Exploring Atmospheric Layers: A Journey through Earth's Skies

1. Order… The Sun Mercury Venus Earth The Moon Mars Phobos Jupiter Europa Saturn Titan Uranus Oberon Neptune Pluto

2. Atmospheric Processes The structure of the atmosphere

3. The structure of the atmosphere • 8th June 1898 – French scientist Léon Teisserenc de Bort used balloons carrying thermometers to record temperature variations within the atmosphere • Temperature decreased with height to 11.8 km above sea level (ASL), then remained constant to 13 km ASL • 206 further balloon ascents over next 4 years showed that temperature begins to increase above 13 km ASL • Teisserenc De Bort had discovered the stratosphere

4. Atmosphere can be divided into four layers: Thermosphere Mesosphere Stratosphere Troposphere Layers reflect differences in ability to absorb solar radiation

5. Atmospheric pressure • Rapid fall in air density and pressure with increasing height above Earth’s surface • 50% of atmospheric mass lies within lowest 5.6 km • >99% of atmospheric mass lies within lowest 40 km • Atmospheric pressure units = millibars (mb or mbar) • Normal pressure at sea-level = 1013.2 mb

6. Troposphere • Derived from the Greek word ‘tropos’ meaning ‘turn’ – referring to the layer’s convective and mixing characteristics • Lowest layer of atmosphere – contains 75% of atmospheric mass • Pressure decreases with altitude • Approximately uniform decrease in temperature with height of c.6.5°C per 1000 m – environmental lapse rate • Contains virtually all the atmosphere’s water vapour, clouds and pollution • Contains the weather

7. Tropopause Troposphere

8. Tropopause • Temperature inversion that acts as a ‘ceiling’ to air rising within the troposphere • Latitudinal variations in height of tropopause ASL: • Equator = 16-18 km (11 miles) • Poles = 8-9 km (5 miles) • Distortions in tropopause occur above mid-latitude jetstreams & tropical cyclones • Dust and water vapour may penetrate up into stratosphere • Dry ozone-rich air drawn down from stratosphere into troposphere

9. Stratosphere • Derived from the Greek word ‘stratum’ meaning ‘layer’ – referring to the layer’s stratified, non-convective nature • Located above troposphere – between c. 10 and 50 km (30 miles) ASL • Temperature increases with height from c. –60OC (lower stratosphere) to c.0°C at c.50 km ASL (stratopause) • Contains small amounts of ozone (Ozone Layer) – absorbs ultraviolet (UV) solar radiation, causing warming of stratosphere • Extremely dry layer with no weather (stable conditions due to cold air below) • Most meteorites entering the atmosphere burn out above the stratosphere

10. Ozone Layer • Discovered by Charles Fabry and Henri Buisson, 1913 • From the Greek – “to smell” • Absorbs 93-99% of the sun’s UV light which could be damaging to life on Earth • Approximately 11-50 km in altitude • Approximately 90% of Ozone in our atmosphere is found here • Created by the Ozone-oxygen cycle

12. Nacreous clouds • Also known as ‘mother of pearl’ or polar stratospheric clouds • Form at c.15-25 km (9-16 miles) ASL during polar winter when lower stratosphere temperatures fall to c. –80OC • Consist of droplets / ice crystals of water, nitric acid and / or sulphuric acid • Only visible before dawn / after dusk as clouds receive sunlight from below horizon and reflect it to ground surface Nacreous clouds Nacreous clouds

13. Mesosphere • Derived from the Greek word ‘meso’ meaning ‘middle’ • Located above stratosphere – between c.50 and 85 km (50 miles) ASL • Temperature again decreases with height from c.0OC (at stratopause) to c.–90OC at c.80 km ASL (mesopause) (lowest value within layers) • There are no gases, particles or water vapour to absorb UV radiation Thermosphere • Derived from the Greek words ‘thermos’ meaning ‘heat’ • Located above mesosphere – between c.85 and 500 km ASL • Temperature increases with height to c.1200OC at 350 km ASL – due to oxygen molecules absorbing ultraviolet (UV) solar radiation

14. Ionosphere - upper mesosphere and thermosphere (above 80km) • Contains many ions (electrically charged particles) • Absorbs UV radiation • Can reflect radio signals • Give rise to the northern and southern lights • There is no clearly defined boundary which marks the end of the atmosphere – gases are continuously lost into space (Exosphere) which is mainly made up of Helium and Hydrogen

15. Noctilucent clouds • Polar mesospheric clouds • Form at c.85 km (50 miles) ASL – highest clouds in atmosphere • Formation not fully understood – mainly composed of water ice • Most commonly observed between 50O and 60O north during summer months • Only visible before dawn / after dusk when lower atmosphere is in Earth’s shadow – otherwise too faint to be seen • First reported in 1885 – shortly after eruption of Krakatoa Noctilucent clouds Noctilucent clouds

16. Aurora borealis Aurora borealis

18. Fly through - NASA • http://svs.gsfc.nasa.gov/vis/a010000/a010000/a010014/ What can I expect in the exam?