AOS 100 & 101: Weather and Climate - Comprehensive Study Notes
Global Atmospheric Circulation and Energy Balance
Global Wind Systems
Midlatitude Jet: A fast-moving, narrow band of strong westerly winds found in the upper troposphere, steering weather systems.
Subtropical Jet: Similar to the midlatitude jet but located poleward of the Hadley cell, also impacting weather systems.
Polar Easterlies: Cold, dry winds blowing from the high-pressure areas of the polar highs at the North and South Poles towards the mid-latitudes.
Polar Front: The boundary between cold polar air and warmer mid-latitude air, often associated with storm systems.
Midlatitude Westerlies: Dominant winds in the middle latitudes ( to latitude), blowing from west to east.
Trade Winds: Persistent easterly winds that blow from the subtropical high-pressure zones towards the equator.
Intertropical Convergence Zone (ITCZ): A belt of low pressure near the equator where the northeast and southeast trade winds converge, leading to significant convection and precipitation.
High Sea-Level Pressure areas are also indicated.
Earth's Energy Budget (Values in 'units'): This budget illustrates the critical balance between incoming solar radiation and outgoing terrestrial radiation, driving Earth's climate system. These 'units' represent global averages.
Incoming Solar Radiation: (equivalent to - The total shortwave radiation received at the top of Earth's atmosphere.
Reflected by Atmosphere/Clouds: - A significant portion of incoming solar radiation is immediately reflected back to space by clouds, aerosols, and the Earth's surface (albedo).
Total Lost at Top of Atmosphere: - This represents the energy returned to space, maintaining Earth's radiative balance.
Outgoing IR: - Thermal infrared radiation emitted directly to space.
Additional loss (unspecified): - This accounts for other minor radiation losses.
Incoming to Earth's Surface: The energy reaching and absorbed by the Earth's surface.
Direct Solar Heat: - Shortwave radiation absorbed by land and oceans.
Incoming IR (from atmosphere): - Longwave radiation re-emitted by greenhouse gases and clouds in the atmosphere, warming the surface.
Total Gained by Earth: - The total energy absorbed by the surface.
Lost by Earth's Surface: The various ways the Earth's surface releases energy back to the atmosphere or space.
Outgoing IR: - Thermal infrared radiation emitted by the Earth's surface.
Evaporation (Latent Heat): - Energy consumed when water evaporates from the surface, transferring heat to the atmosphere as latent heat.
Convection & Conduction: - Direct transfer of sensible heat from the surface to the atmosphere.
Total Lost by Earth: - This perfectly balances the energy gained by the Earth's surface, demonstrating the steady state.
Atmospheric Energy Exchange: (Lost by ATM: / Gained by ATM: ) - The atmosphere itself absorbs and emits energy.
Solar heat absorption: - Shortwave radiation absorbed directly by atmospheric gases and aerosols.
IR absorption: - Longwave radiation absorbed from the Earth's surface by greenhouse gases.
Condensation/Convection: - Latent heat released during condensation and sensible heat from convection, warming the atmosphere.
Outgoing IR (from ATM): - Thermal infrared radiation emitted by the atmosphere to space.
Contemporary Atmospheric Events (August 2021)
Wildfires in Northern California (August 4, 2021, 4:21 PM PDT, NASA GOES 17 Satellite Photo): These significant wildfires, including the Monument Fire, Antelope Fire, River Complex, Dixie Fire, McFarland Fire, and River Fire, collectively caused widespread destruction, air quality issues, and ecological impact across Northern California. Satellite imagery provides crucial data for monitoring their progression and intensity.
Sea Ice Concentration (August 12, 2021, National Snow and Ice Data Center, University of Colorado Boulder): The map displays the percentage of ocean surface covered by sea ice. The comparison to the median ice edge from highlights areas where sea ice extent is above or below the long-term average, serving as an important indicator of climate change and its impact on polar regions. Areas like Oregon, California, Alaska, Russia, Greenland, Canada, and Europe are shown in context, emphasizing the global interconnectedness of climate phenomena.
Instructor's Background and Research
Research Areas: Focuses on understanding the complex interactions within the atmosphere.
Weather systems of the extra-tropics: Investigating the dynamics and characteristics of storms and atmospheric patterns outside the tropical regions.
