Download geography 12 unit 6

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GEOGRAPHY 12
UNIT 6 - WEATHER - REVIEW WORKSHEET KEY
A. CLOUDS
1. Clouds are dense, visible concentrations of H2O droplets and ice particles suspended in
air. They are indicators of overall atmospheric conditions, including stability, moisture
content & weather. Low clouds reflect insolation, cooling the atmosphere, High clouds
absorb outgoing longwave radiation, warming the atmosphere.
2. As an air parcel rises, it cools to dew point, where the relative humidity is 100% It is lifted
further, condensing the vapour into H2O; this H2O can be supercooled below O°C (ie. 12°C) while retaining the liquid phase, and forms a cloud. Condensation nuclei which are
tiny solid aerosols that incl. pollution, dust, soot, volcanic & forest fire ash, sea spray are
required in order for clouds to form.
3. Cloud classification is based on shape & altitude. The 3 root forms are:
STRATIFORM: horizontally developed clouds that are flat, layered, blanket-like & cover
LARGE areas
CUMULIFORM: vertically developed clouds that are puffy & globular, & range in size.
CIRRIFORM: wispy, high clouds made of ice crystals
b) Low clouds (up to 2 km) are composed mostly of H2O droplets
3 types:
Stratus, Stratocumulus and Nimbostratus.
c) Middle Clouds (2-6 km) are mostly composed of H2O droplets (ice crystals if temp. is cold
enough).
2 Types = altostratus, and altocumulus
Altocumulus Lenticularis: resemble a lens that form near mountains
d)High Clouds (6-13 km) are composed of ICE CRYSTALS with white appearance at high
altitudes. They are responsible for optical/colour phenomenon due to ICE CRYSTALS
refracting light, are around -35°C, and do not have much vapour.
3 Types = Cirrus, Cirrostratus, Cirrocumulus
e) Vertically-developed clouds (near surface to 13km) are formed from convection or
frontal uplifting, H2O droplets below; ice crystals above
3 Types = Cumulus, cumulus congestus, cumulonimbus
4. Fog is a near-ground surface cloud that indicates that air is saturated.
Temperature inversion occurs at the upper limit of fog; ground is cool under the fog & the
air above in the sunny skies is warmer.
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5. Advection fog results when a warm, moist air layer moves over a cold surface, eg. lake,
ocean, swimming pool.
Radiation fog is motionless air that cools below the DP due to loss of longwave radiation at
night.
6. Fog can cause car accidents, flight delays, navigational danger for ships, economic loss
& inconvenience to travellers.
7. Humidity refers to the amount of H2O vapour in the air.
Cold, dry air in arctic regions have little H2O vapour
Warm, wet equatorial regions have ~ 4 - 5% vapour
General rule: Warm air can carry MORE H2O vapour than cold air
b) Specific humidity (SH): mass of vapour in a fixed volume of air at a given temp; tells how
much vapour is available for precipitation
Relative humidity (RH): the amount of vapour present in the air relative to the maximum
(saturation) amount of vapour that the air can hold at given temperature
Hygrometer measures RH
c) Increasing the temperature will increase the vapour-carrying capacity ∴ decreasing the
RH
Decreasing the temperature will decrease the vapour-carrying capacity ∴ increasing the
RH
8. Dew point (DP) is the temperature at which the vapour in an air mass saturates from gas
to liquid or solid. Dew forms during clear evenings. The ground loses its heat, & cools the air
above it. As air temperature drops, RH increases until it reaches 100%. The ground
becomes covered by a layer of dew or frost.
9. The adiabatic process is the process by which ∆’s in air temp. occur as a result of ∆’s in
atmospheric pressure, not b/c of gain or loss of heat from outside the air parcel
According to the Laws of Thermodynamics, there is an inverse relationship b/w the volume
of an air parcel & its temp.
10. Adiabatic cooling = as the air parcel is uplifted (buoyant force), pressure will ↓, allowing
it to expand; the air cools b/c molecules are doing work (consuming energy) as they
expand
Adiabatic heating = the lifted air parcel will soon start to sink (gravitational force), &
pressure will ↑ as it descends; the air parcel will then be compressed & ∴ become warmed
b/c the volume has ↓’d
11. Dry Adiabatic Lapse Rate (DALR) is the rate at which rising air is cooled by expansion
without any condensation occurring
• DALR drops 10°C per 1 km ↑ in height
• DALR applies only to an air parcel in vertical motion
• Remains constant
b) Normal Lapse Rate (NLR): this is the average ↓ in temp. with ↑’ing height
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•
•
It is 6.4°C/1 km
NLR only applies to still, calm air & will vary based on local weather conditions
c) What is WALR? What are its characteristics?
Wet Adiabatic Lapse Rate (WALR is rate at which air reaches the dew point & condenses
• With the added moisture, cooling rate ↓s’ to ~ 4.5-5.0°C/km
Rate depends on moisture content & temperature/ pressure of air
B. WEATHER
1. Weather is the short-term, day-to-day condition of the atmosphere
Climate is the prevailing weather conditions at a given place, based on long-term
observations
2. Air mass is a LARGE body of air with fairly uniform temp. & moisture characteristics
• It can be several thousand km across, & can extend to the tropopause
• Each AM has a distinctive surf. temp., & surf.-specific humidity
3. Source region is an extensive land or ocean surface over which a stagnant/slow-moving
AM derives its temp. & moisture characteristics.
Eg. a cold arctic zone will produce a cold AM with LOW vapour content
Eg. a warm equatorial ocean will produce a warm AM with HIGH vapour content
4. When AMs move from 1 region to another under the influence of PGF or jet streams; the
AM will then adopt properties of the new envt, ie. losing heat or gaining vapour
5. Classified based on:
• Source region classification: this determines moisture content
• Latitude: this determines surf. temp. & ELR
6.
