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UIUC / Science / ATMS 100 / What is the difference between weather and climate?

What is the difference between weather and climate?

What is the difference between weather and climate?


School: University of Illinois at Urbana - Champaign
Department: Science
Course: Introduction to Meteorology
Professor: Jeffrey frame
Term: Spring 2016
Tags: Meteorology, Intro to Meteorology, frame, atms, Atmospheric Science, exam, Exam 1, exam 1 study guide, Study Guide, review, Review Sheet, weather, climate, Greenhouse effect, greenhouse gases, clouds, Co2, rain, sleet, snow, ice, sky, and study
Cost: 50
Name: Exam 1 Study Guide
Description: This study guide includes the answers to the questions from lectures 1-8 and the labs. I included pictures in order to better comprehend some concepts. Happy Studying :)
Uploaded: 02/18/2016
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Loved these! I'm a horrible notetaker so I'll be your #1 fan in this class

ATMS-100: EXAM I REVIEW SHEET  https://quizlet.com/_g6i8f 

What is the difference between weather and climate?

Exam: Monday, February 22, IN CLASS.

• You may use a calculator. NO CELL PHONES. Please bring a #2  pencil and your I-Card.

• Study aids: This sheet, lecture notes, textbook, class exercises.  Learn and be able to apply concepts; do NOT simply memorize facts.

• Questions? Come to office hours, ask your TA, post to the discussion  board on Compass.


· Which gases are the primary constituents of the  atmosphere?

1. Nitrogen (78%)

2. Oxygen (21%)

3. Water Vapor Concentration Varies between 0-4%. Depends on  weather.

4. Argon 1%

5. Carbon Dioxide (0.038%)

6. All Others (0.002%)

What is the difference between satellites and radar?

a. Methane (CH4)

i. Natural gas Don't forget about the age old question of What is population?

b. Ozone (O3)

i. Absorbs harmful ultraviolet radiation from sun

c. Chlorofluorocarbons (CFCs) Don't forget about the age old question of What is atlantic slave trade?

i. Formerly used as a coolant in air conditioners

ii. React with and destroy ozone

d. Many others…

· What is the difference between weather and climate? • Weather – Atmospheric conditions at a particular time and place o Elements: Temperature, pressure, humidity, cloud cover,  precipitation, visibility, wind speed and direction

• Climate – The average weather over a long (10+ year) period of time

How do winds blow around high and low pressure systems in the northern hemisphere?

– Weather records (snowfall)

– Climate changes over long periods of time and is changing now • Need to look at long-term trends in weather data to evaluate climate  changes We also discuss several other topics like What are the galton’s three components?

– Often requires detailed statistical analysis

• You CANNOT see climate change by looking out the window!!! • Can’t prove anything by cherry picking a few data points either – Requires statistical analysis

• CANNOT use individual weather events to prove or disprove changes  in climate!

– Climate is what you expect, weather is what you get

• Attribution studies can sometimes determine what role (if any) climate  change played in a particular event We also discuss several other topics like Identify the goals of monetary policy.

• Trends in extreme weather events may also be related to climate  change or other natural cycles (CLIMATE = GPA, WEATHER =  EXAM GRADE)

· What is the difference between satellites and radar? • Satellites – view clouds from space

• Radar – Views precipitation from ground

o Doppler radar – Can sense motion of precipitation particles  toward/away from radar

· What is Doppler radar?

• Doppler radar – Can sense motion of precipitation particles  toward/away from radar

o Velocity


▪ RED = AWAY FROM If you want to learn more check out What are the dangers of mutually assured destruction?

o Strong outbound velocities and strong inbound velocities  on adjacent radials indicate rotation and potentially a  

tornado!!! (SEES WIND, on east side

· How is wind direction defined?

• Station models Wind direction is identified by the direction  FROM which the wind is blowing

o A north wind blows from the north (toward the south)

• Stick on station model identifies wind direction

o Points in direction wind comes from!!

• Barb(s) identify wind speed

o One barb = 10 knots

o Half barb = 5 knots

o Flag = 50 knots

• Top left = Temp

• Bottom left = Dew point

· How do winds blow around high and low pressure systems  in the Northern Hemisphere?

• Examine temperature data (colored) to find areas of warm and cold  air

• Masses of warm and cold air meet at fronts (see next slide) o Cold front – Cold air advances

o Warm front – Cold air retreats

• Examine pressure data to find areas of high and low pressure • Fronts connect to low pressure centers We also discuss several other topics like What did the articles of confederation say?

