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Weather and Climate. Welcome to. Fall Semester 2008 26 August – 16 December. Here’s a Course syllabus. Midterm exam – on Tuesday October 14th Final exam – on Tuesday December 16th Quizzes weekly on Blackboard BEFORE class Homework more than monthly In-class participation and quiz “weekly”

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weather and climate

Weather and Climate

Welcome to

Fall Semester 2008

26 August – 16 December

here s a course syllabus
Here’s a Course syllabus
  • Midterm exam – on Tuesday October 14th
  • Final exam – on Tuesday December 16th
  • Quizzes weekly on Blackboard BEFORE class
  • Homework more than monthly
  • In-class participation and quiz “weekly”
  • For details: See --

The syllabus is a living document, so it changes week to week -- bookmark and check it often! You can also access the syllabus through blackboard

5 of your grade talking about weather
5% of your grade: Talking about weather!
  • This semester, I’ll try something new:
    • Bring in a newspaper clipping to class that discusses some weather-related news event
    • Or, send me the url to an on-line news story.
      • Examples:
        • The fog-related multi-vehicle crash on I-90 in early January
        • The tornado in Kenosha last January 7th
    • Answer any questions live and in person before the rest of the class (I will help you with the answers if the questions are hard)
      • Goals:
        • Make sure you’ve read and understood the news article
        • Make sure you’re comfortable talking about weather
most important things
Most Important Things:
  • Talk to your professors if something in your life is interfering with class work -- almost any professor will be accommodating if they know things before they happen
    • Especially if you will be missing an exam!!
  • Do you work? Talk to your boss(es) and let them know of your commitment to the class time.
  • >>> SHOW UP TO CLASS!! <<<
  • If you don’t understand something, ASK!
    • During class -- makes for a much more interesting class
    • After class
    • via email
some nice blogs on weather look at these daily
Some nice blogs on weather:Look at these daily!
    • Focus is mainly on satellite data and weather phenomena
    • Links to blogs by different forecasters at this well-known forecasting company
  • If you know of others that you like, please let me know!
    • Focus is mainly Chicago and weather in the midwest, and notable weather elsewhere

What is “weather”?

The state of the atmosphere at any particular time and place.

  • Weather “always” changes.
  • Weather in Madison today different than yesterday

Define weather by observing & measuring :

Dew Point Temperature (moisture)

Air Temperature

Air Pressure






weather examples
Weather Examples:
  • The weather in Wisconsin last winter was snowy! ( ~100” at Madison and Milwaukee )
  • Madison had little rain in August, but lots lots lots in June
  • Tropical Storm Fay moved along the Gulf Coast in August

What is “climate”?

The accumulation of daily and seasonal weather events over a long period of time.

  • 30-year averages are the standard for climatic records.
  • Climate data include averages and extremes.
  • Madison’s climate today and yesterday are very similar
climate examples
Climate Examples:

Note how ‘usually’ can fit into these statements!

  • The warmest day in Madison, on average, is July 20th (Normal High: 83o F, Normal Low: 61o F) [It’s all downhill from there!!]
  • San Diego receives most of its rain in winter
  • Buffalo, NY is typically cloudy in winter
  • Hurricanes are most common in September
  • Wisconsin usually has its coldest days in mid-January
when is climate knowledge important
When is climate knowledge important?
  • When you’re planning a vacation
    • What if the climate says May is rainy? Do you want to go somewhere like that in that month?
    • Caribbean vacation in April or September?
  • When you’re insuring against a weather event, like snow on New Year’s Eve
  • When you’re planning a reception outside
    • What time is rain most likely?
    • Will the sun be in your eyes in the photographs?

Weather or Climate?

  • A hurricane is hitting Louisiana.
  • Albuquerque, NM averages 0.4” of precipitation in January.
  • Yesterday’s high temperature was 77o F.
  • It is raining at a rate of 0.5” an hour.
  • The warmest weather in Madison, WI is in July.
  • Hurricanes hit Florida in September.
  • The record low temperature for Madison, WI is -37oF, on January 30, 1951.






what does the earth have that allows it to have weather and climate
What does the Earth have that allows it to have Weather and Climate?
  • Unevenly-heated atmosphere
    • Gases move so that temperature equilibrates
  • An atmosphere at the right temperature
    • The Earth-Sun distance and the temperature of the Sun are such that water can exist in 3 states in the atmosphere/biosphere/lithosphere/ hydrosphere
what drives weather climate
What Drives Weather/Climate?
  • Almost all energy comes from the Sun
  • Energy Exchanges at the Surface of Earth
    • LAND
    • WATER
what s the big difference between hemispheres
What’s the big difference between Hemispheres?