PROPERTIES OF TYPICAL AIR MASSES
Air Mass
Symbol Source Region
Maritime
equatorial
Maritime tropical
mE
mT
Continental
tropical
cT
Maritime polar
mP
Continental
polar
cP
Properties
Warm, equatorial
Warm, v. moist
oceans
Warm tropical oceans Warm, moist, unstable, active
weather; humidity causes
hurricanes. Causes summer
heatwave in Ontario
Subtropical deserts
Warm, dry, generally stable
(New Mexico.,
Arizona)
Midlat. Oceans (BC,
Cool, moist in winter, unstable
E. Cdn Coast)
Northern continental
Cold, dry in winter, stable from
NS
interiors (cP & mT
cause tornadoes)
Temp.
(°°C)
27
24
24
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-11
3
Continental
arctic/Antarctic
cA
cAA
North/South Poles
v. cold, v. dry in winter
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13. Continental Polar (cP) originates over north-central Canada
Winter: forms tongues of cold, dry air that periodically extends southeast to produce
anticyclones, cold temp. & clear skies
Summer: forms cool, dry air that is moderately stable
14. Continental Arctic (cA) develops over the Arctic Ocean (only during the winter)
extremely cold & stable and moves southward over N. America, producing a severe cold
wave.
15. Continental Tropical (cT) originates in N. Mexico & SW USA in summer
Summer: hot, dry air that is stagnant
16. Forms in 2 locations:
Over the N. Pacific Ocean & Bering Strait in the Aleutian Low
Over the North Atlantic Ocean in the Icelandic Low
In the Winter & Summer: air is cool, moist (humid) & unstable; causes precipitation along
coast, especially in winter
17. In the Winter:
The G. of Mexico mT moves northward, bringing warm, moist, unstable air over the eastern
parts
The mT Pacific brings warm, moist, unstable air to California, causing heavy ppt
In the Summer:
The mT Gulf/Atlantic brings hot, moist, v. unstable air to central/eastern US, causing heavy
thunderstorms
The Pacific mT brings moist, stable OR conditionally unstable air to S. California/ Arizona,
causing thunderstorms
15. Convergent Lifting is when air flowing from different directions converges into the same
LOW pressure area; air is heated, ie. due to a warm patch of ground, & it becomes LESS
dense than surrounding air.
Convectional Lifting is the upward motion of a parcel of heated air
Begins when a surface is heated unequally, eg. a farm field surrounded by a forest will
warm faster; since warm air is less dense than cool air, it will rise
16. Urban heat island = urban areas that have higher average temperature than rural
areas; surface heating here will enhance convectional lifting. If unstable conditions, lifting
continues, forming clouds.
C. Cyclones and Anticyclones
1. Anticyclone = divergence & downward motion cause air to descend & warm
adiabatically
NO condensation ∴ fair weather system
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Winds are light & variable
Found in midlats & generally move either eastward or equatorward
2. Cyclone is a low pressure centre with convergence & upward motion
Cyclogenesis (cyclone formation): begins along the polar front, where warm & cold AM’s
converge & move upward
3. Northern Hemisphere: CCW ascending inspirals
Southern Hemisphere: CW ascending inspirals
4. 2 anticyclones come in contact at the polar front. One is a warm, moist maritime AM, the
other is a cold, dry polar AM; both converge from opposite directions on the 2 sides of the
polar front, causing unstable conditions
Stage 1 - Early stage (Cyclogenesis): cold air is turned in a southerly direction & warm air in
a northerly direction; each will advance on the other, forming ppt
Stage 2 - Open stage: the “Low” along the polar front has deepened & intensified; cold air
pushes SE along a cold front, & warm air moves NE along a warm front. The zones of ppt
are much more developed
Stage 3 - Occluded stage: the cold front has overtaken the warm front, producing an
occluded front; the warm AM at the centre of the inspiral is forced OFF the ground, which
intensifies ppt
Stage 4 - Dissolving stage: the polar front is reestablished, but a pool of warm, moist air
remains aloft. As the moisture dries out, ppt ↓’s & clouds disappear
5. Begins as part of a cumulonimbus cloud travelling in front of a cold front where
turbulence is greatest
Occurs when a cold mP AM lifts a warm, moist mT AM
Upper troposphere contains faster winds than at the surf. due to less surf. friction
This creates rotating air that encounters strong frontal updrafts
As more moisture-laden air is drawn up, air rotation becomes more rapid
Funnel clouds pulse from the parent cloud towards the surface, these become tornadoes
6.
A tropical cyclone is found in tropical & subtropical zones (∴ tropical AMs) and develops
b/w 8-15° N & S lat
Effects:
•
Flooding can result
•
Coastline can be severely damaged
•
Property damage ($$$)
•
Coral atolls can be swept over
7. Sleet = ice storms that include freezing rain, ice pellets. It is severely damaging to urban
areas the ice coats power lines & tree limbs
Hail = ice pellets formed within a cumulonimbus cloud. Raindrops circulate throughout
cloud, constantly melting & freezing; this adds layers of ice. When it becomes too heavy for
cloud to support weight, it falls to the ground heavy damage to buildings & cars
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D. Weather Maps
1. Location Q
2. Northwest
3. 15°C
4. 1000.7mb
5. Southwest
6. 10°C
7. 984.2mb
8. Location Z
9. Location W
10. Weather Station W
11. 1001.1mb
12. Clear; less than 1/10th of the sky is covered by clouds
13. 8-12 knots or 15-22 km/h
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