ATMS101

Day	Topic	Ahrens (*)
Monday Jan 7	Introduction, logistics, class overview.
Tuesday Jan 8	Where do we start? How do we observe the atmosphere, the weather? Observations, instruments, measurements, maps, satellites, etc. Weather stations and buoys. Station model: clouds, temperature, pressure, wind direction and wind speed, knots, rain, snow, fog, etc. Westerlies and other -lies. Weather station maps. Wx: Current weather in Washington State, overcast, drizzle, snow in Eastern Washington, temperatures over the ocean vs. E. Washington, change in wind direction and counterclockwise circulation over the Pacific Ocean. Meteograms, temperature rise, temperature drop. UTC vs. PST. Wx: Recent temperature changes in Seattle, temperature rise as the storm was approaching, temperature drop as the storm moves through and decays. Radiosondes and temperature profiles. Temperature increase and decrease with height, overall decrease in the troposphere, increase in the stratosphere, temperature inversion. Wx: Current temperature profile in Quillayute (Washington State coast), wind direction turning in the lower atmosphere, increase in wind speed as we rise in the troposphere, decrease in the stratosphere, wind speed maximum at about 10 km height (tropopause), jet stream. You should have a basic understanding of the station model and you should be comfortable reading meteograms and temperature profiles. Satellites, TIROS in the 1960s, orbits, gravitational and centrifugal forces. Geostationary satellites: What is their advantage? How far are they from the earth? Why? Demo: laser pointer on an inflatable globe, polar-orbiting vs. geostationary satellites, night and day. Gravitational pull vs. centrifugal force, geostationary orbit. Example of satellite loop over the U.S. You should be able to explain how geostationary satellites work.	pp 4, 9-23 ("The Earth's atmosphere")
Wednesday Jan 9	Review: weather stations, meteograms, temperature rise/drop with passage of midlatitude cyclone, temperature profile (WA coast), temperature decrease/increase with height, troposphere, stratosphere, tropopause, wind speed increase/decrease with height, wind speed maximum, jet stream. Satellites, geostationary vs. polar-orbiting, trade-off between altitude (resolution) and time (global coverage). Satellite debris. Example of satellite loop over the U.S. Wx: Midlatitude cyclone over the North Pacific Ocean, cloud structure, rain. Schematics of a midlatitude cyclone, conceptual model for future reference: frontal cloud band, light rain/drizzle, patchy cumulus clouds, counterclockwise rotation. Global satellite imagery (animation): direction of motion and shape of weather systems at the equator vs. the midlatitudes, latitudinal bands, midlatitude cyclones travel from west to east, rotate in opposite directions in the northern vs. southern hemisphere, 5-6 midlatitude cyclones in the SH at all times, summer vs. winter hemisphere, absence of clouds in the tropics. Getting oriented on a world map: equator, tropics, high and low latitudes, midlatitudes, northern and southern hemispheres. You should be able to identify the main latitude bands on a map or satellite image, as well as the main geographic features (continents and oceans). Practice loading up and watching the satellite loop and meteograms. What is air? What is the atmosphere made of? Air Thickness of the atmosphere, vertical extent of clouds, troposphere, stratosphere, tropopause. Demo: air takes up space. (Do it at home.) Air has energy and pressure. Demo: weighing a deflated vs. inflated basketball. Air has mass, air is matter. Atoms, molecules, visual representation of a gas vs. a liquid. Model for solids, liquids, and gases, motion, vibrations. You should be able to describe some of the properties of air, as well as the differences between gases, liquids, and solids.	pp 5-9 ("The Earth's atmosphere")
Thursday Jan 10	Wx: satellite imagery, progression of midlatitude cyclone, cold front sweeping south to California, cold air and clearing in Seattle. Cloud movie: clear skies after the front has moved east, two layers of clouds move in. Sat image and wx station map: northerly flow bringing cold air and snow. Meteograms: T rise and drop, wind speed increase, continuous rain showing in cumulative precipitation. Toward a more complete conceptual model of a midlatitude cyclone: cold air mass and warm sector, heavy rain, showers, and hail along the front vs. light moderate rain under the NE cloud deck. What is air? Review: air takes up space, air has pressure, air hass mass, air is matter. Atoms, molecules, solids, liquids, gases, motion and vibrations. Demo: Making carbon dioxide with baking soda and vinegar. CO₂ is more dense than oxygen. Demo: He and H₂ balloons, testing for the presence of a gas with a flame. Atoms: protons, neutrons, nucleus, electrons, shells. Gases in our atmosphere, single, double, and triple bonds. Composition of the atmosphere, oxygen (O₂), nitrogen (N₂), water (H₂O), carbon dioxide (CO₂), methane (CH₄), ozone (O₃), permanent vs. variable gases. You should know the main gases constituting our atmosphere, at least the % of O₂ and N₂, and the difference between permanent and variable gases.	pp 5-9
Friday Jan 11	Quiz section - Introduction, logistics. Layers of the atmosphere, troposphere, stratosphere, tropopause, temperature, ozone.

Monday Jan 14	Wx: an anticyclone settled over the Pacific Ocean and Seattle over the week-end. A first conceptual model of an anticyclone: clockwise rotation, clear skies, cumulus clouds, low temperatures, diurnal cycle, fog, frost, low wind speeds or no wind, temperature inversion. Review: Properties of gases, CO₂, H₂. History: Joseph Black, Henry Cavendish, Carl Scheele, Antoine Lavoisier. Demo: H₂ and O₂/H₂ balloons, testing for the presence of a gas with a flame, or a boom! Composition of the atmosphere, oxygen (O₂), nitrogen (N₂), water (H₂O), carbon dioxide (CO₂), methane (CH₄), ozone (O₃), permanent vs. variable gases. Ratio of O₂ to N₂ with height. O₃ in the stratosphere (and absorption of UV radiation) vs. O₃ in the troposphere (and respiratory disorders). Has our atmosphere changed over time? Evolution of the atmosphere: changes in the concentration of gases over 10 billion years, relevance to plant and animal life, focus on H₂O, CO₂, photosynthesis, O₂ and the ozone (O₃) layer. You should be able to explain how and why the concentration of the main gases in the atmosphere has changed over the history of the earth. (Approximate dates OK. Focus on the processes.) Is the composition of our atmosphere still changing? Graph: Recent changes in CO₂ concentration measured at Mauna Loa, Hawaii, ppm, range. Seasonal cycle, role of vegetation growth and decay in explaining 5-ppm seasonal variations. 50-year increase, linear vs. exponential growth.
