Download Lecture5-PrecipII

Lecture 5
Precipitation (2)
• Clouds
• Weather Systems
• Global Precipitation Patterns
• Regional Precipitation Patterns
Clouds
Form
Cirrus: fibrous
Stratus: sheets
Cumulus: heaped
Height
High clouds (>6 km)
Mid-level clouds (2-6 km)
Low-level clouds (<2 km)
Aherns, C.D., 1991, Meteorology Today, An Introduction to Weather, Climate and
the Environment. West Publishing Company. Chapter 7.
Clouds
1.
2.
3.
4.
High clouds (5000-13,000 m, mid-latitudes):
Cirrus (Ci)
Cirrostratus (Cs)
Cirrocumulus (Cc)
Middle clouds (2000-7000 m, mid-latitudes):
Altostratus (As)
Altocumulus (Ac)
Low Clouds (0-2000 m)
Stratus (St)
Stratocumulus (Sc)
Nimbostratus (Ns)
Clouds with vertical development
Cumulus (Cu)
Cumulonimbus (Cb)
Aherns, C.D., 1991, Meteorology Today, An Introduction to Weather, Climate and
the Environment. West Publishing Company. Chapter 7.
Cirrus Clouds
thin and wispy
The most common form of highlevel clouds are thin and often
wispy cirrus clouds. Typically
found at heights greater than
20,000 feet (6,000 meters), cirrus
clouds are composed of ice
crystals that originate from the
freezing of supercooled water
droplets. Cirrus generally occur in
fair weather and point in the
direction of air movement at their
elevation.
Cirrostratus Clouds
sheet-like and nearly transparent
Cirrostratus are sheet-like, high-level
clouds composed of ice crystals.
Though cirrostratus can cover the
entire sky and be up to several
thousand feet thick, they are relatively
transparent, as the sun or the moon
can easily be seen through them.
These high-level clouds typically form
when a broad layer of air is lifted by
large-scale convergence
Altocumulus Clouds
parallel bands or rounded masses
Altocumulus may appear as parallel bands (top
photograph) or rounded masses (bottom
photograph). Typically a portion of an
altocumulus cloud is shaded, a characteristic
which makes them distinguishable from the highlevel cirrocumulus. Altocumulus clouds usually
form by convection in an unstable layer aloft,
which may result from the gradual lifting of air in
advance of a cold front. The presence of
altocumulus clouds on a warm and humid
summer morning is commonly followed by
thunderstorms later in the day.
Nimbostratus Clouds
dark, low-level clouds with precipitation
Nimbostratus are dark, low-level clouds accompanied by light to
moderately falling precipitation. Low clouds are primarily composed of
water droplets since their bases generally lie below 6,500 feet (2,000
meters). However, when temperatures are cold enough, these clouds
may also contain ice particles and snow.
Stratocumulus Clouds
low, lumpy layer of clouds
Stratocumulus clouds generally appear as a low, lumpy layer of
clouds that is sometimes accompanied by weak intensity
precipitation. Stratocumulus vary in color from dark gray to light gray
and may appear as rounded masses, rolls, etc., with breaks of clear
sky in between.
Fair Weather Cumulus Clouds
puffy cotton balls floating in the sky
Fair weather cumulus have the appearance of floating cotton and have a
lifetime of 5-40 minutes. Known for their flat bases and distinct outlines, fair
weather cumulus exhibit only slight vertical growth, with the cloud tops
designating the limit of the rising air. Given suitable conditions, however,
harmless fair weather cumulus can later develop into towering
cumulonimbus clouds associated with powerful thunderstorms.
Cumulonimbus Clouds
reaching high into the atmosphere
Cumulonimbus clouds (Cb) are much larger and more vertically
developed than fair weather cumulus. They can exist as individual
towers or form a line of towers called a squall line. Fueled by vigorous
convective updrafts (sometimes in excess 50 knots), the tops of
cumulonimbus clouds can easily reach 39,000 feet (12,000 meters) or
higher.
Global Circulation Pattern
Chrisopherson (2000), Figure 6-13, or Jones (2000), Figure 2.4