MET 10 - 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

 Albedo: The fraction of light reflected by an object or a surface  White objects have high albedos  Black objects have low albedos Increasing albedo

Table 2-2, p. 41

Fig. 2-15, p. 41

Why do we have seasons?

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 sunlight strikes the surface and by how long the sun shines on any latitude (daylight hours).

 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

Fig. 2-18, p. 43

Sun angle

Sun Angle

Sun angle (2)

Notice the angle of tilt of the earth’s axis.

March Sept. June Dec.

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.

Fig. 2-24, p. 50

What month do you think this graph represents? a) December b) March c) June d) September Answer: December

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.

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)

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

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)

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

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.