• Low pressure (L): Counter-clockwise and inward circulation and  clouds/precipitation (clouds & precip)

• High pressure (H): Clockwise and outward circulation and generally  clear skies (clear skies, clear weather)

and how does this influence the temperatures near these  systems?

• Comes together ???? forced to rise

• Clouds before rain/snow

• high pressure = nice weather and low pressure = bad weather


· What is pressure and how does it change with height? • Imagine that each air molecule is a gumball

• Weight of column of air is like weight of column of gumballs • At surface (bottom of machine), there are the most molecules  (gumballs) above you

– Greatest weight

– Greatest pressure

• As you go up through the atmosphere, there are less and less  molecules (gumballs) above you, so weight of column above that  level (pressure) decreases

• Pressure ALWAYS decreases with height 

· What is the average atmospheric pressure (in mb) at sea  level?

• 1013.25 millibars. 

· What is density and how does it change with height? • Pressure change with altitude: 1 mb per 10 m (near surface) • Go up 850 m (2800 feet, about half a mile) and average pressure is  same as in the eye of Hurricane Katrina at landfall

• Atmospheric pressure ALWAYS decreases with height 

• Gravity pulls most air molecules closest to surface

• Air density always decreases with height

• Density = Mass / Volume

• Units = kg/m3 

• FIGURE 1.9 Both air pressure and air density decrease with • increasing altitude. The weight of all the air molecules above the  earth’s

• Surface produces an average pressure near 14.7 lbs/in.2 Why? Less atmosphere is above you (less weight of air!)

· Why is pressure corrected to sea level? 

· What is a lapse rate?

• Lapse rate – The rate at which the temperature decreases with  height

· What is an inversion?

• Inversion – Layer in which the temperature increases with height

· What is the troposphere?

• Lowest layer (8-12 km deep) of the atmosphere

• Contains all of the earth’s weather

• Temperature usually (but not always) decreases with height • Sun heats ground, ground heats air!

· How is the atmosphere divided into layers? What are they? Troposphere (see above)

• Tropopause

• Marks the top of the troposphere

• Approximately 8-12 km above surface

• Acts as lid on weather

• Inversion very stable

• Level of jet stream

• Difficult to breathe because air is so thin

• Blizzards, hurricanes penetrate that layer

• Stable layer – layer that inhibits air, no clouds, no precipitation in  stratosphere

• Level it is difficult to breath

• Pressurize airplane cabins

• Stratosphere

• Temperature increases with height (inversion layer)

• Ozone layer

o Ozone absorbs UV radiation, warming the stratosphere

• If you looked up from the stratosphere, you would see black space,  not blue sky

• Stratopause marks the top of the stratosphere

* O3 cousin of O2 absorbs UV radiation???? heat up

Ozone makes temperature increase with height in stratosphere 1-100mb

• Atmosphere slowly fades away to space.

• Above middle stratosphere, air is so thin, atmosphere fades to black • There is no well-defined “top” of atmosphere

• Stratosphere largely void of clouds and weather

• All clouds (weather) in troposphere

o Tallest thunderstorm clouds only extend to tropopause (8-12  km)

• Mesosphere

o Name means “middle atmosphere”

o Temperature decreases with height

▪ Lack of ozone

o Air very thin: < 0.1% of surface pressure

o Mesopause marks top of mesosphere – coldest temperatures in  atmosphere

* Meso = middle


Above ozone layer

Air is thin

Blood will boil

Generally100 - -40 degrees Celsius

o Thermosphere

o Temperature increases with height

▪ Oxygen absorbs gamma rays and cosmic rays

o Air is very thin

▪ Air molecules can travel 1 km before colliding with another molecule

▪ You will freeze regardless of temperature

o High energy particles from space strikes air molecules, creating  aurora borealis (Northern Lights)

* Misleading temperature because air is so thin so that you would  still freeze …. Nothing there to keep you warm

Aurora borealis  

Exotic particles ~ cosmic waves

Strikes at top

Aurora Borealis - Omit light


· What is temperature?

o Temperature is a measure of the average speed of the molecules of  a substance

o Some molecules move faster, other molecules move slower o When the molecules within an object absorb energy, they move faster o The temperature of the object increases

o More energetic collisions between molecules

o Video: https://www.youtube.com/watch?v=HrdQ7kJWQfc o Note: Molecules in fixed volume in video

o If volume not fixed (as in atmosphere), air will expand as it is  heated owing to more energetic molecular collisions


· How does temperature affect air density?

o Temperature and density

o Warm air is less dense (prone to rise)  

o Cold air is more dense (prone to sink)

· What is sensible heat?

