1. State Objectives 4.c, 4.e, 4.h.

2. Discussion What are some ways in which weather affects your everyday life?

3. What is Weather? Atmosphere layer of gases surrounding Earth. Weather is the conditions of the atmosphere. Temperature Air Pressure Humidity Wind Clouds Precipitation Main cause for changes in weather is energy from the sun.

4. Weather Tools: Hygrometer - an instrument for measuring the water- vapor content of the atmosphere (air) Barometer - an instrument that measures atmospheric pressure (air pressure) Anemometer - also called a wind gauge an instrument for recording the speed and how often the direction of winds changes Psychrometer - an instrument for determining atmospheric humidity by the reading of two thermometers, the bulb of one being kept moist and ventilated and the other remaining dry Rain Gauge - an instrument for measuring rainfall.

5. Temperature Indicates the amount of heat (kinetic energy) in the atmosphere. Represents the speed of the molecules. The higher the temperature, the faster the air molecules are moving. Warmer air rises and cooler air sinks which causes convection currents. Measured with a thermometer. Standard unit is Fahrenheit (°F) SI Unit is Celsius (°C)

6. Convection in the Atmosphere

7. Convection Currents: Convection Currents are formed by the upward movement of warm air and the downward movement of cool air. Convection Currents move heat throughout the troposphere

8. Heat Transfer: Conduction – the direct transfer of heat from one substance to another substance that it is touching Example – a pot on the eye of a stove Convection – transfer of heat by the movement of a fluid Example – rising of warm air versus the sinking of cool air Radiation – direct transfer of energy by electromagnetic waves Example – Microwave oven

9. Air Pressure/Barometric Pressure Air has weight because it has mass. Air pressure is a measure of the force of air being exerted on a given area of Earth’s surface. As temperature increases pressure decreases. Cool air is more dense, which causes it to sink (high pressure). As altitude increases air pressure decreases.

10. Weather and Air Pressure Changes in pressure indicated a change in weather is approaching. Low pressure systems are associated with clouds & precipitation. High pressure systems are associated with clear skies. Steady pressure indicates current conditions will continue. Measured with a barometer in inches of mercury or in millibars.

11. Cyclone: A cyclone is a swirling center of LOW air pressure. Cyclones play a large part in the weather of the United States. As air rises in a cyclone, the air cools, forming clouds and precipitation. Cyclones and decreasing air pressure are associated with clouds, wind, and precipitation.

12. Anticyclones: Anticyclones are HIGH pressure centers of dry air Opposite of a cyclone (LOW pressure) Because air moves out from the center of the anticyclone, cool air moves downward from higher in the troposphere. As the cool air falls, it warms up, so its relative humidity drops. The descending air in an anticyclone generally causes dry, clear weather.

14. Humidity Amount of water vapor in the air. Relative humidity is a percentage of the amount of water vapor in the air compared to the maximum amount of water vapor it can hold at that temperature. The warmer the temperature the more water vapor it can hold. Saturated means the air is holding 100% of the water vapor it can hold at that temperature. Measured with a hygrometer or a psychrometer.

15. Relative Humidity Chart

16. Dew point Dew is the water vapor that has condensed on a surface into a liquid. Depends on two factors: Amount of water vapor in the air Temperature near the surface Dew point is the temperature at which water vapor condenses into a liquid.

17. Wind Caused by differences in air pressure Air moves from areas of high pressure to areas of low pressure Wind Speed Measure of how fast the air is moving. Measured with an anemometer. Wind Direction Direction from which the wind is coming, NOT the direction it is blowing Ex. North winds blow from N to S Measured with a wind vane.

18. Global Wind Patterns Blow steadily across Earth in paths that are thousands of kilometers long Steer weather in certain directions (usually west to east in the U.S.) Caused by thermal energy from the sun The sun does not heat the surface evenly causing uneven heating of the atmosphere.

19. Global Winds

20. Types of Global Winds Surface winds at low altitudes: Trade winds: blow from east to west near the equator. Westerlies: blow from west to east in the mid-latitudes. Coriolis Effect: Earth’s rotation causes winds to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

21. Types of Global Winds Jet streams at high altitudes are bands of strong winds (up to 350 km/h) near the top of the troposphere at the northern and southern boundaries of the prevailing westerlies. Race from west to east Two types: polar & subtropica l

22. Clouds Clouds form when air rises, cools, and condenses. They are classified according to their height and shape.

23. Types of Clouds 1. cumulus- a low, puffy cloud that forms on sunny days when heat from the surface causes warm air to rise. 2. stratus- a low, gray, sheet-like cloud that forms when warm, moist air moves over cooler ground. They are seen most often during the winter and may bring steady rain.

24. Cumulus and Stratus

25. Types of Clouds 3. cumulonimbus (thunderheads) - vertical clouds that may be over four miles tall. They form where cold air forces warm air to rise quickly. 4. cirrus- high, featherlike clouds. They are the highest clouds in the sky. They do not produce precipitation.

26. Cumulonimbus and Cirrus

27. Altocumulus and Altostratus Clouds Part of a cloud’s name may be based on its height. The names of clouds that form between 2 and 6 kilometers about the Earth’s surface have the prefix alto-, which means high. The two main types of these clouds are altocumulus and altostratus. These are “middle-level” clouds that are higher than regular cumulus and stratus clouds, but lower than cirrus and other “high” clouds.

28. Precipitation Precipitation – occurs when drops of water or crystals of ice become too large to be suspended in a cloud and fall in the form of rain, freezing rain, sleet, snow, or hail.

29. The Water Cycle Earth’s surface is about 70% water and it exists in all three states (solid, liquid, gas). The water cycle is the constant movement of water on Earth. The Sun provides the energy for the water cycle.

30. Parts of the Water Cycle 1. Evaporation occurs when water changes from a liquid into a gas after gaining heat energy from the Sun. 2. Transpiration is the evaporation of water from the leaves of plants.

31. Parts of the Water Cycle 3. Condensation occurs when water vapor changes into liquid water to form clouds or fog. 4. Precipitation occurs when water droplets fall to Earth.

33. What is an Air Mass? An air mass is a large body of air that develops over a particular region. It has characteristics of the area over which it develops. Cold, dry air masses come from Canada and warm, dry air masses develop over Mexico.

34. Air Masses

35. Air Mass Locations

36. Weather Maps Satellite map: allow meteorologists to monitor weather on the global scale Radar Map: uses electromagnetic waves to monitor velocity and altitude.

37. Types of Maps

38. Weather Map Symbols

39. HIGH PRESSURE SYMBOL LOW PRESSURE SYSTEM