1. What causes our Weather?
Heat from the Sun, Water Cycle

2. What is Weather and how is it different from Climate? p477
Weather is the daily state of the atmosphere, or air, in any given time and place.
Climate refers to weather patterns of a region over time.
Meteorology is the study of weather
Crash Course: Weather vs Climate

3. What causes weather?
Weather processes (such as wind, clouds, and precipitation) are all the result of uneven heating of the Earth by the Sun.

4. How the Sun’s Energy Affects Weather
Solar energy absorbed by air, water, and land turns into heat energy.
This energy causes winds, the water cycle, ocean currents, and changes in the weather.

5. Three ways Heat is Transferred:
Radiation – through space
Conduction – direct contact
Convection – through motion of air/water

6. Radiation
Radiation –energy from the sun travels to Earth through space as waves).

7. Radiation: Transfer of heat through space
Not all radiation from the sun reaches Earth.
Much gets absorbed by the atmosphere.
Some is scattered and reflected by clouds and gases.

8. Conduction: Heat transferred by Contact
Once sunlight is absorbed by Earth’s surface it is converted into heat energy.
Heat can be transferred from a warm object to a cold one.

9. Convection: Heat transferred by Motion
Warm air or water carries heat from one place to another

10. Water in our Atmosphere
Hydrologic cycle

12. Hydrologic Cycle
Hydrologic Cycle or Water Cycle is the movement of water between the atmosphere, land, and oceans.
Earth is the only planet where water is present in all three states: solid, liquid, gas.
Only about 3 % of all the water on earth is fresh water and 2/3 of that are found in the glaciers.
Most of the water is stored in the oceans

13. How does the water cycle? p499
The water cycle is driven mostly by energy from the sun:
Heat from the sun warms the earth’s surface;
This causes liquid water from the oceans, lakes, rivers, and even the soil to evaporate (turn to water vapor).
As water vapor cools, it may change back to liquid and form clouds, (condensation).
The water droplets eventually fall back to Earth as rain, snow, sleet, or hail (precipitation).

15. Water Cycle is a closed system
The volume of water that is in the hydrosphere today is the same amount of water that has always been present in the Earth system.
Water cycle animation:

16. Water in our Atmosphere
Humidity
Condensation
Clouds
Precipitation

17. What is Humidity?
(Specific) Humidity is the amount of water vapor in the air.
The warmer the air, the more water vapor it can hold.

18. What is Relative Humidity?
Relative humidity is the amount of water vapor in the air compared to the maximum amount it can hold at that temperature.
Formula to calculate Relative Humidity:

19. Calculating Relative Humidity
Example:
1 m3 of air at 25 C can hold up to about 23 g of water vapor. If air at 25 C in a certain place contains only 18g/m3 of water vapor, then the relative humidity is:
18 g/m3 x 100 = 78%
23 g/m3

20. Measuring Relative Humidity
Relative Humidity is measured with an instrument called a psychrometer.
It consists of two thermometers: one is a wet-bulb thermometer, covered with a damp cloth. The other is a dry- bulb thermometer.

21. How a Psychrometer works
As air passes through the cloth on a wet-bulb thermometer, some of the water in the cloth evaporates, cooling the cloth.
The difference in the two reading is the relative humidity.
When humidity is low, water evaporates more quickly, giving a lower reading.
If humidity is high, less water evaporates, yielding very little change in temp from the dry bulb.
The larger the difference the lower the relative humidity.

22. Finding % Relative Humidity using Chart p500-501
The dry-bulb reads 10C.
Wet-bulb reads 7C.
The difference is 3C.
Find where the two columns intersect.
The relative humidity is 66%

23. Practice
Heat Transfer and Weather WS
Calculating Relative Humidity WS

24. Dew Point p503
Dew point is the temperature when relative humidity reaches 100%, the air is saturated with water vapor.

25. Condensation p503
Condensation happens when air is saturated with water vapor. It is the process by which a gas becomes liquid.
For water vapor to condense, air must be cooled below its dew point.
Water needs to condense onto something (eg, dust particles) called cooling nuclei.
Requires: Cooling and Nuclei

26. Condensation Requires Cooling and Nuclei p503
For water vapor to condense, air must be cooled below its dew point. This cooling can happen in four different ways. Air may lose heat by: 1. contacting a colder surface 2. radiating heat 3. Mixing with colder air 4. Expanding when it rises (cloud formation)

27. Air can also become saturated when it cools below its dew point:
Example: When you add ice to a glass of juice, the temperatures of the juice and glass decreases.
The glass absorbs heat from the air, so the temperature of the air near the glass decreases.
The air’s temp drops below its dew point, water vapor condenses on the glass forming droplets on the glass.

28. How does evaporation work?

29. Practice Activity: Build a Zeer Pot (Pot-in-pot refrigerator)
Finish Heat Transfer and Water Cycle WS

30. Factors determining Weather
latitude;
elevation or proximity to mountains;
large bodies of water and
relative temperatures of land and water;
storms