What are the consequences of those differences?

what are the consequences of those differences
What are the consequences of those differences?
  • More land in NH: It changes temperature quickly
  • More water in SH: It changes temperature slowly
  • Antarctica is pretty symmetric, and high
  • Lots of High-latitude land in NH can get covered with snow
what keeps the atmosphere surrounding the earth
What keeps the atmosphere surrounding the Earth?


Heaviest gases are retained on Earth most easily -- lightest gases are most likely to escape to Space

why aren t the heaviest gases at the bottom of the atmosphere
Why aren’t the heaviest gases at the bottom of the atmosphere?


Winds stir the atmosphere

No gaseous molecule is so heavy that it can’t be moved by the wind!

Atmosphere: The gaseous envelope that surrounds the Earth

Biosphere: All the plant and animal life on the Earth

Hydrosphere: Parts of the Earth system that include water: Rivers, lakes, oceans, clouds, rain

Lithosphere: The solid Earth


Each ‘sphere’ influences and is influenced

by each of the other ‘spheres’

Influence can be on very different timescales

To model climate, must model each of the spheres correctly


If Earth was the size of a beachball, how thick would the atmosphere be?

Thinner than a piece of paper!


Why is the atmosphere important?

Without our atmosphere, earth would be like the moon...........





can you read a book in a shadow on the moon
Can you read a book in a shadow on the Moon?
  • Where does the light illuminating the paper come from when the page is in a shadow?
  • Scattering, Reflection, Refraction and Diffraction can all change the direction of a light beam. All require a medium or a surface that the atmosphere provides
  • No atmosphere on the moon, shadow is black (but there is scattering from the surface)
two things heat the surface of the earth
Two things heat the surface of the Earth:
  • THE SUN -- if only the Sun were heating, the temperature on the Earth would be -18 oC (O oF)
  • THE ATMOSPHERE -- the atmosphere has a finite temperature, so it too emits radiation that warms the Earth (this is the ‘Greenhouse effect’). It warms the Earth an addition 33 oC, so the average surface temperature is 15 oC (59 oF)

Everything with a finite temperature emits

radiation, and that radiation transfers energy

greenhouse effect on other planets
Greenhouse Effect on other planets:
  • Venus -- 97% of atmosphere is CO2; the surface temperature on Venus is about 500 C warmer than it would be without the Greenhouse effect there. Surface pressure is 90x that on Earth
  • Mars -- 95% of atmosphere is CO2; the surface temperature on Mars is about 10 C warmer than it would be without any Greenhouse effect there. Surface pressure is about 1% of that on Earth
some constituents of our atmosphere are remarkably constant
Some constituents of our atmosphere are remarkably constant:
  • Nitrogen (N2) : 78% of the atmosphere
  • Oxygen (O2) : 21% of the atmosphere
  • Argon (Ar) : 1% of the atmosphere

(This is something that is always asked about on exams in this class)

some constituents of our atmosphere vary
Some constituents of our atmosphere vary:
  • Water Vapor (H2O) : 0-4% of the atmosphere
  • Carbon Dioxide (CO2) : < .1% of the atmosphere (almost 400 parts per million)
  • Ozone (O3) and Methane (CH4) : < .001% of the atmosphere (a few parts per million)

All the ozone in one layer at the surface would be 1/4 inch thick!

variability of gases caused by cycling
Variability of gases caused by cycling:
  • Carbon Dioxide (CO2) increasing as fossil fuels burn
  • Also an annual cycle as plants grow (remove CO2) and decompose (add CO2)
variability of gases caused by cycling31
Variability of gases caused by cycling:

CO2 is also stored in the ocean -- you can dissolve more in cold water than warm water (Does warm or cold Pepsi lose fizz faster?)

Volcanoes emit CO2

Plants store CO2 in their biomass -- burning releases CO2

Isotherm -- line of equal temperature

Isobar -- line of equal pressure

Isovort -- line of equal wind speed

Isodrosotherm -- line of equal dewpoint

Contour the map you’ve been given, following the instructions on the board

We’ll discuss results in 5 minutes. Work with a neighbor if you want.

hydrologic cycle

Some vapor condenses into clouds, and then falls as precipitation

Hydrologic Cycle

Wind transports water vapor to other regions

Water evaporates back into vapor

Precipitation lands on ground and in water ways.