Tuesday Jan 15	wx: keeping an eye on our anticyclone, clouds move in, suppression of the diurnal cycle, higher nighttime temperatures, no frost. Introducing pressure: midlatitude cyclones correspond to low pressure, anticyclones to high pressure. Sneak preview of pressure maps: eastward progression of "highs" and "lows" (i.e., high pressure regions and low pressure centers). Review: past and future variations in the concentration of atmospheric gases. Demo: plastic molecules, CO₂, CH₄, O₃. Review: monitoring CO₂ concentration at the Mauna Loa observatory. Variations over the last millenium using climate proxys: industrial revolution. Variations over the last 400,000 years using ice cores: ice ages and natural variations. Recent increase put in perspective against variations over the last millenium and over the last 400,000 years: the impact of anthropogenic production of CO₂. You should be able to describe the natural and anthropogenic processes by which [CO₂] is changing over time. Map of ozone concentration, 60% decrease since the 1970s over Antarctica. Why is there a "hole" in the ozone layer? Stratospheric vs. tropospheric ozone. Absorption of UV radiation by ozone in the stratosphere, respiratory problems in the troposphere. Breakdown of ozone by chlorine, recycling of the chlorine atoms, CFCs, lifetime of the chlorine atom and consequences. Future evolution of the ozone layer, Montreal protocol as an example of science influencing international politics. Why is the ozone hole over Antarctica? Southern hemisphere winter, extremely low temperatures in the stratosphere over Antarctica, polar stratospheric clouds. Why is ozone depletion stronger in the spring? UV radiation and optimum chemical breakdown with the return of sunlight in the spring. You should be able to explain why the concentration of O₃ has decreased drastically over the last 40 years, describe the origin of CFCs, explain why the breakdown is so efficient and why it will take 40 to 50 years for the ozone concentration to come back to normal, why the breakdown of O₃ takes place mainly over Antarctica and mainly during southern hemisphere spring (october-november).	pp 412-417 (ozone in "Air pollution")
Wednesday Jan 16	Wx: Clear skies, temperature drop, frost. Fog over the Sound, Strait of Juan de Fuca, Columbia Valley, Eastern Washington. Temperature inversion: hiking up to higher temperatures and overlooking fog and low clouds. Heat and temperature What is heat? Demo: ink in cold and hot water. Definition of heat in liquids, kinetic energy. Thought experiment: metal spoon in hot tea. Conduction, direction of heat transfer by conduction. Definition of heat in solids. Good conductors vs. good insulators, air as a very good insulator, conduction in water vs. air, vacuum as a perfect insulator, double-pane windows. You should be able to define heat and conduction. You should be able to provide examples of good and bad conductors, good and bad insulators. Demo: balloons on a hot plate. Heat in gases, thermal expansion. Thinking in logical steps, showing cause-and-effect relationships. Warm air expands vs. warm air rises. Applications of thermal expansion and thermal contraction, bridges, asphalt and concrete, railroad tracks, doors, etc. Thermal expansion of a column of air, thermal expansion of the atmosphere at the equator, height of the tropopause. You should be able to explain thermal expansion and contraction in logical steps and to provide examples. How do we measure heat? Using thermal expansion of liquids to build a thermometer. History: Galileo and his thermoscope, Hooke, Boyle, Newton, Fahrenheit, Celsius. Fixed points, Celsius vs. Fahrenheit scales. You should be able to describe how a thermometer works. You should understand the notion of fixed points and calibration.	pp 28-33 (heat and conduction in "Warming the earth and the atmosphere") pp 76-79 (thermometer in "Air temperature")
Thursday Jan 17	Wx: fog, diurnal cycle, temperature inversion. Atmospheric pressure starts to drop: transition to a new regime. Review: heat, kinetic energy, conduction. Applications to elephants' ears, birds puffing up in the winter, house insulation, vacuum and double-pane windows. Conduction of heat from the ground to the air during the day, from the air to the ground at night: temperature inversion, diurnal cycle. Air is a poor conductor: how is heat transferred across the globe? Review: heat in gases, thermal expansion, thermometer. Fixed points, Celsius vs. Fahrenheit scales. Calibration, fixed points. Absolute zero, Kelvin temperature scale. Conversions. You should understand the notion of fixed points and calibration. You should be able to explain what absolute zero is and to describe the differences between the three temperature scales (^oC, ^oF and K). You do not need to know the conversion formulas by heart, but you should be able to use them if we provide them to you. How do we analyze temperature maps? Temperature map coloring and contouring, isotherms. Polar cold air mass, tropical warm air mass, cold and warm fronts, midlatitude cyclone. You should understand the notion of isotherm. Given a temperature map that contains a midlatitude cyclone, you should be able to identify air masses and fronts, you should be able to locate and draw the cold and warm fronts with appropriate colors and symbols. What can we learn from temperature loops? World temperature loop: raising questions about temperature variations with latitude, differences between the two hemispheres, land-ocean contrasts, the midlatitude temperature front (polar front), cyclonic activity along the front. How is heat transferred in the atmosphere? (Very important) Conceptual model of a midlatitude cyclone as a weather system transporting heat to the poles (or exchanging cold and warm air) in response to a heat imbalance between the tropics and the poles.
Friday Jan 18	Quiz section - Temperature maps, midlatitude cyclones, cold and warm fronts. Demo: Convection/conduction. Contouring, isotherms, placing the cold front and warm fronts. Temperature gradient.

Monday Jan 21	Martin Luther King Day
Tuesday Jan 22	Wx: fog, meteogram, diurnal cycle, decreasing pressure and change of regime, approaching low pressures/cyclones over the Pacific Ocean. Review: world temperature loop, temperature variations with latitude, differences between the two hemispheres, land-ocean contrasts, isotherms, temperature gradient, the midlatitude temperature front (polar front), cyclonic activity along the front, eastward propagation of midlatitude cyclones. Review of our emerging midlatitude cyclone conceptual model, air masses, fronts, and cyclones as weather systems set in motion to redistribute heat between the tropics and the poles. Contrasting conduction and transport of heat by air motion. What is the relationship between temperature fronts and cloud patterns? Matching the temperature fronts with cloud features, narrow frontal band along the cold front (and showers), extensive cloud shield ahead of the warm front (drizzle and snow). You should be able to locate and draw cold and warm fronts on both temperature maps and the corresponding satellite images. You should know what type of precipitation to expect along a cold front and ahead of a warm front. Why does temperature vary with latitude? Demo: flashlight on a globe, beam spreading (we will talk about 3 other reasons later in the "Radiation" section). What can we learn from average temperature maps? Monthly-mean temperature maps (January, July): raising questions about temperature differences with latitude, between summer and winter, between northern and southern hemisphere, between land and ocean. Why does temperature vary with the seasons? Demo: globe revolving around the sun. Revolution, rotation, axis tilt, seasons, solstice, equinox, hours of insolation, angle of insolation. You should be able to explain why we have seasons. FYI: wobble of the earth axis (precession), changes in the obliquity of the earth axis, changes in the eccentricity of the earth orbit, Milankovic's theory of natural climate changes.	pp 46-54 (seasons in "Warming the earth and the atmosphere")
Wednesday Jan 23	Wx: clouds, rain, rising temperatures, no more fog, no more temp inversion, disruption of the diurnal cycle, slight increase in wind speed, decreasing atmospheric pressure, low clouds from the SW. Satellite loop: identifying the cold front, warm front, warm sector, matching with temperature and pressure, reconciling with observations. Review: average temperature maps, seasons, Milankovic's theory of natural climate changes. Why is the midlatitude front stronger in the winter hemisphere? Demo: back to the earth orbiting the sun, location of the stronger temperature gradients, stronger polar front and stronger cyclones in the winter hemisphere. Why does temperature change over the course of a day? Diurnal cycle, inertia, impact of clouds on the diurnal temperature range, impact of midlatitude cyclones and frontal passage. Why does temperature change with altitude? Conduction, convection, average environmental lapse rate, absorption of UV radiation in the stratosphere, tropopause, temperature inversion. Mesosphere, thermosphere.	pp 58-76
Thursday Jan 24	Wx: frontal passage, clouds and rain followed by clear skies. Wx stations: fog in places, cold pool and fog over Eastern Washington. T profile: temperature inversion in the lowest layer, westerly cold air advection overlying southerly flow. Satellite imagery: new midlatitude cyclone off the coast, contrasting the rugged appearance of the clouds in the cold frontal band (cumulus type) with the smooth appearance of the clouds in the warm front region (stratus type). Northwest radar on the coast: approaching rain. T loop: typical midlatitude cyclone wave structure, cold air advection, warm sector. Pressure loop: low pressure trough associated with the cold front (will revisit later). Review: Polar front, diurnal cycle, T profile, average environmental lapse rate. How do land and water affect temperature? Specific heat of water vs. soil. (Calories vs. food calories.) Comparing 1 gram of water with 1 gram of soil under the same sun exposure. Molecular properties of water, internal vibrational and rotational modes. Thought experiment: beach and ocean under similar incoming sunlight; specific heat of water vs. sand, evaporation, mixing of the upper ocean, transmission and absorption of sunlight in a deeper layer of water. Reflection of sunlight by land vs. ocean. "Buffering" effect of oceans, land-ocean temperature contrasts, continental vs. maritime climate. Temperature range in Seattle vs. continental U.S. Influence of ocean currents, Gulf Stream (poleward transport of heat by ocean currents). You should be able to list and explain all factors affecting temperature (latitude, season, diurnal cycle, altitude, land-ocean contrasts, ocean currents, prevailing winds, clouds). You should be able to explain why continental climates are characterized by wider temperature ranges than maritime climates. How can we forecast the weather with a computer? Gridding of observations, projection into the future, advection of air with its properties, re-gridding and iteration by time steps; propagation of errors and initial uncertainties. Calculating the change in T, wind, pressure, etc. at each grid point, and integrating over time, into the future. New loop: pressure and precipitation, rain associated with lows and fronts, clear weather associated with highs. Wx: upcoming cold front, rain for the afternoon.