Large-scale atmospheric dynamics: Studying the broad movements and forces that govern the atmosphere, crucial for global weather and climate.
Troposphere-Stratosphere coupling: Exploring how events in the lower atmosphere (troposphere) influence the upper atmosphere (stratosphere) and vice-versa, impacts phenomena like the polar vortex.
Focus on midlatitude weather and predictability: Dedicated to improving forecasts and understanding weather events in regions like North America and Europe.
Specific interests: Polar vortex (its variability and impact on extreme cold outbreaks), Winter Storms (forecasting and dynamics), to prediction (developing methods for subseasonal to seasonal forecasts).
Collaborations and partnerships are key: Emphasizes the interdisciplinary and collaborative nature of modern atmospheric science research.
Other Roles: Demonstrates active leadership and contribution to the atmospheric science community.
Member of the National Academies Board of Atmospheric Science and Climate: Advising on national atmospheric research priorities.
Councilor of the American Meteorological Society: Contributing to the scientific and educational goals of the professional society.
Co-lead of NOAA’s Subseasonal to Seasonal Prediction Task Force: Directing efforts to enhance predictions on weekly to monthly timescales.
Associated Editor of an atmospheric science journal: Overseeing the peer-review process and publication of scientific research.
The Polar Vortex: A critical element in understanding polar weather phenomena and mid-latitude cold spells.
Defined as a strong circumpolar jet stream combined with cold air within that jet in the stratosphere. When this vortex weakens or becomes distorted, it can lead to outbreaks of very cold air into lower latitudes.
Recent media examples from Washington Post (Feb 22, 2024; Feb 17, 2023) highlighted the subject: Public interest in the polar vortex often rises when it brings extreme cold to populated areas.
Atmosphere Thickness: The atmosphere is approximately the thickness of the entire planet. This emphasizes how relatively thin the atmospheric layer is compared to Earth's total diameter, yet it contains all the weather and climate processes vital for life.
Course Syllabus - AOS 100 & 101
Location: 1225 W. Dayton St. (across from Union South).
Office Hours: Held in the AOS&S building, providing an opportunity for students to engage directly with the instructor and TAs for clarification and deeper understanding.
Required Tool: Top Hat access is mandatory and part of the first Check-In. This interactive platform is used for real-time engagement and graded activities.
Assignments & Grading Breakdown (Lecture Component: AOS 100/101): The course assessment is designed to encourage continuous engagement and evaluate understanding across various formats.
Check-Ins (20%): These short Canvas assignments are crucial for regular engagement with course topics and immediate feedback.
May include figure interpretation, feedback, short answer, or multiple-choice questions, covering a range of cognitive skills.
, lowest score dropped. Highest grades each contribute 4{ ext{%}} to the final grade, offering a safeguard against one poor performance.
Late Policy: Strict policy to encourage timely submission and allow for prompt solution posting.
Submitted within (2 days) of due date: 70{ ext{%}} of earned points.
Submitted more than after due date: .
Solutions posted after due date on Canvas, making late submissions after this window less beneficial for learning.
Communicate extenuating circumstances to Prof. Lang in advance for potential accommodations.
In-Class Q&A (5% + up to 2% extra credit): Facilitated via Top Hat, these interactive questions promote active learning during lectures.
Graded 50{ ext{%}} participation and 50{ ext{%}} correctness, or 100{ ext{%}} participation, incentivizing thoughtful engagement over just correct answers.
Attendance is not required, but participation contributes to the grade, allowing flexibility while still rewarding engagement.
The top 80{ ext{%}} of Top Hat scores contribute 5{ ext{%}} to the final grade, mitigating the impact of occasional missed questions.
The lowest 20{ ext{%}} of scores can contribute up to 2{ ext{%}} extra credit, further rewarding consistent effort without penalizing initial struggles:
ext{Average of lowest } 20{ ext{%}} = 0 o 0{ ext{%}} ext{ extra credit}
ext{Average of lowest } 20{ ext{%}} = 50{ ext{%}} o 1{ ext{%}} ext{ extra credit}
No need to inform instructor about absences, providing student autonomy.
Homework (32%): Consisting of assignments, these provide deeper application of course material outside of lectures. The highest grades each contributing 8{ ext{%}} of the final grade, offering a buffer.