o Sensible heat – Thermal energy (heat) that can be sensed or  measured with a thermometer

o Warm in here

· What is latent heat?

o Latent heat – The energy absorbed or released during a phase  change

o “Hidden” energy

o Energy to melt ice, water freezes

·What are the phase changes of water?  

o On earth, water exists naturally in all three phases: Solid (Ice), liquid (water), and gas (water vapor)

Which are warming and which are cooling processes? Why? o Warming

o Deposition (water vapor to ice)

o Freezing (water to ice)

o Condensation (water to water vapor)

o Cooling

o Sublimation (ice to water vapor)

o Melting (ice to water)

o Evaporation (water to water vapor)

o Cooling processes absorb latent heat from the environment o Example: Evaporation. This is why you feel cold after getting  out of the shower or swimming pool

o Warming processes release latent heat into the environment o Condensation and evaporation are opposite processes o Thus, the amount of heat energy released during condensation  equals that absorbed during evaporation

· What is conduction?  

o Conduction – Direct transfer of heat within a substance (or from one  substance to another)

o Heat always flows from hot to cold

o Good heat conductors

o Metals

o Transfer heat efficiently

▪ Don’t make houses and buildings out of

• Hot on hot day, cold on cold day

o Poor heat conductors (good insulators)

o Air, water, wood, plastic, fiberglass

o Transfer heat poorly

o Insulators vs. conductors video:

o http://www.youtube.com/watch?v=QEiMEgKxrkY o Ice cube on metal platform melts a lot faster than on the  wooden platform



• Convection – Transfer of heat through fluid flow

– Fluid flow = air (or water) currents

– Generally refers to vertical motions only 

– Air and water are both fluids

• Heats lowest polometer of the air, closest to ground


• Advection – Transfer of heat  

(or moisture) through  

horizontal movements of air

– Example: Sea or lake  


· How does the sun heat the  

lower atmosphere?

o Solar heating  

o Air is largely transparent to sunlight

▪ Sun does not heat the air directly

o The sun heats the surface

o Thin layer of air (1 cm or so) just above surface is heated by  conduction

o Right next to the hot ground

o This hot air expands, becomes less dense, and begins to rise o Hot, less dense air rises, like helium balloons

o This rising air transports heat upward from the surface  (convection)

o The troposphere is heated from the bottom up!

o Blobs (parcels) of hot air rise, like helium balloons o Transport heat upward from the surface (convection)

o Cooler air from aloft sinks and is later heated by surface...

· How does the temperature of air change as it rises and  sinks? Why?

o Rising Air and Temperature

o Think of a blob of air about the size of this room

▪ This is called an air parcel

o As a hot air parcel rises, the pressure around it decreases, so  the air parcel expands

▪ Pressure ALWAYS decreases with height

▪ Balloon in a vacuum pump video:  


o It requires energy for an air parcel to expand

▪ Where does this energy come from?

▪ The temperature of the parcel cools as it expands

o Summary: Hot (less dense) air rises, expands, and cools

o Sinking Air and Temperature

o As an air parcel sinks, the pressure around it increases, so the air  parcel is compressed

▪ Pressure always increases as you go down toward the surface o Compression transfers energy to the parcel

o Sinking air compresses and warms


· What objects emit radiation?


• All objects emit radiation at all times

– At terrestrial (earth) temperatures, this is IR radiation

• Objects with higher temperatures emit shorter wavelength (more  energetic) electromagnetic waves

o Radio/TV Waves

o Microwaves

▪ Infrared (IR) Radiation

o Visible Light

▪ Ultraviolet (UV) Radiation

o X-rays

▪ Gamma Rays

· How is the wavelength of electromagnetic radiation related  to energy?

o Visible spectrum small fraction of EM waves

o Shorter wavelength ???? Greater energy

o Blue/violet ???? Most energetic visible light

o Red ???? Least energetic visible light

o 1 mm = 10-6 m (one millionth of a meter)

o 1 mm = 1/100 of a human hair

o Speed = 3.0 x 108 m/s = 186,000 miles/sec

· What controls the intensity and amount of radiation an  object emits?

o Radiation intensity increases with temperature

o Objects that are hot enough emit visible light

o Red hot, white hot objects

o The sun!

o Objects emit radiation of many different wavelengths

· What type of radiation does the earth primarily emit? The  sun?

o SUN: Your body (or the earth) receives more energy than it emits, so  its temperature increases

o Colder at night because The earth emits more energy than it  receives, so its temperature decreases

· How does the absorption and emission of radiation affect  the temperature of an object?