Water evaporates from oceans

Water runs off land into oceans

hydrologic cycle34
Hydrologic Cycle

Precipitation lands on ground and in water ways.

Some vapor condenses into clouds, and then falls as precipitation

Water evaporates back into vapor

Wind transports water vapor to other regions

Water runs off land into oceans

Water evaporates from oceans


Hydrologic Cycle (Frozen)

Precipitation lands on Polar Ice Cap.

Some vapor condenses into clouds, and then falls as precipitation (Snow!)

Ice/Snow sublimates into the air

Wind transports water vapor to other regions

Ice flows off the polar plateaus, onto the ice shelves, melts into oceans or Icebergs calve and melt into the oceans.

Water evaporates from oceans

if there s a lot of vapor in the atmosphere
If there’s a lot of vapor in the atmosphere….
  • Density decreases
    • Moist air is less dense than cold air!
  • Efficiency of evaporative cooling drops
    • So it feels a lot hotter
  • Where does the vapor come from?
    • Evaporation of water from surface
    • Evapotranspiration from growing plants
weight of dry air
Weight of Dry Air
  • Oxygen (O2) -- 21% of atmosphere
    • Molecular weight = 32, 32 x .21 ~ 6.72
  • Nitrogen (N2) -- 78% of atmosphere
    • Molecular weight = 28, 28 x .78 ~ 21.84
  • Dry air
    • Molecular weight ~ 21.84 + 6.72 = 28.56
weight of moist air
Weight of Moist Air
  • Water Vapor (H2O), 4% of atmosphere
    • Molecular weight = 18, 18 x .04 ~ .72
  • Dry Air
    • Molecular weight = 28.56, 96% of atmosphere
    • 28.56 x .96 ~ 27.417
  • Moist Air
    • Molecular weight : 27.417 + .72 = 28.138

Moist air weighs less!!!!

how has the atmosphere changed
How has the atmosphere changed?
  • First atmosphere mostly hydrogen (H2), helium (He), methane (CH4), ammonia (NH3). Many of these light gases escaped the gravitational pull of Earth to space.
  • Second atmosphere originated from volcanic eruptions: Carbon Dioxide (CO2), water vapor (H20), Nitrogen (N2) -- these are the gases in present-day eruptions too!
    • As the Earth cooled, water vapor condensed out into liquid
how has the atmosphere changed41
How has the atmosphere changed?
  • Third atmosphere :
    • as vapor condenses, proportionate amount of Nitrogen (N2) increases.
    • Photo-dissociation of water (H20) split into Hydrogen atoms, that escape, and Oxygen (O2).
  • Most of the oxygen in the atmosphere today probably came from plants (through photosynthesis), which also removes CO2
  • Photo-dissociation is self-limiting because O2 will eventually form ozone (O3) that absorbs high energy rays.
how does earth s atmosphere differ from other planets
How does Earth’s atmosphere differ from other planets?

Venus should really have 90x the number of jellybeans of Earth, and Mars should have only 1/2 a jellybean!

definition lapse rate
Definition: Lapse Rate
  • How does the temperature change with height? If it decreases -- which is normal near the Earth’s surface (think snow-capped mountains) -- the lapse rate is positive.
  • In parts of the atmosphere, the lapse rate is negative: temperature increases with height! This is a temperature inversion
there are 4 layers in the atmosphere that are defined by lapse rate
There are 4 layers in the atmosphere that are defined by Lapse Rate
  • From the bottom up:
    • Troposphere (Lapse Rate usually positive)
      • Where we live
    • Stratosphere (Lapse Rate negative)
      • Ozone is in the stratosphere and causes warming
    • Mesosphere (Lapse Rate positive)
    • Thermosphere (Lapse Rate negative)

(This is something that is always asked about on exams in this class)


T at top depends

on solar activity

Space Shuttle (250km)