Quizzes (30%): Three quizzes, each counting as 10{ ext{%}} of the final grade, assess comprehension of specific units.
Taken during class, focusing on the most recent unit, ensuring ongoing understanding.
Question types: multiple choice, fill in the blank, short answer, testing various aspects of recall and application.
Review sessions held in the week prior to each quiz to help students prepare effectively.
Final Exam (13%): A comprehensive assessment scheduled for Friday, December 12 (12:25 PM - 2:25 PM).
Covers the fourth unit in depth and cumulative questions from the entire semester, requiring a holistic understanding of the course material.
Exam Conflicts: Students must check schedules early and approach instructors within the first weeks of classes for any conflicts with other scheduled exams, ensuring fair accommodations.
Total Available Grade: 102{ ext{%}} - Provides a slight buffer for students to achieve a high grade through consistent effort.
Academic Integrity: All assignments are to be independent work. Discussion with other students is encouraged for homework to foster collaborative learning of concepts, but actual problems must be worked out individually without AI tools or copying to ensure personal mastery of the material.
Grade Calculation Scale (A-F): Standard grading scale used for final grade determination.
A: 92-100+ { ext{%}}
AB: 88-91.9 { ext{%}}
B: 82-87.9 { ext{%}}
BC: 78-81.9 { ext{%}}
C: 72-77.9 { ext{%}}
D: 66-71.9 { ext{%}}
F: 0-65.9 { ext{%}}
Final grades are not curved, but some low scores are dropped as per the policy, offering a fair assessment structure.
AOS 101 Specifics: The final grade is weighted as 75{ ext{%}} lecture and 25{ ext{%}} discussion section, acknowledging the importance of both theoretical and applied learning. Discussion section TAs will provide their specific grade calculation, as these sections may involve different types of assignments.
Textbook: "Meteorology Today: An Introduction to Weather, Climate, and the Environment" 13E by C. Donald Ahrens and Robert Henson (CENGAGE). A foundational resource for the course content.
Canvas: Course information and updates posted weekly on Fridays. Announcements are important to monitor for essential information and deadlines. Homework submitted via Canvas, serving as the central hub for course management.
Top Hat: Linked from the AOS 100/101 Canvas page, ensuring easy access to this interactive tool.
Pro-Tip: Utilize office hours in the first full week as a low-stakes opportunity to connect with professors and TAs, fostering a supportive learning environment from the start.
Check-In 1: Opens today (Sept 10, 10:45 AM), Due tomorrow (Sept 10, 11:59 PM) in Canvas, initiating student engagement early in the semester.
Course Sections
The course is structured into four main units to systematically cover key aspects of weather and climate:
Atmospheric composition & energy balance: Delving into the gases that make up our atmosphere and how energy flows through it.
The role of water in our atmosphere: Exploring the hydrologic cycle, clouds, and precipitation.
The processes and forces behind weather and climate: Understanding atmospheric pressure, winds, and large-scale circulation patterns.
Bringing it all together: weather and climate phenomena: Applying learned concepts to real-world weather events, climate change, and extreme weather.
Weather and Climate Fundamentals
Atmospheric Science / Meteorology: An application of several physical sciences, including physics, math, and chemistry, to understand the Earth's atmosphere and its phenomena. It combines theoretical knowledge with observational data to predict and explain atmospheric behavior.
Weather: The condition of the atmosphere at a particular moment and in a particular place, encompassing variables like temperature, humidity, precipitation, wind, and cloudiness. It describes short-term atmospheric states.
Climate: The condition of the atmosphere over a long period of time, essentially the average weather conditions for a specific region. It includes statistical descriptions of atmospheric elements over years, decades, or even centuries.
"Climate Normal": Typically calculated over a average (e.g., ), serving as a baseline for comparison to assess current climate trends. This period is chosen to smooth out short-term fluctuations and highlight longer-term climatic patterns.
Local Climate "Record": Considers the entire period of data recording. For Madison, this is from , totaling of data, providing a historical perspective on climate variability and extremes.
Historical Context: In , President Ulysses S. Grant signed a law requiring the Secretary of War to provide meteorological observations and storm warnings via magnetic telegraph and marine signals. This marked the formal beginning of an organized national weather service in the United States, essential for public safety and commerce.
