Atmospheric Dynamics, Climate Systems, and Glacial Geomorphology (copy)
Administrative Details and Course Structure
Lab Schedule: There are only total spread out across the term. There is no lab scheduled for tomorrow or the following week, despite automated notifications indicating weekly meetings.
Midterm Examination Structure: Designed for a lecture slot.
Includes a small number of multiple-choice questions intended for rapid completion.
Includes short-answer questions structured to assess comprehension of synthetic, integrative content.
Earth System Science and Interacting Spheres
Earth System Framework: The planet operates as an integrated system composed of interconnected constituent spheres, which represent conceptual abstractions of interacting physical and biological components.
A change in one sphere directly or indirectly induces alterations across other spheres.
Primary Earth Spheres:
Atmosphere: The gaseous layer surrounding Earth that drives weather patterns and short-term environmental fluctuations.
Cryosphere: The frozen water system of Earth, encompassing glaciers, ice caps, sea ice, and permafrost.
Pedosphere: The outermost layer of Earth composed of soil and subject to soil formation processes.
Biosphere: All biological organisms and living ecosystems, including forests, wetlands, and marine habitats.
Geosphere: The solid lithospheric structure of Earth, involving continental positioning, rock extrusion, plate tectonics, and erosion.
Magnetosphere: The magnetic field surrounding Earth that shields the atmosphere from solar radiation.
Anthroposphere: The expanding domain of human modifications to Earth's surface and systems, which has become so pervasive that its boundaries are difficult to delineate from natural systems.
Atmospheric Dynamics and Solar Radiation
Temporal Dynamics: The atmosphere changes more rapidly than any other sphere, experiencing variable shifts over hourly, daily, and seasonal cycles.
Solar Energy Geometry: Incoming solar radiation is the primary driver of atmospheric circulation and surface temperature distribution.
Equatorial Regions: Sunlight strikes directly at a perpendicular angle, concentrating solar energy over a small surface area and yielding high average temperatures.
Polar Regions: Sunlight strikes at an oblique, shallow angle, distributing the energy across a much larger surface area, resulting in significantly colder baseline temperatures.
Tectonic and Feedback Drivers: Low polar temperatures alone do not fully account for polar ice sheets; ice accumulation requires specific plate tectonic configurations and positive feedback loops.
Atmospheric Circulation Cells:
Atmospheric circulation is partitioned into large-scale circulating cells, including the Hadley cells located around the tropical latitudes.
Cell boundaries strongly govern regional climate and weather phenomena, including tropical hurricane development.
Equatorial Convection and Relative Humidity Dynamics:
High equatorial temperatures heat surface air, causing warm air to rise and creating persistent low-pressure zones.
As air rises, ambient pressure decreases, causing the air to expand and cool adiabatically.
Relative Humidity: Defined as the percentage of water vapor held in an atmospheric air mass relative to the maximum amount it can hold at a given temperature before condensation occurs.
Relative humidity is modified either by altering the total water vapor content or by changing the air temperature.
Air cooling increases relative humidity toward its saturation point ( relative humidity), causing water vapor to condense into clouds and generate heavy precipitation along the equatorial belt.
Subtropical Subsidence and Desert Formation:
Rising atmospheric air moves poleward at high altitudes, loses moisture, cools, and subsequently descends at subtropical latitudes.
The descending air is inherently dry because moisture was lost via equatorial precipitation.
As dry air descends, atmospheric pressure increases, causing the air mass to compress and warm.
Air warming reduces relative humidity, driving the air mass further from its condensation threshold and suppressing precipitation.
Subtropical deserts (such as the Sahara Desert) and cold polar deserts (such as Antarctica) are located directly beneath these descending, high-pressure cell boundaries.
Coriolis Effect and Wind Patterns:
Earth's rotational momentum exerts a deflecting force known as the Coriolis effect on moving air masses.
Deflects air trajectories within circulation cells, curving wind paths and creating prevailing East-to-West Trade Winds near the equator.
Atmospheric cell boundaries are non-static; localized shifts in ocean currents or thermal anomalies alter boundary positions, resulting in unexpected localized weather disruptions.
Jet Streams and the Polar Vortex
Jet Stream Mechanics:
Low-pressure zones generated at the convergence boundaries between distinct atmospheric circulation cells produce high-altitude, high-velocity air currents called jet streams.
Jet streams serve as thermal boundaries separating polar cold air masses from mid-latitude warm air masses.
These currents meander latitudinally due to Earth's rotation (Coriolis effect), pressure differentials, and surface topography.
Polar Vortex Dynamics:
The polar vortex is a massive, persistent upper-altitude low-pressure cold air system bounded by the polar jet stream circling the Arctic and Antarctic poles.
