Comprehensive Study Guide for Exam 2

Chapter 6 – Atmosphere and Oceans A

Solar Radiation and Seasons

• Solar radiation input varies by season because Earth is tilted on its axis (23.5∘) as it orbits the sun

• The sun's rays are most direct at:

  • Summer solstice (June 21): $23.5^\circ$N (Tropic of Cancer)

  • Winter solstice (December 21): $23.5^\circ$S (Tropic of Capricorn)

  • Spring and Fall equinoxes: 0∘ (Equator)

Ice-Albedo Positive Feedback Loop

• Albedo = how reflective a surface is (higher albedo = more reflection)

• Ice has high albedo (reflects 80-90% of sunlight)

• The feedback loop works like this:

  1. Ice melts due to warming

  2. Less ice means less reflection (lower albedo)

  3. More sunlight absorbed by darker surfaces (ocean/land)

  4. More warming occurs

  5. More ice melts, continuing the cycle

• This amplifies warming and is a positive feedback loop (change produces more change in the same direction)

• This affects Earth's heat budget by increasing the amount of heat absorbed and retained

Heat Distribution Forces

The 2 primary forces governing heat distribution on Earth are:

1. Wind (in the atmosphere)

2. Ocean currents (in the oceans)

Atmospheric Composition

• Nitrogen (N$_2$): $\sim$78%

• Oxygen (O$_2$): $\sim$21%

• Other gases make up the remaining 1% (including CO$_2$, water vapor, etc.)

Air Density Factors

Air density is affected by:

• Temperature: Warmer air is less dense (rises), colder air is more dense (sinks)

• Pressure: Higher pressure compresses air molecules (more dense)

• Humidity: Moist air is less dense than dry air (water molecules are lighter than nitrogen/oxygen)

• Altitude: Density decreases with increasing altitude (less air pressure)

Weather vs. Climate

• Weather: Short-term conditions of the atmosphere (day-to-day)

  • Temperature, humidity, precipitation, wind, clouds

  • Can change quickly

  • Local scale

• Climate: Long-term average weather patterns (30+ years)

  • More stable and predictable

  • Regional to global scale

  • Changes more slowly

Coriolis Force

• Coriolis force is the apparent deflection of moving objects due to Earth's rotation

• Not an actual force, but appears to affect movement due to the rotating reference frame

• In Northern Hemisphere: deflects to the RIGHT

• In Southern Hemisphere: deflects to the LEFT

• Stronger at higher latitudes, zero at the equator

• Affects wind patterns, ocean currents, and projectiles traveling long distances

Earth's Wind Patterns and Pressure Systems

Earth has three major circulation cells in each hemisphere:

1. Hadley Cell (0∘-30∘ N/S)

   • Warm air rises at the equator, moves poleward, cools and sinks at 30∘ N/S

   • Creates low pressure at equator, high pressure at 30∘ N/S

2. Ferrel Cell (30∘-60∘ N/S)

   • Indirect circulation cell between tropical and polar regions

   • Air rises at 60∘ N/S and sinks at 30∘ N/S

3. Polar Cell (60∘-90∘ N/S)

   • Cold air sinks at poles, creating high pressure

   • Air flows toward 60∘ N/S where it rises, creating low pressure

Wind Rotation Around Pressure Systems

• In the Northern Hemisphere:

  • High pressure: Clockwise rotation and outward flow

  • Low pressure: Counterclockwise rotation and inward flow

• In the Southern Hemisphere:

  • High pressure: Counterclockwise rotation and outward flow

  • Low pressure: Clockwise rotation and inward flow

This is often remembered with the phrase: "High to the right (Northern Hemisphere) or high to the left (Southern Hemisphere)"

Chapter 6 – Atmosphere and Oceans B

Heat Distribution on Earth's Surface

• Uneven heating occurs because of Earth's spherical shape

• Equator receives most direct sunlight (warmer)

• Poles receive indirect, angled sunlight (cooler)

