Atmospheric Composition and Structure

Weather and Climate• What is weather?

– The state of the atmosphere at a specific time and place. • Defined by: Humidity, temperature, wind speed, clouds,

precipitation, and air pressure

• What is the climate? – The average weather of an area over a long period time.

• Usually several decadesPeople who study the atmosphere and weather are known as meteorologists.

People who study the Earth’s climate are known as climatologists.

Weather or Climate?

• It’s 75°F today. Weather

Climate

Climate

• New England has 4 seasons.

• India has monsoon rains.

• There was a thunderstorm last night.

Weather

What is in the Atmosphere?

• The other gases include...Neon Methane Xenon Ozone Helium Krypton Hydrogen

• The atmosphere is mostly air, which is a mixture of gases.

• Water Vapor (~0-4%) – Varies place to place and day to day.

• Aerosols – Small particles suspended in the atmosphere.

• Dirt, pollen, sea spray, smoke, dust, etc.

Materials in the Air

These are the main ingredients required for making clouds!

Layers of the Atmosphere

– In between are the pauses, which are mini-layers were the temperature remains the same.

• Tropopause, Stratopause, Mesopause

• Troposphere • Stratosphere • Mesosphere • Thermosphere • Exosphere

The Troposphere• Lowest level of the atmosphere

– Thickness: 8-18 km – Contains most of the atmosphere’s mass.

• The most dense layer – Density decreases as you go up in the atmosphere.

• Experiences the most pressure. – Pressure decreases as you go up in the atmosphere.

– Heated by the Earth through conduction.

• According to the temperature profile, as altitude increases, temperature decreases. – Allows for the creation of convection currents.

The Troposphere is characterized by weather!

Instability• Convection currents occur in the troposphere

because the air is unstable. – Instability means that the air has a tendency to rise.

Eventually the air will cool and start to sink creating a convection current.

• Stability is a result of density differences. – Air that is warmer than

its surroundings will rise. – Result: Clouds,

wind, weather

The Stratosphere• Second layer of the atmosphere

– Located from ~18-50 km

• According to the temperature profile, as altitude increases, temperature increases. – There is a temperature

inversion, which means warm air is on top of cold air!

– Air CANNOT rise because it is colder than its surroundings, and cold air sinks!!

What Causes This Temperature Inversion?• The OZONE layer!

– Ozone is made of three oxygen atoms.

• Ozone absorbs UVC radiation from the sun. • UVA and UVB pass through to the troposphere.

– When ozone is struck by UV light, it splits apart.

– During this process, the UV light is transformed into heat, which warms the air in the stratosphere.

The Mesosphere• Third layer of the atmosphere

– Located from ~50-80 km • According to the temperature profile, as altitude

increases, temperature decreases. – Convection can happen!

• The mesosphere is colder because the gases CANNOT absorb the sun’s radiation. – Continues through to the surface

where it is absorbed. – Top of this layer is somewhere

between -90°C and -100°C.The mesosphere is where meteors burn up!

The Thermosphere• Top layer of the atmosphere

– According to the temperature profile, as altitude increases, temperature increases.

The auroras occur here!

• The thermosphere contains gases that absorb the sun’s radiation. – Top part receives the energy first, therefore it is

warmer. • Blocks the x-rays and some uv radiation

• The temperature depends on the sun’s activity. – Can get as hot as 1500°C.

Factors that Influence Climate

Factors that Influence Climate• Unequal heating of Earth’s surface by the Sun.

• Angle of insolation, albedo, proximity to water. • Rain Shadow Effect • Atmospheric Convection Currents

Shape of the Earth

The light is more intense when it hits the Earth’s surface at higher angle.

Earth’s Tilt and Orbit Around the Sun• There are three ingredients that create the seasons

on Earth. – Earth revolves around the sun. – Earth’s axis is tilted. – Earth’s axis always points in the same direction.

• Because of this, the angle of insolation changes in a given location, which changes the: – Intensity of the insolation. – Temperature of the area.

Other Factors To Consider...• Elevation

– Because we live in the troposphere, the temperature decrease with altitude.

– Mountain tops are cooler than sea level.

• Proximity To Water – Because water heats up and

cools down slowly, coastal areas have a more steady climate.

– Warmer winters and cooler summers than inland areas.

Other Factors To Consider...• Mountains

– Air rises up the mountains, the warm, moist air expands and cools to form clouds and rain.

– Air coming down the mountain is dry and contracts so clouds can’t form.

On the windward side there is rainy weather.

On the leeward side there is dry, desert conditions.

Other Factors To Consider...• Albedo

– Some areas reflect the sun’s light better than others. • Use albedo to quantify how well it reflects.

Changes In Albedo• The concern with global warming is the melting of the

polar ice caps, glaciers, and sea ice.

Urban Heat Island Effect• The increase in

temperature of a man-made area in comparison to the area’s natural landscape.

– The annual mean air temperature of a city with 1 million people or more can be 1-3°C warmer than its surroundings.

– In the evening the difference can be as high as 12°C. • More pronounced at night because of the slow release of heat from urban

infrastructure.

Urban Heat Island Effect• The increase in temperature of a man-made area in comparison

to the area’s natural landscape. – Built surfaces replace vegetation and moisture-trapping soils.

• Reduces the amount of insolation used for evapotranspiration, which keeps the air cooler.

– Built surfaces have a lower albedo and therefore absorb the insolation.

• Narrow building arrangements create urban canyons that inhibit the escape of reflected radiation.

– Air conditioners, refrigerators, and industrial processes create heat that is released into the atmosphere.

Conventional paving materials can reach peak summertime temperatures of 48–67°C, transferring excess heat to the air

above them and heating stormwater.

Consequences

• Increased urban temperatures leads to… – Increased energy demands – Elevated Air Pollution

Emissions – Elevated Greenhouse Gas

Emissions – Compromised human

health and comfort – Impaired Water Quality

Solutions• Change the albedo by…

– Cool paving materials – Increasing tree and vegetative cover – Installing cool - mainly reflective - roofs – Creating green roofs