Meteorology Chapter 1-4 Cheat Sheet (DRAFT) by chanhmuoi

Scientific Method
- Make observ­ations
- Make a hypothesis
- Has to be tested
- Make prediction assuming hypothesis is true
- Carry out experi­ments
- Mathem­atics is the tool to understand and predict the natural world
Scientific Method and Meteor­ology
- Atmosphere obeys laws of physics and chemistry
- Instru­ments allow us to quantify the state of the atmosphere
- Thermo­meter
- Hygrometer
- How much humidi­ty/­moi­sture in air
- Barometer
- Air pressure
- Anemometer
- Wind speed/wind direction
- Mathem­atics can project current conditions into the future
- Uses computer models to help with calcul­ating
Weather and Climate
- Weather describes state of the atmosphere at any given time
- Temper­ature
- Air Pressure
- Humidity
- Cloud Cover
- Precip­itation
- Visibility
- WInd Velocity
- Climate describes average atmosp­heric conditions over at least 30 years
- Includes extremes
- The frequency of extremes help differ­entiate between locations with similar averages
Meteor­ology
- Meteor­ologica
- Book on natural philosophy by Aristotle in 340 BC
- How meteor­ology got its name
- Study of the atmosphere and its phenomena
- Began with the invention of weather instru­ments (1450-­1650)
- Quantified the atmosphere
- Allows for the prediction of what the atmosphere will do
- Telegraph (1843)
- Allowed for the transm­ission of current weather conditions across vast areas
- Weather Map Analyses (1869)
- Visual snapshot of current state of the atmosphere
- Unders­tanding of Air Masses adn fronts (1920)
- Key weather features that drive world weather patterns
- Daily weather ballon launches (1940s)
- These radios­ondes provide 3D view of the atmosphere
- Numerical Weather Prediction (NWP)
- Solving the mathem­atical laws of physic­s/c­hem­istry at high speeds
Remote Sensing of the Atmosphere
- Weather Radar (1940s)
- Detects precip­itation targets from over 100 miles away
- Doppler Weather Radar (1990s)
- Detects precip­itation targets and their motion
- “Sees” the wind
- Dual Pole Doppler Weather Radar (2000s)
- Distin­guishes between rain, snow, hail, and bugs
- Weather Satellites (1960s)
- Reveal weather features produced by cloud patterns
- Can supply NWP with data from every location on Earth
- Most Common Type of Satellite
- Geosta­tionary
- Orbits the Earth at the same speed the Earth spins
- GOES 16 and 17 Satellites
- Best View of the US
- Centered over the Equator (0º Latitude) and 75º W | 137ºW Longitude
- 22,300 Miles
Latitude
- the angle made between center of Earth and a point on surface using the Equator as the reference line
- North Pole = 90º N Latitude | South Pole = 90ºS Latitude
- Most of the US is between 30ºN and 50ºN Latitude
Longitude
- the angle made between center of Earth and a point on surface using the Prime Meridian as the reference line
- Runs from N Pole to S Pole through Greenwich, England
- Most of the US lies between 70ºW and 125ºW Longitude
Most Common Type of Storm System
- Middle­-La­titude Cyclonic Storm System
- Extrat­ropical Cyclone
- Cyclon­e=area of low pressure
- Anticy­clo­nes=are of high pressure
Depiction of Winds
- Wind is defined from the direction it is blowing
- Repres­ented by a line - wind barb - drawn parallel to wind
- Points in direction from which the wind is blowing
- Speed is repres­ented by wind flags
- Full flag = 10 knots
- Half flag = 5 knots
Wind Flow
- Counte­rcl­ockwise and inward around lows
- Clockwise and outward around highs
In Southern hemisp­here…
