The Earth and Its Atmosphere:

1. Vertical structure2. Weather and climate

Mass,Weight, Density, Pressure

•Mass M: ♦ property of matter,♦ SI unit: kg. Other units: 1kg=1000 g, 1 lb=450

g

•Weight : ♦ a force, has a magnitude and direction (vector).♦ weight = mass x gravity g(Earth)= 9.78

m/s2

♦ SI unit: kg m/s2 -> N g(Mars)= 3.7 m/s2

•Density : ♦ mass per unit volume: density = mass / volume♦ SI unit: kg/m3, Other: g/cm3

•Pressure p: ♦ p= force/area♦ SI units: Pa=N/m2, Other: 1bar=100 Pa

Wr

Atmospheric pressure

Atmospheric pressure and density decrease with altitude exponentially!!!

RECAP

•Atmospheric composition:

• Permanent gases: N2, O2, Ar, Xe, Ne, H2, He

• Variable gases: CO2,H2O,O3,CH4

•Greenhouse gases: H2O, CO2, NO,CH4

•Mass.

•Weight.

•Density.

•Pressure.

•The atmospheric pressure and density decrease with altitude.

Mid-chapter brief review(s)

•The earth’s atmosphere is a mixture of many gases. In a volume of dry air near the surface, nitrogen (N2) occupies about 78 percent and oxygen (O2) about 21 percent.

•Water vapor, which normally occupies less than 4 percent in a volume of air near the surface, can condense into liquid cloud droplets or transform into delicate ice crystals. Water is the only substance in our atmosphere that is found naturally as a gas (water vapor), as a liquid (water) and as a solid (ice).

•Both water vapor and carbon dioxide (CO2) are important greenhouse gases.

•Ozone (O3) in the stratosphere protects life from harmful ultraviolet (UV) radiation. At the surface, ozone is the main ingredient of photochemical smog.

•The majority of water on our planet is believed to have come from its hot interior through outgassing.

•Atmospheric pressure at any level represents the total mass of air above that level, and atmospheric pressure always decreases with increasing height above the surface.

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Vertical Structure of the Earth’s Atmosphere

99.9%

90%

Lapse rate

Atmospheric layers(according to the temperature)

•Troposphere: ♦ The temperature T decreases with height at a rate of 6.5 K/km.

♦ Well mixed as a result of turbulence and convection♦ Weather phenomena

•Tropopause: ♦ Isothermal (T constant)♦ Located 8-15 km above the ground.

•Stratosphere:♦ The temperature T increases with height♦ O3 layer at 25 km altitude♦ The atmosphere is very stable

•Stratopause: T=const

•Mesosphere:♦ T is decreasing with height: effective cooling through IR emission

♦ Very unhealthy region: hypoxia (oxygen deprivation), UV burns, blood begins to boil

•Mesopause: the coldest region on Earth.

•Thermosphere: fast T increase. Diffusive separation of gases.

Atmospheric layers: other classifications

•Mixing:♦ Homosphere:

•well mixed, •the chemical composition is constant.

♦ Heterosphere:

• no turbulence and mixing,

•diffusive separation of gases

•Ionization: ♦ Ionosphere: part of the atmospheric gas is ionized through photo ionization or impact ionization.

♦ (talk about the atom)

Weather/ Climate

•Weather elements:♦ Air temperature: thermometer (C, F, K)♦ Air pressure: barometer (bar, mbar)♦ Humidity: hygrometer (%)♦ Wind: (m/s , km/h, mi/h)♦ Clouds♦ Precipitation♦ Visibility

•Weather: the daily variations of the atmospheric conditions. “It is partly cloudy today, with a 50% chance of rain”

•Climate: average weather. “The average maximum temperature for the month of January is 35 F.”

Weather Forecasting Using Satellites

isotherm

isobar

streamline

The World

Jupiter as seen from Cassini

Meteorology – a brief history

•Meteorology is the study of the atmosphere and itsphenomena

•In “Meteorologica” (340 B.C.) Aristotle discussed♦ meteors (things which fall from the sky)♦ weather and climate, astronomy, geography…♦ clouds, rain, snow, wind, hail, thunder, hurricanes…

•Invention of weather instruments in the Middle Ages♦ Pressure: barometer (1643, E. Torricelli)♦ Humidity: hygrometer (1783, H. de Saussure)

•Rapid exchange of weather information (telegraph, 1843)

•Crude weather maps (1869)

•Norwegian model of storm development (1920’s)

•Air balloon and high-flying aircraft observations (1940)

•High-speed computers and numerical predictions (1950-)

•Weather satellites (1960-) de Saussure

Aristotle

Simplified surface weather map

Weather phenomena: a preview

Clouds and thunderstorms

Ice storm

Tornadoes

Flooding