o If an object absorbs more radiation than it emits

o Temperature increases (warms)

o If an object emits more radiation than it absorbs

o Temperature decreases (cools)

o If an object emits and absorbs the same amount of radiation o Temperature remains the same, called radiative equilibrium  temperature 

o Earth’s radiative equilibrium temperature is -18oC (0oF) o Does not account for atmosphere

o Actual average surface temperature is 15oC (59oF)

o Why the difference? Atmosphere does NOT behave as  blackbody

o Many gases only absorb/emit radiation at certain wavelengths o These gases are called greenhouse gases 

o More energy reaches surface ???? Warmer Temperatures o

· What is a greenhouse gas? What are examples of  greenhouse gases?

o A gas that contributes to the greenhouse effect by absorbing infrared  radiation, e.g., carbon dioxide and chlorofluorocarbons.

o Gas in atmosphere that absorbs/emits radiation at certain  wavelengths

-selective absorbers

o EX: water vapor, carbon dioxide, methane, nitrous oxide,  and ozone.


· What is the greenhouse effect? Why is it a poorly-named  phenomenon?

o Certain gases absorb radiation at certain wavelengths o Radiant energy is converted to thermal energy – these gases  heat up!

o These gases emit more IR radiation – both upward (to space)  and downward (toward the surface)

o Known as atmospheric greenhouse effect

o Keeps surface average of 59oF warmer

o Agricultural greenhouse traps hot air (prevents warm air from rising) o Nothing to do with IR radiation

o Greenhouse effect = BAD NAME!

o How does an agricultural greenhouse work?

▪ Sunlight enters glass top

▪ Sunlight heats ground, which heats air

▪ Glass prevents hot air from rising

· What is albedo?

o Measure of reflectivity

o Equal to reflected radiation divided by total incoming radiation o Selected albedos:

o Snow: 75-95%

o Earth and atmosphere: 30%

o Water: 10%

o Moon: 7%

· Why is the sky blue?  

o Air molecules scatter blue light four times more than red light o If we look away from the sun, we see four times as much blue light  than red light

o Our eyes detect this mix of colors as blue

o Water appears blue because it reflects the blue sky

o Water does not appear as blue on cloudy days

Why are clouds white?  

o Clouds reflect all colors of light equally well

o Our eyes detect a mixture of all colors of light as white

Why are sunsets red?

o Recall that atmosphere scatters more blue light than red light o At sunset, light takes long path through atmosphere

o Sun low in sky

o Blue and green light scattered away, all that is left is red light


· Why does the earth have seasons?

o Earth’s Orbit

o Earth orbits the sun

▪ Orbit is an ellipse (slightly egg shaped)

▪ Closest to sun on January 3 (perihelion)

▪ Farthest from sun on July 4 (aphelion)

o Year = 365.242 days

o Day = 24 hours

o Southern Hemisphere always has opposite season to Northern  Hemisphere

o Earth’s Axis

o Earth orbits the sun while tilted on its axis

▪ Tilt is 23.5o and is constant throughout the year

o Axial tilt changes intensity/length of sunlight everywhere on  earth throughout the year

o If no tilt, sun would always be overhead at Equator

▪ Solar radiation intensity same every day

▪ No seasons

o Summer occurs when a hemisphere is tilted toward the sun

o More intense sunlight over longer hours yields warm  


o Winter occurs when a hemisphere is tilted away from the sun o Less intense sunlight over shorter hours yields cold  


o Spring/Fall: Hemispheres transition from being tilted toward sun to  tilted away from sun

o Less extreme heat/cold

· How do summer and winter in the Southern Hemisphere  differ from those in the Northern Hemisphere? Why? o Angle of Sun

o Sunlight more intense when directed perpendicular to surface o Summer: More direct sunlight on Hemisphere

o Winter: Less direct sunlight on Hemisphere

· Which general regions of the earth have the largest  difference between summer and winter temperatures?  Why?

o Poles 

o East coast (due to winds and ocean currents) 

o Interior of continents 

The smallest? Why?

o Tropics 

o West coast 

o Exterior of continents 

o Greater seasonal temperature change near the poles, lesser in  tropics

o Affected by latitude, land and water distribution, winds and ocean  currents, and altitude

· How does water influence temperature? Why? o Land and water distribution:

o It takes much more energy to heat water than to heat air or land o Greater seasonal temperature change in interiors of continents,  less over oceans and maritime areas