Friday Jan 25	Quiz section - Heat and temperature. Demo: Crushing cans, pressure gradient force. Homework #2 debrief: ozone destruction cycle and midlatitude cyclone anatomy -- cold/warm front, location of center of cyclone, warm/cold air mass. Advection: how to identify warm and cold air advection. Weather forecasting.

Monday Jan 28	Wx: week-end debrief, matching the passage of low pressure centers, rain, temperature and pressure changes. Understanding temperature increase and decrease in terms of warm sector and cold air advection. Pressure and rain: outlook for the week. Radar loop: winds blowing around the Olympic mountains and converging on the other side, rain in Everett. Paving the road to understand the Puget Sound Convergence Zone. Pressure Review: inverted plastic cup over a cork, air takes up space, intuitive notion of pressure. Demo: syringe, air pressure, force. Pulling on the closed syringe, vacuum, pulling against air pressure. Difference between pressure in all directions and force applied in one single direction. Pressure as force per unit area, force resulting from pressure applied to an area. How does pressure change in a closed container? Changes in pressure due to changes in volume, temperature, and amount of air. Ideal gas law, PV=nRT. Application: Revisiting the can crushing experiment from the point of view of T and n. Revisiting the balloon on the hot-plate from the point of view of T, P, and V. How does pressure change in the free atmosphere? Demo: water flowing out of a tennis ball can through holes at different heights. Pressure as the result of the accumulated weight of the overlying water/air, interplay of gravity and the vertical distribution of pressure. Exponential (vs. linear) decrease in pressure with height. Atmospheric pressure is determined by the weight of the overlying air column, but is still applied (and is the same) in every direction. You should be aware of the difference between pressure in a closed container and pressure in the free atmosphere, and understand the logic behind the vertical distribution of atmospheric pressure. Why do our ears pop when we climb a mountain? Inner ear, Eustachian canal, eardrum, pressure differences, ear popping.	pp 150-159
Tuesday Jan 29	Wx: nothing new, enhancement of precipitation by convergence of the winds over Everett after blowing around the Olympics. Review: pressure, force arising from a pressure difference, atmospheric pressure, ear popping in altitude, congested nose and flying with an ear infection. Other applications: pressurization of planes, getting "sucked out" vs. getting "pushed out" of a plane. Pressure increasing downward into the ocean. Boiling water in altitude: impact of the decreased pressure on the temperature of boiling water (boiling point), cooking pasta "al dente." Introduction to boiling: water vapor bubbles, pressure inside the bubbles vs. atmospheric pressure. Baking cakes: CO2 bubbles in a rising cake, changing the amount of baking powder and the temperature of the oven when baking a cake in altitude. You should be able to explain in words the above phenomena. Where does the wind come from? Demo: water flowing between two tennis ball cans. Pressure gradient, force, acceleration, motion. Analogy: pressure in the ocean and ocean currents. Analogy: atmospheric pressure and wind. Wind speed is proportional to the strength of the pressure gradient (the stronger the pressure difference, the faster the wind). You should be comfortable with the notion of pressure gradient and the concept of air set in motion by the force resulting from a pressure difference/gradient, from high to low pressure. Where do the atmospheric pressure differences come from? (Very important) Sea breeze: full picture with absorption of sunlight, specific heat of soil vs. water and other factors, conduction (+ convection), thermal expansion, pressure gradient, upper-level wind, sea breeze at the surface. Sea breeze circulation: convection (warm air rises), upper-level wind, subsidence, sea breeze. You should be able to describe the mechanisms of the sea breeze.	pp 158159 pp 169-173 (in "Air pressure and wind") pp 178-184 (in "Atmospheric Circulations") pp 152-155
Wednesday Jan 30	Wx: pressure is rising, we are getting there. Review: sea breeze, differential heating, temperature contrast, notion of a system constantly off balance and nature working to bring it back to equilibrium. Slowing down of the sea breeze circulation as the sun sets: temperature difference, pressure gradient, and wind speed all decrease to zero. Reversal of the circulation at night, as the ground cools off more rapidly than the water: land breeze. Cloud preview: clouds tend to form over the warmer surface (convection), while cloud formation is inhibited over the cooler surface (subsidence). Reversal of the wind circulation at night, land breeze. How do we measure pressure? Demo: plastic tube in colored water. Balance of forces, gravity, air pressure. Thought experiment: giant barometer, 10 meters (33 feet) of water balanced by the pressure (weight) of 1 atmosphere. Bar, millibar, 10 meters of water vs. 760 mm (~30 in) of mercury. Increasing and decreasing pressure, barometer. History: Torricelli and the invention of the barometer, improvements by Hooke, Descartes, de Luc. Leibniz and the aneroid barometer, Pascal and the prediction of atmospheric pressure decrease with height. Typical 960-1040 mb observed range of pressure in the midlatitudes. Underwater pressure, 10 meters of water equivalent to 1 atmosphere. 500 mb at about 5.5 km. You should be able to explain how a barometer works and should know the correspondence between water and atmosphere. How do meteorologists use pressure to understand and forecast the weather? Contouring a pressure map: color scale, isobars, regions of high (H) and low (L) pressure, pressure gradient. Raising questions: low pressure centers in the midlatitudes, moving from west to east, vs. higher pressure in the tropics (over the ocean); stronger pressure gradient in the midlatitudes; very high pressure over Siberia and Canada vs. lower pressure over the ocean in the midlatitudes.	pp 152-156 (in "Air pressure and wind")
Thursday Jan 31	Review: barometer, bars, calibration. Correction due to changes in temperature and thermal expansion of the mercury. Pressure loop: lows, highs, troughs and ridges. Analogy with topographic maps. Comparing pressure patterns and clouds in satellite images: low pressure center in a midlatitude cyclone, concentric closed isobars around the low, toward a more complete conceptual model. Does wind really blow from high to low pressure? Comparing winds observed by satellite and a low pressure area, the wind tends to blow parallel (rather than perpendicular) to the isobars, counterclockwise winds around a low, clockwise around a high (in the northern hemisphere). Stronger winds around lows, weak to no wind around highs, and all directions are reversed in the southern hemisphere: what's up with that?... Why does the wind not blow in straight lines from high to low pressure? Demo: weight-lifter spinning on a chair. Conservation of angular momentum, speed of rotation, radius of rotation. Apparent motion of an air parcel over the rotating earth, apparent deflection to the right of the direction of motion (in the northern hemisphere), apparent acceleration/force acting to the right, Coriolis force. Apparent force acting to the left in the southern hemisphere. Coriolis force: perpendicular and to the right of the direction of motion (northern hemisphere), proportional to wind speed, function of latitude, zero Coriolis force at the equator. You do not need to fully understand the details of the origin and mechanisms of the Coriolis force. In particular, you do not need to be able to explain why there is a Coriolis force. But you need to know how it is manifested in the atmosphere (the last item above).	pp 160-161 (in "Air pressure and wind")
Friday Feb 1	Quiz section - Coriolis force, pressure contouring, highs and lows, troughs and ridges, fronts.

