WeatherPart 1

Temperature

Introduction to weather

– Weather • Is the short term condition of the atmosphere at

any location • It is made up of the connection and relationship

of – Temperature– Humidity – Air pressure

– Wind

Temperature Introduction

– at any given place temperature is connected to the heat energy present in the atmosphere at that location

– Solar radiation is the amount and how long the sun is on a particular location and how strong it is.

– Therefore anything that changes solar radiation will also change the air temperature

What are factors that can effects solar radiation ?

– The following are factors that can change the amount of solar radiation a place has

• The angle that solar radiation hits the Earth – this changes throughout the

day because of the Earth rotation » Solar radiation is only

present during the day– similar changes also happen

when the Earth moves around the sun » we call these slower

changes seasons • number of hours of solar radiation

during the day • the reflection • refraction • absorption of solar radiation

– for example clouds block and absorb the amount and intensity of the sun

• and the type of surface (ex: water and land)

How do we measure air temperature?

– Temperature is measured with thermometers • Works on a simple principle

– Matter expands when heated and contracts as it cools.

– There are many scales of measuring temperature that are named after the people who made them up • Celsius • Fahrenheit • Kelvin

– We use in the USA Fahrenheit the rest of the world uses Celsius

– Meteorologist ( people who study weather ) use a thermograph as a thermometer

Weather Part 2

Air Pressure

Introduction – Air is a mixture of different

gases – Gas consists (made up of)

many different tiny molecules that move around rapidly and are far apart from each other.

• They are kept contained either by a container or in the case of the atmospheres by the Earth’s Gravity

– Gases put pressure on the surfaces that they are in contact with.

– In the case of air pressure this pressure is due to the gas particles bumping into the surface

• Since they move rapidly in all direction they balance out this pressure in all directions

How does air pressure help us forecast weather

– You cant sense air pressure like you can with temperature

– Nor can you forecast the weather based on the air pressure in a location

– 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.

• Rising pressure usually means fair weather

• Low Pressure usually means an approach of a storm

How is air pressure measured?

• We use a barometer to measure air pressure.

– there are two common barometers used

• 1. Mercury Barometer

• 2. Aneroid barometer

• air pressure is measured based on units of force per a unit area

» atmosphere (atm) is the average air pressure at sea level

Mercury Barometer

• air pressure forces liquid mercury up a tube

• the more pressure the higher the mercury level will be

• we usually name the number with inches or millimeters attached to the number

Aneroid Barometer

• aneroid means no liquid

• it is a can with a spring scale on it

• the amount of pressure on the sides of the can will either push down or loosen the spring scale

WeatherPart 3

Wind

Air Movements

– The reason why air circulates is because of density differences

• How thick the air is.

Air Currents

• Air currents are the rising and sinking vertical movements of the air

• 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.

• When these air currents expand horizontally it forms wind. – Wind is described

by

» Speed

» Direction

• is measured by an instrument called an Anemometer.

• An Anemometer is 3-4 cups mounted on an axis that is attached to a compass.

• The wind moves the cups causing the axis to spin.

• The speed of the axis’s movements depends on the speed of the wind.

• Wind Speed is measured by knots – 1 knot= 1.15 miles an

hour

• Measured by a wind vane

• A wind vane is a pointer on an axis that is also attached to a compass

• The tail of the pointer is larger than the tip

• This makes sure more pressure is put on the tail

• Therefore it will point to the direction that the wind is coming

Weather Part 4

Humidity

Introduction to humidity

• Is the amount of Moisture in the air

• IT IS NOT a liquid water in the air but rather it is water vapor (gas) – water vapor is a

colorless, odorless gas that enters the atmosphere when liquid water evaporates or ice sublimes ( changes straight from solid to gas)

Humidity is Important

• Humidity is a very important weather factor because the water vapor in the air is what condenses to form– cloud

– fogs

– precipitation

Changes of water

• Water molecules are always changing from the three forms of matter – solid – liquid – gas

• So therefore it looks like this

• Ice Water • Water Vapor

How does water enter the atmosphere?

– Most water enters the atmosphere from the form of liquid to gas

• called evaporation

– or ice to gas• called sublimation

How does water leave the atmosphere?

• Condensation – Water forming and

leaving the atmosphere

• (We will talk later why water falls)

– Deposition • Is when the vapor

form into solid crystal without turning into

water first

Point of Information

• This constant flow of water molecules throughout these phrases results in the change of humidity

Most of the change is between atmosphere and hydrosphere

• The molecule of water from the hydrosphere gain energy from sunlight and surroundings may become energetic enough to escape the liquid phrase and turn into water vapor

• When water vapor molecule come in contact with the hydrosphere they sometimes get attached and stay there

• it is a two way street.