· Why does the West  

Coast experience less  

seasonality than the East  


o Winds and ocean currents

o Greater seasonal  

temperature changes on  

east coast of continents,  

less on west coast

· How does altitude of a  

region affect its  


o Altitude:

o Colder temperatures at higher elevations

o Remember: Lower atmosphere heats from ground up

· When do daily high and low temperatures typically occur? o Recall that the troposphere is heated from below

o Sun heats the ground, the ground heats the air

o Solar radiation (sunlight) typically most intense around noon o High temperature typically occurs around 3:00 – 5:00 pm o Why the lag?

o See similar 5 week lag in seasonal temperatures

o When incoming solar radiation is greater than outgoing longwave  radiation, the surface warms

o Absorption greater than emission

o As sun gets lower in sky, solar radiation becomes less intense, so  surface begins to emit more radiation than it absorbs from sun o Cools

o Daily High Temperatures

o On bright sunny days, warmest temperatures generally right at  surface

o Sun heats ground, ground heats air

· What factors maximize nocturnal cooling?

o At night, air is cooled from below by cold ground

o Ground is blackbody; emits longwave radiation and cools  

rapidly at night

o Shallow layer of cold air forms just above ground

o Nocturnal inversion

o Typically a few 100 m deep

o Inversions are stable, prevent convection

o Cold air does not convert upward like hot air does

o Coldest temperatures typically right around sunrise

o Ground cools all night

o Calm nights tend to be colder than windy nights because the wind  mixes the cold air near the ground with warmer air aloft

· How do clouds influence daytime and nighttime  temperatures?

o Clouds and precipitation result in relatively cooler temperatures  during the day and relatively warmer temperatures at night


· Which gas is the most important to daily weather? o Humidity (in general) is a measure of water vapor in the atmosphere o Does not only mean relative humidity

o There are many ways to measure atmospheric moisture!

o We will learn 3!

o Evaporation: Liquid water molecules break bonds with other water  molecules and become gas

o Water absorbs latent heat

o Cools surroundings

o Condensation: Water vapor molecules form bonds with other water  molecules and become liquid

o Releases latent heat

o Warms surroundings

o Water molecules continuously transition between liquid and gaseous  states at the surface of liquid water

o If more molecules evaporate than condense, water vapor  concentration in air increases

o If more molecules condense than evaporate, water vapor  concentration in air decreases

o Let’s do some thought experiments…

· What is saturation? What mathematical relationships are  true at saturation?

o Assume that air in jar is initially unsaturated and jar remains at  constant temperature

o Initially, more water molecules evaporate from water surface than  condense onto it

o Evaporation > Condensation

o Water vapor concentration in jar increases

o Condensation rate increases

o More water vapor in the air to condense

o Evaporation rate remains constant

o Eventually, rates of evaporation and condensation become equal o This is called SATURATION 

o Saturation: The water vapor concentration in the air at which  evaporation and condensation rates are equal

Water level slightly drops

o Uncover jar and what happens?

o Water vapor from inside jar escapes into atmosphere

o Condensation rate decreases  

o Less vapor in air to condense

o Evaporation rate remains constant

o Net evaporation

o Water level will continue to drop and water in glass will dry up o Conclusion: Wind increases evaporation

o Saturation occurs when evaporation and condensation rates are  equal

o Air is NEVER so “full of water” that there is no room for any more o AIR IS NOT A SPONGE! 

o Most of air (and everything) is nothing:

o Molecules are very far apart

o If air molecules are tennis balls, they would be 4.75 feet away  from each other (on average)

o There are not “pockets” in air for water vapor like in a sponge!

· What is vapor pressure?

o Every gas in a mixture of gases contributes to the total pressure o Every blue gumball in the machine contributes to the total mass  (pressure) of the gumballs in the machine

o Water vapor is a small fraction (< 4%) of air, so the pressure exerted  by the water vapor is a small fraction of the total pressure o Called vapor pressure (unit: pressure; mb)

o Like pressure of only blue gumballs

o More water vapor air the air yields a greater vapor pressure o EXAMPLE: Vapor Pressure: How many kids on bus

·What is saturation vapor pressure? How is it related to  temperature?

• Saturation Vapor Pressure (SVP)

– Saturation vapor pressure is the vapor pressure required to  saturate the air

• Warm air contains more water vapor at saturation than  cold air

• It takes more water vapor to saturate air at higher  


• SVP increases with temperature

– SVP does NOT measure the actual amount of water vapor in  the air

– SVP tell us how much water vapor the air NEEDS to be  saturated, not how much vapor IS in the air!!