Monday Feb 4	Wx: anticyclone, fog, mountain snow and clouds on a visible image of Washington State. Week-end debrief and outlook for the week: lows and rain on Tu-We-Th, high pressure on Fri-Sun. Review: air moving on a rotating earth, deflection to the right of the direction of motion, apparent acceleration/force acting to the right (in the northern hemisphere), Coriolis force. History: Gaspard-Gustave Coriolis and Buys-Ballot. Coriolis force perpendicular and to the right of the direction of motion, proportional to wind speed, function of latitude, zero Coriolis force at the equator. Thought experiment: air parcel embedded in a pressure gradient. Pressure gradient force (PGF), Coriolis force (COR), deflection to the right until balance of forces: geostrophic balance. Rule of thumb #1 (COR to the right, PGF to the left, WIND blows parallel to the isobars). Thought experiment: parcel accelerated in a strengthening pressure gradient. PGF increases, wind speed increases, COR increases, new balance is reached. Rule of thumb #2: wind speed is proportional to pressure gradient (and tightness of isobars). You do not need to be able to re-explain the conservation of angular momentum and the geostrophic balance, but you need to know the rules-of-thumb by heart and be able to apply them (given PGF, COR, or WIND, in which direction are the others pointing). From a pressure map, how do we infer the geostrophic wind at any point? Working out forces and wind speed anywhere on a pressure map. Rule of thumb #3: Analogy with topography, mountains and valleys, hiking, snowboarding facing high pressure (or low pressure if you are goofy), skiing with high pressure on your right... find an analogy that works for you. Application to lows and highs, cyclones and anticyclones, clockwise vs. counterclockwise (northern hemisphere). Rule of thumb #4: clockwise around highs, counterclockwise around lows (northern hemisphere). Overlaying temperature (colors) and isobars (contours) on the same map: verifying how pressure and temperature work in concert. Advection of warm and cold air in a midlatitude cyclone, completing the picture: how pressure, wind, temperature, air masses, and fronts work together to create a midlatitude cyclone.	pp 162-164
Tuesday Feb 5	Wx: frontal passage, minimum pressure, radar view of frontal rain band. Review: geostrophic balance, highs and lows, analogy with water flowing between riverbanks. Completing our conceptual model of a midlatitude cyclone, fronts in relation to the "kink" in the isobars, explained by the abrupt change in wind direction, cold vs. warm air advection. Wx: low pressure centers forming and reforming in the Gulf of Alaska, identifying troughs and fronts, rain, outlook for the rest of the week. Isobars and winds: the wind seems to cross the isobars, rather than blowing parrallel to the isobars, as geostrophic balance would suggest. What's up with that? Why is the geostrophic balance disrupted close to the ground? Demo: water spinning in a beaker. PGF and centrifugal force, friction, and analogy with a cyclone. Friction, wind speed decreases, COR decreases, but PGF stays the same and pushes the air toward low pressures. Rule of thumb #5: At the surface, the wind crosses the isobars from high to low pressure, surface convergence into lows, surface divergence out of highs. Cloud preview: convergence means upward motion and clouds+rain, divergence means subsidence and no cloud. Decay of a cyclone as the converging winds bring mass inwards and the pressue increases: "the low fills in." Conservation of angular momentum: the wind speeds up in lows, consistently with tighter isobars, and slows down in highs (isobars are wide apart). Given a pressure map, you should be able to determine the wind direction and speed at any point assuming that the wind is in geostrophic balance. If asked to consider friction, you should know how to deflect the wind vectors inward or outward accordingly. Light, radiation What is light? Demo: apple in a box. Emission, absorption, reflection, white, black, examples (moon, snow, etc.) Visible satellite image: brightness of clouds, land vs. ocean.	pp 34-36 (in "Warming the earth and the atmosphere")
Wednesday Feb 6	Review: emission, absorption, reflection, transmission, white, black. Demo: color transparencies (red+green), absorption and transmission of colors. Visible satellite image: brightness of clouds, snow, outer space, land vs. ocean. Albedo: moon, Venus, ice/snow, earth+atmosphere, forest, etc. Positive and negative feedback loops. You should be able to apply the concepts of absorption and reflection and to work your way through a simple chain of causes and effects and determine if it is a positive or a negative feedback loop. Demo: white light refracted through a prism. Colors and radiational energy. Particle theory vs. wave theory (photons vs. electromagnetic waves). Wavelength, micrometers, microns, shorter wavelengths correspond to higher energy levels. You should be comfortable using the concepts of photons and electromagnetic waves of different wavelengths and energy levels. Are there other types of light/radiation? William Herschel and the "invisible" light. Full radiation spectrum, radio waves, microwaves, IR, VIS, UV, X-rays, gamma rays. Radiation emitted by the sun at different wavelengths, emission spectrum of the sun, emission peak. What determines the wavelength of emission of different materials? Demo: infrared thermometer (IR gun). Infrared radiation, emission of IR in relation to temperature. Predator. Infrared zoo, security systems and presence detectors. Toward the emission of infrared radiation by the earth system.
