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Weather and Climate

Weather and Climate

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Weather and Climate

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  1. Weather and Climate Welcome to Fall Semester 2008 26 August – 16 December

  2. 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 http://matcmadison.edu/faculty/slindstrom/syllabus.html -- 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

  3. 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

  4. 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

  5. Some nice blogs on weather:Look at these daily! • http://cimss.ssec.wisc.edu/goes/blog • Focus is mainly on satellite data and weather phenomena • http://www.accuweather.com • Links to blogs by different forecasters at this well-known forecasting company • If you know of others that you like, please let me know! • http://blogs.trb.com/news/weather/weblog/wgnweather/ • Focus is mainly Chicago and weather in the midwest, and notable weather elsewhere

  6. What is “weather”? The state of the atmosphere at any particular time and place. • Weather “always” changes. • Weather in Madison today different than yesterday

  7. Define weather by observing & measuring : Dew Point Temperature (moisture) Air Temperature Air Pressure Clouds Wind Visibility Precipitation Precipitation

  8. 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

  9. Interesting Weather from last August

  10. Interesting Weather from August

  11. 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

  12. 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

  13. 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?

  14. 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. weather climate weather weather climate

  15. 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

  16. What Drives Weather/Climate? • Almost all energy comes from the Sun • Energy Exchanges at the Surface of Earth • LAND • WATER

  17. What’s the big difference between Hemispheres? What are the consequences of those differences?

  18. 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

  19. What keeps the atmosphere surrounding the Earth? GRAVITY Heaviest gases are retained on Earth most easily -- lightest gases are most likely to escape to Space

  20. Why aren’t the heaviest gases at the bottom of the atmosphere? TURBULENCE Winds stir the atmosphere No gaseous molecule is so heavy that it can’t be moved by the wind!

  21. 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 Definitions:

  22. 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

  23. If Earth was the size of a beachball, how thick would the atmosphere be? Thinner than a piece of paper!

  24. Why is the atmosphere important? Without our atmosphere, earth would be like the moon........... SUN SHADE  HOT! COLD!

  25. 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)

  26. 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

  27. 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

  28. 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)

  29. 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!

  30. 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)

  31. 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

  32. 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. Contouring

  33. 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

  34. 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

  35. 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

  36. Water Vapor is a Gas in the Atmosphere, just like Nitrogen and Oxygen

  37. 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

  38. 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

  39. 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!!!!

  40. 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

  41. 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.

  42. 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!

  43. 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

  44. 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)

  45. T at top depends on solar activity Space Shuttle (250km) Heterosphere Aurora MESOPAUSE .01 mb Meteorites Homosphere STRATOPAUSE 1 mb Ozone TROPOPAUSE 200 mb Weather 1000 mb

  46. 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

  47. 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]

  48. 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

  49. 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]

  50. 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