The document discusses key concepts about weather including: 1. It defines weather as the short term conditions of the atmosphere including temperature, humidity, air pressure, and wind. 2. Temperature is influenced by solar radiation, with factors like the sun's angle and seasons affecting the amount of radiation. Temperature is measured using thermometers. 3. Air pressure is caused by gas particles exerting force and is measured using barometers like mercury or aneroid barometers. Changes in air pressure can help forecast weather. 4. Humidity refers to the amount of moisture in the air as water vapor. Evaporation and condensation influence humidity levels, which affect cloud formation and precipitation. Humidity is measured

1. 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
1

2. Earth Science Weather
7. refraction
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
2

3. Earth Science Weather
III. Air Pressure
a. Introduction
i. Air is a mixture of different gases
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.
3

4. Earth Science Weather
d. there are two common barometers used
1. Mercury Barometer 2. Aneroid Barometer
•air pressure forces liquid mercury •aneroid means no liquid
up a tube •it is a can with a spring scale on it
•the more pressure the higher the •the amount of pressure on the sides
mercury level will be of the can will either push down or
•we usually name the number with loosen the spring scale
inches or millimeters attached to the
number
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
4

5. Earth Science Weather
Based on the Lesson on Temperature and air pressure
Please identify the following terms
1. weather-
__________________________________________________________
_________________________________________________________________
_
2. Temperature -
______________________________________________________
_________________________________________________________________
_
3. Solar radiation -
___________________________________________________
_________________________________________________________________
4. thermometer -
______________________________________________________
_________________________________________________________________
_
5. Seasons
-_________________________________________________________
_________________________________________________________________
6. Air pressure -
______________________________________________________
_________________________________________________________________
_
7. Barometer-
________________________________________________________
5

6. Earth Science Weather
_________________________________________________________________
_
Please answer the following questions.
1. How does solar radiation affect temperature?
a. __________________________________________________________
__________________________________________________________
_______________________________________________________
2. Name 5 things that can affect solar radiation?
a. __________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
____________________________________________________
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?
6

7. Earth Science 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
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.
7

8. Earth Science Weather
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.
8

9. Earth Science Weather
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
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
9

10. Earth Science Weather
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
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
10

11. Earth Science Weather
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
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
11

12. Earth Science Weather
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
Water vapor in atmosphere
Relative humidity = ------------------------------------------------------ X100
Water vapor in atmosphere at equilibrium
2. relative humidity is a way to of comparing the
flows of water molecules leaving and arriving at a
surface.
12

13. Earth Science Weather
3. it is useful in predicting how the air will feel to a
person AND whether evaporation or
condensation would more likely occur.
Point of information
1. Relative humidity 20% means that the air only
has 20% of the water vapor it would have during
equilibrium
2. relative humidity of 100% means that the air
contains 100% of the water vapor it has during
equilibrium
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
13

14. Earth Science Weather
c. THIS IS THE TEMPRATURE AT WHICH
THE AMOUNT OF WATE VAPOR IN THE
AIR 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
14

15. Earth Science Weather
molecules in liquid water
are the ones that have
enough energy to
escape
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?
15

16. Earth Science Weather
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
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.
16

17. Earth Science Weather
17