Comma Cloud Pattern
Two uses for the term "comma cloud" in relation to
satellite image
patterns.
(1) traditional meaning refers to cloud
pattern
associated with mature midlatitude cyclonic storm systems.
(2) west coast meaning refers to a
non-frontal
single air-mass area
of enhanced clouds associated with an upper level cyclonic
vorticity
maximum.
Both literally shaped like a comma.
Comma Cloud
Associated With
Midlatitude Cyclone
Comma-shaped with a head, tail, and socalled dry-slot
region to
west of tail.
Associated with synoptic scale weather features of a
midlatitude
cyclone.
16 March 1998
Comma cloud pattern is essentially created by so-called
"conveyor belt"
circulations of midlatitude storm systems:
Dry slot region forms from "dry conveyor belt." Dry
upper
tropospheric and lower stratospheric air descends behind
cold front:
Example of Comma Cloud
Associated with
a Midlatitude Cyclone:
01 Feb. 2006 Unenhanced IR of comma cloud pattern associated
with
occluding low pressure center.
01 Feb. 2006 Enhanced IR of comma cloud pattern
associated
with occluding low pressure center.
Dry slot region shows up in satellite water vapor imagery:
Comma Cloud
Associated With
Non-frontal Single Air Mass Enhanced Clouds (West Coast
Usage):
West Coast meteorologists use the term comma cloud to refer
to
non-frontal areas of enhanced cloudiness associated with an
upper-level
vorticity maximum, often well behind the front in the cold
air
mass. They are much smaller than the classical frontal
comma
cloud formation.
Click on this loop
of
non-frontal comma cloud behind a more classical comma
cloud feature approaching the west coast of the U.S.
This "comma" forms as a propagating upper-level vorticity
maximum moves over an area of open cell convection.
The lifting
environment in the positive vorticity advection area ahead
of the
vort-max allows for deeper convection and higher, colder
cloud
tops.
Monteverdi (1976) asserts that these single air-mass
disturbances were
associated with an average of 30% of the annual
precipitation at San
Francisco.
Reference
Monteverdi, John P.
The Single Air Mass Disturbance and Precipitation
Characteristics at
San Francisco
Monthly Weather Review
1976
104: 1289-1296