Weather and Weather and the the

AtmosphereAtmosphere

NSAP Short NSAP Short Course for SEs Course for SEs

and SAsand SAs

About the courseAbout the course

• Selected topics and lectures from Selected topics and lectures from a CU course – ATOC 1050 (45, 50-a CU course – ATOC 1050 (45, 50-min. classes).min. classes).

• Because of varied backgrounds – Because of varied backgrounds – no significant memory of calculus no significant memory of calculus or differential equations is or differential equations is assumedassumed

• Please interrupt with short questions Please interrupt with short questions when necessary.when necessary.

• Course content goes beyond what is Course content goes beyond what is applicable for any individual RAL applicable for any individual RAL project, but most is related to some project, but most is related to some project.project.

• Terminology is important as well as Terminology is important as well as concepts.concepts.

• Course web site with notes at Course web site with notes at

http://www.rap.ucar.edu/general/http://www.rap.ucar.edu/general/events.htmlevents.html

ContentContent

• Part 1 – Composition, mean structure, Part 1 – Composition, mean structure, variables, diurnal and annual cyclesvariables, diurnal and annual cycles

• Part 2 – Water in the atmosphere, cloud and Part 2 – Water in the atmosphere, cloud and precip formationprecip formation

• Part 3 – Winds and their cause; air-masses, Part 3 – Winds and their cause; air-masses, fronts and cyclonesfronts and cyclones

• Part 4 – Mesoscale processes, severe Part 4 – Mesoscale processes, severe weatherweather

SESSION 1

SESSION 2

Part 1Part 1Composition of the Composition of the

AtmosphereAtmosphere

The atmosphere – A molecular The atmosphere – A molecular cocktailcocktail

COMPOSITION OF THE COMPOSITION OF THE ATMOSPHEREATMOSPHERE

NEAR EARTH’S SURFACE NEAR EARTH’S SURFACE

““Permanent” gases (percent is about the same Permanent” gases (percent is about the same everywhere)everywhere)

• Nitrogen – 78 %Nitrogen – 78 %

• Oxygen – 21 %Oxygen – 21 %

• Hydrogen - .00006 %Hydrogen - .00006 %

• Others (less than 1 %) – ozone, methane, helium, Others (less than 1 %) – ozone, methane, helium, etc.etc.

Variable gases (amount depends on place and Variable gases (amount depends on place and time)time)

• Water vapor – 0-4 %Water vapor – 0-4 %

• Carbon dioxide – about .037 %Carbon dioxide – about .037 %

Water vapor – dark-dry, light-Water vapor – dark-dry, light-humidhumid

COCO22 varies with time varies with time Upward trend from 1958-2000, plus Upward trend from 1958-2000, plus

seasonal variationalseasonal variational

Not zero

Content of the atmosphere Content of the atmosphere in addition to gasesin addition to gases

•Mineral particlesMineral particles – dust from – dust from ground, man-made pollutionground, man-made pollution

•Water dropletsWater droplets – clouds, fog – clouds, fog

•Water dropsWater drops – rain – rain

• IceIce – small crystals, snow flakes, – small crystals, snow flakes, hailhail

Structure of the Structure of the atmosphereatmosphere

• Varies depending on the Varies depending on the meteorological conditionsmeteorological conditions

• But we can talk about average But we can talk about average conditionsconditions

- horizontal structure (as shown on a - horizontal structure (as shown on a weather map)weather map)

- - vertical structurevertical structure

Vertical structure of the Vertical structure of the atmosphereatmosphere

• First – how deep is it?First – how deep is it?

Earth

White line is the thickness of the

atmosphere (99% of molecules)

Within this thin Within this thin atmosphere, there are atmosphere, there are

different ways of defining different ways of defining layers layers

• How temperature changes with height How temperature changes with height (increase versus decrease with height)(increase versus decrease with height)

• Composition (mixture of gases)Composition (mixture of gases)• Electrical structureElectrical structure• Turbulence intensityTurbulence intensity

Different Layers of the Different Layers of the AtmosphereAtmosphere

Planetary boundary

layer – more later

A Glossary of Weather A Glossary of Weather VariablesVariables

• Air temperatureAir temperature

• Air pressureAir pressure

• Humidity – amount of water vaporHumidity – amount of water vapor

• CloudsClouds

• Precipitation – rate, type, distributionPrecipitation – rate, type, distribution

• Wind – direction and speed, Wind – direction and speed, turbulence intensityturbulence intensity

• VisibilityVisibility

Air TemperatureAir Temperature

TemperatureTemperature• Related to rate of motion of molecules: The Related to rate of motion of molecules: The

warmer the air, the more rapidly the warmer the air, the more rapidly the molecules move.molecules move.

