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Tuesday, April 26, 2011
Chapters 9, 10 & 15
Weather & Climate
Chapter 9: Weather Patterns
• Polar Front Theory (1800s)
• Mid-latitude Cyclone
• Low pressure system
• Mid-latitudes
• 600+ miles in size
• Fronts
• Boundary surfaces that separate different air masses
• Usually having different temperature and humidity
• Fronts said to be Overrunning one another
• Warm Front, Cold Front, Stationary Front, & Occluded Front
• Life cycle of a mid-latitude cyclone
• Formation - Cyclongenesis
• Cyclonic flow development
• Occlusion
• THE FOLLOWING ARE NOT INCLUDED:
• Idealized weather of a mid-latitude cyclone
• Formation – Cyclongenesis
• The Conveyor Belt Model (the modern viewpoint)
• Warm, Cold and Dry Conveyors
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Polar Front Theory
• Polar Front Theory (1800s)
• Mid-latitude Cyclone
• Low pressure system
• Cyclone
• Counter-clockwise rotation
• Air spinning into the Low
• Mid-latitudes
• Continental US to Southern Alaska
• 600+ miles in size
• Term “Fronts” first used after WWI(the air masses acted like army „fronts‟)
Fronts
• Fronts
• Boundary surfaces that separate different air masses
• Different temperature and humidity
• Fronts said to be Overrunning one another
• One front is overtaking the other
• Synoptic indication (how we show on a weather map)
• Colors
• Symbol
• Point in direction of movement
• Types of Fronts
• Warm Front – Warm air overrunning Cold
• Cold Front – Cold air overrunning Warm
• Stationary Front – Air masses moving parallel
• Occluded Front – Three air masses combining
• Cold-type – The first front is colder than the last
• Warm-type – The first front is warmer than the last
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Fronts
Warm Fronts
• Warm Front – Warm air overrunning ColdWarm Cold
• Wedge shaped – gentle slope
• Usually lighter, long-lasting rain
• Red line with semi-circles
• Has two types that tend to differ by season
• Summer:
• Air tends to be unstable (warmer than surrounding air)
• Precipitation tends to form in Cumulonimbus clouds(heavy, shorter rain)
• Other times of the year:
• Air tends to be stable (cooler than surrounding air)
• Precipitation tends to form in stratus clouds(lighter, longer rain)
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Warm Fronts
Warm Fronts
SUMMER:
(unstable air)
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Cold Fronts
• Cold Front – Cold air overrunning WarmCold Warm
• Plow shaped (snowplow) – steep slope
• Clouds tend to be Cumulonimbus
• Usually heavy, short-lived rain
• Often form into thunderstorms
• Can produce tornadoes
• Blue line with triangles
Cold Fronts
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Stationary Fronts
• Stationary Front – Air masses moving parallelW↓↑W C↑↑W W↑↑W C↓↑W C↓↑C
• Fronts NOT overrunning each other
• Move either in same direction or opposite
• Can also be in a rotational relationship
• Alternating blue & red lines (with appropriate symbols)
Occluded Fronts
• Occluded Front – Three air masses combining
• A cold front overrunning a warm front……which is overrunning a cold front
• More gentle slopes
• Tend to bring medium to light rain
• Purple line with BOTH symbols
• Cold-typeThe first front is colder than the last
• Cold Warm Cool
• Warm-typeThe first front is warmer than the last
• Cool Warm Cold
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Occluded Fronts
Life Cycle of a Mid-latitude Cyclone
• Formation – Cyclongenesis
• Begining stage of cyclone development
• Cyclonic flow development
• Due to clash of cold and warm air masses
• Warm air rises… begins the interaction
• Low pressure forms, causing CCW movement
• Occlusion – the end begins…
• Eventually, warm air is lifted over cold
• This inversion stops vertical development
• Process eventually stops
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Life Cycle of a Mid-latitude Cyclone
Idealized Weather of the Mid-latitude Cyclone
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Chapter 10: Thunderstorms
• Thunderstorms
• A storm that generates lightning and thunder
• Frequency & Location
• Two types of Thunderstorms
• Air-Mass Thunderstorm
• Thunderstorm which occur within one air mass (mT)
• Localized, short-lived thunderstorms
• Stages of Development
• Cumulus Stage
• Mature Stage
• Dissipating Stage
• Severe Thunderstorm
• Supercell Thunderstorms
• Lightning and Thunder
• A thunderstorm is only a thunderstorm IF thunder is heard!
