MET Lecture 3 Radiation Continued Dr. Craig Clements San Jose State University

Scattered and reflected light When solar radiation enters the atmosphere, a number of Interactions take place Some energy is absorbed (by ozone in stratosphere) and some is deflected. When sunlight strikes very small objects, such as air molecules and dust particles, the light itself is deflected in all directions– forward, sideways and backwards. The distribution of light in this manner is called Scattering. Because air molecules are much smaller than the wavelengths of visible light, they are more effective scatterers of the shorter (blue) wavelengths than longer (red) wavelengths.

Fig. 2-13, p. 40

Fig. 2-14, p. 40

Scattering gives us our blue sky

…and reddish sunsets and sunrises.

Sunlight can be reflected from objects. Generally, reflection differs from scattering in that during the process of reflection more light is sent backwards. Albedo is the percent of radiation returning from a given surface compared to the amount of radiation initially striking that surface. Scattered and reflected light

Table 2-2, p. 41

Fig. 2-15, p. 41

Albedo Field Experiment: Report Due TBA  We are going to measure the albedo of different surfaces at SJSU.  Your report should explain: 1.What we did. 2.How and with what? 3.Measurement results 4.Explain what surface should absorb more energy. You will need to take notes during this experiment.

12 MET 112 Global Climate Change Why do we have seasons?

13 MET 112 Global Climate Change Seasons Why do we have seasons? Seasons are regulated by the amount of solar energy received at the earth’s surface. This amount is determined by the angle at which sunlight strikes the surface and by how long the sun shines on any latitude (daylight hours).

14 MET 112 Global Climate Change  Insolation –  Solstice –  Equinox – Incoming solar radiation day of the year when the sun shines directly over 23.5°S or 23.5°N days of the year when the sun shines directly over the equator

15 MET 112 Global Climate Change Fig. 2-18, p. 43

16 MET 112 Global Climate Change Sun angle

17 MET 112 Global Climate Change Sun Angle

18 MET 112 Global Climate Change Sun angle (2)

19 MET 112 Global Climate Change Notice the angle of tilt of the earth’s axis.

March Sept. June Dec.

21 MET 112 Global Climate Change What influences incoming solar energy?  The Sun’s angle of incidence: –Lower sun angle, –Higher sun angle,  Length of time the Sun shines each day: –Summer season, –Winter season, more incoming energy less incoming energy less sun hours more sun hours These are caused by the tilt of the earth’s axis The earth’s axis points to the same direction in space all year long.

22 MET 112 Global Climate Change Fig. 2-24, p. 50

23 MET 112 Global Climate Change What month do you think this graph represents? a) December b) March c) June d) September Answer: December

24 MET 112 Global Climate Change

25 MET 112 Global Climate Change Earth’s energy: latitudinal perspective  A majority of the sun’s energy enters the Earth system in the tropics.  The tropics thus becomes quite warm, while the poles relatively cool.  The atmosphere attempts to bring the tropics and high latitude into equilibrium –Weather systems ultimately act to bring warm air to higher latitudes and cold air to lower latitudes.

26 MET 112 Global Climate Change On June 21 st, at what latitude is the sun directly overhead at noon? 1.Equator (0) °N °S 4.90°N (north pole) 5.90°S (south pole)

27 MET 112 Global Climate Change How many hours of daylight are present at the South Pole on February 20 th ? 1.0 hours 2.6 hours 3.12 hours 4.18 hours 5.24 hours

28 MET 112 Global Climate Change On September 22 nd, at what latitude is the sun directly overhead at noon? 1.Equator (0) °N °S 4.90°N (north pole) 5.90°S (south pole)

29 MET 112 Global Climate Change Where would you expect to have longer days; 45 ° N on June 21 st or 50°S on Dec 21 st ? 1.45°N 2.50°S 3.They are the same 4.Impossible to tell

30 MET 112 Global Climate Change Seasons Review  A season is one of the major divisions of the year, generally based on yearly periodic changes in weather.  In temperate and polar regions generally four seasons are recognized: spring, summer, autumn (fall), and winter.  In some tropical and subtropical regions it is more common to speak of the rainy (or wet, or monsoon) season versus the dry season, as the amount of precipitation may vary more dramatically than the average temperature.  In some parts of the world, special "seasons" are loosely defined based upon important events such as a hurricane season, tornado season or a wildfire season.