• EXAMPLE: Saturation Vapor Pressure: How many seats on bus

• Increase Temperature

– Assume saturation

– If the temperature increases, the evaporation rate increases • Liquid water molecules move faster at higher  

temperatures, and become more likely to escape from  

liquid and become gas

– Evaporation > Condensation

• Water vapor concentration in air increases

– Condensation rate also increases because there is more water  in air

• Eventually balances evaporation rate

– Warmer air becomes saturated at a higher water vapor  concentration than does colder air

• Decrease Temperature

– Assume saturation

– If we decrease the temperature, the condensation rate  increases

• Water vapor molecules move slower, more likely to “stick”  to the water surface and become liquid

– Condensation > Evaporation

• Water vapor concentration in air decreases

– Colder air becomes saturated at a lower water vapor  concentration than does warmer air

· What is relative humidity (RH)? What are the two ways to  increase or decrease it?

o Ratio of water vapor in air (VP) to that required for saturation (SVP) o RH does NOT indicate actual amount of water vapor in air o Higher RH does NOT necessarily mean there is more moisture  in the air

o Higher RH means air is closer to saturation

o Called relative humidity because it is relative to the temperature  (SVP)

o At saturation, RH = 100% (VP = SVP)


= ⋅100%



o Increase relative humidity:

o Add moisture to the air (increase VP)

o Cool the air (decrease SVP)

o Decrease relative humidity:

o Remove moisture from the air (decrease VP)

o Warm the air (increase SVP)

·What is dewpoint? Why is it useful?

• We can saturate the air in two ways:

– Add water to the air (while keeping temperature constant) – Cool the air (while keeping moisture constant)

– If we cool the air while keeping moisture constant, the  temperature at which saturation occurs is called the dewpoint  temperature  

• Dew forms


= ⋅100%


· What is the best way to compare atmospheric moisture  concentrations between two locations?

o Dewpoint Temperature 

· What are dew and frost? When are they most likely? Why? o Surface emits IR radiation (always)

o Cools rapidly, especially on clear calm nights

o Air above surface cools via conduction

o If surface cools below dewpoint of air, get condensation on the  surface

o Like on a cold glass in summer

o Frost forms if surface cools below freezing

o Dew and frost more likely on clear, calm nights

o Nocturnal cooling maximized

o Most common first thing in the morning

o A higher dewpoint always means there is more moisture in the air o Dewpoint of 50°F means there is enough water vapor in air to  saturate air with a temperature of 50°F

o Dewpoint of 70°F means there is enough water vapor in air to  saturate air with a temperature of 70°F

o Warmer air contains more moisture at saturation than does  cooler air!!!

o Dewpoint is always less than or equal to the temperature o Must cool air to reach saturation (unless air is already  saturated)

o Dewpoint takes units of temperature (°F, °C)

o On most days, can get a first-guess forecast of overnight low  temperature by looking at afternoon dewpoint  


· Why is rising air crucial to cloud formation? o Most clouds form in RISING air

o Why is rising air important?

o As air rises, it expands and cools

o Amount of water vapor in air does not change as air rises

o As temperature decreases, relative humidity increases o Air eventually rises high enough (cools enough) to become  saturated (RH = 100%)

o When air saturates, a cloud forms

o More ascent = Greater cooling

o What causes air to rise?

o Surface heating/convection (thermals; see right)

o Uplift by topography (mountains)

o Surface convergence (after exam)

o Fronts (after exam)

· What are clouds made of?

o Clouds are made of billions of microscopic water droplets or ice  crystals

o Water droplets require small particles on which to condense o Small particles called condensation nuclei

o Sizes 0.1 – 1.0 mm in diameter

o µm = 1 millionth of a meter

o About 100 – 1000 nuclei per cm3 of air

o Sources of condensation nuclei: Dust, ash, smoke, pollution, salt,  plankton, skin, etc

· What are condensation nuclei and why are they important  to cloud formation?

o Condensation Nuclei: 

o Small particles required for water droplets to condense ▪ lead to cloud formation 

• EX: dust, ash, smoke 

o Most cloud droplets are small (20 mm)

o This is 100 times smaller than the average raindrop!

o How do cloud droplets grow into rain?

o Most clouds do not produce precipitation

o Two ways:

o Collision and coalescence (warm cloud)

o Bergeron Process (cold cloud)

· What is collision and coalescence?

o Collision: Two droplets collide

o Coalescence: Two droplets stick together

o Collision does not necessarily result in coalescence

o Larger droplets fall faster than and collide with smaller droplets o Also called “warm cloud” process because there is NO ICE involved

· What is supercooled water?

o Water can remain liquid below freezing

o Called supercooled water

o Freezes into ice when it contacts something cold

o http://www.youtube.com/watch?v=13unrtlvfrw

· What is the Bergeron Process?

o Vapor molecules diffuse (travel) from near water droplets to near ice  crystals

o They go from where there is more water vapor to where there is  less!

