Transcript Weather Dynamics II

Weather Dynamics
Science 10
G.Burgess
2007
• Our weather is dependant on the
movements of air and water.
• Light from the sun heats the Earth
and oceans which in turn heat the
surrounding air making weather
patterns.
We will be discussing the effects of the
sunlight and water on our weather.
Source of energy
• Light from the sun is the driving force for our
weather
• Solar radiation (radiation from the sun) is
absorbed by the waters and soils of the Earth.
• Absorbed light energy is converted into heat.
The more direct the light, the warmer it feels.
• Excess energy absorbed by the Earth is reradiated out into space as infra-red radiation
Radiant Energy
• Sunlight and infrared
radiation is called
radiant energy.
• It is energy coming
from a source
• Another example of
radiant energy is the
energy given off by
your stove to heat a
pot of soup.
Atmosphere
• the atmosphere
has several
layers
• Temperatures
change through
each layer
• Troposphere:
region closest to
the ground (first
10km)
• Most of our
weather occurs
Other layers of the Atmosphere
• Ozone layer: absorbs
harmful ultraviolet rays
before they reach the
Earth.
• Stratosphere: as altitude
increases through this
layer, the temperature
increases as well, due to
the absorbed heat from
the ozone layer
• Next is the mesosphere;
temperature decreases
as the altitude increases
• Lastly, the thermosphere,
this is the hottest layer of
all
• It is also where the
auroras (aurora borealis)
originate.
• Auroras are caused by
the solar winds of the sun
colliding with gases in the
atmosphere
What happens when sunlight
reaches the Oceans?
• Converted to heat energy
• Different objects are able to absorb different amounts of
heat
- specific heat capacity
• Water has different specific heat capacities depending
on its state (solid, liquid, or gas)
• Ice has a specific heat capacity of about 2.10J/gºC,
water about 4.18J/gºC and steam 2.08J/gºC.
• Snow and ice can reflect as much as 90% of the
incoming radiation
• Water is the only substance known that can be in all
three stages at temperatures found on Earth.
Properties of Water
• Absorbs more heat than other substances (Sp
Heat Capacity: 4.18J/gºC)
• Thus absorbing a lot of the heat generated by
sunlight.
• Latent heat of fusion: the amount of heat needed
to change ice into water (333J/g°C)
• Latent heat of vaporization: the amount of heat
needed to change water from a liquid to a gas
(2260J/g°C)
Graph of Effects of heat on Water
http://www.nku.edu/~cinsam/intsci/sci110/worksheets/heatfusion.html, accessed
Jan.11, 2007.
Water in the Air
• As stated earlier, the higher up the troposphere you go,
the cooler the air gets.
• Warm water vapor will rise with warm air
• As the air rises, the moisture in it condenses on dust
particle to form condensation nuclei and then clouds
• The amount of water vapor in the air is called humidity.
The actual amount of water in the air expressed in gram
of water to kilograms of air is called the Absolute
Humidity.
• Weather forecasters use the term Relative humidity
referring to the percent of water in the air relative to the
amount of water the air can hold.
• When the clouds are saturated with water (100% relative
humidity), they release it as precipitation
What happens when sunlight
reaches land?
• Land does not absorb as much heat
energy as water
• This is the reason why pavement and
beach sand feel hot on your feet, while
lake water feels cool.
• YES, their temperatures are different, but
they are being bombarded with the same
amount of heat energy.
Example:
**Radiation entering water also travels deeper than soil or
pavement. Only the top of the pavement absorbs the light
energy.
Light Absorption and conversion
into heat energy.
Effects of heat absorption land
versus Ocean breezes
• During a summer’s day, the sun heats up
the land and water
• Since the land cannot absorb much
sunlight, it releases heat energy and
warms up the air
• The air rises and moves toward cooler
areas (over the ocean)
• Ocean air moves toward the land
During the Day
During the Night
• When there is not sun present, the land
cools quickly absorbing energy from the
air and cooling the air
• The ocean water with its stored energy is
able to heat the air
• The warm air rises and travels toward the
cooler air over the land.
During the night
Air Masses
• Large portions of air often remain at the
same place long enough to take on the
temperature and moisture characteristics
of the land or ocean below.
• Air mass: a large portion of air that is
nearly uniform in temperature and
humidity
Types of air masses
1.
2.
3.
4.
•
Continental (drier)
Maritime (moist)
Polar (cool)
Tropical (warm)
These types air masses are combined to
explain the conditions.
– ie. Continental polar, continental tropical,
maritime polar, maritime tropical
Air masses (con’t)
• Once these air masses start to move (due
to wind) and collide, they form Fronts.
• Read pp 466 and 467
– Do qstns 1-4 468, 1-3 480, and 1-3 501.
Cloud formation
• Conditions needed; water vapour,
saturated air and condensation nuclei
• As air condenses it loses its ability to hold
moisture. The temperature at which air
forms water droplets is called its dew
point.
– Air is cooled with increased altitude and also
expands as it rises
– Air is also cooled by cold land.
How do they grow?
• First, the air must condense
• Water droplets collide and blend together
forming larger water droplets (this method is
most common in warm air regions)
• Once the water droplets are large enough, they
fall as precipitate
• Snow; water vapour condenses as ice crystals
and the ice crystals grow as more water is
added.
• Read pp 494-495 do qst 1-5.
Types of clouds
• Cumulus
– puffy with flat bases
– “cauliflower clouds”
– Formed by air masses meeting
• Stratus
– Form in layers
– Flat, without shape
– Formed by meeting air masses or masses rising over
mountain
– Similar to ground level fog.
• Cirrus
– Formed by ice crystals when very little water in the air
– Air needs to rise very high to reach dew point
• Nimbus
– Rain or snow cloud
• Clouds may be formed as combinations of these
types;
– ie. Nimbostratus, cumulonimbus
Altitude and clouds
• Low clouds: <2000m
– Almost all stratus clouds
• Middle clouds: 2000-6000m
– “alto”
• High clouds: >6000m
– Cirro or cirrus clouds
– Most are formed from ice crystals
Rain or no rain
• Dependant on the size of the water
droplets
– Most clouds have water droplets ~0.2mm
– Rain requires water droplets ~0.5mm (fine
mist)
– The average rain drop is ~0.2mm
Frontal systems
• The region between two air masses is called
a FRONT.
• Cold fronts: occur when cold air mass
pushes a warm air mass.
– The cold air pushes the warm air upward
– This causes the air to condense and form
cumulus clouds, rain usually comes from the
formation of cold fronts
• Warm Fronts: occur when warm air
overtakes a cold air mass.
– The warm air rises gradually forming stratus and
cirrus clouds
– May cause precipitation, however the rain may
last longer than if formed by a cold front.
• Stationary Front: when cold air mass and
warm air mass are in contact but are not
moving.
• Warm air drifts up and over cold air mass.
• Causes overcast weather