Thursday Feb 7	Wx: frontal passage, minimum low pressure, rain, temperature increase and decrease, high pressure building throughout the week-end. Review: infrared radiation. Any object/material that contains some energy (some heat) emits radiation. Conceptual model: thinking about absorption of radiation in terms of "excited" electrons jumping to higher orbits/higher energy levels; emission in terms of electrons returning to their original level. Absorption of radiation = temperature increase; emission of radiation = loss of energy = temperature decrease. Application: sleeping with and without a blanket. Application: cooling of the ground at night by emission of IR radiation + conduction of heat from the air to the ground = temperature inversion. Wien's law: the peak of emission is a function of the temperature of the material emitting the radiation. Application: if the Sun emits mostly at 0.5 microns, then T=6000 K; if the temperature of the Earth is T=288 K, then it emits mostly at 10 microns (in the IR). The earth as a system in radiative equilibrium: what comes in as VIS radiation must go out as IR radiation --> absorption of VIS and emission of IR. Stefan-Boltzmann's law: the total amount of emitted radiation is a function of temperature; a small increase in temperature leads to large increase (fourth power) in the amount of emitted radiation. Wien's law and Stefan-Boltzmann's law combined: as the temperature increases, the wavelength of peak emission shifts toward shorter wavelength (more energetic) and the total amount of emitted radiation increases. Applications: infrared zoo, electric stove turning red and white, security systems and presence detectors. You do not need to know Wien's law and Stefan-Boltzmann's law by heart, but you need to understand what they mean in practice. You should be able to explain them in words. Infrared satellite image: 1.Constructing a "fake" color scale to display the radiation emitted by clouds (ocean, land). 2. Using Wien's law and Stefan-Boltzmann's law to estimate temperature based on the wavelength of peak emission and on the total emitted energy --> estimating the temperature of cloud tops by measuring the radiation they emit. 3. Using a temperature profile to estimate the altitude of cloud tops. You should be able to, both, explain in words how we can estimate the altitude of cloud tops from a satellite image, and work your way step by step through the estimation if we provide you with the appropriate figures and graphs. The earth absorbs VIS only during the day, but emits IR all the time. Wx: IR satellite loop. Tall clouds at the equator (white, cold cloud tops : thunderstorms, cumulonimbus. High, cold clouds in the comma head of midlatitude cyclones, lower cloud tops in the tail of the cold front. Low clouds (gray, warm cloud tops) under anticyclones (shallow cumulus).
Friday Feb 8	Quiz section - Sea breeze/land breeze, pressure and geostrophic balance, inferring wind vectors from a pressure map. Midterm review.

Monday Feb 11	Midterm (50 minutes)
Tuesday Feb 12	Review: radiation, IR, satellite images, snow in midlatitude cyclones, superstorm Nemo. Energy balance of the Earth: if the outgoing IR radiation emitted by the Earth is in equilibrium with the incoming solar radiation, then the temperature of the Earth should be -18^oC = 255K. Actual mean annual Earth temperature = 15^oC = 288K. Why is the Earth so much warmer? Absorption of radiation at specific wavelengths by individual gases: ozone, water vapor, carbon dioxide. Application: the burning feeling of the desert sun vs. Seattle sun. Absorption by the full atmosphere: Visible Atmospheric Window (VAW) and Infrared Atmospheric Window (IAW). What are the implications of the existence of "atmospheric windows"? We can "see" VIS light from the sun. Some of the IR emitted by the ground is transmitted through and back out to space. But not all of it! What happens to the rest? Absorption of Earth's IR radiation by selective absorbers: H2O, CO2, CH4, O3. Absorption and re-emission: greenhouse effect (+15oC instead of -18oC). You should understand that different molecules absorb at different wavelengths and you should be able to explain in words how the greenhouse effect works. H2O as the main greenhouse gas (GHG), CO2 as a key GHG because of CO2 increase. Reconstruction of the temperature record from gas bubbles trapped in ice cores: comparison with the record of CO2 concentration. CO2, methane (CH4) and the industrial revolution, 0.8^oC temperature increase over the last 150 years, enhancement of the GH effect, global warming. You should be able to explain how GHG warm the surface through absorption and reemission of IR, and how increasing the amount of these GHG leads to global warming. You should know the difference between greenhouse effect and global warming.	pp 37-47 (in "Warming the earth and the atmosphere")
Wednesday Feb 13	Review: greenhouse gases, global warming. Word of caution about the role played by ozone in the ozone layer issue, as opposed to its role as a GHG. Low (warm) clouds as good reflectors of VIS and good emitters of IR = cool down the earth. High (cold) clouds as poor reflectors of VIS and poor emitters of IR = warm up the earth. Aerosols reduce the penetration of sunlight = cool down the earth. Combination of greenhouse effect and reflection of VIS light in determining the net effect of low clouds, high clouds, and aerosols on the temperature of the earth. Why does temperature vary with altitude? Transmission of VIS (and IR) from the sun through the atmosphere, absorption by the ground, conduction and emission of IR by the ground (+ convection), average environmental lapse rate. Absorption of UV by ozone in the stratosphere, temperature inversion. Why are the tropics warmer than the poles? Review: 1. Beam spreading. Why is the sky blue? Scattering of blue light by oxygen molecules. 2. Beam depletion by scattering. 3. Enhanced reflection of sunlight at shallow angles. Video: sea ice around Antarctica, sea ice in the Arctic Ocean. 4. Albedo of snow and ice near poles. You should know what causes the difference in temperature between the equator and the poles. Closing the loop: linking radiation, heat imbalance, and midlatitude cyclones in a single picture. Water Wx: water vapor satellite imagery, concentration of moisture in fronts and lows, flux of moisture from the tropics. What is the role of water in our atmosphere? How is it cycled through? Review: boiling, water vapor, forced phase change at 100^oC. Evaporation, phase change at any temperature. Latent heat. Demo: hair-drier on a wet hand, latent heat of evaporation. Why do we feel cold when we step out of the shower? Evaporation of water from our skin, body heat used as latent heat. Why do we sweat? Perspiration, latent heat of evaporation, cooling off by using body heat as latent heat to evaporate sweat. Contrast between specific heat and latent heat.	pp 84-87 (in "Humidiy, Condensation, and Clouds")
Thursday Feb 14	Review: phase changes, latent heat. Phase changes: evaporation, condensation, melting, freezing. Intake and release of latent heat. Demo: flame under a paper cup, conduction of heat, specific and latent heat of water. Evaporation of water in the tropics, transport to the midlatitudes, condensation and release of latent heat, net transport of water vapor (+latent heat) by the atmospheric circulation from the equator/tropics to the midlatitudes/poles. What is the source of energy of hurricanes? Why do hurricanes die when they make landfall? Hurricane preview: evaporation of ocean water, lifting, condensation, release of latent heat, further convection, and fueling of the hurricane circulation (we will come back to this). Cutoff of the source of energy over land. You should thoroughly understand the concepts of phase change and latent heat (including the difference with specific heat). How do we measure, calculate, express humidity? Absolute humidity, specific humidity, mixing ratio, water vapor pressure (e), mb. Thought experiment: evaporation from an open and closed pan, equilibrium, saturation, saturation water vapor pressure (e_s). Relative humidity (RH), examples. Sweating in saturated air, risks of heat strokes. You should be able to calculate RH given e and e_s. You should understand the difference between actual water vapor content and relative humidity, as two different measures of humidity. Increasing T: the capacity for water vapor increases. Saturation is a function of temperature. Changes in saturation vapor pressure with temperature, saturation vapor pressure curve. How to calculate RH knowing e and T, examples. Example of differences in T, RH, and therefore e in Canada vs. Death Valley: e can be large when T is large, even though RH is small. You should be able to calculate RH given e and T.	pp 87-89 (in "Humidiy, Condensation, and Clouds")
Friday Feb 15	Quiz section - Radiation demo, latent heat demo, wx discussion.