- Clockw­ise­/inward around lows
- Counte­rcl­ock­wis­e/o­utward around highs
- Wind does not cycle around the equator
- No hurricanes but tornados can still happen
Vertical Wind Flow Around High and Lows
- Air converges and rises in the center of low pressure (cyclone)
- Clouds­/pr­eci­pit­ation
- Air diverges and sinks in the center of high pressure (antic­yclone)
- Clear skies
Weather Fronts
- Cold front
- Boundary that separates colder air from warmer air
- When colder air advances and replaces warmer air
- Warm front
- Boundary that separates colder air from warmer air
- When warmer air advances and replaces colder air
- Occluded front
- When cold front merges with warm front
- All fronts are usually but not always associated with rising air, clouds, and precip­itation
Impacts of Weather and Climate
- Weather dictates the clothes we wear on any given day
- Climate dictates the clothes we have in our wardrobe
- Climate dictates the type of crops we can grow
- Weather dictates whether the crops can be harvested
When Weather is Not What it Seems
- Wind Chill
- Body perceives a lower temper­ature than it really is
- Hypoth­ermia
- Frostbite
- Heat Index
- Body perceives a higher temper­ature than it really is
- Hypert­hermia
- Heat Exhaustion or Heatstroke
Other Biological Impacts
- Rapid pressure falls/­rising humidity
- Can induce expansion of joints and cause joint pain
- Wind flowing downhill heats up - Chinook winds/ Santa Ana
- Incidence of depression increases
Economical Impacts of Weather
- Warm winters = lower heating bills
- Beware of unusual winter severe weather outbreaks
- Cold winters = higher heating bills
- Severe Artic air cold snaps can threaten human lives/­inf­ras­tru­cture damage­/ma­ssive crop losses
- Heat Waves and Drought
- Crops losses
- Wildfires increase
- #1 in weathe­r-r­elated fatalities
Climate Change Bringing More Extremes
- Heat waves and drought increasing
- Flooding events increasing
- Hurricane intensity increasing
Other Weather Hazards
- Severe Thunde­rstorms
- 50 knot (58 mph) winds
- 1-in hail
- Tornado
- It has to fulfill one condition to be considered
- Flash Flooding
- Slow-m­oving thunde­rstorms
- “Training” storms
- Downburst winds
- Macrob­urst- greater than 4 km (2.5 mi) in diameter
- Microburst - less than 4 km in diameter
- Both produce Wind Shear
- Change in wind speed/­dir­ection over short distance
Who Studies This?
- Meteor­ologist
- Profes­sionaly trained, college degree in atmosp­heric science
- Weathe­rcaster
- Good commun­icator of weather inform­ation
Weather Business is Expanding
- Private Meteor­olo­gical
- App Develo­pment
- Forensic services
Fundam­entals of Meteor­ology
The atmosphere is a mixture of gases
- Nitrogen
- Oxygen
- Argon
- Water Vapor (highly variable)
- Carbon Dioxide (generally increa­sing)
Most of the gases are near the surface
- Air gets “thinner” as you go up
99% of atmosphere is within 19 mi of teh surface
- Blocks deadly solar radiation from reaching the surface
The First Atmosphere
- 4.6 BYA the atmosphere was mostly hydrogen and helium
- Some methane and ammonia thrown in
- Hydrogen and helium escaped into space
- Earth’s gravity not strong enough
The Second Atmosphere
- Outgassing from Earth’s hot interior (volca­noes)
- Mostly water vapor (80%), carbon dioxide (10%), and some nitrogen
- Water vapor “conde­nsed” into clouds with rain lasting 1000s of years
- Combined with astero­id/­comet collisions that formed the oceans
Water Vapor Levels in Atmosphere Drop
