tuesday, april 26, 2011 chapters 9, 10 & 15 weather &...

4/26/2011

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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


• Severe Thunderstorm

• Very powerful (and dangerous) thunderstorms58+ mph winds and/or ¾”+ hail


• 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


• 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


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• 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


• Most destructive severe thunderstorms

• 2,000 – 3,000 per year in US… but responsible for most damage and deaths


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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.


Hybrid of multiple climates due to altitude change

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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



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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Tropical Moist Climates (Af) RAINFOREST


B – Dry Climates

Dry Climates are characterized by little rain

and a huge daily temperature range.


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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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.


B – Dry Climates

Dry Tropical Climate (Bw) DESERT BIOME

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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.


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



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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Mediterranean Climate (Cs) CHAPARRAL BIOME


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.


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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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.


D – Moist, Mid-Lat: Cold Winter

Boreal forest Climate ( Dfc) TAIGA BIOME

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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.


E Climates

Cold climates of the northern

latitudes. All months must average

below 10ºC.

t: tundra

f: polar or ice cap climate


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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E – Polar Climate

Tundra Climate (Et) TUNDRA BIOME



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.


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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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.


H - Highland Climate

Alpine Climate (H)

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