earth's atmosphere

earth energy sources

• internal (geothermal)

• external (solar)

weather disasters

• storms, tornadoes, hurricanes, and floods mainly driven by solar energy instead of energy from within the earth

• sun is main energy sources from atmosphere and hydrosphere

air & atmosphere

air: a mixture of gases that make up the Earth’s atmosphere

atmosphere: a layer of gas that surrounds the Earth

earth’s atmosphere composition

• 78.08% Nitrogen

• 20.95% Oxygen

• 0.93% Argon

• 0.04% Carbon Dioxide

solar radiation

• half of radiation hitting Earth is absorbed by surface

• some reflected into space

• some absorbed by atmosphere 

• about 4000 x more heat from sun than from interior of Earth

lapse rate

the change of temperature with altitude ~6.5℃/km

troposphere, stratosphere, mesosphere, thermosphere

troposphere (0-12km): heated by infrared radiation from Earth’s land & water

stratosphere (12-50km): heated by ozone (O3) absorbing ultraviolet light

mesosphere (50-80km): cools due to lack of ozone (O3)

thermosphere (80-700km): high-energy radiation absorbed by gases

solar energy distribution

• unequal

• excess heat at equator

• heat move to polar regions through oceans and atmospheres

wind

• operates in 3 dimensions

• driven by pressure differences (vertical motion) and Coriolis effect (horizontal motion)

Coriolis effect

the deflection of the atmosphere sets up the complex global wind patterns which drive surface ocean currents

how does Earth’s rotation affect atmospheric circulation?

• deflects atmosphere toward the right in the Northern Hemisphere

• deflects atmosphere toward the left in the Southern Hemisphere

• results in curved paths

what happens to warm, moist air over the equator?

• cools and rains in tropics

• drier air sinks down

• some flows poleward and some back to equator

atmospheric pressure & density

• air pressure and density decreases as altitude increases

• air pressure drops by ~50% for every 5.6 km of altitude gain

distribution of atmosphere

• ~50% of atmosphere lies below 5.6 km

• ~75% of atmosphere lies below 11.2 km

• ~99.9% of atmosphere lies below 50 km

highest & lowest recorded air pressure

highest recorded air pressure: 1085 mb in Siberia

lowest recorded air pressure: 870 mb inside a typhoon

northern hemisphere high vs low pressure

high: wind spirals out of a high pressure, clockwise

low: wind spirals into a low pressure, counterclockwise

cyclone vs anticyclone

cyclone: air flows upwards & counterclockwise

anticyclone: air flows downward & clockwise

Hadley cells

• density-driven convection flows

• tropical air warms, rises, and flows toward poles

• subtropical air cools, sinks, and flows toward equator

• circulation controls distribution in low latitudes

trade winds

• result as Hadley Cell air flows toward equator

• Northern hemisphere surface winds curve southwest 

• Southern hemisphere surface winds curve northwest 

intertropical convergence zone (ITCZ)

• where N and S hemisphere trade winds converge

• shifts N of equator during N hemisphere summer

• shifts S of equator during S hemisphere summer

• areas under ITCZ subject to intense rainfall

air pressure zones: southern hemisphere

has more water so seasonal changes not as great (water buffers temperature changes)

air pressure zones: northern hemisphere

• winter = cold polar high pressure zones with cold air flowing off continents and rising in Icelandic Aleutian lows

• summer = highs over ocean, onshore flow of moist air and monsoons

ocean surface circulation

• surface oceanic currents are driven by wind and movement patterns

• deep ocean currents are caused by variability in water temperature and salinity

normal Walker circulation

• model to understand air flow in the tropics

• Western Pacific is warmer than Eastern

  • warm water in the West causes rising, low-pressure air

  • high-altitude air flows east, cools, and sinks in the East

• surface air moves west, causing water to rise in the West

  • 10-20 cm higher than in East

  • nutrient-rich cool water upwells in East (fish)

• strong Walker circulation creates La Niña conditions

La Niña

• strong trade winds, resulting in warm water and heavy rainfall moving west

• declared when the average sea surface temperature is 0.5℃ below the normal for three consecutive months 

El Niño

• Eastern surface winds weaken, sea surface flattens

• Western warm water flows east

• Eastern water warms up

  • less cold, nutrient-rich upwelling

  • fish populations diminish

ENSO: El Niño Southern Oscillation

• modification of the ocean and atmospheric circulation which occurs every 3-6 years

• begins in southern Pacific

• slowing of easterly winds which causes rainfall and warm ocean water to shift eastwards

• called when the average sea surface temperature is more than 0.5℃ for five consecutive months

ENSO affects global weather patterns

• droughts in Australia and Indonesia

• storms and floods along west coasts of N and S America

ENSO event

• torrential downpours

• 3-4 years when warm water from eastern Pacific Basin override the Peru current

• Peru, Ecuador, Argentina, Columbia affected

cold vs warm front

cold

• cold air from north wedges under warmer air, forcing it upwards

• creates thunderstorms and rain

warm

• warm air runs up over colder air

• clouds form

polar-front jet stream

• boundary that separates warm air that originates in the tropics from cold air that originates in polar/subpolar region

• very fast wind, 10 km high, flowing over the polar front

• flows in wave-like undulations 

wave-like undulations: ridge vs trough

ridge: jet stream curves toward the poles

trough: jet stream curves toward the equator

mid-latitude circulation

• jet stream air flow is uneven

  • more air can flow out of a region than into it

• divergence: an air deficit at the tropopause

• creates low-pressure centre

  • surface air rises into low-pressure centre

  • rising air cools, and its vapour forms

mid-latitude / extratropical cyclones

• large system of clouds that develops around low-pressure centre in the N hemisphere 

• clouds run on a counterclockwise direction around the low-pressure centre 

• can produce thunderstorms, blizzards, and tornadoes

• typically reach max intensity at ~36-48 hours from initiation

mid-latitude cyclones: comma shape

• head/top of comma has cyclones warm and occluded fronts

  • in winter, may manifest as blizzards/ice storms

• tail of comma is trace of cold front - precipitating clouds

  • can create thunderstorms, tornadoes, windstorms 

mid latitude cyclones formation

• warm front extends E of low pressure centre, cold front extends from the centre toward the S or SW

• low-altitude air spirals counterclockwise around the low-pressure centre, the cold front advances rapidly

• cold front progressively warps around the low-pressure centre and catches up with the warm front

• cool air north of the warm front undergoes lifting along face of cold front

Cascadia earthquake

• magnitude 9

• 37% chance of occurring w/ in next 50 years

top 5 things to have in your home to prepare for earthquakes

1. shelf stable food

2. water

3. fire extinguisher

4. bucket toilet 

5. gas shut off tool

which way does the Earth rotate?

counterclockwise, west to east