• Primary temperature scalesPrimary temperature scales– Fahrenheit (F): freezing point of water = 32 F, Fahrenheit (F): freezing point of water = 32 F,

boiling point = 212 Fboiling point = 212 F– Celsius (C): freezing = 0 C, boiling =100 CCelsius (C): freezing = 0 C, boiling =100 C– Absolute (A) or Kelvin (K): absolute zero = 0 A = Absolute (A) or Kelvin (K): absolute zero = 0 A =

-273 C (all molecular motion stops) -273 C (all molecular motion stops)

• Temperature observations near the surface Temperature observations near the surface (2 m) are reported in degrees F, and above (2 m) are reported in degrees F, and above that are reported in degrees C.that are reported in degrees C.

Vertical Temperature Vertical Temperature Structure Structure

of the of the AtmosphereAtmosphere

Commercial Aircraft

All the Weather

Denver temperature profile at 5:00 Denver temperature profile at 5:00 AM 28 Feb 03AM 28 Feb 03

Tropopause

Troposphere

Stratosphere

Up

Tem

p

Dry adiabatic lapse rate reference

lines

Air PressureAir Pressure

Why do we care about Why do we care about pressure?pressure?

Air Pressure - DefinitionAir Pressure - Definition

• Pressure = force/area (e.g., pounds Pressure = force/area (e.g., pounds per square inch)per square inch)

1) Hydrostatic pressure – weight of 1) Hydrostatic pressure – weight of the atmosphere above the surfacethe atmosphere above the surface

2) Dynamic pressure – force of the 2) Dynamic pressure – force of the wind (e.g., against a door)wind (e.g., against a door)

Air Pressure - UnitsAir Pressure - Units

• In this course, pressure is expressed in In this course, pressure is expressed in millibars (mb) – average sea-level pressure millibars (mb) – average sea-level pressure = 1013 mb= 1013 mb

• In the science literature, it is expresses in In the science literature, it is expresses in hecta Pascals (hPa = 1 mb)hecta Pascals (hPa = 1 mb)

• Sometimes (e.g., in public weather Sometimes (e.g., in public weather forecasts) it is given in inches of mercury – forecasts) it is given in inches of mercury – average = 29.92 in. mercuryaverage = 29.92 in. mercury

• Surface pressure values are “adjusted” to Surface pressure values are “adjusted” to sea level, so that values show high and low sea level, so that values show high and low pressure patterns rather than the elevation pressure patterns rather than the elevation of the observation of the observation

How is sea-level pressure How is sea-level pressure estimated for plotting on weather estimated for plotting on weather

maps?maps?

Vertical Pressure Variation in the Vertical Pressure Variation in the AtmosphereAtmosphere

Air DensityAir Density

• General definition of density - Mass General definition of density - Mass per unit volume per unit volume

• Air density – Mass (e.g., kilograms) of Air density – Mass (e.g., kilograms) of air molecules per unit volume (cubic air molecules per unit volume (cubic meter)meter)

********************************************

* * * * * * * * * * * * * * * * * * * *

More dense

Less Dense

Density Variation With HeightDensity Variation With Height

HumidityHumidity

• A measure of the amount of water vapor in A measure of the amount of water vapor in the airthe air

• There are many different measures of There are many different measures of humidityhumidity– Relative humidityRelative humidity– Vapor pressureVapor pressure– Dew point temperatureDew point temperature– Specific humiditySpecific humidity– Absolute humidityAbsolute humidity

CloudsClouds

• Percent of sky covered by cloudsPercent of sky covered by clouds

• Types of cloudsTypes of clouds– CumulusCumulus– CirrusCirrus– Stratus, etc.Stratus, etc.