o This reduces water vapor around droplet and increases water vapor  around ice crystal

o Air around water droplet becomes unsaturated

o Droplet begins to evaporate (water to gas)

o Air around ice crystal becomes supersaturated

o Ice crystal grows via deposition (gas to ice)

o Vapor continues to diffuse, process continues

o Result: Ice crystals grow at the expense of water droplets

· How are rain drops shaped?

o Precipitation begins as snowflakes high in atmosphere. Rain greater than 0.5mm, drizzle less than 0.5mm

o Ice crystals grow, become heavy, begin to fall

o Snowflakes melt if they fall into warmer air

o If it’s cold, they don’t melt at all!

o Most precipitation, even during the summer, begins as snowflakes  high in the atmosphere

o Precipitation types can change between the cloud base and the  ground

o Even a hurricane is a hellacious blizzard at 20,000 feet!

o Bergeron Process also called Cold Cloud Process because ice is  involved

· What is virga?

o Virga is precipitation that evaporates before reaching the ground o Typically, there is dry air below cloud base

· How much water typically results from melting a foot of  snow?

o Precipitation in the form of ice crystals

o Snow contains a lot of air!

o Can easily be compacted

o Typically, if you melt 10-12 inches of snow, you will only get one inch  of liquid water! (10:1 or 12:1 ratio) 

o Warmer temperatures – Ratio 6:1

o Colder temperatures – Ratio 20:1 or even 30:1

o Temperatures and vertical motions within cloud also affect snowflake  growth

· What is sleet?  

o Falling snowflakes melt when they encounter warm (above freezing)  air

o Become raindrops

o If raindrops then fall into a deep layer of cold air, they refreeze into  ice pellets

o Sleet requires thin above freezing layer of air aloft and deep below  freezing layer near surface

o Sleet – Tiny ice pellet (frozen rain drop)

o Produces pinging sound

o Accumulates at 2:1 or 3:1 ratio

o Much like driving through or shoveling sand or sugar

Freezing rain?

o Freezing Rain – Falling supercooled  


o Snow falls into warm layer of air,  


o Layer of cold air near surface is not  

thick enough to refreeze droplet

o Droplets become supercooled

o Droplets instantly freeze when they hit  

something below freezing

o Creates icy glaze over  


o Very hazardous

o Freezing rain requires deep above  

freezing layer of air aloft and thin  

below freezing layer near surface

· What environmental conditions are required to support  sleet and freezing rain?

o Deep above freezing layer of air aloft and thin below freezing layer  near surface


· What natural factors cause climate change? o Continental drift

o Changes in earth orbit

o Solar variability

o Volcanoes

o Aerosols

o Increases in greenhouse gases (e.g., CO2)

o Climate changes with time

o Ice and snow is reflective

▪ High albedo

▪ Additional cooling effect

o As the continents move around the earth, their climates shift o A continent that moves poleward will cool

o A continent that moves equatorward will warm

o This takes millions of years!!!


• The sun gradually gets  

brighter throughout its

lifetime (billions of years)

• Sun spot cycles

– Reaches maximum every 11 years

– Long term variations (poorly understood)

– Small (0.1%) fluctuations in solar output

• Contributed to early 20th Century warming, but not recent warming

· Why does increasing atmospheric carbon dioxide  concentrations lead to  

warmer temperatures?

o Increased greenhouse gas  

concentrations due to  

burning fossil fuels are very 

likely the cause of most of 

this warming

· Which areas of the earth  

are projected to see the  

greatest temperature  

increases? Why?

o Artic because there is a loss of sea ice

o Every summer it melts

▪ Same time each year???? General decrease in Artic Sea Ice  Extent

• Decreasing over decades

o Northern Hemisphere

o Land

· Why is sea level rising?

o Melting glaciers on LAND contributes to sea level rise

o Melting sea ice does NOT  

o Melting ice on land increases sea levels

o Water also expands as it is heated

o Projected sea level rise of 0.6 to 1.6 feet by 2100 using middle of the  road emissions scenario

o Maximum rise could be 3 feet by 2100

o Half the world’s population lives close to sea level

· What is the scientific consensus on climate change? o Proof of climate changes requires detailed statistical analysis of  past conditions over long periods of time (decades) 

o Has occurred due to increased anthropogenic CO2 emissions

o Anthropogenic climate change is real, but cannot be seen by  looking out the window

o Look outside, you will see weather, not climate

o CO2 one of many controls of climate

o Due to natural variability, each year is not necessarily  warmer than the last

o Same way like each day is necessarily not colder than the  last during fall

· What are the sources of uncertainty in climate predictions? • Uncertainty is a natural part of science!!

