Week 5 – July 20th, 2020


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:




Atmospheric Temperature Criterion

Four distinct temperature zones




Ozone here!


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 (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?


Changes in density through which insolation passes causes a change in its direction and speed

Light is bent



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


What do you think would happen if Earth’s albedo increased?


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:



Cloud Cover

Land-Water Heating Differences


Remember, latitude affects insolation, sun angles, and daylength


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


Energy is stored as latent heat, resulting in lower temperatures

Happens more in marine locations than over land


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


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



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:


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!