Atmosphere structure, Solar Inputs and the Transport of Heat

Heat, winds, and currents We will address the following topics.... Why do the winds blow? The source of the winds is ultimately the Sun. We’ll discuss how heating by the Sun generates air flow. What influence does the Earth’s rotation have on winds? Earth’s rotation causes the winds and currents to turn…without this rotation the climate would be very different. Solar Insolation controls almost everything: But it is not just what we get, it is what we keep that defines the thermal balances.

Structure of the Modern Atmosphere Pressure: force exerted per unit area by the weight of overlying air (1 mb = 100 Pa; 1000 mb ~ 1bar ~1 atm) Temperature: measure of the molecular kinetic energy.

Thermosphere Thermosphere: upper atmospheric layer with temperature increasing with altitude Heated by absorption of high-energy radiation by oxygen Atmosphere is extremely thin, nearly a vacuum. As a result, Sun’s energy can heat air molecules to very high temperatures (2500 °C) during the day. But there are so few, it doesn’t really matter Auroras occur in thermosphere

Mesosphere Temperatures as low as -100 C Million of meteors burn up daily in the mesosphere, due to collision with air molecules Mesosphere: middle atmospheric layers where temperature decreases with altitude Noctilucent clouds (blue-white) over Finland.

Stratosphere Ozone is concentrated around an altitude of 25 km in the “ozone layer” Ozone layer protects surface from harmful UV radiation Stratosphere: temperature increases with altitude due to absorption of UV by ozone

Troposphere Temperature determined by surface heating Well mixed by weather Troposphere: lowest layer in atmosphere, temperature decreases with altitude

ANNUAL Shortwave radiation Earth receives more solar radiation at low latitudes than high latitudes. Ultimately, it is this solar insolation that provides the heat that controls weather and climate. It is the imbalance across the Earth’s surface that controls winds and currents.

Shortwave radiation Beam spreading: each unit of shortwave radiation is spread over a larger area away from the equator 3 factors influence the shortwave radiation received at Earth’s surface

Shortwave radiation Beam spreading: each unit of shortwave radiation is spread over a larger area away from the equator Beam depletion: radiation is absorbed and reflected as it passes through atmosphere 3 factors influence the shortwave radiation received at Earth’s surface

Shortwave radiation Beam spreading: each unit of shortwave radiation is spread over a larger area away from the equator Beam depletion: radiation is absorbed and reflected as it passes through atmosphere Day length: hours of daylight varies with latitude and season 3 factors influence the shortwave radiation received at Earth’s surface

No tilt Tilted Shortwave radiation Earth has seasons because its axis is tilted 23.5º with respect to the plane of the ecliptic

Why do we have seasons? Seasonal variations in insolation are greatest at high latitudes

Dec-Jan-Feb. Jun-Jul-Aug Shortwave radiation Earth receives more solar radiation at low latitudes than high latitudes

Longwave radiation Earth emits more longwave radiation at low latitudes than high latitudes

Dec-Jan-Feb. Jun-Jul-Aug Longwave radiation Earth emits more longwave radiation at low latitudes than high latitudes Why is there a difference between Winter and Summer?

Net radiation Net radiation: total radiation Net radiation: shortwave - longwave There is an energy imbalance!

Global Energy Balance

To make the energy balance, there must be a transport of energy from low to high latitudes. Radiation is converted to other forms of energy that can be transported by winds and currents Sensible heat: heat that you can feel (stored in a substance as a change in temperature) Latent heat: heat required to changes phases (solid --> liquid --> gas) Energy Transport

Newton’s first law: A body at rest remains at rest and a body in motion remains in constant motion unless acted upon by an external force Fluid Flow Fluid flow is driven by forces Forces include - Pressure - Coriolis - Friction

Pressure gradient force: fluid flows from high pressure to low pressure Fluid Flow Pressure: force exerted against a surface due to the weight of air

Fluid Flow Pressure gradient force: fluid flows from high pressure to low pressure - Flow in direction from H to L - Larger gradient = faster flow Pressure: force exerted against a surface due to the weight of air

Heating air causes it to expand In this example, the masses of the 2 air columns, A and B, are equal Equal masses of air SURFACE HOT COLD AB Pressure Differences Pressure differences arise from temperature differences.

SURFACE HOT COLD Top of Atmos. COLD The mass of air overlying column A is greater than that overlying column B > mass < mass AB Pressure Differences Pressure differences arise from temperature differences.

HOT COLD BONUS! HIGHLOW Because the mass is greater in column A, the surface pressure (i.e., the weight of the overlying air) is greater. Top of Atmos. AB Pressure Differences Pressure differences arise from temperature differences.

Pressure Differences Pressure differences arise from temperature differences.

General Circulation of the Atmosphere Circulation on a non-rotating Earth

Coriolis force is an artificial force that arises because we are riding on a rotating rock. Fluid Flow Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame

Consider two children throwing a ball on a moving merry-go- round. Stationary Observer’s Perspective Rotating Observer’s Perspective Fluid Flow Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame

The stationary observer sees the ball moving in a straight line, and Johnny and Jill moving in a circle. Stationary observer Fluid Flow Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame

Johnny and Jill on the merry- go-round perceive that they are stationary. They see the ball move to the right. Moving observer Fluid Flow Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame

Fluid Flow Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame

General Circulation of the Atmosphere Trade winds Mid-latitude westerlies Polar easterlies Circulation on a rotating Earth

DESERTS – THE CONVERGENCE OF ATMOSPHERIC CIRCULATION CELLS AND THE SURFACE OF THE EARTH

Net radiation Net radiation: total radiation Net radiation: shortwave - longwave There is an energy imbalance! Cold Poles and Hot Tropics – the drive for circulation in both the atmosphere and the ocean systems

Circulation of the Ocean Thermohaline Driving Mechanism

THE ATLANTIC GULF STREAM WARMING THE POLES – COOLING THE TROPICS

MAJOR OCEAN CURRENT SYSTEMS

GLOBAL SCALE CIRCULATION OF OCEANS – A THERMAL TRANSFER.

SURFACE TEMPERATURE ANOMOLIES