WEATHER•Heating the Earth•Air pressure•Winds•Moisture in the Air•Clouds•Weather Instruments•Weather Patterns•Predicting the Weather

Weather factors

• Air temperature• Wind• Humidity• Relative humidity

Heating The Earth

Heat Transfer in the Atmosphere•1. Conduction – direct

transfer of heat energy from one substance to another.Ouch!

•2. Convection – the transfer of heat energy in a fluid (gas or liquid)

•3. Radiation – transfer of heat energy through empty space.

Greenhouse Effect•Ultraviolet (UV) rays from the sun pass

easily through the atmosphere to the Earth.

However, infrared rays cannot pass back out as easily. It helps the Earth keep nice and warm!

Infrar

ed ra

ys

UV Rays

Without the Greenhouse Effect the Earth would be

a frozen tundra!

Temperature Variations

•The Earth has varying temperatures due to the different angles at which the sun’s rays strike the Earth.

HOTTEST

TEMPERATURESCOLDER TEMPERATURES

Air Pressure

Factors That Affect Air Pressure

•W (water vapor)

•E (elevation)

•T (temperature)

Water Vapor•Moist air is less dense than dry air. This is because a water molecule has less mass than an oxygen molecule.

•The MORE water vapor in the air…the

LESS air pressure there is.•This is an INVERSE relationship!

Elevation

•The higher the elevation (height above sea level), the less dense (thinner) the air.

•The GREATER the elevation above sea level, the LOWER the air pressure.

•This is an INVERSE relationship!

Temperature•Hot temperatures have low air pressure

Cool temperatures have high air pressure. (think of the lava lamp!)

•Places with HIGH (hot) temperatures have LOW air pressure.

•Places with LOW (cold) temperatures have HIGH air pressure.

• This is an INVERSE relationship!

Air Pressure and Weather•When the air pressure in an area is

HIGH, it is preventing clouds from entering the area…therefore, the weather is usually fair (nice).

•Conversely, when the air pressure in an area is LOW, it allows clouds to enter the area…bringing rainy weather!

Winds

How does wind form?•When air moves from an area of high pressure to an area of low pressure….winds form!

•Two types of winds:•1. Local winds•2. Global winds

Local Winds•Winds that occur over a small area.•Two types:•1. Sea Breeze – flow of air from the sea to the land.

•2. Land Breeze – flow of air from theland to the sea.

Global Winds•Due to temperature variation, the Earth is heated unevenly…this causes global winds!

•Because of the Earth’s rotation, all winds shift to the right in the N. Hemisphere and to the left in the S. Hemisphere. This shift is called the Coriolis Effect.

Global Wind Systems• 1. Doldrums – located at

the equator: very calm• 2. Trade Winds - 30°N

and S of the equator: calm…horse latitudes

• 3. Prevailing Westerlies - 40°-60° N. and S…strong

• 4. Polar Easterlies – approaching 90°N and S…cold but weak

Jet Streams•Discovered in the 1940’s…narrow belt of strong, high speed, high pressure air.

•Flows approximately 7 miles in altitude…airplane pilots use the jet stream to increase speed and save fuel.

Moisture in the Air

The Water Cycle

HUMIDITY•During the process of evaporation, the sun turns water into a water vapor. This moisture in the air is called humidity.

•Winds transport moisture all over the Earth!

Relative Humidity•Relative humidity is the percentage of moisture the air holds relative to the amount it could hold at a particular temperature!

•To find relative humidity, meteorologists use a Relative Humidity Chart.

How to determine relative humidity…

•1. Determine the dry-bulb thermometer reading.

•2. Find the difference between the dry-bulb temperature and the wet-bulb temperature.

•3. Use the chart to find the relative humidity expressed as a percentage.

°C 1 2 3 4 5

10 88 77 66 55 44

11 89 78 67 56 46

12 89 78 68 58 48

13 89 79 69 59 50

14 90 79 70 60 51

15 90 80 71 61 53

16 90 81 71 63 54

17 90 81 72 64 55

18 91 82 73 65 57

19 91 82 74 65 58

20 91 83 74 66 59

21 91 83 75 67 60

22 92 83 76 68 61

23 92 84 76 69 62

24 92 84 77 69 62

25 92 84 77 70 63

26 92 85 78 71 67

27 92 85 78 71 65

28 93 85 78 72 65

29 93 86 79 72 66

30 93 86 79 73 67

RELATIVE HUMIDITY CHART

CloudsClouds form when moisture in the air condenses on small particles of dust or other solids in the air.

Three Types of Clouds•1. Cumulus – fluffy and white with flat bottoms. Indicate fair weather

•2. Stratus – gray clouds that cover the entire sky. Indicate rain and drizzle

•3. Cirrus – feathery clouds highest in the sky. Made of ice crystals because of its high altitude. Indicate rain or snow in several hours.

•Anything with the word “NIMBO” means rain!

4 types of precipitation•1. Rain 2. Hail

•3. Sleet 4. Snow

Weather Instruments

•A RAIN GAUGE is used to measure the amount of rain in a particular area.

•A THERMOMETER is used to measure air temperature

•A BAROMETER is used to measure air pressure.

•A WIND VANE is used to measure wind direction.

•An ANEMOMETER is used to measure wind speed!

•You measure RELATIVE HUMIDITY with a psychrometer!

Weather Patterns

Air Masses•Changes in the weather are caused by movements of large bodies of air. These large bodies are called air masses.

•There are 4 major types of air masses:•1. Maritime tropical•2. Maritime polar•3. Continental tropical•4. Continental polar

Let’s break down these words…

•Maritime means “relating to the sea”

•Continental means “of the land”

•Tropical means “warm”

•Polar means “cold”

•So….an air mass that is maritime tropical means that it is over WATER and HOT!

•Remember…evaporation takes place over water so it is over water where there is a lot of moisture or water vapor.

Fronts•Fronts form where two air masses meet

•There are 4 types of fronts:

COLD FRONT

WARM FRONT

OCCLUDED FRONT

STATIONARY FRONT

Storms•1. Rainstorms and snowstorms – both develop when two different fronts collide. It falls as rain if above 32°F and snow if 32°F or below.

•2. Thunderstorms – When a cold front moves in and meets a warm front, CUMULONIMBUS clouds form. Remember…nimbus means rain!

•3. Cyclones and Anticyclones – both are affected by air pressure. An area of LOW pressure that contains rising warm air is a cyclone. An area of HIGH pressure that contains cold, dry air is called an anticyclone.

•4. Hurricanes – A powerful cyclone that forms over TROPICAL OCEANS!

•5. Tornadoes – a whirling, funnel-shaped cloud. Develops in low, heavy cumulonimbus clouds.

Predicting the WeatherPredicting the Weather

Weather Maps• Some information included on a

weather map:1.Cloud cover2.Air pressure3.Temperature4.Wind speed5.Wind direction

•H Area of high pressure (nice weather)

•L Area of low pressure (cloudy, rainy weather)

ISOTHERM AND ISOBAR•Let’s break down these words:•ISO means equal or the same•THERM reminds me of a thermometer (which

measures air temperature)•So an isotherm means areas with the same air temperature

•BAR reminds me of a barometer (which measures air pressure)

•So an isobar means areas with the same air pressure

Isobar Map (each color represents areas with the

same air pressure)

Isotherm Map (each line represents areas with the

same air temperature)

Cloud Seeding (changing the weather)

•Most effective use so far is at the airport to reduce fog for incoming planes.