Vortex Perturbation: Disruptions caused by atmospheric warm air pockets weaken the bounding polar jet stream, causing it to become sinuous, fluid, and unstable.
Weakened jet streams can split the primary polar vortex into two distinct vortices or allow cold arctic air masses to dip southwards.
In regional zones like Ontario, polar vortex breakdowns during winter produce anomalous weather spikes, such as () of snowfall over a period.
Climate Change Paradox:
Stratospheric warming weakens the structural integrity of the polar jet stream, forcing it into severe undulations.
Counterintuitively, overall global warming increases the frequency of polar vortex instability, leading to localized episodes of extreme cold, intense snowfall, and severe winter weather despite rising mean global temperatures.
Climate, Weather, and Temporal Scales
Weather vs. Climate:
Weather: Day-to-day atmospheric conditions and localized scale meteorological phenomena occurring at specific moments.
Climate: The long-term statistical average of weather parameters calculated over a standard baseline of . Climate establishes the baseline probability distribution of weather outcomes.
Distribution Shifts: A shift in the mean climate alters the entire probability curve; extreme cold events can still occur as tail-end probabilities within a warming distribution.
Temporal Scales of Climate Drivers:
Anthropogenic Forcing: Changes driven by human greenhouse gas emissions () operating on rapid time scales of several years to decades.
External Planetary Forcing: Orbital variations (Milankovitch cycles) and solar forcing operating over cyclical periods of to .
Tectonic Forcing: Lithospheric movement and continental shifting operating over tens to hundreds of millions of years.
Observational Baselines and Qualitative Evidence:
Shifting baseline surveys quantify changes across human generational memory.
In Greenland, local populations report that icebergs discharging from the Ilulissat Icefjord have reduced to half the size recorded in previous decades.
Paleoclimate Modeling and Uncertainty:
Historical climate curves reconstructed across the Phanerozoic Eon (spanning complex fossil life) incorporate probabilistic component ranges.
Paleoclimate models express climate states as ranges of likelihood rather than absolute values, reflecting inherent statistical uncertainty.
Hydrologic Cycle and Groundwater Dynamics
Global Hydrologic Budget: Water transitions between finite storage reservoirs (oceans, atmosphere, groundwater, ice sheets) via evaporation, precipitation, runoff, and infiltration.
Groundwater Dynamics:
Subsurface groundwater represents a major freshwater reservoir critical for municipal drinking supplies (such as in Ontario).
Flow velocity is exceptionally slow, advancing at rates measured in fractions of a meter per unit time.
Extreme residence time makes groundwater recharge rates dependent on regional precipitation and leaves aquifers exceptionally vulnerable to long-term contamination that is nearly impossible to remediate rapidly.
Glacial Water Storage:
Cold climate intervals lock up vast volumes of freshwater in terrestrial glaciers and ice sheets (with Antarctic continental ice exceeding millions of years in age).
Terrestrial ice storage decreases global liquid ocean volume, lowering sea levels during glacial periods and elevating sea levels during interglacial melting.
Ocean Circulation and the Thermohaline Conveyor Belt
Oceanic Drivers: Ocean surface currents are driven by atmospheric winds, while deep ocean currents are driven by thermohaline dynamics (variations in water temperature and salinity affecting density).
Regional Thermal Anomalies:
Oceanic currents strongly influence local terrestrial climates.
The Galapagos Islands, located on the equator, feature unexpectedly cold oceanic surface waters due to deep cold-water upwelling currents.
Thermohaline Circulation Mechanism:
Derived from thermo (temperature) and haline (salinity, referencing halite/rock salt).
Functions as a global oceanic conveyor belt:
Cold, dense, saline, nutrient-rich water upwells in the Eastern Pacific and Southern Indian Oceans.
Upwelled water warms as it flows through Southeast Asia, across the Indian Ocean, around the southern tip of Africa, and northward along the eastern coasts of South and North America via the Gulf Stream.
The warm current crosses the North Atlantic toward Greenland and the Arctic, releasing thermal energy to the atmosphere.
In the Arctic, water cools, increases in density, sinks to the deep ocean floor, and flows southward to restart the loop.
Atlantic Meridional Overturning Circulation (AMOC) Vulnerability:
The warm northward transport of the AMOC maintains temperate climate conditions across Western Europe and Great Britain.
Disruption Risk: Rapid melting of the Greenland ice sheet discharges massive volumes of cold, low-density freshwater into the North Atlantic.
Influx of freshwater reduces surface salinity and alters density gradients, threatening to disrupt or collapse deep-water sinking.
A collapse or southward shift of the AMOC mixing zone (projected in climate models past the year ) would significantly cool Western Europe and increase regional snowfall, though it would not trigger instantaneous continental glaciation.