- Most of the water vapor converted to liquid water
- Atmosphere now just a few % water vapor
CO2 Levels Drop
- CO2 readily dissolves in water
- Combined with chemicals in the ocean to form limestone
N2 Levels Increase
- Nitrogen is not very chemically reactive
- Once in the atmosp­here, tends to stay
O2
- Solar radiation splits water vapor into hydrogen and oxygen
- Hydrogen escaped into space
- Oxygen left behind
- 2.4 BYA, something wonderful happens
- Cyanob­acteria (blue-­green algae) produce O2 from photos­ynt­hesis
- Earth begins to cool
- O2 combines with O to form O3 (ozone)
- O3 in upper atmosphere absorbs incoming radiation cooling the Earth
- Methane breaks down in the presence of O2
- Warming effect of methane weakens
- Earth becomes very cold
- Cyanob­acteria prolif­erate around the world removing CO2 from atmosphere
- Warming effect of carbon dioxide weakens
First Mass Extinction
- Earth gets covered in ice
- Frigid Earth no longer supporting life
- No O2 being produced
- O2 is highly reacti­ve/­com­bines with other elements to form rocks
- O2 levels drop worldwide
Life Gets a Second Chance
-- Outgassing increases water vapor/­carbon dioxide (volca­noes)
- H2O and CO2 are warming gases
- Takes over a billion years for new photos­ynt­hes­izing life to reappear
- After another 1/2 billion years, O2 levels are where they are today
Water Vapor
- 0% to 4% of the atmosphere
- Always invisible
- Become visible when vapor molecules “jump” on each other to form droplets or ice crystals
- Conden­sation form droplets
- Deposition form ice crystals
- Evapor­ation is when liquid turns to gas
- Water is only substance that can exist in all 3 phases at normal temper­atu­re/­pre­ssure
Charac­ter­istics
- Greenhouse Gas
- Very effective at absorbing outgoing radiation emitted by Earth
- Re-emits some of this energy back keeping the Earth warmer
Carbon Dioxide
- Greenhouse Gas
- Comes from the decay of vegetation
- Volcanic eruptions
- Burning of coal, oil, natural gas (fossil fuels)
- Removed by photos­ynt­hesis of land and ocean plants
- CO2 gets stored in roots, branches, and leaves
- Chemical weathering of rocks
- CO2 dissolves in rainwater
- Forms carbonic acid
- Combines with minerals in rocks and becomes part of the rock
- Dissolves in Ocean water
- Used by sea critters to make shells
- Eventually sinks to bottom of the sea
Vertical Structure of the Atmosphere
Air is compre­ssible
- Gravity pulls most -but not all- air molecules near the surface
- Air Density = # of air molecules in a given volume
- Mass/v­olume
Air Density and Air Pressure
- Force exerted by air molecules against a surface
- Same thing as the weight of the air above you
- At sea level, air weighs 14.7 lbs per square inch
Measuring Air Pressure
- 14.7 lbs/in2
- 1013.25 millibars (mb)
- 29.92 in Hg
Atmosphere is Very Thin
- Half of the air molecules is below 5.5 km (18,000 ft)
- 99.9% is below 50 km (160,000 ft)
Layers of the Atmosphere
- Atmosp­heric layers are defined by how the temper­ature changes with height
- Lapse Rate= rate at which temper­ature decreases with height
- In lower atmosp­here, lapse rate = 6.5ºC per km (3.6ºF per 1000 ft)
- Temper­ature can INCREASE with height
- This is called temper­ature inversion
- Lapse rate is negative
- Tropos­phere
- Strato­sphere
- Mesosphere
- Thermo­sphere
- Ionosphere
- Lower part of the Thermo­sphere
- Solar energy strips electrons from N2 and O2 causing them to glow
Northern and Southern Lights
- Aurora Borealis - N. Lights
- Aurora Australis - S. Lights

