4 ESSAY QUESTION FROM LECTURES and NCA reading
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week5.pptxPROCESSES
Week 5 – July 20th, 2020
Announcements
Lab #3 is due Sunday, July 26th by midnight
Lecture Outline
Introduction to the atmosphere (atm)
Basics of energy
Heat and Controls on Temps
Atmospheric (atm) pressure
Forces Controlling Global Winds
Atmospheric Circulation
This lecture slide is dense. It’s best to review these slides in tandem with Chp. 6 in your textbook.
Readings With Lecture
Week 5 Readings Include:
Chp. 6 in textbook
Atmospheric Profile
Earth’s atmosphere is composed of “shells” held to the planet by gravity.
Classified by:
Composition
Temperature
Function
Atmospheric Temperature Criterion
Four distinct temperature zones
Thermosphere
Mesosphere
Stratosphere
Ozone here!
Troposphere
Weather here!
Most mass in atm here!
Energy Pathways and Insolation
Passage of shortwave and longwave energy through either the atmosphere or water is transmission
Insolation at Earth’s Surface
Notice the highest locations are about 30°N and S. These are often also places of intense aridity.
Insolation Input
Four ways incoming energy is transmitted:
Scattering
Refraction
Reflection
Absorption
Scattering (Diffuse Radiation)
Scattering - The molecules change the direction of the insolation without changing the wavelength.
Diffuse radiation is the downward component of scattered light
Rayleigh Scattering
The shorter the wavelength, the greater the scattering
On the visible light spectrum, which color is the shortest wavelength? The longest?
Refraction
Changes in density through which insolation passes causes a change in its direction and speed
Light is bent
(refraction)
Reflection
Reflection – energy hitting Earth and bouncing back into space, without being absorbed or performing work
Albedo – the reflective quality of a surface measured in percent
Controls the amount of absorption for a surface
Albedo
What do you think would happen if Earth’s albedo increased?
Absorption
Absorption – assimilation (take in) of radiation by molecules of matter and its conversion from one form of energy to another
Plants absorb energy for photosynthesis
Converted to longwave radiation
Atmospheric Disruption
Mt. Pinatubo eruption in 1991
Massive amounts of sulfur dioxide droplets were shot into the stratosphere
The globe experienced a temporary cooling of 0.5°C
Atmospheric Disruption
Mt. Tambora eruption in 1815
Stratovolcano eruption shot ash and aerosol ejecta into the stratosphere
Created the Year Without A Summer in 1816
Tropical surpluses and polar deficits drive global circulation!
Introduction to Heat
Four modes of heat transfer on Earth:
Conduction – molecule-to-molecule
Convection – physical mixing of gas or liquid in a vertical motion
Advection – physical mixing of gas or liquid in a horizontal motion
Radiation – transfer using electromagnetic waves
Introduction to Heat
Latent heat of evaporation – the energy stored in water vapor as water evaporates
Water absorbs energy to change from liquid to gas
Sensible Heat – back-and-forth transfer through convection and conduction
Principal Temperature Controls
Temperature is not uniform across the globe
Influences upon temperature include:
Latitude
Altitude/Elevation
Cloud Cover
Land-Water Heating Differences
Latitude
Remember, latitude affects insolation, sun angles, and daylength
Altitude/Elevation
Temperatures decreases higher up
Thin atmosphere means less sensible heat
Check out this graph which tracks the normal lapse rate with elevation
High Elevation
Cloud Cover
Land-Water Heating Differences
Continents and oceans are physically different
Land-Water Differences
Evaporation
Energy is stored as latent heat, resulting in lower temperatures
Happens more in marine locations than over land
Transparency
Land is opaque, water is transparent
Energy can penetrate deeper into water than soil, creating a larger heat reservoir
Land-Water Differences
Specific Heat – the heat capacity of a substance
Water heats slower, but retains heat longer
Movement
Oceans flow and mix/redistribute heat energy over a greater volume than land
Horizontal and vertical mixing
Marine Effect vs. Continentality
The only difference between these two locations is the left is closer to water. This demonstrates the marine effect, or essentially the buffering impact of water on local climate.
