs when a fluid is
heated at the bottom.
Open cell convection over the ocean.
Rayleigh-Benard cells in cylindrical vessel.
• Cold air moves over warmer water behind
cold fronts, west and south of low pressure
• Generally found in mid- to-high latitude locations over
the oceans, usually during cold season.
• In GOES imagery of the northern hemisphere, we are
most likely to see them over the North Atlantic and
North Pacific (not at subtropical latitudes!).
• Typical open cell pattern in the Pacific—it
is mainly a cold-season phenomenon.
• Closer view shows that some cells have cirrus
anvils. They can bring showery weather,
thunder, and small hail, but their tops are low
(20-25K ft.) compared to summer t-storms.
• Open cells occur with showery blustery
Sfc analysis for previous slides: open cells are in
northerly flow on west side of low pressure center,
behind cold front.
300 mb jet stream pattern: trough illustrates that cold
air has come southward off west coast.
• Notice open cells forming only over
Hudson Bay where water warmer than air
has destablized lower atmosphere.
Open vs. Closed Cells
• Closed cells occur where there is not as much
temperature difference between the water and
the air.
• They may be relatively lower level
stratocumulus clouds.
• Open cells occur in a more unstable
atmosphere; they are more convective.
• Open cells are rings of clouds surrounding clear
airpattern is more black than white.
• Closed cells are rings of clear air surrounding
cloudsmore white than black.
• Open cells common in high latitudes.
• Closed cells common in low latitudes.
• Transition from open to closed can mark the
position of jet stream…see following slides.
jet stream
“open” cells (more black
than white)
Jet stream axis
“closed” cells (more white
than black)
Documentation of jet stream.
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