Atmospheric Scale: 99{ ext{%}} of all atmospheric molecules reside within () from Earth’s surface. Gravity is responsible for keeping these molecules close to the surface, resulting in higher pressure and density nearer the ground.
Earth's Atmosphere: Evolution and Composition
Earth's Early Atmosphere: The atmosphere has undergone dramatic changes since Earth's formation.
Earth is the planet from the Sun and currently has a unique atmosphere that has evolved over the last , setting the stage for life.
Earliest Atmosphere: Primarily Hydrogen () and Helium (), light gases abundant in the early solar system. Most of this drifted into space due to Earth's weaker early gravitational field and intense solar winds stripping away lighter elements.
Second Atmosphere: Formed from volcanic outgassing, it was predominantly composed of water () vapor, carbon dioxide (), methane (), and ammonia (). There was little free oxygen. This atmosphere was maintained by continuous emissions from active volcanoes, releasing trapped gases from Earth's interior.
Evolution to Present Day: A series of critical processes transformed this second atmosphere.
High-energy ultraviolet light from the sun caused photodissociation: the breakdown of water vapor ( ext{H}*2 ext{O}} ) into hydrogen () and oxygen (), allowing for the slow accumulation of oxygen.
Early life, such as cyanobacteria (blue-green algae), performed photosynthesis, which led to the creation of significant amounts of Nitrogen () and Oxygen () in the atmosphere. This biological activity was key to creating an oxygen-rich environment suitable for complex life.
Much of the initial dissolved into the oceans, forming carbonates, which locked carbon away from the atmosphere and reduced its concentration.
What is the Atmosphere? A dynamic envelope of gases surrounding Earth, essential for life.
Earth's atmosphere weighs approximately (), a vast but finite mass held by gravity.
Composed mostly of invisible gases, some liquids (e.g., cloud droplets), and some solids (e.g., dust, aerosols).
Acts as a fluid in constant motion, taking the shape of its container, driven by solar heating and Earth's rotation, leading to weather patterns.
Since it consists of molecules, the atmosphere has a measurable mass (Weight = mass x gravity), which exerts pressure on the Earth's surface.
Atmospheric Composition: Divided into permanent and variable gases.
Permanent Gases (by Volume, Dry Air): These gases remain relatively constant in concentration up to about and are largely unreactive in atmospheric processes.
Nitrogen (): 78.08{ ext{%}} - The most abundant gas, relatively inert, crucial for biological processes, and dilutes oxygen.
Oxygen (): 20.95{ ext{%}} - Essential for respiration and combustion, plays a key role in atmospheric chemistry.
Argon (): 0.93{ ext{%}} - An inert noble gas.
Neon (): 0.0018{ ext{%}}
Helium (): 0.0005{ ext{%}}
Hydrogen (): 0.00006{ ext{%}}
Xenon (): 0.000009{ ext{%}}
Note: Together, N2 and O2 make up approximately 99{ ext{%}} of the dry air, forming the bulk of the atmosphere.
Variable Gases and Particulates (by Volume, Parts per Million - ppm): Though present in smaller quantities, these gases have a disproportionately large impact on weather, climate, and atmospheric chemistry due to their active roles.
Water vapor (): 0 ext{ to } 4{ ext{%}} - Highly variable, a potent natural greenhouse gas, and crucial for cloud formation and precipitation.
Carbon dioxide (): 0.041{ ext{%}} () - A vital greenhouse gas and a key component of the carbon cycle, its increasing concentration is a primary driver of global warming.
Methane (): 0.00018{ ext{%}} () - Another powerful greenhouse gas, more potent per molecule than CO2, though less abundant.
Nitrous oxide (): 0.00003{ ext{%}} () - A greenhouse gas and ozone-depleting substance.
Ozone (): 0.000004{ ext{%}} () - In the stratosphere, it protects Earth from harmful UV radiation; in the troposphere, it is a pollutant.
Particles (dust, soot, etc.): 0.000001{ ext{%}} () - Atmospheric aerosols, influencing cloud formation, radiation scattering, and air quality.
Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs): 0.00000001{ ext{%}} () - Synthetic compounds with strong greenhouse effects, known for ozone depletion, though regulated.
Note: These are considered trace gases and play significant roles despite their small quantities, often acting as active components in radiative forcing and chemical reactions.