Earth’s Temperature Patterns
Isotherm – a line on a temperature map that connects points of equal temperature
Thermal equator – isotherm connecting all points of highest mean temperature
Shifts with seasons
North Pole vs. South Pole
North Pole Winter
South Pole Winter
Annual Temp Range Maps
Highlights areas of high to low temp range (difference between hottest summer temp and coldest winter temp).
Why are areas of greatest difference mainly in the North?
Ok, break! This first part of the lecture was focused primarily on energy and temperature.
The next half of lecture focuses on pressure and wind. Go back and review core topics on principal controls on temperature before moving on!
Essentials of High Pressure
Descending air from above, OR
Air that is colder, and heavier that stays at the surface
Prevents convection because air can’t rise and mix
Air is diverging at the surface
Stable weather
Essentials of Low Pressure
Ascending/Rising air from below, OR
Air that is warmer and rising above the surface
Promotes convection because air can rise and mix
Air converging at the surface
Weather events
Wind Basics
Wind – Horizontal movement of air across Earth’s surface
Produced by differences in pressure between one location and another
Anemometer
Vane
Wind Maps
Isobar- line connecting points of equal air pressure
Contour intervals
Wind Direction
Winds are always named after the direction from which they are blowing.
Driving Forces of Global Wind
Several Factors influence the patterns of wind on a global scale:
Gravity
Pressure Gradient Force
Friction Force
Coriolis Force
Pressure Gradient Force
Differences in pressure across Earth’s surface encourages air flow
The stronger the difference, the stronger the wind
Closeness of isobars determines the strength of the difference or gradient between high and low.
Pressure Gradient and Isobars
Pressure + Coriolis + Friction
Global Circulation System
Dynamic Pressure Area –pressure area stimulated primarily by movement or mechanical factors
Thermal Pressure Area– pressure area stimulated primarily by temperature or thermal factors
Equatorial Low Pressure trough
Thermal low pressure area
High sun angles, consistent daylength
Warm, less dense air, rises consistently
Equatorial Low Pressure Trough
Intertropical Convergence Zone (ITCZ)
Area of extreme low pressure
Calm winds under the ITCZ because of low pressure gradient and vertically rising air
Equatorial Low Pressure Trough
Zone of convergence by rising air being replaced by air moving in from the north and south
Equatorial Low Pressure Trough
Hadley Cells – the circuit completed by winds rising along the ITCZ
Trade winds – prevailing winds caused by Hadley circulation cell
N.H. = northeast
S.H. = southeast
Sub-Tropical High Pressure Cell
Dynamic descending air from the Hadley cell creates areas of high pressure (about 20-35° N and S)
Air is heated by compression as it is forced downward creating hot/dry conditions
Sub-Tropical High Pressure Cell
Westerlies – dominant surface winds from the subtropics to high latitudes resulting from divergence at the Hadley cell
Sub-Polar Low Pressure Cell
Dynamic low pressure area from ascending air at about 60° N and S
Cold air from higher latitudes and warm air from lower latitudes converge causing rising air
Spreading air masses from the poles form the polar front
Polar High Pressure Cells
Thermal high pressure area from frigid descending air at the poles
Descending air diverges at the surface and form the weak, variable polar easterlies
Coriolis deflects wind from a straight southward path
Rossby Waves
Polar front – the line of conflict between colder air from the north and warmer air from the south
Dynamically active area creates disturbances in the upper air circulation and jet stream
Rossby Waves
Wave-and-eddy formations occur and create lobes of cold air that flow away from poles.
Jet Streams
Jet streams – irregular and concentrated upper level westerly winds (2 per hemisphere)
Jet Streams
Ocean Currents
Surface Currents AND Deep Currents form the Thermohaline Circulation
Thermohaline Circulation
Ocean Currents
Driving force for ocean currents is the wind!
Frictional drag along the surface
Creates vital link between atmospheric and oceanic circulation systems
Coriolis force, density differences (temperature and salinity), placement of the continents, tides…
Whew! I think that’s enough for now.
There’s always more to learn about earth surface and atmospheric processes, so if you’re interested in these materials, reach out! I teach upper level courses in weather and climate and biogeography!
Looking Ahead…
Next week we delve into climate modeling!
Please be sure that you’re confident with this week’s course materials before we move on to Week 6!
As always, don’t hesitate to reach out with questions!