• Thunder can only be heard if lightning happens first
• Interesting facts
Thunderstorms
Thunderstorms
• A storm that generates lightning and thunder
• Frequently includes
• Gusty winds
• Heavy rain
• Sometimes includes
• Hail
• Tornadoes
• Frequency
• 2,000 thunderstorms occurring right now (worldwide)
• 100,000 per year in US
• More than 1,000,000 lightning strikes per year in US
• Location
• Hot and Moist environments = more
• US pattern of Thunderstorms
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Thunderstorms
Thunderstorms
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Thunderstorms
Thunderstorms
Two types of Thunderstorms
• Based on strength and (potential) destructiveness
• Air-Mass Thunderstorm
• Thunderstorm which occur within one air mass (mT)
• Produce heavy rain for a short periods, then light rain
• Stages of Development
• Cumulus Stage
• Mature Stage
• Dissipating Stage
• Severe Thunderstorm
• Very powerful (and dangerous) thunderstorms58+ mph winds and/or ¾”+ hail
• Supercell Thunderstorms
• Most destructive thunderstorms
• 2 – 3,000 per year in US… most damage and deaths
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Air-Mass Thunderstorm
•Air-Mass Thunderstorm
• Thunderstorm which occur within one air mass
•Often mT (maritime Tropical – Humid and Hot)
• Earth‟s heating is the cause
•Spring & Summer ground heating
•Mid- to Late-Afternoon ground heating
• Localized, short-lived thunderstorms
• Storms are scattered, isolated clouds, or small cloud cells
•Cloud Cell = Grouping of several individual clouds
• Produce heavy rain for a short period, then changing to light rain
Stages of Development:
Cumulus Stage
• Start with mT air mass (Humid and Hot)
• Add heating from the earth (summer/afternoon)
• Warm air rises Expands/cools Condenses Cumulus Clouds
• This rising air is called Updrafts (convection)
• As the updrafts continue, the cloud gets larger and higher
• Precipitation (Bergeron) begins to form above the freezing line
• Precipitation begins to fall
• Entrainment begins
• Falling rain pulls in cold, dry air from outside the cloud top
• The cold dry air follows the path of the falling rain
• It evaporates most (all?) of the rain…
• … but continues falling (colder = denser = heavier)
• evaporation also helps cool the air (endothermic)
• Cold Downdrafts (or Gusts) blow out ahead of the storm cloud
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Stages of Development: Mature & Dissipating
• Mature Stage
• Precipitation increases and cold downdrafts continue
• Updrafts continue, bringing moisture and energy (latent heat)
• Expect:
• Updrafts
• Cold downdrafts
• Heavy precipitation
• Lightning and thunder
• Possible hail and occasional tornadoes
• Dissipating Stage
• Updrafts begin to slow and stop
• No additional moist, hot air is entering cloud
• Moisture within the cloud begins to lessen
• Entrainment weakens: less precipitation forms and falls
• Precipitation becomes light
• Eventually the rain and downdrafts stop
Stages of Development
Entrainment
Updrafts
Downdrafts
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Severe Thunderstorms
• Severe Thunderstorms are very powerful thunderstorms which produce
• winds > 58 mph and/or
• hail > 3/4”
• They also tend to include:
• heavy downpours
• flash flooding
• Straight-line winds
• Non-rotating, fast, local-scale winds. Very destructive.
• Large hail
• Frequent lightning
• Potential Tornadoes
Severe Thunderstorms
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Severe Thunderstorms
• Severe Thunderstorms
• The structure of these thunderstorms allow the warm updrafts to reach great heights
• Updrafts tilt due to wind sheer(rapid horizontal and/or vertical movement)
• Entrainment does NOT interfere with the updrafts
• Thus they reach higher altitudes and build up more power
• The updrafts can actually create more updrafts, adding to the storms intensity
• Supercell Thunderstorms
• Most destructive severe thunderstorms
• 2,000 – 3,000 per year in US… but responsible for most damage and deaths
Severe Thunderstorms
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Lightning and Thunder
•Thunderstorm
• A thunderstorm is only a thunderstorm IF thunder is heard!
• Thunder can only be heard if lightning happens first
•Lightning
• Lightning is the discharge of an electric charge from a cloud
• Most lightning strikes occur from cloud to cloud (sheet lightning)
•Only 20% of strikes are cloud to ground
•But these account for most lightning caused damage and death
•Thunder
• Lightning bolt discharges in a small “tube” of air (10cm +/-)
• Air is superheated to 50,000°F in less than 1 second!