Evaporation

• Is when the molecules get enough energy and form into water vapor in the atmosphere – at higher temperatures

molecules have more energy so more molecules will have the energy to escape and form into vapor

• HIGHER TEMP MORE EVAPORATE

Condensation

• Is when the water vapor molecules form a liquid and attach themselves onto the surface

• This depends on how densely populated the molecules are. The more populated in a small area the more will attach themselves onto the surface

• like being squeezed out of an elevator

Net evaporation and net condensation

• Net evaporation – is when there is

more molecules leaving the surface than there are attaching to the surface

• Net condensation – is when there is

more molecules leaving the atmosphere and attaching to the surface than those leaving the surface

They go in a circle – 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

– eventually a point is reached where their is an equilibrium

– If the temperature drops suddenly then the water vapor will be more then the equilibrium

Relative Humidity /Absolute humidity

• The amount of water vapor in the air is usually referred to absolute or relative humidity

Absolute Humidity

– is the amount of vapor found 1 cubic meter of the air.

– since it is very hard to isolate the water vapor in the air in order to measure it absolute humidity is very rarely

measured

Relative humidity

• is the ratio of water vapor present in the atmosphere to the water vapor present when evaporation and condensation are equal at that temperature X 100

Water vapor in atmosphereRelative humidity = ------------------------------------------------------ X100

Water vapor in atmosphere at equilibrium

Relative humidity

• relative humidity is a way to of comparing the flows of water molecules leaving and arriving at a surface

• 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

• Relative humidity 20% means that the air only has 20% of the water vapor it would have during equilibrium

• relative humidity of 100% means that the air contains 100% of the water vapor it has during equilibrium

Relative humidity con’t

– The higher the relative humidity the (stickier) the air will feel.

– If the relative humidity is 100% it does not mean that the air is 100% water vapor it still has oxygen and nitrogen etc……..

High relative humidity

– Means that the WV in the air is close to it’s equilibrium amount

– 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

Dew point – This leads us to dew

point • Dew point is the

temperature at which water vapor in the air will begin to condense into liquid water

• THIS IS THE TEMPRATURE AT WHICH THE AMOUNT OF WATE VAPOR IN THE AIR EQUALS THE AMOUNT OF EQUALIBRUIM FOR THAT TEMP

How is humidity measured?

• There are two different tools used to measure humidity

– Hygrometer – Psychrometer

Hygrometer

• Consists of strands of human hair attached to a pointer

• Human hair grows slightly as humidity increases

• and shrinks when it decreases

– The pointer changes position based on the length of the hair

Psychrometer – Is made of two

thermometers – Dry bulb

- The bulb is kept dry – Wet bulb – the bulb is kept

wet by a covered cloth wick soaked in water

– Evaporation from the wet wick causes cooling because the fastest molecules in liquid water are the ones that have enough energy to escape

– The slower molecules have a lower average energy.

– Therefore the liquid temperature decreases due to the loss of energy.

– This cooling effect is KEY to measuring relative humidity

– The lower the relative humidity the more water can evaporate from the wet bulb and the more the thermometer is cooled.

– The Dry Bulb Temp. remains unchanged. • Therefore the difference between the dry bulb

and wet bulb temperature is directly related to the relative humidity of the air.

How do we figure out Relative humidity?

– You subtract the dry bulb e from the wet bulb temp

• Find in the table where the dry bulb temp (right side) and the difference temp # meet

– That number is your relative humidity percent

How do we figure out the Dew Point?

• The difference between the wet and dry bulb is also directly related to dew point.

• The higher the relative humidity the closer the air is being filled to capacity.

• Cooling air decreases the capacity to hold water

• So we will use a different table • you will figure out the

difference between Wet and dry

• You will then see where it meets with the dry bulb temperature

• That number at the intersection is the dew point in degrees of C.

Weather

How do these variables relate to each other?

What are the relationships amongst the variables – Introduction

– The atmospheric variables that we learned previously are interrelated (there is a direct correlation)

– A change in one would probably affect another

– This is best understood even though we have the kinetic theory of gases

Kinetic gas theory

• Gas is made out of tiny, individual that do not interact with each other except when they collide

• The molecules are far apart and constantly moving

• Temperature of gas is proportional to the speed in which it is traveling.

The relationship between air temperature and air pressure

What we already know

– Air pressure is the result of the forces of gas colliding with each other and surfaces

– Air temperature depends on the speed of gas molecules

If there was a change in temperature

• Air pressure and temperature are related because both involve the motion of the molecules

• You would therefore think………….

– The higher the temperature the more force they collide with higher the air pressure

– Therefore it would make sense the higher the temperature the higher the air pressure. HOWEVER………..

THIS IS FALSE…….• This is not true because the

atmosphere does not have walls rather its has open space

• When the atmosphere’s

temperature increases the molecules move faster and collide more vigorously

• As a result the molecules will bounce father away from each other at the atmosphere expands

• Even though the molecules are moving faster there are fewer collisions because they are farther apart.

So what is the relationship is the temorature changes

• THEREFORE WE SEE A DECREASE IN AIR PRESSURE WHEN THE AIR TEMPRATURE INCREASES.

Let us say there is a change in the air pressure what would happen to

the air temperature?• The main cause of change in the air pressure is the

rising or falling of the air in convection currents. – convection currents are fluid movements set in motion by fluid

density changes

• So if a group of air sinks there would be less (more density) if the group of air rises there will be more room to expand.

• Any gas that is allowed to expand because the surrounding expanded will become cooler

• Any gas that shrinks in space will become warmer

TIME OUTAdiabatic changes

• Are the rise and fall of temperature that has NOTHING to do with heat being added from outside forces?

