Chapter 16

Weather

Section 1 What is Weather?

·        Weather- the state of the atmosphere at a specific time  & place

·        Sun provides energy-energy evaporates water into the atmosphere where it forms clouds-eventually falls back to Earth as rain or snow

·        Sun is also a source of heat- which is absorbed by Earth’s surface- which heats the air above it

·        Weather is the result of heat & Earth’s air & water

·        Weather Factors: describe weather conditions–

o       Air temperature- air is made up of molecules that are always moving randomly- high temperature is rapidly moving molecules (when air is heated, it expands & becomes less dense with low pressure)- low temperature molecules move less rapidly (condense, become more dense with high pressure)

o       Wind- air moving in a specific direction- warm air has low pressure- cool air has high pressure

·        wind results because air moves from high pressure to low pressure

·        wind direction is measured with a wind vane or wind sock

·        wind speed measured with an anemometer- has rotating cups that spin fast when wind is strong 

o       Humidity- the amount of water vapor present in the air

·        water molecules fit into spaces among air molecules

·        warm temperature water molecules move quickly & don’t easily come together

·        cool temperature water molecules move slowly & collide to form droplets

·        liquid from vapor is called condensation- the air is saturated

o       Relative humidity- the measure of the amount of water vapor present in the air compared to the amount needed for saturation- (50% humidity means that the air contains 50% of the water needed for the air to be saturated)

o       Dew point-the temperature at which air is saturated & condensation occurs

·        lower temperature less water vapor in the air

·        when air near the ground cools to its dew point, dew forms and when it is 32% frost will form

Forming Clouds:

1.     clouds form when warm air is forced upward, expands, & cools

2.     when air cools, less water vapor is needed for saturation so relative humidity increases

3.     when saturation occurs, water vapor condenses in tiny droplets around small particles such as dust & salt

4.     these droplets are so small they remain suspended in the air

5.     billions of these droplets form a cloud

Ways that warm, moist air form clouds:

1.  sun heats the ground & air next to it- warm air rises and then cools- if air is moist, water vapor condenses & forms clouds

2.  moist warm air moves over mountains, is lifted & cooled

3.  cool air meets warm, moist air & the warm air is lifted & cools

Classifying Clouds-by shape & height 

Shape-1. stratus- smooth, even sheets (layers)- form at low      

altitudes- associated with fair weather or rain or snow- fog is a stratus cloud near the ground that has been cooled to its dew point

                   2. cumulus-puffy, white clouds with flat bases-

                        Sometimes tower to great height- associated

                        with fair weather or thunderstorms

  3. cirrus-curly or fibrous- high, thin, white,

            feathery made of ice crystals- associated with

            fair, but may mean approaching storms

Height-some prefixes describe height of cloud base

1.   cirro- high clouds

2.   alto- middle-elevation clouds

3.   strato- low elevation

Some names combine shape & height-

(ex) cirrostratus

             Rain-or Snow-Producing Clouds

Usually have the word “nimbus” attached to them- means “dark rain cloud” – the water content is so high that little sunlight can pass through-

(ex) cumulonimbus-towering thunderstorm

       nimbostratus- layered rain or snow clouds

Precipitation

·        water falling from clouds- when cloud droplets combine & grow large enough to fall to Earth

·        size of raindrop depend on strength of updrafts in a cloud- a strong updraft keeps the drops suspended in the air longer & they can combine with other drops & grow larger

·        the rate of evaporation can also affect the size of the raindrop- (ex) dry air reduces the size or evaporates it altogether

·        air temperature determines whether water forms rain, snow, sleet, or hail

1.      drops falling in temperatures above freezing is rain

2.    snow is when air temp is so cold that vapor changes directly to a solid

3.    sleet when rain (water above freezing) passes through a layer of freezing air near Earth’s surface

4.    hail (page 469) lumps of ice- when water freezes in layers around a small nucleus of ice that forms inside a cloud- they grow larger each time they are tossed up & down by the air

o       The role of water vapor  explains the weather

o       Relative humidity of the air helps determine if it will be dry or experience precipitation

o       Temperature of the atmosphere determines the form of precipitation

o       Studying clouds helps forecast weather

Chapter 16

Section 2:  Weather Patterns

A.  Weather Changes

      1.  Air Masses are large bodies of air that have properties

          similar to the part of the Earth’s surface over which it

          develops.