Water Vapor (): The most important variable gas for weather and climate.
An invisible gas; clouds are visible tiny water droplets or ice crystals suspended in the atmosphere, not water vapor itself.
Its quantity varies geographically, from near 0{ ext{%}} in arid polar regions to up to 4{ ext{%}} of atmospheric volume in humid tropical areas, reflecting its dynamic nature.
Condensation: A process that removes (acts as a sink for) water vapor from the air, simultaneously releasing latent heat to the environment, which warms the atmosphere and fuels storms.
Evaporation: A process that adds (acts as a source for) water vapor to the air, consuming latent heat from the environment, leading to cooling of the surface.
Water is unique in that it is the only substance on Earth that can naturally exist in all three states (solid, liquid, gas) in abundance, allowing for complex energy exchanges in the atmosphere.
This property is crucial to the planet's energy budget, acting as a potent greenhouse gas (absorbing and re-emitting infrared radiation) and through latent heat processes (transferring vast amounts of energy during phase changes).
Example: Satellite images can distinguish cold land/snow/ice clouds (red) from warm land/water clouds (blue) based on IR signatures, illustrating how remote sensing helps study atmospheric water.
Hydrologic Cycle: The continuous movement of water on, above, and below the surface of the Earth, fundamentally driven by solar energy and gravity, involving phase changes that redistribute energy.
The phase change of water involves latent heat (energy uptake or release):
Processes that require energy (cooling the environment):
Solid Liquid (Melting): e.g., ice to water.
Liquid Gas (Evaporation): e.g., water to vapor from oceans.
Solid Gas (Sublimation): e.g., ice directly to vapor.
Processes that release energy (warming the environment):
Gas Liquid (Condensation): e.g., vapor to cloud droplets.
Liquid Solid (Freezing): e.g., water to ice.
Gas Solid (Deposition): e.g., vapor directly to ice (frost).
This latent heat exchange profoundly influences atmospheric stability and storm development.
Carbon Dioxide (): A critical trace gas with immense influence on Earth's climate system.
A small natural component of Earth's atmosphere, but with a huge impact as a primary greenhouse gas.
Sources:
Decay of vegetation: Natural decomposition releases CO2.
Volcanic eruptions: Release CO2 from Earth's interior over geological timescales.
Burning of fossil fuels (coal, natural gas, oil): The largest anthropogenic source, releasing ancient carbon rapidly.
Deforestation: Removes carbon sinks (trees) and releases stored carbon when vegetation decays or burns.
Sinks: Processes that remove CO2 from the atmosphere.
Photosynthesis (by plants and phytoplankton): Biological absorption of CO2 to produce organic matter.
Oceans (dissolving into water and uptake by phytoplankton): Oceans act as a major reservoir, but absorption also leads to ocean acidification.
concentrations have been notably increasing over the last century due to human activities, especially since the industrial revolution, leading to enhanced greenhouse effect.
It is a critical greenhouse gas, playing a vital role in Earth's energy budget by absorbing and re-emitting infrared radiation, trapping heat, and warming the planet.
The Atmospheric Carbon Cycle (Figure 1.5): A complex biogeochemical cycle illustrating the continuous exchange of between the atmosphere, oceans, biosphere (living and dead), and geological processes. Human activities, particularly the burning of fossil fuels and land-use changes, have significantly altered the natural balance of this cycle, leading to a net increase of CO2 in the atmosphere.
Key pathways include fuel combustion, volcanic activity, respiration, burning of plants, dissolving into oceans, photosynthesis, chemical weathering, and marine life, showcasing the interconnectedness of Earth's systems.
The Keeling Curve: An iconic and globally significant observation record showing the increasing atmospheric concentration of , measured continuously at Mauna Loa Observatory, Hawaii, since 1958.
The curve indicates a general upward trend, for example, from approximately in an earlier period to about as of September 3, 2025. This rising trend is primarily attributed to anthropogenic emissions from fossil fuel burning and deforestation.
It also shows an annual oscillatory pattern due to seasonal changes in Northern Hemisphere plant growth (photosynthesis in spring/summer reduces CO2, decomposition in fall/winter releases it). This data is part of a global observation network (e.g., NOAA/ESRL/GMD), providing irrefutable evidence of rising atmospheric CO2.