- Energy
- The ability to do “work”: when an object moves
- Kinetic Energy
- Energy of motion- transl­ati­onal, rotational and vibrat­ional
- Potential Energy
- Energy that can convert to kinetic energy
- Water that is behind a dam
- Object suspended in the sky
- Temper­ature
- Average kinetic energy of atoms in a substance
- Some move fast, others not so fast
- Average motion = temper­ature
- When molecules move, rotate, and/or vibrate, we say that the object has a temper­ature
- When air molecules move slowly, they crowd together
- It is cold and air is dense
- When air molecules move quickly, they spread out
- We say it is warm and the air is less dense
- Internal Energy (Heat energy)
- The total kinetic and potential energy of all atoms or molecules
- Heat
- Heat is the transfer of energy from warmer objects to cooler ones
- The bigger the temper­ature differ­ence, the faster the energy transfer
- Know how to convert temper­ature scales

## Temper­ature Measur­ements

- Important Temper­ature Values
- Ice point
- Ice melts, water freezes
- 32ºF, 0ºC, 273.15K
- Steam point
- Water boils
- 212ºF, 100ºC, 373.15 K

## Types of Heat Energy

- Sensible Heat
- Heat energy that can be absorbed or released by a substance that results in a change of temper­ature
- Latent Heat
- Heat energy that is absorbed or released by a substance when the substance undergoes a phase change
- Temper­ature of substance does not change
- Let ice at 32ºF absorb heat energy
- Ice melts, but its temp remains at 32ºF
- Only after the ice completely melts will the water warm up
- If water freezes, it releases the same heat it took to cause it to melt in the first place but water temp does not change
- The surrou­nding air does warm
- How does heat energy get transf­erred?
- Conduction
- Heat transfer by contact of one substance with another
- Energy gets transf­erred from one molecule to the next
- Some materials transfer heat better than others
- Metals are good conductors
- Fiberg­lass, cork, wood, cloth, glass, water are poor conductors
- Air is a poor conductor of heat
- Heat (Thermal) Conduc­tivity
- Measure of how well a substance transfers heat energy

## Why Temper­ature Decreases with Height

- Atmosphere is mostly “trans­parent” to incoming sunlight
- Sun does not heat air directly
- Atmosphere can be heated by conduction
- Ground absorbs sunlight
- Air in contact with ground gets heated
- Heat energy does not get conducted to higher altitudes very well

## How Does Heat Energy Get Transf­erred?

- Convection
- Heat transf­erred due to the movement of a substance from one place to another
- Much more efficient than conduction
- Moving heat energy vertically and horizo­ntally
- Convection - vertical air motions, also called thermals
- Advection - horizontal air motions
- Radiation (Elect­rom­agnetic Radiation or Radiant Energy)
- The only heat transfer possible in a vacuum
- Can also transfer heat in air or water
- Energy is carried by photon particles defined by their wavelength
- nm=nan­ometer= billionth of a meter
- µm=mic­rometer or micron= millionth of a meter

## Radiation Laws

- Facts
- All objects above Absolute Zero radiate (emit) energy at ALL wavele­ngths
- 0K = -273.15ºC= -459.67ºF
- Even in inters­tellar space, the temper­ature is between 2.7K and 5K
- Total Radiation emitted = Sum of energy emitted from every wavelength
- Total Energy emitted by every square meter of an object is given by the Stefan­-Bo­ltzmann Law
- E=o x T^{4 (results is in Watts per square meter, W/m}2 or W m^-2
- Watts=­Joules per second, J/s or Js^-1
- Temper­ature has to be in Kelvins
- o is constant variable
- Hot objects emit more radiation than cooler objects
- There is one wavelength (λ_max) that an object will emit most of its radiation
- Wien’s Displa­cement Law
- λ_max = 2897/T (answer is in µm)
- T must be expressed in Kelvin
- Stefan­-Bo­ltzmann and Wien’s Law
- Only valid if object is a blackbody object
- An object that is a perfect absorber and perfect emitter of radiation
- Absorbs all radiation that strikes it and then emits max possible radiation
- Absorption and Emission
- If an object absorbs radiation, it must also emit radiation
- If absorption is greater than emission, object heats up
- If absorption is less than emission, object cools down
- If absorption = emission, object’s temper­ature remains the same
- Radiative Equili­brium Temper­ature
- Absorption
- Gas molecules are picky about which type of radiation they will absorb
- Selective Absorbers
- Some will only eat shortwave radiation
- Shortwave is less than 1.4µm
- Some will only eat longwave radiation
- Longwave is greater than 1.4 µm
- Some will eat both or neither
- Air is mostly transp­arent to incoming solar radiation
- Air is not transp­arent to outgoing terres­trial radiation
- Some gases absorb Earth’s outgoing radiation and then reemit some of it back to the surface

## Main Greenhouse Gases

- Water Vapor
- Carbon Dioxide
- Methane
- Nitrous Oxide
- Ozone

### Benefit of the Greenhouse Effect

- Average temper­ature of the Earth is 59ªF
- Without greenhouse gases, it would be 0ºF

## What Else Happens to Radiation When it Enters the Atmosp­here?

- Transm­ission
- Radiation passing through air molecules without intera­cting with any of them
- About 55% of incoming solar radiation is transm­itted
- Reflection
- Radiation that bounces off an object at the same angle object, and it leaves at the same intensity
- Scattering
- Produces a large number of rays traveling in all different directions
- Scattered radiation is weaker than what originally hit the object
- Gasses scatter solar radiation prefer­ent­ially
- Some wavele­ngths are scattered better
- Atmosp­heric gases - mostly N2 and O2 scatter blue/v­iolet more effect­ively than reds/o­ranges
- Violet is scattered best
- Blue is at higher intensity level than violet
- Human eye detects blue better than violet
- When Sun is on horizon, light travels through a lot more atmosphere than when Sun is overhead