          Ex.  Air mass over land is dry

                 Air mass over the tropics is warmer than one over the

                  northern regions.

          Weather changes are due to the movement of air masses.

            Six major air masses affect weather in the U.S.

2.      Highs and Lows

-Atmospheric pressure varies over the Earth’s surface

  (high and low pressure systems)

-Cyclones are caused by winds blowing into a low pressure

 area in the northern hemisphere.  These winds turn in a

 counterclockwise direction due to the Coriolis effect and

 are associated with stormy weather.

-Anticyclones are winds moving from high pressure areas

 and turning in a clockwise direction in the northern

  hemisphere.  High pressure areas are associated with

 fair weather.

 -A barometer is an instrument used to measure air

  pressure.

  -Changes in atmospheric pressure affect the weather:

     a.  low pressure (rising air) = cloudy weather

     b.  high pressure (sinking air) = good weather

B.      Fronts-boundary between 2 air masses of different

    density, moisture, and temperature. (Curving lines on

    a weather map)

     Types of Fronts:

a.      Cold front – (blue line with triangles) occurs when

     cold are moves toward warm air.  The cold air

     moves under the warm air to lift it.  The warm air

     cools and condenses to form clouds.  If the

     temperature differences are large, thunderstorms

     and tornadoes may form.

b.      Warm front – (red line with red semicircles) occurs

   when warm air moves over cold air.  This leads to

    wet weather.

c.      Occluded front - (purple lines with triangles and

    semicircles) involves 3 air masses of different

      temperatures (cold, cool, warm).  Cold air moves

      toward cool air with warm air in between the two. 

      Cold air forces the warm air up closing it off from

      the surface.

d.      Stationary front- (alternating red and blue line)

Occurs when a boundary between air masses stops

advancing; may remain in the same place for several

days producing light wind and precipitation.

C.       Severe Weather – poses danger to people,

                                   structures, and animals

1.      Thunderstorms occur in warm, moist air masses

   along fronts. (heavy rain, lightning, thunder,

   and hail)

     a.  Warm, moist air rises to form cumulonimbus

          clouds.

b.      Water vapor condenses into water droplets or

      ice crystals.

c.       Small droplets collide to form larger droplets.

d.      Droplets fall toward Earth colliding with more droplets to form even larger droplets.

e.       Raindrops cool the air.

f.       Cool, dense air sinks and spreads over Earth’s surface.

g.       Sinking, rain-cooled air and updrafts of warm air create strong winds.

h.       Hail may form as ice crystals fall to warmer layers and lift back into colder layers by updrafts in cumulonimbus clouds.

Thunderstorm damage- flash flooding, wind damage, and hail damage to cars, aluminum siding, and crops.

2.     Lightning and Thunder

a.  Lightning occurs in a storm cloud when warm

     air is lifted rapidly as cooler air sinks.  This

     causes different parts of the cloud to become

     oppositely charged.  Currents flowing between

     opposite electrical charges creates lightning

     flashes.

    (Occurs within clouds or between

   clouds and the ground.)

b.      Thunder results from the rapid heating of air

    around a bolt of lightning.  Lightning can

                               reach temperatures 3x’s the temperature of

                               the Sun’s surface (30,000^oC).

                              Sound waves, heard as thunder, are created

                                as a result of the air, around the lightning,

                                rapidly expanding, cooling, and contracting.

c.       Tornadoes are violent, whirling winds that

    move in a narrow path over land.

     A wind shear (difference in wind speed and

     direction) forms a rotating column of air

     parallel to the ground.  A thunderstorm’s

     updraft can tilt the column to form a funnel

     cloud.  A tornado is created when a funnel

     cloud makes contact with Earth’s surface.

    Tornado damage:  uproot trees, rip buildings

    apart, lift off rooftops and blow out walls,

      lift animals, lift cars, lift houses.

      Lasts a few minutes.

     May 1999:  More than 70 tornadoes in Kansas,

                        Oklahoma, and Texas.

d.      Hurricane (most powerful storm) is a large, swirling, low-pressure system that forms over the Atlantic Ocean; it turns heat energy into winds of at least 119 km/h; similar to low-pressure systems on land.

Similar storms in the Indian Ocean are called cyclones.  In the Pacific Ocean they are called typhoons.