• Heat moves from warm equator toward cooler poles through:

  • Atmospheric circulation (winds)

  • Ocean currents

  • Seasonal changes help distribute heat

Wind Causes and Direction

• Winds exist because of temperature and pressure differences

• Air moves from high pressure to low pressure areas

• Direction is influenced by:

  • Pressure gradient force (high to low pressure)

  • Coriolis effect (deflects movement right in Northern Hemisphere, left in Southern)

  • Friction with Earth's surface (slows wind near ground)

Major Wind Bands and Latitudes

• Trade Winds (0∘-30∘ N/S): Blow from northeast (NH) or southeast (SH) toward equator

• Westerlies (30∘-60∘ N/S): Blow from southwest (NH) or northwest (SH) toward poles

• Polar Easterlies (60∘-90∘ N/S): Blow from northeast (NH) or southeast (SH) toward 60∘ latitude

• Doldrums (near equator): Light, variable winds due to rising air

• Horse Latitudes (30∘ N/S): Light, variable winds due to sinking air

Ice/Albedo Feedback Loop (repeated from above)

• Ice and snow reflect most solar radiation back to space (high albedo)

• When ice melts, darker surfaces absorb more solar radiation

• More absorption leads to more warming and more melting

• This creates a positive feedback loop (self-reinforcing cycle)

Coastal Wind Patterns (Land/Sea Breezes)

• Daytime (Sea Breeze):

  • Land heats up faster than water

  • Warm air over land rises

  • Cooler air from sea flows toward land

  • Creates onshore breeze

• Nighttime (Land Breeze):

  • Land cools faster than water

  • Warm air over water rises

  • Cooler air from land flows toward sea

  • Creates offshore breeze

• Relation to Monsoons in India:

  • Monsoons work on the same principle but on a larger scale and seasonal timeframe

  • Summer: Land heats up, creates low pressure, draws in moist air from ocean (wet season)

  • Winter: Land cools, creates high pressure, pushes dry air toward ocean (dry season)

El Niño/La Niña

• Normal conditions: Strong trade winds push warm surface water westward, cold water upwells along South America

• El Niño:

  • Trade winds weaken

  • Warm water moves eastward toward South America

  • Suppresses upwelling of cold, nutrient-rich water

  • Causes: Heavy rainfall in eastern Pacific, droughts in western Pacific, disruption of global weather patterns

• La Niña:

  • Stronger than normal trade winds

  • Cold water extends further west in Pacific

  • Enhances upwelling along South America

  • Causes: Intensified normal conditions, more hurricanes in Atlantic, droughts in southern U.S.

Chapter 7 – Ocean Structure and Circulation

Ocean Temperature and Salinity vs. Depth

• Temperature vs. depth:

  • Surface layer: Warm, well-mixed (varies by season and latitude)

  • Thermocline: Zone of rapid temperature decrease with depth (typically 100-1000m)

  • Deep ocean: Cold, stable temperature (about 2-4$^\circ$C)

• Salinity vs. depth:

  • Surface layer: Variable (affected by evaporation, precipitation, river input)

  • Halocline: Zone of rapid salinity change with depth

  • Deep ocean: Relatively stable salinity

Seasonal Thermocline at Mid-Latitudes

• Summer:

  • Strong sunlight warms surface waters

  • Thin mixed layer (top 10-30m)

  • Sharp thermocline below

• Fall:

  • Surface water cools

  • Wind-driven mixing deepens the mixed layer

  • Thermocline weakens and deepens

• Winter:

  • Cold temperatures and strong winds

  • Deep mixed layer (can reach 100-200m)

  • Weak or absent thermocline

• Spring:

  • Surface warming begins

  • New shallow thermocline forms

  • Mixed layer becomes thinner

Water Masses

Four different water masses include:

1. North Atlantic Deep Water (NADW)

   • Forms in the North Atlantic (near Greenland and Labrador)