WindWind

• Speed – miles per hour or knots (nautical Speed – miles per hour or knots (nautical miles per hour), meters per secondmiles per hour), meters per second

• Direction - Given in terms of the direction Direction - Given in terms of the direction from whichfrom which the wind is blowing. A the wind is blowing. A northwesterly wind is blowing from the northwesterly wind is blowing from the northwest.northwest.

• Gustiness – turbulent component of windGustiness – turbulent component of wind

• Horizontal wind is measured, but vertical Horizontal wind is measured, but vertical wind is also very importantwind is also very important

Turbulence near the groundTurbulence near the ground

VisibilityVisibility

• The maximum distance at which an The maximum distance at which an observer can distinguish an object observer can distinguish an object against the sky as a backgroundagainst the sky as a background

• May be limited by fog, air pollution, May be limited by fog, air pollution, etc.etc.

PrecipitationPrecipitation

•Type of precipitationType of precipitation

- rain, snow, sleet, hail, etc.- rain, snow, sleet, hail, etc.

•Rate at which it is falling Rate at which it is falling (inches/hour)(inches/hour)

Scales of atmospheric motion -Scales of atmospheric motion -Storms of all sizesStorms of all sizes

• Mid-latitude cyclones – 1000+ mileMid-latitude cyclones – 1000+ mile

• Hurricanes – 500+ milesHurricanes – 500+ miles

• Thunderstorms – 1-100 milesThunderstorms – 1-100 miles

• Tornadoes – few hundred yardsTornadoes – few hundred yards

• Turbulence – centimeters-metersTurbulence – centimeters-meters

Measuring the Measuring the atmosphereatmosphere

• Weather balloons, or radiosondes Weather balloons, or radiosondes make “upper-air” measurements of make “upper-air” measurements of horizontal wind, temperature and horizontal wind, temperature and humidity.humidity.

Radiosonde Radiosonde ––helium helium balloon withballoon withmeasurememeasurement nt instrumentsinstruments

Measuring the Measuring the atmosphereatmosphere

• Weather balloons, or radiosondes Weather balloons, or radiosondes make “upper-air” measurements of make “upper-air” measurements of horizontal wind, temperature and horizontal wind, temperature and humidity.humidity.

• Surface weather stations (land and Surface weather stations (land and seas) measure horizontal wind, seas) measure horizontal wind, temperature, humidity, cloud covertemperature, humidity, cloud cover

• Satellites can estimate winds, Satellites can estimate winds, temperature and humiditytemperature and humidity

Radiosonde launch Radiosonde launch locationslocations

““Surface” observations - NWSSurface” observations - NWS

Zooming in to see even Zooming in to see even moremore

Northern Utah

Other data sourcesOther data sources

• Cloud-track windsCloud-track winds

• Water-vapor-track windsWater-vapor-track winds

• NEXRAD radar winds and reflectivityNEXRAD radar winds and reflectivity

• Doppler lidar windsDoppler lidar winds

• Wind profilersWind profilers

• Commercial aircraft – TAMDAR, Commercial aircraft – TAMDAR, AMDARAMDAR

The Planetary Boundary Layer – The Planetary Boundary Layer – more later, but here’s a previewmore later, but here’s a preview

• BL - the region of the troposphere BL - the region of the troposphere immediately above Earth’s surface where immediately above Earth’s surface where vertical turbulent transfers of heat, vertical turbulent transfers of heat, moisture and momentum are large moisture and momentum are large compared to the troposphere above.compared to the troposphere above.

• Daytime temperature lapse rate is nearly Daytime temperature lapse rate is nearly dry adiabatic, or neutral (9.8 C/km).dry adiabatic, or neutral (9.8 C/km).

• Nighttime temperature lapse rate is Nighttime temperature lapse rate is typically stable (inversion).typically stable (inversion).

