Download ATMOSPHERE

ATMOSPHERE
MOISTURE IN THE
ATMOSPHERE
MOISTURE IN THE ATMOSPHERE
• Humidity vs. Relative
Humidity
– Atmosphere contains
water vapor
– Humidity: amount of
water vapor in the air
• Humidity is to blame for
that muggy, steam-room
feeling you experience on
certain summer days
MOISTURE IN THE ATMOSPHERE
• Humidity vs. Relative Humidity
– Relative Humidity: the ratio of water vapor
in a volume of air relative to how much
water vapor that volume of air is capable
of holding.
• Expressed as a percentage (%)
• Warm air can hold more moisture than cool air
• A reading of 100% means that the air is totally
saturated with water vapor and cannot hold
any more, creating the possibility of rain.
MOISTURE IN THE ATMOSPHERE
• Cloud Formation:
– Clouds form when
warm, moist air
rises, expands,
and cools in
convection current
– When millions of
droplets of water
collect, a cloud
forms
MOISTURE IN THE ATMOSPHERE
• Cloud formation:
– Orographic lifting:
• Wind encounters a mountain
and has no place to go but up
• This rising causes the air to
expand and cool creating a
cloud
• Also, if a warm mass of air
collides with a cooler mass of
air, the warm air is forced above
the cool air creating clouds
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Background:
• Air rises
• Water Vapor condenses into droplets of liquid
water
• If density great enough, droplets become visible
• Classification:
• Grouped by altitude of formation and shape
• Low clouds (STRATO) = below 2000 m
• Middle clouds (ALTO) = between 2000 m and 6000
m
• High clouds (CIRRO) = above 6000 m
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Low Clouds (STRATO):
• Radiation causes surface to become warmer
than surrounding air
• Temperature rises = air expands
• Air rises and begins to cool
• Water vapor condenses into water droplets
creating a visible cloud
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Low Clouds (STRATO):
• Cumulus cloud: if air does not stay warmer
than surrounding air, cumulus cloud forms
• Flat cloud and spread horizontally
• Puffy, lumpy looking clouds
• “Cumulus” = Pile or heap
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Low Clouds (STRATO):
• Nimbus cloud:
• Low, gray rain clouds
• “Nimbus” = cloud
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Low Clouds (STRATO):
• Stratus: if fog lifts away from Earth’s surface,
stratus clouds form
• Forms at heights below 2000m
• Layered cloud that covers much or all of sky in given
area
• Featureless sheets of clouds
• “Stratus” = layer
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Middle Clouds (ALTO):
• Either altocumulus or
altostratus
• Forms between 2000 m
and 6000 m
• Can be mixture of
liquid and ice crystals
• Usually layered
• Altocumulus resemble
white fish scales
• Altostratus are dark but
thin veils of clouds
• Can produce mild
precipitation
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• High Clouds (CIRRO):
• Form above heights of 6000 m
• Made up of ice crystals due to low
temperatures
• Cirrus clouds: appear wispy and stringy
• “Cirrus” = hair
• Cirrostratus: forms as a continuous layer that
sometimes covers sky
• Can vary in thickness from being almost transparent
to being able to block out Sun or Moon
MOISTURE IN THE ATMOSPHERE
• Types of Clouds:
• Vertical Development Clouds:
• If air that makes up cumulus cloud is unstable,
cloud will be warmer than surface or
surrounding air and will grow
• As it rises, water vapor condenses
• Air receives additional warmth
• Cumulonimbus = anvil shaped
• Produces torrential rains and strong winds
• Associated with thunderstorms
MOISTURE IN THE ATMOSPHERE
• Precipitation:
• Cloud droplets collide and join
together
• Coalescence: the process in
which a larger droplet forms
from collision of cloud droplets
• If droplet becomes too heavy to be
held in the air, gravity pulls the
droplet down as precipitation.
• Precipitation: all forms of water
both liquid and solid that fall from
clouds
MOISTURE IN THE ATMOSPHERE
• How do we get snow?
• If precipitation forms at cold temperatures,
it takes the form of snow
• How do we get hailstone or sleet?
• Convective currents carry droplets up and
down through freezing and nonfreezing air