   • Cold, salty, dense water that sinks to great depths

   • Formed by cooling of Gulf Stream water

2. Antarctic Bottom Water (AABW)

   • Forms around Antarctica

   • Very cold, slightly less salty than NADW

   • Densest water mass, flows along ocean bottom

3. Antarctic Intermediate Water (AAIW)

   • Forms at Antarctic Convergence

   • Cold, relatively fresh

   • Flows at intermediate depths (500-1500m)

4. Mediterranean Water

   • Forms in the Mediterranean Sea

   • Warm, very salty

   • Flows into Atlantic at mid-depths

Surface Current Gyres

• Gyres are large circular ocean current systems

• Formed by the interaction of:

  • Global wind patterns (trade winds, westerlies)

  • Coriolis effect

  • Continental boundaries

• Creates clockwise rotation in Northern Hemisphere

• Creates counterclockwise rotation in Southern Hemisphere

Major Currents in Each Gyre

• North Atlantic Gyre:

  • Gulf Stream (western boundary)

  • North Atlantic Current

  • Canary Current (eastern boundary)

  • North Equatorial Current

• South Atlantic Gyre:

  • Brazil Current (western boundary)

  • South Atlantic Current

  • Benguela Current (eastern boundary)

  • South Equatorial Current

• North Pacific Gyre:

  • Kuroshio Current (western boundary)

  • North Pacific Current

  • California Current (eastern boundary)

  • North Equatorial Current

• South Pacific Gyre:

  • East Australian Current (western boundary)

  • South Pacific Current

  • Humboldt/Peru Current (eastern boundary)

  • South Equatorial Current

• Indian Ocean Gyre:

  • Agulhas Current (western boundary)

  • West Australian Current (eastern boundary)

  • South Equatorial Current

Wind-Driven Currents

• Equatorial currents (North and South Equatorial) are wind-driven by trade winds

• Eastern boundary currents (Canary, Benguela, California, Humboldt) are wind-driven by trade winds

• Surface currents are primarily driven by prevailing winds

Water Masses in the Atlantic Ocean

From surface to bottom across the Atlantic:

• Surface water (warm, variable salinity) - top 100-200m

• Central water (moderate temperature and salinity) - 200-600m

• Antarctic Intermediate Water (cold, low salinity) - 600-1500m

• Mediterranean Water (warm, high salinity) - 1000-1500m (in North Atlantic only)

• North Atlantic Deep Water (cold, high salinity) - 1500-4000m

• Antarctic Bottom Water (very cold, moderate salinity) - below 4000m

The Great Ocean Conveyor Belt

• Also called thermohaline circulation

• Global system of surface and deep ocean currents

• Connects all ocean basins

• Path:

  1. Warm surface currents flow northward in Atlantic

  2. Water cools, becomes dense, sinks near Greenland and Norway

  3. Deep cold currents flow southward in Atlantic

  4. Currents continue eastward around Antarctica

  5. Branches into Indian and Pacific Oceans

  6. Gradually warms and rises in Pacific and Indian Oceans

  7. Returns to Atlantic as surface currents

• This circulation is important for climate regulation and takes about 1000 years to complete a full cycle

Chapter 8 – Waves

Wave Formation Process

• Wave generating force: Usually wind (also earthquakes, landslides, or objects)

• Restoring force: Gravity pulls water back down

• Process:

  1. Wind blows across water surface

  2. Friction between air and water creates small ripples

  3. Wind pushes against these ripples, transferring more energy

  4. Waves grow larger with continued wind

  5. Gravity acts as a restoring force, pulling water down

Basic Wave Characteristics

• Wave crest: Highest point of the wave

• Wave trough: Lowest point of the wave

• Wave height (H): Vertical distance from trough to crest

• Wavelength (L): Horizontal distance between two consecutive crests (or troughs)

Wave Definitions

• Wavelength (L): Distance between successive crests (measured in meters)

• Wave period (T): Time it takes for one complete wave to pass a fixed point (measured in seconds)

