1. Weather and Climate
8th grade science STAAR

2. What is Weather vs. Climate
Weather is the current atmospheric conditions, which includes temperature, wind, humidity, etc.
The average weather in a given area is the climate for that area.
Example: The weather in Lake Dallas, Tx on June 5th is 95° F and warm, but the climate for the area during summer is hot and dry.

3. Latitude and Longitude
What is latitude? Longitude?
Latitude = lines that measure North to South - go from the poles at 0° to the equator at 90°
Longitude =is measured from the Prime Meridian with positive values going east and negative values going west.
For example: at the equator what is the climate like? What about at the north and south poles?

4. What affects an area’s climate.
Cycling of water in and out of the atmosphere plays an important role in determining weather and climatic patterns.
What is the cycling of water in the atmosphere called? WATER CYCLE
Terms to know: Precipitation, Condensation, Evaporation, Transpiration, Run-off, Groundwater, Surface water

5. Water Cycle

6. What affects an area’s climate.
CONVECTION CURRENTS –
Uneven heating of the Earth's surface that produces weather systems.
Where hot air rises (less dense) and cooler air sinks (more dense).

7. Sun’s role in convection currents
You know that it is warmer at the Equator than at the poles because Earth is tilted!
Direct rays of sun at the equator and indirect rays at the poles.
The warmer, lighter air at the Equator moves toward the cooler air at the poles. The cold heavy air at the poles moves toward the Equator. 
This causes a constant movement of air movement called convection currents.

8. Convection currents drive (cause) wind patterns that affect climate.

9. Air Masses Cold = dry, dense Warm = moist, less dense
Air masses are moved by convection currents
There are two types of air masses; cold and warm.
Cold = dry, dense
Warm = moist, less dense
Cold air masses come from higher latitudes to lower latitudes. Warm air masses do the opposite. When they meet in the middle some interesting weather happens!

10. Cold Meets The Warm
Why is the warm air rising and going on top of the cold air mass?
Warm air is LESS dense.

11. Air Masses Air masses are classified by TWO letters.
The first letter shows what the air mass forms over:
Continental (c)- dry air masses that form over land
Maritime (m) – moist air masses that form over water.

12. Air Masses Second Letter represents the LATITUDE and the temp.
Arctic (A) – cold, dry air mass
Polar (P) – cold dry air mass (not as cold as artic
Equatorial (E) – warmest air mass
Tropical (T) – warm air mass (not as warm as equatorial.

13. Air Masses on Globe

14. Air Pressure This is how scientists measure air pressure.
Air pressure is the amount of pressure exerted on a surface by the atmosphere above it.
Barometers are used to measure this with units in millibars (mb).

15. What is this graph telling us?
As the altitude increases what happened to the air pressure?
It decreases!

16. High Pressure System
The air molecules packed in to the center of a high pressure system doesn’t make the right conditions for cloud and precipitation development
So weather is generally calm around a high pressure center.

17. Low Pressure System
This is an area where air is rising and this fuels weather change. With rising air means rising water vapors which leads to clouds and the rest of the water cycle.
Hurricanes, cyclones and other storms are associated with low pressure.

18. Fronts Fronts- boundaries between two air masses.
they are created when high pressure systems moves in around low pressure systems.
They bring WEATHER CHANGES!

19. What Are Main Types of Fronts?
A cold front forms when a fast cold air mass runs into a slow warm air mass.
A cold front brings heavy rain or snow.
After the front passes, cold dry air moves in, skies clear, winds shift, and temperatures drop. 19

20. What Are Main Types of Fronts?
A warm front forms when a fast-moving warm air mass overtakes a slower-moving cold air mass.
After the front passes, weather tends to be warmer and more humid. 20

21. What Are Main Types of Fronts?
An occluded front forms when a warm air mass is caught between two cooler air masses.
Occluded fronts cause weather to turn cloudy and rain or snow may fall.
A stationary front forms when air masses meet, but neither can move the other.
Stationary fronts often bring many days of clouds and precipitation. 21

22. Front Symbols Cold front – Warm front – Stationary Front –
All symbols are put on an isobar
Isobars are lines that show areas with equal air pressure
Cold front –
Warm front –
Stationary Front –
Occluded Front -

23. Weather Maps
A weather map can be used to predict temperature and precipitation for several days in a given area
See if you can find the pressure systems and fronts on the following maps

24. Can you read the map?

25. Station Symbols
You will see symbols like these from weather stations scattered about.
They tell information about cloud cover, barometric pressure, dew point, temperature, current precipitation, etc.

26. Station Model

27. Winds Winds move excess heat around the Earth.
They are caused by air flowing from high pressures to low pressures!
When air moves downward you have HIGH PRESSURE develop.
When air rises you have LOW PRESSUE develop.

28. Winds…
Winds do not all blow the same direction though they are effected by two main things:
Coriolis Effect – Winds are forced to the right in the northern hemisphere and to the left in the southern hemisphere
Convection cells – Heat from the sun powers these.

29. Wind Directions

30. Ocean Currents
Ocean currents affect local and global weather conditions.
They have a much slower, long lasting effect on climate than winds.
They move slowly and retain more heat than the atmosphere.
They are driven by the Sun and the rotation of the earth (Coriolis Effect).

31. Types of Ocean Currents
Surface Currents – driven by winds, only 10% of water in the ocean- only the top layer.
Gulf Stream – a surface current that travels along eastern part of the US – causes warmer climates in Europe.
Deep Water Currents – these are colder (denser) layers that make up 90% of the ocean currents. They are caused by the the change in density causes these currents

32. El Niño
El Niño is a mass of warm water that moves eastward as trade winds relax. Originates in the PACIFIC OCEAN.
El Niño causes warm water brings torrential rains to parts of the world that are not prepared for such weather.
For reasons that scientists still do not completely comprehend, every few years the trade winds blow less or stop blowing at all. They can also change direction.
It causes a build-up of warm water off the coast of South America and Africa and causes weather changes all over the globe.

33. Tracking El Nino

34. Hurricanes and Cyclones
A cyclone is a huge revolving storm that is caused by winds blowing around a low pressure area.
Tornadoes are also a type of cyclone with a tighter, faster spinning vortex of wind.
Cyclones develop over the oceans near the equator. A cyclone will not develop unless the surface water temperature is at least 26° C (80° F). Warm air rises and creates area of low pressure.

35. Hurricanes and Cyclones
A hurricane is a huge storm that forms over warm ocean water! Hurricanes can cause extreme amounts of damage depending on their size and wind speeds.
The main purpose of a hurricane is to move heat away from the tropics. So the sun is the main energy source for hurricanes.
Types of damage caused by hurricanes reaching land are strong winds, flooding, storm surge, and tornadoes.

36. Which would you rather experience?
Hurricane!
Cyclone!