• How will carbon dioxide emissions change in the future? • How will warmer temperatures affect atmospheric humidity? – Water vapor is a greenhouse gas ???? Warms

– Water vapor can result in cloud formation ???? Cools

• Current climate models do not handle cloud systems very well – Thunderstorms, hurricanes

• Must consider natural oscillations (e.g., El Niño, ocean currents, etc) – Not every year warmer than previous one!!! 

• Not the same as forecasting the weather!!

• All else being equal, more CO2 will yield a warmer climate

o Anthropogenic climate change is real, but cannot be seen by looking  out the window

o Look outside, you will see weather, not climate

o CO2 one of many controls of climate

o Due to natural variability, each year is not necessarily warmer than  the last

o Same way like each day is necessarily not colder than the last during  fall

o how CO2 emissions will change in the future 

-how will warmer temp affect atmospheric humidity

-current climate models don't handle cloud systems very well -natural oscillations


· How do you read a station model?

· How do you convert to/from Central Time and UTC?

o To convert 18 UTC into your local time, subtract 6 hours, to get 12  CST. During daylight saving (summer) time, you would only subtract  5 hours, so 18 UTC would convert to 13 CDT. Or, let's say you're in  Paris, France, which is in Central European Time. 

Toconvert 18 UTC into your local time, add 1 hour, to get 19 CET o


· How do you read a sounding?

· What is dewpoint depression?

o The difference between the temperature and dew point temperature  at a given level (humidity of the air)

o = T – Td  

o Temperature minus dew point temperature

o When the dew point depression is large, very dry air

o When the dew point depression is 2°C or less, very humid air (clouds  are present)

· What is wind chill? Why is it lower than the temperature? o A measure of how cold it really feels (oF)

o Increased wind speeds accelerate heat loss from exposed skin

o The inanimate object will not cool below the actual air temperature.  For example, if the temperature outside is -5 degrees Fahrenheit and the wind chill temperature is -31 degrees Fahrenheit, then your  car's radiator will not drop lower than -5 degrees Fahrenheit.

· What is the heat index? Why is it typically higher than the  temperature?

o A measure of how hot is really feels when relative humidity is factored  in with the actual air temperature (oF)

o Also referred to as apparent temperature or “Feels like” temperature o Our bodies want to maintain a temperature of 98.6 oF

o Normally when we sweat, the water is able to evaporate and cool the  skin

o With high RH, the air contains close to the maximum amount of water  vapor in the air

o The water on our skin is not readily able to evaporate, which prevents  the body from cooling

o The human body normally cools itself by perspiration, or sweating,  which evaporates and carries heat away from the body. However,  when the relative humidity is high, the evaporation rate is reduced, so  heat is removed from the body at a lower rate causing it to retain  more heat than it would in dry air. Measurements have been taken  based on subjective descriptions of how hot subjects feel for a given  temperature and humidity, allowing an index to be made which  corresponds a temperature and humidity combination to a higher  temperature in dry air.

o At high temperatures, the level of relative humidity needed to make  the heat index higher than the actual temperature is lower than at  cooler temperatures. For example, at 27°C (approximately 80°F), the  heat index will agree with the actual temperature if the relative  humidity is 45%, but at 43°C (roughly 110°F), any relative humidity  reading above 17% will make the Heat Index higher than 43°C.  Humidity is deemed not to raise the apparent temperature at all if the  actual temperature is below approximately 20°C (68°F) essentially  the same temperature colder than which wind chill is thought to  commence. Humidex and heat indexes are based on temperature  measurements taken in the shade and not the sun, so extra care  must be taken while in the sun.

o A good example of the difference between heat index and true  temperature would be comparing the climates of Miami and Phoenix.  Miami averages around 35°C in summer due to the easterly trade  winds coming from the Atlantic Ocean, but it has a high humidity (e.g.  75%). Phoenix averages around 40°C in summer, but typically has a  low humidity (e.g. 10%). According to the heat index, the relative  temperature in Miami will be 44°C, but the relative temperature in  Phoenix will be lowered due to the lower humidity, to around 37°C.  Given sunshine, Miami is likely to feel hotter than Phoenix.

· What are the Latin roots of cloud classification? How do  they relate to cloud types?

o Cloud Height:

o “Cirro-” → high

o “Alto-” → middle

o Appearance:

o “Stratus” → typically cover entire sky; “layered”

o “Cumulus → puffy, round

o “Nimbus” → precipitating clouds

· How can various factors cause or influence climate change?

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