• The air expands explosively and creates a sonic boom = thunder
Cloud to Cloud Lightning (80%)
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Cloud to Ground Lightning (20%)
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Lightning Formation
•Lightning
• How lightning forms
•Lightning Flash: Bright streak of lightning, made up of multiple strokes (3-4)
•Lightning Stroke: Individual discharge, lights up the pathway
•As a cloud forms it begins to develop an electrical charge
•Since opposite charges attract and like charges repel…
Positive and Negative Charges
Like charges repel
(+) (+)
(-) (-)
Opposite charges attract
(-) (+)
(+) (-)
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Lightning Formation
How lightning forms
• As a cloud forms it begins to develop an electrical charge
• Scientists believe the cold ice crystals (Bergeron process) create a positive charge (+) in the upper cloud
• The warmer, lower cloud forms a negative charge (-)
• Under the cloud, the ground begins neutral: neither (+) or (-)
• Since opposite charges attract and like charges repel…
• The negative charge at the bottom of the cloud…
• Pushes away the negative (-) ground charges and
• Attracts the positive (+) ground charges
• The ground under the cloud becomes positively (+) charged
Lightning Formation
+ + + + ++ + + + ++ + + + ++ + + + +
- - - - - - -- - - - - - -- - - - - - -- - - - - - -
+ + + + +
+ + + + ++ + + + +
Positive
Negative
< air >
Positive
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Lightning Formation
• Step leaders (downward ionized air pathways)
form from the cloud bottom
• These “step” down to the surface
• As it nears the ground, the ground charge
rises to meet the leader
• Now, negative (-) charged particles in the leader
flow to the ground
• The Return Stroke, is the upward movement of the initial
discharge making its way to the cloud base.
• When it reaches the cloud base, the negative charges flow
from the cloud to the ground in several strokes.
• Each following stroke begins with a Dart Leader
(a smaller ionized pathway) that allows the process to continue.
• The cloud base is now fully discharged of its
negative charge and begins to build up again.
Lightning Formation
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Lightning Formation
Chapter 10: Thunderstorms
• Thunder
• The sound emitted from a lightning bolt heating the air it is passing through
• A lightning bolt discharges in a relatively small “tube” of air (10cm +/-)
• The air within that pathway is superheated
• It can rise 50,000°F in less than 1 second!
• The air expands explosively and creates a sonic boom = thunder
• Heat lightning
• When lightning occurs more than 12 miles away, we often do not hear the thunder
• We only see the lightning and this is referred to as heat lightning
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Lightning and Thunder
• Interesting facts
• Lightning bolts can be up to five miles long
• It is not uncommon for lightning to strike out of the blue sky
• A single lightning bolt can pack a wallop! 100,000,000 Volts!
• Lightning can kill! 4,000+ killed in US since 1960
• Odds of being hit by lightning?
• 1 : 700,000 per year
• 1: 3,000 in your lifetime!
• You can judge how far away thelightning is by counting the secondsbetween the flash, and when you hear the thunder…
• 5 seconds = 1 mile
Chapter 15: World Climates
Köppen Climate Classification SystemClimate Types – are based on… Temperature
Monthly and Yearly average
Precipitation
Monthly and Yearly totals
6 Climate Types
A - Tropical Moist Climates
All months avg. above 18° C
B - Dry Climates
Little precipitation much of the year
C - Moist Mid-latitude Climates with Mild Winters
D - Moist Mid-Latitude Climates with Cold Winters
E - Polar Climates
Extremely cold winters and summers
H – Highland Climates
Hybrid of multiple climate types due to change in altitude (colder temperatures at higher elevation)
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Climate Classification:
Köppen Classification System
The Köppen Climate Classification System is the most widely used for classifying the world's climates. Most classification systems used today are based on the one introduced in 1900 by the Russian-German climatologist Wladimir Köppen
Köppen divided the Earth's surface into climatic regions that generally coincided with world patterns of vegetation and soils
The Köppen system recognizes five major climate types based on the annual and monthly averages of temperature and precipitation. One additional type is a hybrid of the others based on altitude changes. Each type is designated by a capital letter.
Climate Classification: Köppen Classification System
A - Tropical Moist Climates
All months avg. above 18° C
B - Dry Climates
Little precipitation during most of the year.
