Introduction to weather

Earth Science Weather

I. Introduction to weather

a. Weather

i. Is the short term condition of the atmosphere at any

location

ii. It is made up of the connection and relationship of

1. Temperature

2. Humidity

3. Air pressure

4. Wind

II. Temperature Introduction

a. at any given place temperature is connected to the heat

energy present in the atmosphere at that location

b. Solar radiation is the amount and how long the sun is on a

particular location and how strong it is.

c. Therefore anything that changes solar radiation will also

change the air temperature

d. What are factors that can effects solar radiation?

i. The following are factors that can change the amount

of solar radiation a place has

1. The angle that solar radiation hits the Earth

2. this changes throughout the day because of

the Earth rotation

3. Solar radiation is only present during the day

4. similar changes also happen when the Earth

moves around the sun

a. we call these slower changes seasons

5. number of hours of solar radiation during the

day

6. the reflection

7. refraction

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8. absorption of solar radiation

a. for example clouds block and absorb the

amount and intensity of the sun

9. and the type of surface (ex: water and land)

e. How do we measure air temperature?

i. Temperature is measured with thermometers

1. Works on a simple principle

2. Matter expands when heated and contracts as

it cools.

ii. There are many scales of measuring temperature

that are named after the people who made them up

1. Celsius

2. Fahrenheit

3. Kelvin

iii. Here in America we use Fahrenheit the rest of the

world uses Celsius

iv. Meteorologist ( people who study weather ) use a

thermograph as a thermometer

III. Air Pressure

a. Introduction

i. Air is a mixture of different gases

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ii. Gas consists (made up of) many different tiny

molecules that move around rapidly and are far apart

from each other.

1. They are kept contained either by a container

or in the case of the atmospheres by the

Earth’s Gravity

iii. Gases put pressure on the surfaces that they are in

contact with.

iv. In the case of air pressure this pressure is due to the

gas particles bumping into the surface

v. Since they move rapidly in all direction they balance

out this pressure in all directions

b. How does air pressure help us forecast weather

i. You cant sense air pressure like you can with

temperature

ii. Nor can you forecast the weather based on the air

pressure in a location

iii. BUT since we have isoclines of the air pressure, we

can study the changes of the air pressure and the

different masses and temperatures that come with it.

1. Rising pressure usually means fair weather

2. Low Pressure usually means an approach of a

storm

c. How is air pressure measured?

i. We use a barometer to measure air pressure.

d. there are two common barometers used

1. Mercury Barometer 2. Aneroid Barometer

• air pressure forces liquid

mercury up a tube

• the more pressure the higher

• aneroid means no liquid

• it is a can with a spring scale

on it

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the mercury level will be

• we usually name the number

with inches or millimeters attached

to the number

• the amount of pressure on

the sides of the can will either push

down or loosen the spring scale

e. air pressure is measured based on units of force per a unit

area

1. atmosphere (atm) is the average air pressure

at sea level

Homework

Based on the Lesson on Temperature and air pressure

Please identify the following terms

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1. weather-

__________________________________________________________

__________________________________________________________________

2. Temperature -

______________________________________________________

__________________________________________________________________

3. Solar radiation -

___________________________________________________

_________________________________________________________________

4. thermometer -

______________________________________________________

__________________________________________________________________

5. Seasons -

_________________________________________________________

_________________________________________________________________

6. Air pressure -

______________________________________________________

__________________________________________________________________

7. Barometer-

________________________________________________________

__________________________________________________________________

Please answer the following questions.

1. How does solar radiation affect temperature?

a. __________________________________________________________

__________________________________________________________

_______________________________________________________

2. Name 5 things that can affect solar radiation?

a. __________________________________________________________

__________________________________________________________

__________________________________________________________

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__________________________________________________________

__________________________________________________________

____________________________________________________

3. How do we measure temperature? How do scientist measures

air temperature?

a. ________________________________________________________

4. What are the three scales of measuring temperature? Which

one do we use?

a. __________________________________________________________

__________________________________________________________

_______________________________________________________

5. How does gravity help air pressure?

a. __________________________________________________________

________________________________________________________

6. How does Air pressure help us forecast the weather?

a. __________________________________________________________

__________________________________________________________

_______________________________________________________

7. What are the differences between the aneroid and mercury

barometers?

IV. Air Movements

a. The reason why air circulates is because of density

differences

b. Air Currents

i. Air currents are the rising and sinking vertical

movements of the air

ii. When these air currents sink and they reach the

earth’s surface it does spread out horizontally. When

the rising air expands it also spreads out horizontally.

c. Wind

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i. When these air currents expand horizontally it forms

wind.

1. Wind is described by

a. Speed

b. Direction

ii. Speed

1. is measured by an instrument called an

Anemometer.

a. An Anemometer is 3-4 cups mounted on

an axis that is attached to a compass.

b. The wind moves the cups causing the

axis to spin.

c. The speed of the axis’s movements

depends on the speed of the wind.

d. Wind Speed is measured by knots

i. 1 knot= 1.15 miles an hour

iii. Wind Direction

1. Measured by a wind vane

a. A wind vane is a pointer on an axis that is

also attached to a compass

b. The tail of the pointer is larger than the

tip

i. This makes sure more pressure is

put on the tail

ii. Therefore it will point to the

direction that the wind is coming.