Why care about boundary Why care about boundary layerslayers• We live there.We live there.• Transport and diffusion of plumes takes Transport and diffusion of plumes takes

place primarily in the boundary layer.place primarily in the boundary layer.• Some of our meteorological conditions at Some of our meteorological conditions at

the surface originate higher in the the surface originate higher in the troposphere (precip, large scale T changes, troposphere (precip, large scale T changes, etc.), but many develop within the BL.etc.), but many develop within the BL.– Air pollution (public health) –most originates at Air pollution (public health) –most originates at

surface and stays within BLsurface and stays within BL– Diurnal temperature fluctuationsDiurnal temperature fluctuations– Mesoscale wind circulationsMesoscale wind circulations

Jaxonville, Jaxonville, Florida Florida soundingsounding

7 PM local7 PM local

1.5 km

JaxonvilleJaxonville, Florida , Florida soundingsounding

7 AM 7 AM locallocal

Part 2Part 2Warming Earth and its Warming Earth and its

Atmosphere – The Atmosphere – The Diurnal and Seasonal Diurnal and Seasonal

CyclesCycles

Or, what happens to the Or, what happens to the energy received from the energy received from the

sun?sun?

First – We Need to Understand First – We Need to Understand The Ways in Which Heat Can The Ways in Which Heat Can

be Transferred in the be Transferred in the AtmosphereAtmosphere

•ConvectionConvection

•Latent heat Latent heat

•ConductionConduction

•AdvectionAdvection

•RadiationRadiation

1. Convection1. Convection

Heat transfer in the vertical Heat transfer in the vertical through buoyant motionthrough buoyant motion

Atmospheric convectionAtmospheric convection

Cumulus Cloud

Upward Heat

Transfer

2. Latent heat – the 2. Latent heat – the conceptconcept

Personal Experiences – Personal Experiences – Latent Heat Latent Heat ConsumptionConsumption by by

EvaporationEvaporation

• Chill stepping out of a shower – Chill stepping out of a shower – evaporation consumes heatevaporation consumes heat

• Use of “swamp coolers” instead of air Use of “swamp coolers” instead of air conditioners in dry climatesconditioners in dry climates

• It is cooler over green grass than over a It is cooler over green grass than over a stone surface – evaporation from leavesstone surface – evaporation from leaves

• Cool breeze with thunderstorms in Cool breeze with thunderstorms in vicinity – evaporation of rain below the vicinity – evaporation of rain below the cloud cloud

Personal Experiences – Personal Experiences – Latent Heat Latent Heat ReleaseRelease by by

Condensation or FreezingCondensation or Freezing

• Spraying fruit trees with water when Spraying fruit trees with water when frost damage is possible – freezing of frost damage is possible – freezing of water releases heatwater releases heat

• The “bubbly” appearance of cumulus The “bubbly” appearance of cumulus clouds – released latent heat in cloud clouds – released latent heat in cloud makes them buoyantmakes them buoyant

The Transport of Latent The Transport of Latent HeatHeat

Evaporation – Heat Taken From Ocean

**********

Water Vapor

Air Moves

Condensation

Vapor to Cloud

Droplets

Heat Released

In Cloud

• Transfer of heat from molecule to Transfer of heat from molecule to moleculemolecule

• Think of heat in terms of how fast the Think of heat in terms of how fast the molecules are movingmolecules are moving

• Fast moving molecules where something Fast moving molecules where something is hot collide with adjacent slow moving is hot collide with adjacent slow moving molecules where it is cooler, causing the molecules where it is cooler, causing the slower molecules to speed (heat) up.slower molecules to speed (heat) up.

3. Conduction3. Conduction

Heat conductivity – ability Heat conductivity – ability of material to conduct heatof material to conduct heat

• Air - Air - .02 (Watts per meter .02 (Watts per meter per per ooC) C)

• Wood - Wood - .08.08

• Water - Water - .60.60

• Wet soil -Wet soil - 2.12.1

• Stone - Stone - 2.72.7

• Iron -Iron - 80. 80.

Thus, Air is a Poor Thus, Air is a Poor ConductorConductor of Heat of Heat

(ever think about why (ever think about why thermopane windows thermopane windows

work?)work?)

4. Advection4. Advection

Warm air

Cold air

Wind direction

X

YOU ARE HERE (Temperature will increase)

5. Radiation5. Radiation

• electromagneticelectromagnetic radiation radiation

• Different names are used for different Different names are used for different wavelengths of electromagnetic wavelengths of electromagnetic radiation.radiation.

Everything with a TemperatureEverything with a Temperatureabove absolute zero emits EMRabove absolute zero emits EMR

Intensity of Light Versus Intensity of Light Versus WavelengthWavelength

(µm)(µm)

Temperature of the sun = 6000° K (10,500° F)

The Sun’s Emission Spectrum The Sun’s Emission Spectrum Versus Earth’sVersus Earth’s

What Interferes with What Interferes with Transmission of Light Transmission of Light

Through the Through the Atmosphere?Atmosphere?