.01 mb




1 mb



200 mb


1000 mb

pressure measurements
Pressure measurements
  • Height of mercury: 29.92” or 760 mm
      • [33.9 feet of water!!]
  • 14.7 pounds/square inch
  • millibars (mb) or hectopascals (hPa)
    • Normal sea level pressure : 1013.26 mb
    • 870-1084 mb is the range of surface pressures
    • Wilma dropped to 882 mb last year, lowest in Atlantic Basin
changes with height
Changes with height
  • Density and pressure always decrease with height
  • The change is exponential
  • Pressure falls off more rapidly with height in colder air than in warmer air. [Why? Related to molecular motion changes as temperatures change]
halfway up in the atmosphere
Halfway up in the atmosphere
  • Half the atmosphere is below about 5.5 km (this varies with temperature)
  • What is the pressure 5.5 km up?
    • Sea level pressure: 1013.26 / 29.92 “ / 14.7 pounds
      • halfway up
        • ~500 mb,
        • ~14.96” of Hg
        • ~7.35 pounds/in2
other useful levels in the atmosphere for forecasting
Other useful levels in the atmosphere for forecasting
  • 850 mb: good for low-level moisture [about 1.5 km above the surface]
  • 700 mb: mid-level dry air [about 3 km above the surface]
  • 300 mb: upper level jet stream [about 9-10 km above the surface]
how do you observe the upper levels
How do you observe the upper levels?
  • Launch a radiosonde, which is a package of instruments attached to a balloon. Observations are radioed back to the surface.
  • This is done 2x a day at >100 stations in the USA, >1000 stations around the world
temperature scales
Temperature Scales
  • Daniel Gabriel Fahrenheit [1686-1736]
    • First Mercury-in-glass thermometer
    • Top of scale: body temperature [90 oF]
    • Bottom of scale: coldest temperature with water/salt [0 oF]
    • Melting point of ice: [30 oF] (later revised to 32o)
  • 32 oF is the melting point of water, 212 oF is the boiling point of water at sea level
  • Surface temperatures in the USA are in oF
temperature scales52
Temperature Scales
  • Anders Celsius [1701-1744]
    • Boiling Point of water at sea level: 0 oC
    • Melting Point of water: 100 oC
    • 100 steps between melting and boiling, so the scale is a centigrade scale
  • The scale was flipped after Celsius’ death
  • Upper-level temperatures are always given in oC
  • Surface temperatures in the world (except the USA) are in oC
how to convert temperatures
If you have the Fahrenheit temperature and want Celsius:

oC = 5/9 x ( oF - 32 )

It’s 50o F -- what’s the Celsius temperature?

oC = 5/9x(50-32)

oC = 5/9*18

oC = 10

What is normal body temperature in oC?

oC = 5/9x(98.6-32)

oC = 5/9x(66.6)

oC = 37

If you have the Celsius temperature and want Fahrenheit:

oF = 9/5 oC + 32

It’s 20o C -- what is oF?

oF = (9/5)*[20] + 32

oF = 36 + 32

oF = 68

It’s -20o C -- what is oF?

oF = (9/5)*[-20] + 32

oF = -36 + 32

oF = -4

How to convert temperatures
temperature conversions continued
Temperature Conversions, continued
  • A Celsius increment is larger than a Fahrenheit increment. 1 Celsius degree is 1.8 Fahrenheit degrees
  • When the Celsius temperature increases by 10, Fahrenheit goes up by 18

32o F = 0o C, so 10o C is 32o F + 18o F = 50o F

temperature conversions continued55
Temperature Conversions, continued
  • To convert Celsius to Fahrenheit: Add 40, multiply by 1.8, subtract 40
  • To convert Fahrenheit to Celsius: Add 40, divide by 1.8, subtract 40

Because Celsius degrees are

larger than Fahrenheit degrees

Because Fahrenheit degrees

are smaller than Celsius degrees

development of meteorological instrumentation
Development of meteorological instrumentation
  • Make observations more accurate!
    • Thermometer: Galileo, 1500s, to measure Temperature
    • Barometer: Toricelli, 1643, to measure Pressure
    • Anemometer: Hooke, 1667, to measure winds
    • Hygrometer: de Saussure, 1780, to measure humidity
    • Weather Satellite: Suomi/Plant, 1960, to measure radiance from Space and to observe the entire globe at once
other important inventions
Other important inventions
  • Telegraph: add ability to see many observations near the time they were taken
  • Computer: use computational ability to simulate motions in the atmosphere
  • Radar: (Radio detection and ranging) used to observe rain/snow in storms
radar image examples
Radar imageexamples

Radar Dome at

NWS office

First hook echo on radar related to tornado

radar images today are colorful
Radar images today are colorful!

Precipitation intensity

Horizontal winds