C - Moist Mid-latitude Climates with Mild Winters
D - Moist Mid-Latitude Climates with Cold Winters
E - Polar Climates
Extremely cold winters and summers.
H – Highland Climates
Hybrid of multiple climates due to altitude change
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Köppen Classification System
A – Moist Tropical
Moist Tropical Climates are known for their
high temperatures year round
and for their large amount of year round rain.
Climate types Further divisions
A Climates
Tropical climates with
abundant precipitation
during a portion of the
year. Mean monthly
climates must exceed
18ºC; precipitation
exceeds evaporation.
f: mean precipitation of each month is at least 6cm
m: short dry season is compensated for by surplus
precipitation in wetter months
w: well defined dry season producing a period of water
shortage
Köppen Classification System
A – Moist Tropical
Tropical Moist Climates (Af) RAINFOREST
• Rainfall is heavy in all months (total is often more than 100 in.)
• There are seasonal differences in monthly rainfall, but temperatures of 80°F are found year round. Humidity is between 77% and 88%.
• High surface heat and humidity cause cumulus clouds to form early in the afternoons almost every day.
• The climate on eastern sides of continents are influenced by maritime tropical air masses. These air masses flow out from the moist western sides of oceanic high-pressure cells, and bring lots of summer rainfall.
• The summers are warm and very humid. It also rains a lot in the winter
– Average temperature: 18°C (°F)
– Annual Precipitation: 262 cm. (103 in.)
– Latitude Range: 10°S to 25°N
• Global Position: Amazon Basin; Congo Basin of equatorial Africa; East Indies, from Sumatra to New Guinea.
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Köppen Classification System
A – Moist Tropical
Tropical Moist Climates (Af) RAINFOREST
Köppen Classification System
B – Dry Climates
Dry Climates are characterized by little rain
and a huge daily temperature range.
Climate types Further divisions
B Climates
Arid and semiarid climates
of the low and middle
latitudes Evaporation
exceeds precipitation.
w: arid
s: semiarid
h: mean annual temperature above 18ºC
k: mean annual temperature below 18ºC
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Köppen Classification System
B – Dry Climates
Dry Tropical Climate (Bw) DESERT BIOME
• These desert climates are found in low-latitude deserts approximately between 15° to 30° in both hemispheres
• These latitude belts are centered on the tropics of Cancer and Capricorn and coincide with the edge of the equatorial subtropical high pressure belt and trade winds
• Winds are light, which allows for the evaporation of moisture in the intense heat.
• Air flow is dominated by subsidence (downward) thus they get little rain. This makes for a very dry heat. The dry arid desert is a true desert climate, and covers 12% of the Earth's surface.
– Temperature Range: 16°C
– Annual Precipitation: 0.25 cm (0.1 in). All months less than 0.25 cm (0.1 in).
– Latitude Range: 15°- 25° N and S.
• Global Range: southwestern United States and northern Mexico; Argentina; north Africa; south Africa; central part of Australia.
Köppen Classification System
B – Dry Climates
Dry Tropical Climate (Bw) DESERT BIOME
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Köppen Classification System
C – Moist, Mid-Latitude: Mild Winter
In Humid Middle Latitude Climates,
maritime/continental differences play a large part.
These climates have warm, dry summers and cool, wet winters.
Climate types Further divisions
C Climates
Mild and humid climates primarily
in the lower middle latitudes. Mean
monthly temperature of the coldest
month must be between 18 and –
3ºC; at least one month must have
a mean temperature of 10 ºC or
higher.
s: summer dry season
w: winter dry season
f: no dry season
a: hot summer season
b: long mild summer
c: short cool summer
Köppen Classification System
C – Moist, Mid-Latitude: Mild Winter
Mediterranean Climate (Cs) CHAPARRAL BIOME
• This is a wet-winter, dry-summer climate
• Extremely dry summers are caused by the sinking air (subtropical high) and may last for up to five months
• Plants have adapted to the extreme difference in rainfall and temperature between winter and summer seasons
– Sclerophyll plants range in formations from forests, to woodland, and scrub.
– Eucalyptus forests cover most of the chaparral biome in Australia.