Monday Feb 18	President's Day
Tuesday Feb 19	Review: humidity, water vapor pressure, saturation, relative humidity. Two ways of increasing RH: increasing e, or decreasing e_s by decreasing T. Wx: meteogram, increase in RH due to the decrease in T at night. How does dew/frost form? Temperature decrease, increasing RH by decreasing T, and therefore decreasing e_s -- when e_s becomes equal to e, we are at saturation - a further T decrease leads to a phase change, dew, frost. Dew point temperature. Formation of dew/frost by radiational cooling, temperature inversion, temperature decrease to the dew point. Dew and frost after calm, cloudless nights. You should be able to calculate e_s and RH knowing T and e. You should be able to explain the formation of dew. Meaning of the dew point temperature: decreasing the temperature of moist air parcel vs. a dry air parcel. Rule-of-thumb: high T_d close to T = moist air; low T_d far below T = dry air. Wx: radiosonde temperature profile, moist and dry layers. Meteogram: moist and dry events. Given a weather station map, you should be able to identify regions where dew, frost (fog) is likely to form, as opposed to dry areas. Given a radiosonde profile, dry and moist layers. Given a meteogram, dry and moist events. About the measurement of T_d and why T and T_d are easier to measure than e_s and e. Determining e knowing T_d. Calculating RH knowing T and T_d. You should be able to use the saturation vapor pressure curve in every direction to calculate one variable knowing the others. In particular, you should be able to calculate RH knowing T and T_d.	pp 89-97 (in "Humidiy, Condensation, and Clouds")
Wednesday Feb 20	Wx: IR satellite loop, low and frontal band, approaching rain on radar, outlook for the rest of the week, shift to a midlatitude cyclone regime, rain, rain, rain. Clouds Review: saturation, relative humidity, dew point temperature, from condensation to clouds. What are the necessary conditions for a cloud to form? Demo: cloud in a jar, water vapor, solid particles, and... temperature decrease? Adiabatic processes. Demo: warming in a bike pump. Fast compression = adiabatic warming. (Adiabatic expansion to be contrasted with thermal expansion.) Adiabatic cooling by expansion, conceptual model, loss of energy as air molecules work to expand against the outside air. Fast expansion = adiabatic cooling. Water vapor + condensation nuclei + T decrease to the dew point: recipe for a cloud. You should understand the concept of adiabatic cooling. Why does water vapor need a condensation nucleus to form a droplet? Thought experiment: evaporation from a flat, concave, and convex surface, supersaturated air. Initiation of condensation from a solid surface. How does fog form? Radiation fog: clear skies, cold and calm night, cooling of the ground by IR emission, cooling of the air by conduction, temperature decrease to the dew point, dew, frost, fog. Temperature inversion, mixing of the cold and warm air in the inversion layer by wind. Fog burn-off.	pp 96-100 (in "Humidiy, Condensation, and Clouds")
Thursday Feb 21	Wx: forecast verification, rain, pressure, RH, Td. IR loop, cold front tail, more clouds and rain, but where is the rain in Seattle? Radar: rain on the western side of mountains, rain shadow over Seattle. Forecast: displacement of the rain shadow depending on the wind direction. Review: radiation fog. Advection fog: warm air over cold water, cooling by conduction, temperature decrease to the dew point, fog. San Francisco Bay fog, warm, moist marine westerlies over cold California current. London fog, warmer, moist marine southerlies over cold land, smog. Evaporation fog: cold air over warm water, evaporation, saturation, fog, warming of the air by conduction, "rising" fog. Fog dispersal. You should be able to describe the mechanism behind each type of fog, and you should be able to provide examples of each type of fog. Cloud classification: type (cirrus, cumulus, stratus) and height. Cirrus, ice crystals, "mare's tails." Cirrocumulus ("mackerel sky"), cirrostratus, refraction of sunlight through ice crystals, 22^o halo, omen of a coming cyclone. Altocumulus, liquid water droplets, altostratus. Stratus, stratocumulus, nimbostratus. You should know the main types of clouds, especially in relation to their content (ice crystals vs. liquid droplets), their characteristics (ex: halo), and their height. You should be able to name the clouds when they fall clearly in one category. (Confusing altocumulus and stratocumulus, for example, is okay.) Fair-weather cumulus: toward convective clouds.	pp 97-112 (in "Humidiy, Condensation, and Clouds")
Friday Feb 22	Quiz section - Radiation homework problems, cloud in a jar demo, cloud types (slides), relative humidity and dew point temperature. Wx discussion: week-end outlook.

Monday Feb 25	Wx: week-end debrief, outlook for the week, lows and fronts until Sunday (high pressure). Strong winds before, during, and after frontal passage. Review of cloud classification: cirrus, cumulus, stratus, cloud height. Fair-weather cumulus, flat base, cauliflower appearance, alternance of cloud and cloud-free air. Cumulus congestus, supercooled liquid water droplets and ice crystals. Cumulonimbus, thunderstorms, hail, lightning, anvil shape, mammatus clouds. (We will return to thunderstorms in a couple weeks.) You should be able to recognize cumuliform clouds and you should know the typical sequence from fair-weather cumulus to cumulus congestus to cumulonimbus. History: Lamarck, Luke Howard, Abercrombie, Munich 1891 international conference. Lenticularis clouds, pileus clouds, nacreous clouds (stratosphere), noctilucent clouds (mesosphere). Cloud formation How does vertical motion lead to the formation of clouds? Air parcel rising up in the atmosphere: adiabatic expansion and cooling. Dry adiabatic lapse rate (10^oC/km). Cooling to the dew point, condensation, latent heat release, saturated lifting: moist adiabatic lapse rate (6^oC/km). Air parcel rising up along the side of a mountain (orographic lifting): condensation, cloud formation and precipitation on the windward side, warming in the lee of the moutain.	pp 125-127 (in "Cloud Development and Precipitation")
Tuesday Feb 26	Wx: frontal passage tonight. Review: dry and moist adiabatic lapse rate, adiabatic compression with and without evaporation of liquid water. Orographic lifting: condensation, cloud formation and precipitation on the windward side of the mountain. Enhanced warming in the lee of the moutain, temperature contrast, moisture contrast. Applications: rainy and green on the westward side of the Cascades, warmer and arid in Eastern Washington. Olympic mountains, Hoh rain forest. Chinook (Rocky Mountains), Santa Ana winds (California), foehn (Alps). Olympic rain shadow, Sequim micro-climate. You should know the dry and moist adiabatic lapse rate, you should know how and when to apply them, and you should be able to work your way through a calculation similar to the mountain example. What are the other lifting mechanisms leading to cloud formation? Convergence. Seattle: rain shadow vs. convergence zone. Frontal lifting. Midlatitude storms and air masses: clouds and rain in frontal regions. Cold front: cumuliform clouds, showers. Warm front: stratiform clouds, drizzle, cloud sequence (cirrostratus, altostratus, stratus, nimbostratus). You should be able to explain why and how we can have either a rain shadow or a convergence zone in Seattle. You should be able to describe the typical cloud formations and precipitation type associated with each type of front.