## Quanti­fying Reflected Radiation

- Albedo
- Percentage of radiation reflected by an object
- Average albedo for Earth is about 30 percent
- Average albedo for the Moon is about 7 to 12 percent
- A perfect reflector would have an albedo of 100%
- Saturn’s moon Enceladus has an albedo of almost 100%

## What Causes Temper­ature Differ­ences?

- Solar Radiation Intensity largely determines temper­ature
- High solar radiation intens­ity­=tr­opical areas
- Low solar radiation intensity = arctic­/an­tarctic area
- Solar Radiation Intensity = Power/Area
- Partly determined by height of Sun above horizon
- Midday sun always high in the sky in the Tropics
- Midday sun never high in the sky in Arctic­/An­tarctic areas

## Important Dates to Remember

- Solstices and Equinoxes
- Summer solstice: June 21 or 22
- At solar noon, sun’s rays are vertical at Tropic of Cancer 23 1/2º N Latitude
- Longest day
- WInter solstice: December 21 or 22
- Vertical rays at Tropic of Capricorn: 23 1/2ºS Latitude
- Shortest day
- Autumnal equinox: September 22 or 23
- Vertical rays at the equator
- day and night are equal
- Vernal (spring) equinox: March 21 or 22
- Vertical rays at the equator
- 12 hour days/n­ights everywhere

## Solar Noon

- The time when the sun reaches its highest point in the sky
- halfway between sunrise and sunset

## Solar Declin­ation

- The latitude where Sun is directly overhead at solar noon
- Can only be in the tropics on any given day

## Solar Elevation Angle (SEA)

- Angle the Sun makes with horizon at any time
- When sun is on horizon, SEA is 0º
- Halfway up into the sky, the SEA is 45º
- If sun is directly overhead, SEA is 90º

## Solar Noon Angle (SNA)

- Angle the Sun makes with the horizon at solar noon
- Sun will be at its highest point in the sky at solar noon on any given day
- Sun will be at absolute highest point in the sky at solar noon on the first day of summer
- Sun will be at its absolute lowest point in the sky at solar noon on the first day of winter

## Procedure to Finding the Solar Noon Angle

1. Where is the Solar Declin­ation
2. Calculate latitude difference to the SD
3. Subtract this difference between 90º

## Temper­ature Defini­tions

- Daily Mean
- Average of the 24 hourly­-te­mpe­rature readings
- Add high | low and divide by two
- Daily Temper­ature Range
- Difference between high and low
- Monthly Mean
- Average of daily means for the month
- Annual Mean
- Average of the 12 monthl­y-means for the year
- Annual Temper­ature Range
- Difference between highest and lowest monthly mean

## Controls of Temper­ature

Anything that determines the temper­ature of a location is called “Control of Temper­ature”

- #1 Control: Amount of Solar Radiation received
- Solar Angle
- Length of daylight
- Latitude determines solar angle and day length
- Areas on same latitude have the same solar angles and number of daylight hours on any given day
- So latitude is no. 1 control
- Differ­ential heating of land and water
- Land and water do not heat up/cool down at the same rate
- Water requires 3-5x as much energy than land to heat up to the same temper­ature
- Geographic position
- If prevailing winds blow from sea to land (windward coast), temper­atures will not change much
- Tend to have a small annual temper­ature range
- If prevailing winds blow from land to sea (leeward coast), temper­atures will fluctuate much more
- Tend to have a larger annual temper­ature range
- Ocean currents
- Warm Gulf Stream
- “River” of warm water transports heat to northern latitudes
- Western Europe is much milder than it should be
- Effects of warm ocean currents
- Palm Trees in England and Ireland
- Effects of Cold/Warm Ocean Currents
- Poleward currents bring warmer conditions
- Equato­rward current bring cooler conditions
- Another Effect of Cold Ocean Currents
- Land is pretty dry
- Ex. Atacama Desert is the driest place on Earth due to the cold Peru Ocean Current
- Elevation
- Temper­atures usually decrease with altitude in the tropos­phere
- Atmosphere is mostly transp­arent to solar radiation but the ground absorbs almost all radiation that hits it
- Air in contact with ground (condu­ction) heats up the most
- Atmosphere is heated from bottom up
- Cloud cover
- Clouds (or water vapor) lower surface temper­atures during the day
- Clouds (or water vapor) increase surface temper­atures at night
- Albedo variations
- High albedo reduces surface temper­ature
- Low albedo increases surface temper­ature