So therefore……………

• SO if the gas is rising and is allowed to expand then their will be more room form the molecules to live in and less collision would occur.

• But if the space for the air is reduced than their will be more collisions and higher temperatures

The results are

• IF AIR PRESSURE GOES UP- TEMP GOES UP

• IF PRESSURE GOES DOWN TEMP WILL GO DOWN

The relationship between air pressure and humidity

– The greater the mass of molecules the more collisions will occur

– The mass of elements in the air depends on the mass composition of the air

– The air as we know is mostly nitrogen and oxygen they are both denser then water vapor molecules

• The more water vapor in the air takes the place of the nitrogen and oxygen the lighter the force of air pressure it will be

– SO THE HIGHER THE HUMIDITY THE LOWER THE AIR PRESSURE

– THE LOWER THE HUMIDITY THE HIGHER THE AIR PRESSURE

• When it is very humid outside and then it rains you can feel the release of air pressure in the air.

Air temperature and humidity

– We know the higher the air temperature the more water vapor is going to be in the air before equilibrium

• Therefore warmer air contains more vapor than cooler air • At any given temp a fixed amount of vapor will be present

in the air when we reach equilibrium • At a higher temperature more of the molecules will be able

to break free and become vapor – As the vapor becomes more crowded with molecules it is

more likely that it will condense

• Therefore the water vapor warm air will increase until a new equilibrium status is reached 9depends on the Temp.)

• The amount of vapor in the air is greater in temp than lower temps

– Since the amount of water vapor in the air at equilibrium changes with temperature = the relative humidity is also affected by the temperature

– So if the temperature increases that will cause the equilibrium mark to increase which will make the relative humidity decrease.

• Because the higher the temperature and equilibrium mark. The more vapor is needed to raise the humidity.

– The reverse is true as well. If the temperature decreases the equilibrium mark will decrease and the amount of vapor in the air remains the same, relative humidity will increase.

– As we know, as the temp decreases it eventually reaches the dew point.

• At that point the relative humidity is 100 percent

– If the temp decreases more, than condensation will form at a faster rate. Than evaporation until equilibrium is reestablished.

– Therefore, as temperature reaches dew point precipitation becomes more likely.

Air Pressure and Wind

General rule…….

– Winds blow from regions (places) of high air pressure to regions of low pressure.

• IN OTHER WORDS AIR BEING PUSHED BY HIGH AIR PRESSURE WILL ADVANCE AGAINST THE PERSON SIR BEING PUSHED WITH LOW AIR PRESSURE.

– The net movement of air is from HIGH pressure to LOW Pressure

Land and sea breezes

• Land and sea show the air movement from high to low pressure very clearly – difference of air

pressure between adjacent (next to ) places occur when ever land and water meet

During the day • SO DURING THE DAY when

sunlight is out. The land gets hotter than the sea

• Therefore land during the day will have a higher air temperature than the water during the day.

• Since warm air has less pressure than cool air the pressure over the land will be cooler

• THEREFORE wind during the day will go from the water inwards to the land.

• This wind is called SEA BREEZE

At Night……..

• Land cools faster than water and therefore will have more pressure than the water.

• The wind will therefore will blow from the land out to sea.

• This is called a land breeze

• Differences in pressure between regions also effect on a global scale

• Unequal heating of the atmosphere at different latitudes cause three large atmospheric convention cells to form in the northern and southern hemisphere

• Rising air in these convection cells produces LOW pressure belts that circle the earth at the equator, artic circle(60) and the Antarctic circle (90)

• Sinking air makes high pressure belts at the poles , tropic of cancer (30) and Capricorn (30 S)

• THEREFORE A SERIES OF ALTERNATING HIGH AND LOW PRESSURE BELTS CIRCLE EARTH, GIVING RISE TO A SERIES OF GLOBAL WIND BELTS AS AIR MOVES FROM REGIONS OF HIGH PRESSURE TO REGIONS OF LOW PRESSURE

– (look at the wind belt diagram) the global wind that blow from high pressure belts at 30 N and south towards low pressured equator

» This is called trade winds.

Coliotis Effect

– is the deflection of motion due to the rotation of the earth

• This causes these large scale winds to curve to the right in the Northern hemisphere

• They blow North east• This also causes the

wind to curve to the left in the Southern Hemisphere

• They blow South east

– Winds blow from regions (places) of high air pressure to regions of low pressure.

• IN OTHER WORDS AIR BEING PUSHED BY HIGH AIR PRESSURE WILL ADVANCE AGAINST THE PERSON SIR BEING PUSHED WITH LOW AIR PRESSURE.

• The net movement of air is from HIGH pressure to LOW Pressure

• Global winds also blow from the high pressure belts at 30 S and N towards the low pressure belts at the 60 N and S – They are called

Prevailing winds

– The colitis effect causes these winds to blow southwest in the north and South east in the South

– The global winds that blow from regions over the poles towards the low pressure regions of 60 N and S are known as polar easterlies.

• The coriolis effect causes these winds to blow from the northeast in the north and southeast in the south