Wednesday Feb 27	Wx: weather debrief, frontal passage during the night, next storm to come. Review: lifting mechanisms, frontal lifting. Frontal clouds in satellite imagery. Convergence into lows leads to clouds and rain. Divergence out of highs leads to subsidence and cloud inhibition, clear and sunny weather. How do cumulus clouds form? Demo: eggs in salt and fresh water. Density, stability, equilibrium, balance of forces, pressure gradient force, buoyancy force vs. gravity (weight). Thought experiment: warm water (air) rises, cold water (air) sinks, buoyancy, convection. Warm air rises, cold air sinks, valley fog. How far does warm air rise? Temperature of a lifted parcel vs. environmental temperature, dry adiabatic lapse rate vs. environmental lapse rate. Profile A: stable air. Profile B: unstable air, thermals.	pp 118-125 (in "Cloud Development and Precipitation")
Thursday Feb 28	Wx: warm front, stratiform clouds, more continuous rain, review of warm sector, overrunning, etc. Outlook for the week-end, high pressure on Sunday. Review: Buoyancy, warm air rises, environmental temperature vs. air parcel temperature as it cools adiabatically. Profile A: stable air. Temperature inversion, fog, pollution, smog. Stratospheric temperature inversion, lid on weather. Frontal inversion: warm air overrunning cold air is stable. Subsidence inversion: stable under highs, fog and pollution. Profile B: unstable air. Applications: thermals, gliders, hawks, vultures, and such. What if the temperature decreases below the dew point? Profile C: unstable air, shallow (fair-weather) cumulus. Lifting condensation level (LCL), cloud base, cloud top. Flat cloud base, convective cells, subsidence. Profile D: forced convection, free convection, deep cumulus, cumulonimbus. Level of free convection (LFC). Given a temperature profile, you should be able to determine whether the surface layer is stable or not. If unstable, and given the dew point at the surface, you should be able to determine the cloud base (LCL) and cloud top. If convectively unstable, you should be able to determine LFC, LCL, and cloud top.	pp 118-125 (in "Cloud Development and Precipitation")
Friday Mar 1	Quiz section

Monday Mar 4	Wx: week-end debrief, outlook for week, rain Tu-W, high pressure building afterward. Air masses, fronts, and midlatitude cyclones Typical air masses over North America (cP, cA, mP, mT, cT). Fronts, friction and frontal slopes. Midlatitude cyclone life cycle: stationary front, incipient stage, developing stage, mature stage, cold front catching up with warm front, closing warm sector, decaying stage, occluded front (occlusion), Norwegian model, T-bone model. History: the 1920s, the Bergen school, Vilhelm and Jacob Bjerkness, Norwegian cyclone model, air masses and fronts. You should know the full life cycle in detail and be able to describe the air masses, pressure, wind, fronts, areas of clouds and precipitation, etc. What initiates cyclones, why do they intensify? The upper levels History: Japan, the U.S., and the Second World War, B29 bombers, the "Fugo" bombs. Thought model: two air columns on each side of the midlatitude temperature front, thermal expansion and resulting pressure gradients, westerlies of increasing speed, 250-mb maximum wind speed, jet stream. You do not need to be able to explain the origin of the jets, but you should have a basic understanding of the jet stream, why it exists, where it is found in the atmosphere (level and latitude), and in which direction it is blowing.	pp 156-157 (optional) pp 166-169 (in "Air Pressure and Winds")
Tuesday Mar 5	Review: jet stream. Wx: Checking the jet stream theory against real-time pressure maps, 500-mb flow, 250-mb jets, maximum wind speed at 250 mb in the midlatitudes (northern and southern hemisphere). Hemispheric view of the jet stream: undulations and eastward progression of the waves. How is the jet stream connected to surface weather? 3D picture of the atmosphere above a cyclone, 300-mb flow, ridge and trough, areas of convergence and divergence in the jet in relation to surface high and low pressure regions. Correspondance between convergence in the jet stream and subsidence over a high. Correspondance between divergence in the jet stream and upward motion over a low. Jet stream divergence sucks air up and enhances the convergence into the surface low, deepening the cyclone. Upper-level trough over the low: the low "fills in." Wx: combined 500-mb and surface pressure loop, cyclones developing east of the troughs under regions of upper-level divergence and decaying after the surface low moves back under the trough. Rule of thumb: approaching trough (low and rain) vs. ridge (subsidence and nice weather). Looking at the upper-level jet as "steering" the midlatitude cyclones. This is more advanced material, but you should know how the upper-level troughs and ridges are connected to surface cyclones and highs. In particular, you should be able to tell whether a low is intensifying or decaying by looking at the maps. You should be able to forecast approaching cyclones by looking at the upper-level isobars in relation to the surface pressure patterns (this loop). Completing our picture of midlatitude cyclones: conveyor belts (another way to look at things). Warm conveyor belt: warm air overrunning colder air and catching up with the upper-level jet. Cold conveyor belt: rising cold air and snow. Dry conveyor belt, dry upper-level air subsiding and mixing within the low center.
Wednesday Mar 6	Review: upper-levels vs. surface, jet stream, undulations, troughs and ridges, storm intensification and decay. Wx: the low is over us, going from stratiform precipitation (drizzle, light) to more intense as the low moves over. Waiting for the ridge to build on Friday. Radiosonde profile: signature of the jet stream in the winds. Post-frontal ("pop-corn") convection: fair-weather cumulus clouds form in the cold air over warm water (behind the cold front), unstable air capped by subsidence in the anticyclone. Precipitation How do clouds produce precipitation? Cloud microphysics: understanding how we get from cloud droplets (0.02 mm) to rain (2 mm), condensation vs. other process. Warm clouds: fall speed, collision and coalescence. Drag and shape of a rain drop. Upward motion, convection, updrafts, weight vs. drag. Cumulonimbus clouds and hail. Cool and cold clouds: regions of the cloud containing ice crystals, supercooled liquid water droplets, or a mixture of both. Ice nuclei, saturation water vapor pressure over ice and water. Bergeron-Findeisen process: deposition of water onto ice crystal. Depletion of excess water vapor, ice growth at the expense of liquid cloud drops. History: Alfred Wegener, Tor Bergeron, and Walter Findeisen. Cirrus clouds, fall streaks, virga, snow. Snow flakes, dendrites, plates, etc. What is the structure of snow crystals and snow flakes? Molecular structure of water, arrangement of water molecules at freezing. Six-sided structure of ice crystals, types of crystal as a function of temperature (plates, needles, columns, dendrites). Deposition, riming (accretion), ice fragmentation, ice crystals are good ice nuclei, aggregation. Graupel, wet snow, and powder. Snow squalls, snow showers and snow flurries from the more convective clouds, light and longer-lasting from stratiform clouds. Blizzard.	pp 128-145 (in "Cloud Development and Precipitation")
Thursday Mar 7	Wx: decaying low, building high pressure. Review: From ice crystal to snow. Deposition, riming (accretion), ice fragmentation, ice crystals are good ice nuclei, aggregation. Why are there different types of precipitation? "Lake effect" around the Great Lakes, advection of cold air, evaporation, conduction, convection, drag, convergence, snow. Great Lakes, fetch, cloud streets, and snow. You should now be very familiar with the various processes (mechanisms) that lead to the formation of different types of clouds and precipitation. Precipitation ahead of a warm front: overrunning, stratiform clouds, melting of snow through a warm layer, re-freezing in the cold air mass, rain, freezing rain, sleet, snow. Combining a bird's eye view and a cross-section of a warm front. You should now be able to completely describe a midlatitude cyclone, including the air masses, fronts, conveyor belts, areas of precipitation, upper-level and surface patterns, etc. You should know all possible types of precipitation in a midlatitude cyclone (showers, drizzle, snow, sleet, etc.). Thunderstorms Air mass thunderstorm stages: cumulus, growing, mature, dissipation. Initiation by surface heating, convection, condensation, evaporation, moistening (pre-conditioning). Toward more instability, LFC, free growth to the tropopause, anvil, overshooting. Mixing (entrainment), evaporation, cooling, downdrafts, gust front. Decay due to cold downdraft, dissipation. You should be able to describe the life cycle of an air mass thunderstorm. In particular, you should be able to explain the origin of the downdrafts and how they contribute to the demise of the thunderstorm.	pp 274-295 (in "Thunderstorms and Tornadoes")