## Conseq­uences of Being Next to Large Body of Water

- Inland Winnipeg and Coastal Vancouver
- Cities are located at a similar latitude
- Vancouver has a milder climate
- Temper­atures in S. hemisphere do not fluctuate as much
- S. Hemisphere is the “water hemisp­here”
- Water moderates temper­atures

## Minimum and Maximum Temper­atures of the Day/Year

- Delay in reaching high temper­ature: Lag of the Maximum
- Also applies to the seasons

## Urban Heat Island Effect

- Interior sections of cities tend to be warmer than surrou­nding rural areas

## Temper­ature Measur­ements

- Mechanical thermo­meter
- Liquid in glass | expands when heated, contracts when cooled
- Maximum thermo­meter - mercury
- Minimum thermo­meter - alcohol
- Thermo­graph
- Two metals in the strip will expand­/co­ntract differ­ently depending on the temper­ature
- Electrical thermo­meters
- Thermistor measures the resistance to electric current
- Provides accurate temper­ature reading even when temper­ature changes quickly (radio­sondes)
- Instrument shelters
- White box
- Louvered sides (slits in the housing unit)
- Over grass and away from buildings
- 1/5m (5 feet) above ground

## Crop Protection Against the Cold

- Frost/­Freeze Prevention
- Water sprinklers add heat from the latent heat of fusion when the water freezes
- Air mixing uses wind machines to mix warm and cool air
- Orchard heaters produce the most successful results, but fuel cost and pollution can be signif­icant

## Heat Stress and Wind Chill: Indices of Human Discomfort

- Heat Stress Index: Temper­ature the body perceives when you include effects of humidity
- Evapor­ation of sweat is reduced when humidity is high
- Apparent Temper­ature: temper­ature a person perceives
- Wind Chill Index: Temper­ature the body perceives when you include effects of wind
- Cold, dry air will evaporate moisture from the body
- Wind will blow away isolating air layer that surrounds the body

## Temper­ature and the Economy

- Heating Degree Days
- Gives a sense of how often one needs to heat a building
- Assump­tion: Heating not required when daily mean temper­ature is ≥65ºF, then there is zero heating degree days
- For each degree the mean temper­ature < 65ºF, this is counted as one Heating Degree Day
- Cooling Degree Days
- Cooling not required when daily mean temper­ature is 65ºF or lower
- Each degree of temper­ature > 65ºF is counted as one Cooling Degree Day
- Heatin­g/C­ooling Degree Days and Electric Bills
- Heating bill correlates with heating degree days
- Growing Degree Days
- A way to determine if a crop can be succes­sfully grown in any given area
- Assumes a BASE temper­ature for any given crop
- If daily mean is below the base, the plant goes dormant
- The difference between this BASE temper­ature and the daily mean temper­ature is a Growing Degree Day
- Some crops go dormant if daily mean is too high
- If daily mean > 86ºF, many plants stress out, go dormant
- In this event, the number of GDD is set at zero

## Water: A Unique Substance

### Hydrogen Bonding

- The attractive force between $H_2O$ molecules
- Hydrogen side of $H_2O$ is “+” charged | Oxygen side is “-” charged
- + Hydrogen side attracted to oxygen side of other $H_2O$ molecules

### Formation of Ice

- When it’s cold, $H_2O$ molecules cannot break their bonds
- Remain fixed in a crysta­lline structure, ice
- Lowest kinetic energy state

### Liquid Water

- When it’s warmer, $H_2O$ molecules break bonds tempor­arily
- Flow over each other but remain connected, liquid water
- Higher kinetic energy state

### Water Vapor

- When it’s very warm, $H_2O$ molecules break bonds completely
- Molecules scatter in random direct­ions, gaseous water = water vapor
- Highest kinetic energy state

