1. The atmosphere Hálfdán Ágústsson, with contributions from Guðrún Nína Petersen, Einar Sveinbjörnsson and Halldór Björnsson

2. Weather happens here

3. Some facts Weather happens in the troposphere, where roughly 90% of the mass of the atmosphere is located The tropopause is at roughly at 10-14 km above the surface, higher at the equator than at the poles The temperature on average decreases with elevation in the troposphere but increases in the stratosphere

4. Atmospheric pressure is a measure of the weight of the above air column

5. Atmospheric pressure decreases with height

6. Gas% of volume N2N2 78,08 0202 20,95 Ar0,93 +trace amounts of some gasses Gas% of volume H2OH2O0-4 CO 2 0,038 CH 4 (metan)0,00003 O 3 (ozon)0,01 Atmospheric composition

8. Aerosols Pollution: Natural and anthropogenic

9. Cloud condensation nuclei

10. Radiation The atmosphere absorbs radiation Gas, particles, water drops Ultraviolet radiation and ozon Visible radiation absorbed Infrared radiation absorbed by GHG The atmosphere reflects and scatters Raileigh scattering Mie scattering

11. Raileigh scattering Gasses Short wavelengths Mostly visible light Blue sky Red sunsets and sunrises

12. Mie scattering Particles, pollution, dust All wavelengths Mostly visible light Redder sunsets and sunrises Dublin 16. apríl 2010

13. Solar radiation Solar constant 1372 W/m2 Rotation axis tilt 23.5° Heats the surface and the atmosphere Einar Sveinbjörnsson

14. Solar radiation

17. Incoming and outgoing radiation

18. P = T x ρ x C P – pressure (hPa) T – temperature (K) ρ – density (kg/m 3) C - constant P ~ T x ρ If the temperature is the same then the pressure is only dependant on the density Equation of state for an ideal gas

19. AB What is the pressure at the surface under two columns of identical height and temperature? P = T x ρ x C PP Equation of state for an ideal gas

20. AB What if A – gets warmer B - gets colder Not so simple as an increase in temperature will lead to an expansion of the gas P = T x ρ x C Equation of state for an ideal gas

21. Distances between pressure levels Cold

22. Atmospheric forces and airflow 0. Gravity 1. Pressure gradient force 2. Coriolis force 3. Frictional force at surface (4. centripetal force) ma = Σ F = F g + F pg + C + F f +...

23. 0. Gravity Hydrostatic equilibrium Height gravity Pressure gradient Pressure gradient = gravititional force

24. HL 1020 hPa980 hPa Pressure gradient 1000 km 40 hPa / 1000 km 1. Pressure gradient forces

25. tvær myndir + MÁE

26. Because of the rotation of the earth, all moving particles in the atmosphere experience the Coriolis effect / force. 2. Coriolis force 2 f Ω sin φ, where φ is the latitude and Ω is the angular speed of the rotation.

27. Geostrophic wind Equilibrium of the Coriolis and pressure gradient forces

28. Denser isobars -> stronger winds

29. Geostrophic wind at 300 hPa - No surface friction

30. Surface friction

31. Surface winds, with surface friction

32. Differential versions of equation describing atmospheric motion Momentum Equation of state Continuity Equation of state Thermodynamic

33. Differential versions of equation describing atmospheric motion Momentum Equation of state Continuity Equation of state Thermodynamic

35. Atmospheric water Absolute humidity vs. specific humidity

36. Atmospheric water Specific humidity Absolute humitity Relative humidity How close to saturation? Warmer air can „hold“ more water vapour than colder air When saturated we will have clouds forming Dew point Vapor pressure Saturation vapor pressure

37. Temp. (°C) Max and min temperature and precip. Precip (mm) Phoenix, Arizona

38. Temp. (°C) RH (%) Phoenix, Arizona Max and min temperature and relative humidity.

39. Relative humidity

40. Saturation vapor pressure

41. Cloud condensation nuclei

43. P>E P<E Evaporation and precipitation

45. Mean evaporation on land in july 1985-1999 (mm/month) Evaporation