Tectonic History, Paleoclimate, and the Antarctic Circumpolar Current
Antarctic Tectonic Position:
Antarctica has occupied a polar position at the South Pole for over (and was similarly positioned during the Ordovician period approximately ).
Polar position alone does not guarantee glaciation; during the Cretaceous period, Antarctica was ice-free, densely vegetated, and inhabited by dinosaurs.
Dinosaurs living in polar Cretaceous Antarctica adapted to continuous winter darkness and summer daylight under the aurora australis.
The Antarctic Circumpolar Current (ACC):
Approximately , plate tectonic movement separated the Antarctic Peninsula from the southern tip of South America (Tierra del Fuego), opening the Drake Passage.
Opening the Drake Passage created an unobstructed, continuous ocean corridor around Antarctica, giving rise to the Antarctic Circumpolar Current.
The ACC thermally isolated Antarctica from warm equatorial ocean currents, trapping cold waters around the continent and initiating continental ice sheet formation.
The Drake Passage generates extreme oceanic turbulence, producing marine wave swells reaching heights up to .
El Niño-Southern Oscillation (ENSO) Dynamics
System Definition: Coupled atmospheric-oceanic climate pattern in the Pacific Ocean consisting of El Niño (oceanic thermal shift) and the Southern Oscillation (atmospheric pressure/wind shift).
Normal Pacific Conditions:
Strong trade winds blow westward from Central America (Panama) toward Southeast Asia.
Warm surface water is pushed westward, creating a steep thermocline (boundary between warm surface water and cold deep water) that is deep in the western Pacific and shallow in the eastern Pacific.
El Niño Conditions:
Trade winds weaken significantly, allowing the accumulated warm water mass in the western Pacific to flow back eastward toward North and South America.
Shifts the thermocline and raises sea surface temperatures along the eastern Pacific coast.
Climatic Impacts: Causes intense rainfall, atmospheric instability, and severe flooding along the West Coast of North and South America (e.g., California), while causing extreme drought, crop failure, and famine across Indonesia and Southeast Asia.
A severe historic ENSO event occurred in .
La Niña Conditions:
Trade winds become stronger than normal, pushing warm surface water even further west into the Pacific.
Suppresses eastern Pacific warm water, leading to abnormally cold sea surface temperatures, prolonged dry spells, severe agricultural droughts, and crop failures along the American west coast.
La Niña states often persist continuously across multiple consecutive years.
The Cryosphere and Glacial Dynamics
Climate Regime Oscillations:
Icehouse Conditions: Cold global climates characterized by expanded continental ice sheets, locking up freshwater and lowering sea levels.
Greenhouse Conditions: Warm global climates characterized by absent or restricted polar ice sheets, melting terrestrial ice and elevating sea levels.
Glacial-Interglacial Cycles:
Glacial intervals are long and stable, requiring strong external orbital forcing to transition Earth into warm, short interglacial periods.
The current interglacial period began approximately to . All recorded human civilization developed within this interglacial climate window.
Uncontrolled anthropogenic forcing risks pushing the global climate system out of normal interglacial bounds into greenhouse conditions unexperienced by modern biological species since the Cretaceous.
Glacial Mass Balance Mechanics:
Governed by mass balance: .
Advancement: When accumulation exceeds ablation, glacial mass increases. Gravity forces the ice mass to deform plastically and flow outward/downward towards lower latitudes or altitudes (aided by basal meltwater reducing bedrock friction).
Recession/Retreat: When ablation exceeds accumulation, the glacier melts back. Glaciers never physically reverse direction; retreat occurs strictly through localized melting exceeding advance rates.
Glacial Geomorphology and Landscape Features
Alpine Glacial Features:
High-altitude mountain glaciers carve distinct erosional landforms.
U-Shaped Valleys: Advancing glaciers grind pre-existing V-shaped river valleys into broad, steep-sided U-shaped glacial troughs.
Continental Glacial Features:
Striations and Polished Bedrock: Massive continental ice sheets scour and polish hard underlying bedrock exposures (such as the Canadian Shield in Ontario).
Moraines: Accumulations of unsorted glacial till and rock debris pushed forward or laterally by advancing ice sheets and deposited upon glacial retreat.
Eskers: Sinuous, elevated ridges of sorted sand and gravel formed by subglacial meltwater streams flowing through tunnels beneath the ice sheet.
Kettle Lakes: Depressions formed when isolated blocks of glacial ice are buried in sediment; when the ice block melts, it leaves a landlocked water body disconnected from regional surface hydrology.
Glacial Erratics: Massive boulders transported hundreds of kilometers by ice sheets and deposited onto bedrock of completely different lithology (e.g., large igneous granite boulders sitting atop sedimentary limestone bedrock in Ontario). Erratics provided early geologists with definitive evidence of past continental-scale glaciation.