1. Meteorology
Chapter 12

2. The Causes of Weather
Meteorology- The study of atmospheric phenomena and weather
Weather- current state of the atmosphere
Climate- long term variation in earth’s weather.
Usually an average over 30 years or more

3. The Causes of Weather
Different parts of the world receive differing amounts of energy form the sun
The constant movement of air and water currents distributes this energy around the globe

4. The Causes of Weather
Air Masses- a large body of air that takes on the characteristics of the area over which it forms.
Continental tropical (cT)- warm and dry
Maritime tropical (mT)- warm and wet
Continental polar (cP)- cold and dry
Maritime polar (mP)- cold and wet

5. The Causes of Weather
Air Masses:

6. The Causes of Weather

7. The Causes of Weather
Air mass modification occurs when air masses move from one area to another and start to take on the characteristics of the new area.

8. Weather Systems
Coriolis Effect- moving particles, such as air, are moved to the right in the northern hemisphere and the left in the southern hemisphere because of the rotation of the earth.

9. Weather Systems
Wind systems- three basic zones in the northern and southern hemisphere
Trade winds- 0o and 30o (Hadley’s cell)
Horse latitudes- very little air movement at 30o
Intertropical convergence zone (ITCZ)- also known as the doldrums at equator
Prevailing Westerlies- 30o and 60o
Polar Easterlies- 60o and 90o

10. Weather Systems

11. Weather Systems
Jet Stream- Narrow bands of fast, high-altitude, westerly winds

12. Weather Systems Fronts- a narrow region separating two air masses.
Can bring dramatic changes in local weather

13. Weather Systems
Cold Front- cold, dense air displaces warmer air and forces it up along a steep front.
Can cause the most sever weather

14. Weather Systems Warm Front- warm air displaces cooler air.
Typical cloudiness and precipitation

15. Weather Systems
Stationary Front- two air masses meet but neither moves into the other’s territory.
Occur because the air masses have been modified to an extent that they are not very different from each other
Usually will not have extensive cloudiness or precipitation.

16. Weather Systems
Occluded front- sometimes a cold air mass will move rapidly enough to over take a warm air mass moving the same direction.

17. Weather Systems Pressure systems- Rising air = low pressure
Rainy weather
Falling sir = high pressure
Clear weather

18. Gathering Weather Data
Surface Data-
Thermometer- temperature
Barometer- air pressure
Anemometer- wind speed
Hygrometer- humidity
Ceilometer- cloud height

19. Gathering Weather Data
Upper level data-
Radiosonde- carried by weather balloon
Wind speed and direction
Temperature and humidity

20. Gathering Weather Data
Weather Radar-
Doppler Radar- plots the direction that rain drops move toward or away from the radar.

21. Gathering Weather Data
Weather Satellites-
Gathers data on cloud type and precipitation
Infrared imagery- detect differences in thermal energy

22. Weather Analysis
Station model- a record of weather data at a particular site at a particular time.

23. Weather Analysis
Isopleths- lines that connect points of equal or constant values
Isobars- connect points of equal pressure.
Isobars close together indicate strong winds. Widely spaced isobars indicate weaker winds

24. Weather Analysis
Digital forecast- use of computer models to process data for forecasting
Analog forecast- involves comparing current weather patterns with patterns that took place in the past.