• Some gases – called optically active Some gases – called optically active gases. Different gases absorb different gases. Different gases absorb different wavelengthswavelengths

• Particles of dust – natural and man-madeParticles of dust – natural and man-made

• Clouds and fogClouds and fog

Now That We Know How Now That We Know How Heat is Transferred in the Heat is Transferred in the

Atmosphere!Atmosphere!--------------------------------------------

Putting it All TogetherPutting it All Together

The Atmospheric Energy Checkbook – The Atmospheric Energy Checkbook – Balance Gains and Losses (On the Average)Balance Gains and Losses (On the Average)

Putting the Balance Under a Putting the Balance Under a MicroscopeMicroscope

Ground

Conduction in lowest millimeter

Convection

How the Warm GroundHow the Warm GroundHeats the Air In Contact With Heats the Air In Contact With

ItIt

The Diurnal and The Diurnal and SeasonalSeasonal

Cycles of Heating – Cycles of Heating –

Exist Because of the Exist Because of the Earth-Sun Geometry Earth-Sun Geometry

The CyclesThe Cycles

• DiurnalDiurnal – Rotation of Earth on – Rotation of Earth on axis every 24 haxis every 24 h

• AnnualAnnual or seasonal – Revolution or seasonal – Revolution of Earth around the sun every of Earth around the sun every 365.25 days365.25 days

Equinoxes: Points in Earth’s orbit around the sun where the sun is directly over the equator (12 hrs light & 12 hrs of darkness).Solstice: Points in orbit where the sun is “displaced” farthest N or S.

Seasonal CycleSeasonal Cycle -Causes--Causes-

• The sun heats the ground less The sun heats the ground less intensely when it is at a low angle intensely when it is at a low angle in the sky (winter), and more in the sky (winter), and more intensely when it is at a high angle intensely when it is at a high angle above the horizon (summer).above the horizon (summer).

• The suns heat the ground less The suns heat the ground less when the daylight is shorter when the daylight is shorter (winter), etc.(winter), etc.

Factors That Cause Factors That Cause TemperatureTemperature

Variation From Place to PlaceVariation From Place to Place

•Latitude – warmer to southLatitude – warmer to south•Land and water distribution Land and water distribution

winter winter → warmer near water→ warmer near watersummersummer → cooler near water→ cooler near water

•Ocean currents Ocean currents Warm currents generally on east side of Warm currents generally on east side of continents, cold currents on the west continents, cold currents on the west sideside

•Elevation of the surface above sea Elevation of the surface above sea levellevel

Temperature decreases with elevationTemperature decreases with elevation

• Surface type – e.g., urban Surface type – e.g., urban versus ruralversus rural

• Surface wetnessSurface wetness

Warmer to South - More

Radiation

Warmer Over Ocean in Winter

Cooler of Higher Elev.

Two cities Two cities with the with the same mean same mean annual annual temperaturtemperature but with e but with very very different different climatesclimates

Daily Temperature CycleDaily Temperature Cycle

Balance of Incoming Solar Balance of Incoming Solar and Outgoing Infraredand Outgoing Infrared

Max

Temperature Profile Near The Ground

profile

Note: Temperatures almost always decrease with height

DAY

Inversion: Temperatures increase with height

NIGHT

FROST

What Can Effect The Day- What Can Effect The Day- Night Temperature Night Temperature

Change? Change? • Cloud cover reduces diurnal Cloud cover reduces diurnal

variabilityvariability

• Terrain: surface type, mountains, Terrain: surface type, mountains, canyons,…canyons,…

• Wind: causes turbulent mixing of the Wind: causes turbulent mixing of the atmosphere which reduces diurnal atmosphere which reduces diurnal variabilityvariability

• Approaching weather systems: cold Approaching weather systems: cold fronts, warm fronts, squall lines, fronts, warm fronts, squall lines, hurricaneshurricanes

• HumidityHumidity

Topographic Effects on Topographic Effects on Nighttime TemperatureNighttime Temperature

Cold air pooling