Hurricane damage (on land):  high winds, tornadoes, heavy rain, high waves, floods, destroys crops, destroys buildings.

Hurricanes lose power upon reaching land because its supply of energy from the warm, moist ocean air is lost.

e.       Blizzards are winter storms that result from

    winds of 56 km/h, low temperature,  and

      visibility less than 400 m from falling and

      blowing snow.  Conditions usually persist for 3

      hours or more.  Always stay indoors.

f.       Severe Weather Safety

The National Weather Service issues a watch or warning when severe weather threatens.

Watches are issued when conditions are favorable for severe thunderstorms, tornadoes, floods, blizzards, and hurricanes.

Stay tuned to a radio or television station.

Warnings are issued when severe weather conditions already exist.  You should take immediate action (evacuate, take shelter in a basement or room in the middle of the house away from windows.).

Chapter 17

“Climate”

Section 1 “ What is Climate?”

Climate- the pattern of weather that occurs in an area over many years

·        It determines the types of plants or animals that can survive

·        It influences how people live

·        It is determined by averaging the weather of a region over a long period of time (30 years)

Scientists determine the climate by averaging:

Ø     temperature

Ø     precipitation

Ø     air pressure

Ø     humidity

Ø     number of days of sunshine

Factors that affect climate:

Ø     latitude

Ø     landforms

Ø     location of lakes and oceans

Ø     ocean currents

Zones

·        tropics- region between latitudes 23.5˚N and 23.5˚S

o       most solar radiation  (refer to figure 15 page 447)

o       always hot except at high elevations

·        polar zones- extend from 66.5˚N & 66.5˚S to the poles

o       never warm- low angle of solar radiation

·        temperate zones- between the tropics and polar zones-23.5˚to 66.5˚ both N & S of the equator

o       moderate temperature

o       most of United States is located in this zone

Other Factors that affect climate

1.    large bodies of water

o       take longer to heat & cool than land

o       coastal areas are warmer in the winter & cooler in the summer than inland areas of the same latitude

2.    ocean currents-

o       warm currents begin near the equator & flow toward higher latitudes, warming the land they pass then when they cool off & flow back toward the equator they cool the air & climate

o       winds blowing from the sea are usually moister so coastal areas have a wetter climate

3.    mountains

o       thinner atmosphere so fewer molecules to absorb heat so cooler

4.    rainshadows –

o       windward side often has heavy precipitation- air rises, cools, and drops moisture

o       leeward side (away from the wind) deserts are common- air descends, heats up, and dries the land

5.    cities

o       large cities have lots of streets, parking lots, & buildings that heat up & therefore heat the air above it-could be 5˚C higher than surrounding rural area

o       air pollution also traps this heat & creates a “heat-island” (when paved surfaces heat up & air pollution traps heat)

Section 2:  Climate Types

A.  Classifying Climates

     Climatologist – person who studies climates

        The system used to classify climates was developed in 1918,

         by Wladimir Koppen.  He classified climates by using the

         temperature and precipitation of regions that had 

         different plant types.

        Climate Classification System

1.      tropical

2.    mild

3.    dry

4.    continental

5.    polar

6.    high

B.  Adaptations – any structure or behavior that helps an

       organism survive in its environment. 

a.      Inherited

b.     Develop in a population over a long period of time

c.      Organisms may not be able to survive in other climates once they adapt to a particular climate.

1.      Structural Adaptations – structures that help organisms

     survive in certain climates.

a.      Fur on mammals – insulation in cold temperatures

b.      Cactus’ stem is thick, fleshy, waxy, and has spiny leaves so that it can hold water and prevent water loss.

2.  Behavioral Adaptations

        a.  hibernation –a period of greatly reduced activity

             for mammals during the winter due to cooler

             temperatures, shorter days, and lack of food

             Examples:  body temperature drops, body

                                        processes reduced

b.     Bees cluster together to conserve heat during cold weather.

c.     Desert snakes hide under rocks on hot, sunny days.

d.     Desert turtles and lizards obtain moisture from food instead of drinking water.

       3.  Estivation – a period of intense heat that causes lungfish

    to enter an inactive state.  The fish burrows into the mud

             and covers itself with mud and mucus.  It lives this way

             until the warm, dry months pass.