• Fires occur frequently in Mediterranean climate zones
– Temperature Range: 7°C (12 °F)
– Annual Precipitation: 42 cm (17 in)
– Latitude Range: 30°- 50° N and S
• Global Position: central and southern California; coastal zones bordering the Mediterranean Sea; coastal Western Australia and South Australia; Chilean coast; Cape Town region of South Africa
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Köppen Classification System
C – Moist, Mid-Latitude: Mild Winter
Mediterranean Climate (Cs) CHAPARRAL BIOME
Köppen Classification System
D – Moist, Mid-Latitude: Cold Winter
Continental Climates can be found in the
interior regions of large land masses.
Total precipitation is not very high
and seasonal temperatures vary widely.
Climate types Further divisions
D Climates
Found in the upper middle
latitudes and subpolar regions of
the northern hemisphere. Humid
continental climates with cold
winters; mean monthly
temperature of coldest month
below -3ºC; mean monthly
temperature of the warmest month
must be 10ºC or higher.
s: summer dry season
w: winter dry season
f: no dry season
a: hot summer season
b: long mild summer
c: short cool summer
d: extremely cold winter
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Köppen Classification System
D – Moist, Mid-Latitude: Cold Winter
Boreal forest Climate ( Dfc) TAIGA BIOME
• This is a continental climate with long, very cold winters, and short, cool summers.
• This climate is found in the polar air mass region. Very cold air masses from the arctic often move in.
• The temperature range is larger than any other climate.
• Precipitation increases during summer months, although annual precipitation is still small.
• Much of the boreal forest climate is considered humid. However, large areas in western Canada and Siberia receive very little precipitation and fall into the subhumid or semiarid climate type.
– Temp Range: 41°C (74 °F), lows; -25°C (-14 °F), highs; 16°C (60 °F).
– Average Annual Precipitation: 31 cm (12 in).
– Latitude Range: 50° - 70° N and S.
• Global Position: central and western Alaska; Canada, from the Yukon Territory to Labrador; Eurasia, from northern Europe across all of Siberia to the Pacific Ocean.
Köppen Classification System
D – Moist, Mid-Lat: Cold Winter
Boreal forest Climate ( Dfc) TAIGA BIOME
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Köppen Classification System
E – Polar Climates
Cold Climates describe this climate type perfectly. These climates are part of areas where
permanent ice and tundra are always present. Only about four months of the year have above freezing temperatures.
Climate types Further divisions
E Climates
Cold climates of the northern
latitudes. All months must average
below 10ºC.
t: tundra
f: polar or ice cap climate
Köppen Classification System
E – Polar Climate
Tundra Climate (Et) TUNDRA BIOME
• The tundra climate is found along arctic coastal areas.
• Polar and arctic air masses dominate the tundra climate.
• The winter season is long and severe.
• A short, mild season exists, but not a true summer season.
• Moderating ocean winds keep the temperatures from being as severe as interior regions.
– Temperature Range: -22°C to 6°C (-10°F to 41°F).
– Average Annual Precipitation: 20 cm (8 in).
– Latitude Range: 60° - 75° N.
• Global Position: arctic zone of North America; Hudson Bay region; Greenland coast; northern Siberia bordering the Arctic Ocean.
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Köppen Classification System
E – Polar Climate
Tundra Climate (Et) TUNDRA BIOME
Köppen Classification System
H – Highland Climates
Highland climates experience a rapid change
in temperature over a short distance due to elevation.
They maintain similar climate patterns to the major
Climate area in which they belong.
Climate types Further divisions
H Climates
Hybrid climates that have
significant change in altitude which
brings colder temperatures with
elevation increases
None:
Climate is dominated by the seasonal patterns
of temperature and precipitation of the major
climate they are located within.
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Köppen Classification System
H – Highland Climate
Alpine Climate (H)
• Highland climates are cool to cold, found in mountains and high plateaus
• Climates change rapidly on mountains, becoming colder with increased altitude
• The climate of a highland area is closely related to the climate of the surrounding biome. The highlands have the same seasons and wet and dry periods as the biome they are in
• Mountain climates are very important to midlatitude biomes.
• They work as water storage areas. Snow is kept back until spring and summer when it is released slowly as water through melting.
– Temperature Range: -18 °C to 10 °C (-2 °F to 50°F)
– Average Annual Precipitation: 23 cm (9 in.)
– Latitude Range: found all over the world
• Global Position: Rocky Mountain Range in North America, the Andean mountain range in South America, the Alps in Europe, Mt. Kilimanjaro in Africa, the Himalayans in Tibet, Mt. Fuji in Japan.
Köppen Classification System
H - Highland Climate
Alpine Climate (H)