The World of Weather

Introduction to the Earth’s Atmosphere The atmosphere: Acts as a radiation shield by reflecting heat and light Causes our weather patterns Consists of gases: 78% N 2, 21% O 2, 1% other (CO 2, Ar, H 2 O, CH 4 )

Troposphere (0-10 km thick, avg temp of -57  C) All weather occurs here Air rises and falls

Stratosphere (10-50 km, -2  C) Higher temperature because the ozone (O 3 ) in the upper stratosphere absorbs UV rays Air flows horizontal

Mesosphere (50-90 km, -100  C) Meteors burn up here

Thermosphere (90 km +, temperatures up to 800  C) Aurora occur here due to high energy charged particles (the solar wind) colliding with gases in atmosphere, exciting atoms Single oxygen atoms absorb UV light, and this increases the temperature

Ionosphere Occurs within the thermosphere and mesosphere Atoms and molecules absorb UV radiation, causing them to eject electrons and become ions The ions bend radio waves and that allows radio signals to be transmitted long distances

The Sun’s Energy The sun is the source of all the energy which drives the weather Forms of energy from the sun include: Infrared (sensed as heat) Visible light (sensed as different colours) Ultraviolet light (not senses by humans; harmful to humans – sunburn or cancer)

There are three methods of heat transfer that move the Sun’s energy through space: Conduction: The transfer of thermal energy from the collision of molecules (energy is transferred from high to low energy molecules)

Convection: Transfer of thermal energy when highly energetic molecules move form one place to another (liquids and gases) Radiation: Transfer of thermal energy in which the sun’s molecules emit electromagnetic waves (pure energy) which transfer heat when they contact matter on earth

The solar constant is the amount of energy produced from the sun that reaches the Earth’s outer atmosphere (1367 J/m s) 30% of the energy is immediately reflected back to space, atmospheric molecules absorb 20%, and 50% is absorbed by the earth’s surface

The Earth is able to maintain a steady temperature because for the amount of energy that is absorbed by the earth’s surface, an equal amount is radiated back to space Increased greenhouse gases such as CO 2 are trapping heat in our atmosphere and stopping it from being radiated back in to space

Interactions of Solar Energy Water (Hydrosphere) Capable of absorbing huge amounts of heat energy (becomes a heat sink – a region that absorbs and stores heat energy) This is possible because water has a high specific heat capacity – the amount of energy required to change 1 g of water by 1  C is comparatively large.

Q = mc  t  t = temperature change m = mass (g) c = specific heat capacity Q = heat energy (J or kJ) For example, how much energy will it take to heat 100g of water from 20  C to 50  C?

(Q) is the amount of heat energy that is required to cause a certain temperature change in a mass of a particular substance If there is a change of state occurring, no temperature change is happening, but vast quantities of energy are still involved

Since 2/3 of Earth is covered in water, which can absorb heat and then release it, water acts as a moderator of our temperatures and drives our weather systems The absorption of solar energy is also what drives the water cycle

Humidity is the amount of water vapour in the air. This varies with temperature Absolute humidity: the actual amount of water vapour in the air Relative humidity: percentage of water vapour in the air compared with the amount of water vapour the air would contain if it was saturated

Actual amount x 100% Maximum amount As temperature decreases, some water vapour will condense and form droplets around tiny particles called condensation nuclei

Land & Sea Breezes Land Has a lower specific heat capacity so if it absorbs the same quantity of heat as water, the temperature of the land will increase more than water’s will Air Heated by radiation and: Conduction when air particles close to the surface collide with land molecules Convection when the warmer air particles move upwards and cooler particles move down Uneven heating of air causes wind