• Wave frequency (f): Number of waves passing a fixed point per second (f=1/T, measured in Hz)

• Wave steepness: Ratio of wave height to wavelength (H/L)

When Waves Break

A wave will break when:

• Wave steepness exceeds 1:7 (height/length ratio)

• Wave enters shallow water (depth less than half the wavelength, d<L/2)

• The wave becomes unstable as the bottom slows down the lower part of the wave while the top continues forward

• Breaking occurs because the orbital motion of water particles is disrupted by the seafloor

Wave Dispersion with Distance from Storm

• Wave dispersion: Separation of waves by wavelength and period

• Longer wavelength waves travel faster than shorter wavelength waves

• As distance from storm increases:

  1. Waves sort themselves by speed (longer, faster waves arrive first)

  2. Wave pattern becomes more organized and regular

  3. Wave height decreases due to energy spreading out

  4. "Swell" (regular, smooth waves) develops far from storm source

Factors Affecting Wave Size

• Wind speed: Faster winds create larger waves

• Wind duration: Longer wind duration allows for more energy transfer

• Fetch: Distance over which wind blows across water (longer fetch = bigger waves)

• Water depth: Shallow water affects wave shape and height

• Obstacles: Islands, reefs, or structures can block or reduce waves

Shallow vs. Deep Water Waves

• Deep water waves (depth d>L/2):

  • Circular water motion doesn't interact with bottom

  • Wave speed (C) depends on wavelength (C=gL/2π​)

  • Energy travels at half the speed of wave crests

  • No loss of energy from bottom friction

• Shallow water waves (depth d<L/20):

  • Water motion affected by seafloor

  • Circular motion becomes elliptical then flat

  • Wave speed (C) depends on water depth (C=gd​)

  • Bottom friction slows waves and reduces energy

  • Waves can bend (refraction) around obstacles

• Transitional waves (L/20<d<L/2):

  • Have characteristics of both deep and shallow water waves

Wave Interactions

• Reflection: Waves bounce off barriers (like seawalls)

• Refraction: Waves bend as they approach shore at an angle

• Diffraction: Waves bend around obstacles and spread into sheltered areas

• Interference:

  • Constructive: When crests align with crests (bigger waves)

  • Destructive: When crests align with troughs (smaller or no waves)

• Standing waves: Waves that appear to stand in place due to perfect reflection

Tsunami

• Not wind-generated but caused by underwater disturbances (earthquakes, landslides, volcanic eruptions)

• In deep water:

  • Very long wavelength (L>100 km)

  • Small height (H<1 m)

  • Fast speed (C>700 km/h)

  • Hard to detect in open ocean

• As tsunami approaches shore:

  • Wave slows down

  • Wavelength decreases

  • Height increases dramatically (H>30 m possible)

  • May initially appear as rapid water withdrawal before massive wave arrives

• Can travel across entire ocean basins with little energy loss

• Not a single wave but a series of waves (wave train)

Chapter 9 – Tides

Tide as a Wave

• Crests: High tides (bulges of water)

• Troughs: Low tides

• Wavelength: Half the circumference of Earth (huge!)

• Wave height: Vertical difference between high and low tide

• Amplitude: Half the tide range (high to low)

• Period: Time between successive high tides (12.4 hours for semidiurnal)

Lunar vs. Solar Tides

• Lunar tides:

  • Caused by Moon's gravitational pull

  • Stronger effect than solar tides (2.2 times greater)

  • Primary influence on Earth's tides

  • Creates two bulges (one facing Moon, one on opposite side of Earth)

  • Cycle follows Moon's 24.8-hour orbital period

• Solar tides:

  • Caused by Sun's gravitational pull

  • Weaker than lunar tides despite Sun's greater mass

  • Creates two smaller bulges

  • Cycle follows 24-hour day

Wave Velocity at Each Phase of the Tide

• Rising tide (flood tide): Water moves