Friday Mar 8	Quiz section - Air mass thunderstorm, severe thunderstorms, hail, lightning, thunder. Mesoscale convective systems, wind shear. Supercells, rotating updrafts, mesocyclones, tornadoes.	pp 295-308 (in "Thunderstorms and Tornadoes")

Monday Mar 11	Wx: week-end debrief, upper-level ridge, shift to westerlies, next ridge for next week. Weather forecasting How do meteorologists forecast the weather? Review: numerical modeling, step-by-step integration in time of the equations of motion. Why are weather forecasts less accurate beyond a couple days? Demo: analogy with a falling sheet of paper. Sensitivity of motion to air turbulence, sensitivity to slight differences in the initial conditions. Chaos theory, random motion and coherent structures, organization of turbulence by constraining forces at various scales. Analogy with a temperature forecast, one-day vs. two-, three-, five-day forecasts. Ensemble forecasting and probabilities. You should be able to provide different reasons for the inaccuracy of weather forecasting beyond 5 days. General circulation How does everything fit into a big picture of the large weather patterns in our atmosphere? Warm-up exercise #1: average pressure maps, lower pressure at the equator, lows in the midlatitude, Aleutian low and icelandic low, subtropical highs, Pacific (Hawaiian) high, Bermuda (Azores) high. Warm-up exercise #2: rain forests (Amazon, SE Asia, Congo basin) and deserts (Sahara, Kalahari, Atacama, Patagonia, Australia, Arabia, Mongolia/Gobi), equator and tropics. Thought model: sea-breeze analogy, one-cell model, convection, clouds and rain at the equator. Why do upper-level winds blow northeastward and low-level wind blow southwestward at the equator? IR imagery, convection and cumulonimbus clouds at the equator, rotation of the earth, three-cell model. Regions of convection and subsidence, lows and highs.	pp 246-270 (in "Weather Forecasting")
Tuesday Mar 12	Wx: rain shadow. Review: single-cell model, three-cell model. Hadley cells, polar cells, regions of convection and subsidence, lows and highs, polar front, midlatitude cyclones, Ferrel cells, subtropical highs, trade winds, intertropical convergence zone (ITCZ), doldrums, westerlies, jets. History: Halley, Hadley, Ferrel. You should know the general circulation model very well and in detail: cells, ITCZ, winds, highs and lows by name and location, especially in relation to the typical weather patterns they explain. Confronting the conceptual three-cell model to average pressure maps, winter vs. summer. Subtropical highs, lower pressure at the equator, lows in the midlatitude, easterlies on each side of the equator, westerlies in the midlatitudes, converging wind at the equator, stronger highs in summer, stronger lows in winter. Impact of land masses on the distribution of H and L in the northern vs. southern hemisphere. Seasonal shift of the ITCZ, impact of land masses on the ITCZ. Pressure patterns leading to the chinook and Santa Ana winds in the U.S. Low-frequency electromagnetic waves and possible interactions with cortical activity, migraines and other disorders associated with Santa Ana winds. Pressure patterns leading to the foehn in Europe. Seasonal shift of the ITCZ, Sahel vs. Sahara desert and rain forests. High pressure and cold, dense air over Antarctica, katabatic winds, penguins and cold air advection feeding midlatitude cyclones over the Southern Ocean. Indian monsoon: shifts in the ITCZ position, lows and highs, trade winds, convergence and divergence of the subtropical jet, subsidence and convection, adiabatic warming, additional sea-breeze effect, orographic precipitation, Mei-yu front. You should be able to reproduce the above examples. Given a pressure map of a region of the world such as the above, you should be able to describe the weather you would expect.	pp 184-202 (in "Atmospheric Circulations")
Wednesday Mar 13	Review: general circulation. Hawaii in the trade winds, orographic precipitation. Impact of Pacific high and Aleutian low on Seattle weather, Pacific high and dry, cool west coast summer vs. Bermuda high and humid, rainy east coast summer. Review: Indian monsoon. History: Sir Gilbert Walker and the 1898 India drought and famine. El Niño What is El Niño/Southern Oscillation (ENSO)? Observation of sea-surface temperature shifts over the equatorial Pacific Ocean: "cold tongue", warmer waters and heavy precipitation in Indonesia, disappearance of the "cold tongue" and invasion of warmer waters throughout the entire equatorial ocean. Coastal upwelling of cold, nutrient rich waters, impact on temperature and fishing (California, Peru). Convergence of the trade winds at the ITCZ, diverging transport of water and upwelling along the equator, "cold tongue". Thought model: Walker circulation. La Niña phase: cold tongue and warm waters, upwelling, thermocline, H and L, trade winds, convection, precipitation, subsidence. El Niño phase: shift of the convection zone, weaker Walker circulation, secondary circulation over Indonesia, subsidence, drier weather. How is El Niño initiated and killed? Positive feedback loop: weaker trade winds, less upwelling, weaker Walker circulation, weaker trade winds. Thinking of the ocean and atmosphere as constantly animated by large-scale waves, analogy with a pond, initiation and death of El Niño, oscillations. Teleconnections: impact of ENSO on the rest of the world. Seattle: upper-level ridge during El Niño, straight jet and increased snow during La Niña winters. Florida: subtropical jet and increased rain during El Niño. Examples of other atmospheric oscillations. You should be able to describe the two phases of ENSO, the positive feedback loop that reinforces El Niño, and the impact of ENSO on the weather in the Pacific Northwest..	pp 202-209 (in "Atmospheric Circulations")
Thursday Mar 14	Wx: more rain tonight! Looking back and contemplating on learning: global composite IR satellite imagery, putting all the pieces together and answering all our early driving questions. Hurricanes What can we learn from observing hurricanes? Observations: where, how many, in what direction? Hurricanes, typhoons, and tropical cyclones. Preferred locations for hurricane tracks, away from equator, away from the midlatitudes, musings about the possible role of ocean heat, and the apparent role of the trade winds and the subtropical highs. From tropical disturbance to tropical depression to tropical storm to hurricane, categories. Naming convention, retired hurricane names. Deaths, casualties, impact of hurricanes in developing countries vs. U.S., examples of Galveston hurricane (1900), Bangladesh (1970), hurricane Mitch, hurricane Andrew, forecasting hurricanes and evacuating the population. Cloud structure, cyclonic rotation, spiraling rain bands. Overshooting of individual thunderstorm towers in hurricane Katrina. Size of tornadoes, thunderstorms, and hurricanes. Eye and eye wall, example of Emily's eye. Inside the eye: cloud wall vs. clear eye, radar echo, fair-weather cumulus clouds, subsidence, warming. Toward a conceptual model of hurricane structure. Conceptual model: warm and cold air columns, high and low pressure, upper-level divergence and surface convergence, surface wind, evaporation, convection, cloud droplet formation, latent heat release, warm core, more convection, more convergence, speed increase (conservation of angular momentum), more evaporation: positive feedback loop. Conditions for hurricane formation: impact of sea-surface temperature, rotation, vertical shear, stability. How do hurricanes acquire rotation and get organized? Mid-level African easterly jet, rotation, organization of thunderstorms around a warm core, formation of the eye, intensification given favorable conditions. You should know the conditions for hurricane formation, the positive feedback loop that sustains them until landfall, and the basic strucutre and mechanisms inside a hurricane.	pp 314-340 (in "Hurricanes")
Friday Mar 15	Quiz section - Final exam review.

Monday Mar 18	Final exam - Kane 220 from 8:30 to 10:20 a.m.

(*) Indicates the chapters and/or pages in Ahrens corresponding to the material covered in class.

Last modified: Thursday, 14 March 2013