7 lecture

The Atmosphere (1)

The atmosphere is composed of

Gases:

• 78.1% Nitrogen,

• 20.9% Oxygen,

• ~1% Argon,

• 0.035% Carbon dioxide,

• Trace amounts of Methane, Hydrogen, Ozone, Water vapor, Carbon monoxide, Sulfur dioxide, Nitrogen oxides.

The Atmosphere (2)

Particulates - solid and liquid particles found in the atmosphere: Natural: smoke from forest fires, volcanic ash, sand and salt particles. Antropogenic: industrial & car emissions, smoke / soot from fires.

Particulates affect weather and climate by:

• 1. Absorbing water and accumulating water, cloud formation.

• 2. Absorbing or reflecting sun light, so changing the portion of solar radiation that falls on Earth.

The Atmosphere (3)

troposphere ~10 km stratosphere ~10-50km mesosphere ~50-80 km thermosphere ~80-120 km

The troposphere extends from the Earth’s surface to about 10 km above the Earth.

The stratosphere extends from the top of the troposphere to about 50 km above the Earth.

Most ozone is located in a band between 15 and 30 km.

The mesosphere extends from 50-80 km above the Earth.

The thermosphere extends to about 300 km above the Earth.

Weather and Climate

are defined by the atmosphere

Weather: atmospheric conditions (short-run) existing at a given time and location.

• Immediate

Climate: weather conditions over a long period of time (years, decades, centuries).

• long-term and general

Weather & Climate Elements

• Temperature

• Pressure

• Wind

• Moisture content

Atmospheric Pressure, Temperature & Wind

Atmospheric pressure: force exerted by air molecules on the earth’s surface (per square unit)

• at Sea level: 1 atm or 760 mm Hg = 101.325 kPa ~ 1.03 kg/cm2

• more gas molecules at Sea level than on mountain peak à

higher pressure is at Sea level (NEXT SLIDE).

Temperature & Pressure (based on Gas Laws)

• very warm air has low pressure

• rising air produces low pressure

• very cold air has high pressure

• sharply descending air produces high pressure

Wind

= horizontal air movement

Insolation → Unequal heating → Temperature gradients → Pressure gradients → WIND

• Air moves from high to low pressure area

• Wind levels off the uneven distribution of air pressure

• Main driving forces of the wind:

  • Pressure gradient

  • Coriolis Force

  • Friction

Wind

as the result of pressure gradients

Physical phenomena in atmosphere

• Evaporation:

phase transition “liquid à vapor”

• Latent heat:

heat absorbed (or released) during phase transition Latent heat for water is high: 540 cal/g

• Condensation

phase transition “liquid à vapor”

• Convection currents –

heat (energy) transfer in liquid or gas

Convection and Atmospheric Pressure

• Horse latitudes:

30 Degrees n & s

• Trade winds, or passats:

NE winds in Northern hemisphere

SE winds in Southern hemisphere

• Air pressure differences

• Coriolis effect – wind deflections as the result of earth rotation

Compare latitudes:

Almaty – 43.25 N

Boston – 41.78 N

Hstory: sailors gave the region name "horse latitudes" because ships relying on wind power stalled; fearful of running out of food and water, sailors threw their horses and cattle overboard to save on provisions.

Blowing from horse latitudes toward the low pressure equator are TRADE WINDS. They quickly move (propel) trading ships across the ocean, the trade winds between about 30° latitude and the equator are steady and blow about 11-13 miles/ h. In the Northern Hemisphere, the trade winds blow from the northeast: NE Trade Winds; in the Southern Hemisphere they blow from the southeast: SE Trade Winds.

Movement of the atmosphere has a reproducible general pattern caused by earth spinning, and heating / cooling at the cooler N and S poles relative to the warmer equator. These conditions produce movement of air around the earth through convection: Hadley cells. Dominant winds: Trade Winds and Westerlies, occur within these convection cells. These forces dictate to a large extent the movement and dispersal of pollutants and other substances through the atmosphere.

Coriolis Force

an artifact of the earth's rotation

Coriolis effect produces steady reliable wind patterns controlled by the earth’s spin:

Trade winds (passats) blowing from 30N to equator – bend right in N hemisphere à

They become NorthEast winds.

Object deflects:

• to the right in N Hemisphere

- To the left in S hemisphere

Global Winds & Storms

• Passats (trade winds): blow from 30’s latitudes to equator: NE wind in Northern hemisphere

SE wind in Southern hemisphere

• Monsoons – seasonal winds on ‘water-land’ boundaries:

  • Summer: heavy rainfalls ‘wateràland’

  • Winter: dry weather/winds ‘landàwater’

• Hurricane, typhoon, tropical cyclone – tropical revolving storms, originated above water (oceans/seas): à Katrina, Dennis, Rita, etc.

• Tornado – twister, forming funnel in thundercloud: destructive, high speed: 65-500 km/h, low pressure inside.

• Tsunami – underground earthquakes as predecessors of ‘Tsunami’ storms

• Sirocco – Mediterranian hurricane coming from Sahara

Hurricane Katrina will be the most costly disaster in US history, though the loss of life was not as high as some other disasters.