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V. Humidity

a. Humidity

i. Is the amount of Moisture in the air

ii. IT IS NOT a liquid water in the air but rather it is

water vapor (gas)

1. water vapor is a colorless, odorless gas that

enters the atmosphere when liquid water

evaporates or ice sublimes ( changes straight

from solid to gas)

iii. Humidity is a very important weather factor because

the water vapor in the air is what condenses to form

1. cloud

2. fogs

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3. precipitation

b. The changing of water

i. Water molecules are always changing from the three

forms of matter

1. solid

2. liquid

3. gas

ii. So therefore it looks like this

Ice Water

Water Vapor

c. How does water enter the atmosphere

i. Most water enters the atmosphere from the form of

liquid to gas

1. called evaporation

ii. or ice to gas

1. called sublimation

d. How does water leave the atmosphere?

i. Condensation

1. Water forming and leaving the atmosphere

(We will talk later why water falls)

ii. Deposition

1. Is when the vapor form into solid crystal

without turning into water first

e. This constant flow of water molecules throughout these

phrases results in the change of humidity

f. The greatest amount of change in water molecules occurs

between the atmosphere and hydrosphere (water)

i. The molecule of water from the hydrosphere gain

energy from sunlight and surroundings may become

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energetic enough to escape the liquid phase and turn

into water vapor

ii. When water vapor molecule come in contact with the

hydrosphere they sometimes get attached and stay

there

iii. it is a two way street.

g. Evaporation

i. Is when the molecules get enough energy and form

into water vapor in the atmosphere

1. at higher temperatures molecules have more

energy so more molecules will have the energy

to escape and form into vapor

HIGHER TEMP MORE EVAPORATE

h. Condensation

i. Is when the water vapor molecules form a liquid and

attach themselves onto the surface

ii. This depends on how densely populated the

molecules are. The more populated in a small area

the more will attach themselves onto the surface

1. like being squeezed out of an elevator

i. Net Evaporation and Net Condensation

i. Net evaporation

1. is when there is more molecules leaving the

surface than there are attaching to the surface

ii. Net condensation

1. is when there is more molecules leaving the

atmosphere and attaching to the surface than

those leaving the surface

iii. They go in a circle though

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1. if there is a net evaporation the more water

vapor there is in the air which means the

denser it will get and more vapor gets pushed

out and stuck to the surface

2. eventually a point is reached where their is an

equilibrium

3. If the temperature drops suddenly then the

water vapor will be more then the equilibrium

j. Relative Humidity /Absolute humidity

i. The amount of water vapor in the air is usually

referred to absolute or relative humidity

ii. Absolute Humidity – is the amount of vapor found 1

cubic meter of the air.

1. since it is very hard to isolate the water vapor

in the air in order to measure it absolute

humidity is very rarely measured

iii. Relative humidity

1. is the ratio of water vapor bow present in the

atmosphere to the water vapor present when

evaporation and condensation are equal at that

temperature X 100

2. relative humidity is a way to of comparing the

flows of water molecules leaving and arriving

at a surface.

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Water vapor in atmosphereRelative humidity = ------------------------------------------------------ X100 Water vapor in atmosphere at equilibrium


3. it is useful in predicting how the air will feel to

a person AND whether evaporation or

condensation would more likely occur.

4. The higher the relative humidity the (stickier)

the air will feel.

5. If the relative humidity is 100% it does not

mean that the air is 100% water vapor it still

has oxygen and nitrogen etc……..

6. High relative humidity

a. Means that the WV in the air is close to

it’s equilibrium amount

b. A decrease in temperature (will also

decrease the temperature amount

needed for condensation) will decrease

equilibrium amount needed for

condensation which makes fog, clouds,

or precipitation

7. Dew Point

a. This leads us to dew point

b. Dew point is the temperature at which

water vapor in the air will begin to

condense into liquid water

c. THIS IS THE TEMPRATURE AT WHICH THE

AMOUNT OF WATE VAPOR IN THE AIR

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Point of information 1. Relative humidity 20% means that the air only has 20%

of the water vapor it would have during equilibrium2. relative humidity of 100% means that the air contains

100% of the water vapor it has during equilibrium


EQUALS THE AMOUNT OF EQUALIBRUIM

FOR THAT TEMP.

8. How is Humidity measured?

a. There are two different tools used to

measure humidity

i. Hygrometer

ii. Psychrometer

b. Hygrometer

i. Consists of strands of human hair

attached to a pointer

ii. Human hair grows slightly as

humidity increases

1. and shrinks when it

decreases

iii. The pointer changes position based

on the length of the hair

c. Psychrometer

i. Is made of two thermometers

1. Dry bulb

a. The bulb is kept dry

2. Wet bulb – the bulb is kept

wet by a covered cloth wick

soaked in water

a. Evaporation from the

wet wick causes

cooling because the

fastest molecules in

liquid water are the

ones that have enough

energy to escape

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b. The slower molecules

have a lower average

energy.

c. Therefore the liquid

temperature decreases

due to the loss of

energy.

3. This cooling effect is KEY to

measuring relative humidity

4. The lower the relative

humidity the more water can

evaporate from the wet bulb

and the more the

thermometer is cooled.

5. The Dry Bulb Temp. remains

unchanged.

6. Therefore the difference

between the dry bulb and

wet bulb temperature is

directly related to the

relative humidity of the air.

d. How do we figure out the relative

humidity?

i. You subtract the dry bulb e from

the wet bulb temp

ii. Find in the table where the dry bulb

temp (right side) and the difference

temp # meet

iii. That number is your relative

humidity percent

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e. How do I figure out the dew point in the

air?

i. The difference between the wet

and dry bulb is also directly related

to dew point.

ii. The higher the relative humidity

the closer the air is being filled to

capacity.

iii. Cooling air decreases the capacity

to hold water

iv. So we will use a different table

1. you will figure out the

difference between Wet and

dry

2. You will then see where it

meets with the dry bulb

temperature

3. That number at the

intersection is the dew point

in degrees of C.

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Introduction to weather

Technology

Transcript of Introduction to weather