GCM’s Heating of the Earth Uneven Solar Energy Inputs: Earth is heated unevenly by the sun due to different angles of incidence between the horizon and Sun This angle of incidence is affected two factors: Latitude: solar inputs are most dense when the sun is overhead in the tropics; reflection is low. The reverse holds true in polar regions. Season: Due to Earth’s annual orbit around the Sun on an axis tilted by 23.5º.

Autumnal equinox Sept 22nd Vernal equinox March 22nd Winter solstice Dec 22nd Autumnal equinox Sept 22nd Summer solstice June 22nd

Earth receiving solar energy When solar radiation reaches the Earth……. Equator receives a greater amount of short-wave radiation. Differential heating Poles receive less sunlight due to the inclination of the poles compared to the incoming electromagnetic radiation. The graph below states = more heat is received and gained between 30 degrees north and south of the Equator. Compared to the polar regions (60 degrees – 90 degrees N/S of the equator = experiences a loss of heat. The Global Heat Budget with Latitude: Losses by long-wave radiation is fairly constant at most latitudes, whereas inputs are variable and greatest in the tropics

Solar Radiation and Heating of the Earth’s surface Heat inputs from the tropics are delivered to the poles via atmospheric and ocean circulation, each delivering about 50% of the tropical heat. These circulation patterns are partly due to heat gradients, or more accurately pressure gradients. What does this unbalance of heating create on the EARTH?

What happens to the radiation once it hits the Earth’s atmosphere and surfaces. Solar constant = constant amount of energy being received from the Sun by the Earth = 100% Out of the 100% of solar radiation - 47% of incoming solar radiation is absorbed by Earth’s surface 30% is radiated and transferred back into space 23% is absorbed by atmospheric gases, clouds and particles Earth absorbs 47% of solar radiation, of which 50% is transferred into the atmosphere by evaporation and latent heat of vaporization

Convection Currents in the Atmosphere WARM AIR RISES – COLD AIR SINKS Solar Radiation is received by the EARTH Lithosphere/crust is heated by radiative energy from the Sun. 47% of electromagnetic spectrum received Conduction occurs with the Earth’s rocky surface heating the lowest layer of the atmosphere – troposphere. The heated tropospheric air RISES due to movement and density (energy). As the parcel of air moves further away from the surface (heat) temperature decreases. The colder air at higher altitudes starts to become dense and starts to SINK

HADLEY CELL Discovered in 1735 by George Hadley – formalized the wind pattern associated with trade winds. Equator is heated unevenly and consistently with incoming solar radiation Troposphere is heated by the surface due to radiated heat by the tropics and equatorial regions. Warm moist (evaporation) air mass is caused to rise towards the tropopause. Convection current is created when the rising air is pushed poleward and descends due to a change in temperature Air pressure at the equator is low due to rising air – this DRAGS in air from the surrounding latitudes to replace the rising air. Low pressure (cyclonic) system exists over the equatorial regions Descending air (30^N/S) from the troposphere contains little to no water vapor and creates high pressure.

Ferrel & Polar Polar cell: Dominated by a persistent descending air over the polar regions 80-90^N/S which creates high pressure (anticyclone) system – no rain Surface level winds moving equatorial regions towards 60^ low pressure belt. Ferrel The in-between convection cell created in an ideal model between HADLEY and POLAR. Air movement is characterized by the joining of the Polar and Hadley cells across the mid-latitudes both north and south of the equator. 30-60^N/S Between 30^ high pressure and 60^ low pressure. At each end of the Ferrel convective cell – JET STREAMS are produced at the 7-12km altitude due to changes in pressure and temperature between the POLAR- FERREL – HADLEY cells. Low pressure belt is created when the rising air at 60^ is being constantly replaced by air Mixing of the northern air mass (cold) and southern air mass (warm) Creation of the WESTERLIES which move surface level air from 30^-60^ from the west to the east .

Ferrel & Polar Cells

Ferrel & Polar Cells

The Atmospheric Circulation System

Wind Patterns created by low/high pressure and convection currents Convection currents in the troposphere create areas of low pressure and high pressure. Low pressure = drags air towards (converging air) High pressure = air is moved away and dragged towards the low pressure (diverging air) These global areas of high and low pressure create stable and consistent wind belts across the Earth’s surface. Westerlies = wind comes from the WEST Easterlies = wind comes from the EAST Doldrums = converging air mass, area in-between the converging & lifting air. Doldrums also called the ITCZ Intertropical convergence zone WESTERLIES – air is being dragged towards the sub-polar LOW pressure and away from the sub-tropical HIGH. EASTERLIES – air is being diverted away from the sub-tropical HIGH and Drawn/dragged towards the ITCZ.

Wind Patterns created by low/high pressure and convection currents Again, there are three atmospheric convection cells per hemisphere (Hadley, Ferrel, and Polar). Low pressure belts are where air rises and climate is wet (Intertropical Convergence Zone (0º) and Polar Front (60º)). High pressure belts are where climate is dry (Horse Latitudes (30º) and Polar High (90º)). Surface winds converge at low pressure belts: ITCZ: NE & SE Trade Winds (easterlies). Polar Front: Westerlies and Polar Easterlies. There are latitudinal shifts in these patterns with season.

JET STREAMS – Rivers of AIR - “Fast flowing, narrow air currents found in the atmosphere between 7-12km” Troposphere Two sets of jet streams in each hemisphere – Sub-tropical and polar or mid-latitude Located at different pressures according to their strength and consequential wind speed Located between two large air masses Created by large differences in temperature caused by meeting atmospheric convection cells. Mid-latitude jet stream – Polar and Ferrel cell Sub-tropical jet stream – Ferrel and Hadley