### Ice-Wa­ter­-Water Vapor

- When water absorbs or releases internal energy, it can change phase

## Heat Energy

One calorie of heat energy is required to raise 1 gram of water 1ºC

## Water: Changing Phases

- Latent Heat of Melting: 80 calories
- 80 calories of heat absorbed by 1g of ice melts into 1g of water
- No temper­ature change in the ice, but surrou­nding air gets colder
- Latent Heat of Fusion: 80 calories
- 80 calories of heat released by 1g of liquid water freezes to 1g of ice
- No temper­ature change in the water but surrou­nding air does heat up
- Latent Heat of Vapori­zation: between 540 and 600 calories
- 540 to 600 calories absorbed by 1g of liquid water evaporate to 1g water vapor
- Heat is taken from surrou­nding air resulting in decrease air temper­ature
- Latent Heat of Conden­sation: between 540 and 600 calories
- 540 to 600 calories released by 1g water vapor condenses to 1g liquid water
- Heat is added to the surrou­nding air resulting in a temper­ature increase
- Latent Heat of Sublim­ation: about 680 calories
- 680 calories of heat absorbed by 1g of ice to sublime to 1g of water vapor
- Heat removed from surrou­nding air greatly cools the air around the ice
- Latent Heat of Deposi­tion: about 680 calories
- 680 calories of heat released by 1g of water vapor deposits to 1g of ice
- Heat added to the enviro­nment greatly warms the air around the ice

## Measuring Water Vapor

- Mixing Ratio
- Mass of water vapor/mass of dry air it is in
- Water vapor measured in grams
- Dry air measured in kg
- Actual mass of water vapor in the air
- Saturation Mixing Ratio
- Max amount of water vapor allowed in the air (mostly determined by temper­ature)
- Vapor Pressure
- Pressure exerted by water vapor
- Total air pressure = sum of pressure from each gas
- The more water vapor in the air, the greater its contri­bution to the total air pressure
- Relative Humidity
- Mass of water vapor/mass of water vapor allowed to be in the air
- RH=mixing ratio/­sat­uration mixing ratio
- RH=vapor pressu­re/­sat­uration vapor pressure
- Relative humidity can be misleading
- Does not tell you how much water vapor is in the air unless you know the temper­ature of the air
- RH does tell you how close you are to saturating the air
- When air is saturated, conden­sation occurs
- The lower the RH, the faster water evaporates
- Watering lawn in the morning is more effective than watering in the afternoon
- RH can be over 100% but not for long (super­sat­ura­tion)
- Violent updrafts in thunde­rstorms can supers­aturate
- Dew Point Temper­ature (Td)
- Temper­ature at which saturation occurs
- Better way of measuring actual water vapor content
- Absolute Humidity
- Specific Humidity

### Relati­onship Between T, Td, and RH

- When T and Td are close, RH is high
- When T and Td are far apart, RH is low

### Water Vapor Rule

- Air can only hold so much water vapor
- When it has as much water vapor as physics allow, we say the air is saturated

## Saturation Vapor Pressure

- Pressure exerted by water vapor when the air is saturated with it
- Amount of water vapor allowed in air is mostly determined by temper­ature
- Warmer temper­atures allow for more water vapor

## When Air is Saturated

Some kind of Conden­sation (Depos­ition) Occurs

- Dew forms
- Frost forms (if below freezing)
- Fog forms
- Cloud forms

## Formation of Dew

Ideal Conditions

- Clear skies, light winds
- Allows for maximum radiat­ional cooling of the ground
- Air in contact with ground cools to the dew point
- If air continues to cool below freezing, frozen dew occurs

## Formation of Frost

When Deposition occurs instead of conden­sation

## Clouds

Bringing Air to Saturation

- Cooling air is the easiest way to saturate the air
- Air always cools as it rises

### Formation of Clouds

- Clouds result from conden­sation and/or deposition
- There usually needs to be conden­sation nuclei for it to form
- Dust, smoke, ash, salt, sulfate particles, and even bacteria
- Without these, clouds would not form and RH would need to be greater than 100% to form
- Deposition can occur in bitterly cold air without nuclei
- Conden­sation or deposition will always occur when RH reaches 100% (in this class)

### Fog

- Cloud with base at the ground
- Forms when air temper­ature = dew temper­ature
- 4 types
1. Radiation
1. Ground cools rapidly and causes saturation near the ground
2. Nocturnal inversion can prevent higher fog
3. Clear skies, light winds, high relative humidity
4. Also called Valley frog
2. Advection
1. Warm, moist air blowing horizo­nta­lly­(ad­vec­ting) over a “cold” surface
3. Upslope
1. Humid air moves up a hill or mountain
1. The upward flow causes the air to expand, cool, which can eventually reach 100%
4. Evapor­ative
- Process of Evapor­ation involved
- Rain falls, partially evaporates
- Adds water vapor to air, leads to saturation
- Evapor­ation also chills air, assiting in bringing air to saturation
- Precip­itation Fog
- Steam Fog
- Cool dry air moves over warm surface, esp. water
- Common over lakes in autumn when lake is still warm from summer and air above it is cold and dry

### Classi­fic­ation of Clouds

- Jean-B­aptiste Lamarck (1802)
- Luke Howard (1803)
- Abercromby and Hildeb­ran­dsson (1887)

Clouds are classified by appear­ance, shape, and how high they are.

High Clouds

- Cirrus Clouds
- Composed mostly of ice crystals
- Thin due to limited water vapor
- Cirroc­umulus
- Composed of mostly ice crystals but with lumps
- Cirros­tratus
- Composed of mostly ice crystals and when thin, often causes a halo around sun/moon
- Can be thicker but usually, sun still partially shines through

Middle Clouds

- Altocu­mulus
- Mostly water droplets
- Darker regions noted
- Can signal the possib­ility of afternoon storms
- Altost­ratus
- Mostly water droplets with a “frosted glass” sun appearance
- Usually does not permit shadows to be cast

Low Clouds

- Stratus
- Layer of low clouds covering the sky
- Often seen after fog “lifts”
- Can have mist or drizzle
- Nimbos­tratus
- Light to moderate rain or snow
- Strato­cumulus
- Lumpy clouds that appear in rows with some separation
- Lower than altocu­mulus with larger cloud elements

Clouds of Vertical Develo­pment

- Cumulus
- Caulif­lower or cotton ball clouds
- Rising air below clouds, sinking air between clouds
- Cumulus Humilis
- Fair weather clouds
- Humble clouds that do not threaten to build into storms
- Cumulus Congestus
- May develop into thunde­rstorms
- Cumulo­nimbus
- Most intense rainmaker
- Oversh­ooting top
- When the cloud punches through the strato­sphere

Special Latin Descri­ptive Terms

- Cloud Varieties
- Uncinus
- Hooked shaped, often appear before stormy weather moves in
- Cirrus uncinus
- Fractus
- Stratus or cumulus clouds that appear broken
- Cumulus fractus better known as scud clouds
- Mammatus
- Udder-­shaped protub­erances often associated with the underside of a cumulo­nimbus anvil cloud
- Only cloud that forms in sinking air

Unusual Clouds

- Lentiular
- Lens-s­haped and common over mountains and downwind of high terrain
- Pileus
- Cap clouds
- Form when moist air is pushed up under a devele­oping cumulus cloud
- Banner Cloud
- Forms downwind of an isolated mountain peak
- Asperitas Clouds
- Often forming near precip­ita­tio­n-b­earing clouds
- Undulating up and down like ocean waves

*Super­-high Clouds*

- Nacreous
- Strato­phere
- Noctil­ucent
- Mesosphere

Reminder: Rising air cools, temper­ature drops to dew point, condenses

- Excess water vapor condenses into tiny droplets
- Excess water vapor used up very quickly
- This results in Billions of teeny tiny water droplets whose radii are 20 microns or less

## Observing Clouds from Spage

- Polar orbiting satellite
- Geosta­tionary satellite
- Infrared imagery provides extra detail
- Darker shades of grey indicate warm clouds, thus low altitude
- Brighter grays and whites indicate cold clouds thus high altitude

## Water Vapor Imagery

- Shows air motions (wind) even in cloud-free areas
- Detects water vapor at the 6.9µm wavelength
- Colorized to differ­entiate between dry and moist air

## Two Main Types of Nuclei

- Conden­sation Nuclei
- Hygros­copic (water­-se­eking) nuclei
- Most effective conden­sation nuclei
- Salt crystals are the best
- Only RH ~75% required
- Hydrop­hobic (water­-re­pel­ling) nuclei
- Least effective conden­satioin nuclei
- Waxes and oil droplets discourage but do not totally prevent conden­sation
- RH must be 100% or even tempor­arily higher