EarthLabs > Climate and the Biosphere > Lab 3: Climatology Basics > 3A: Planetary Circulation Patterns

Climatology Basics

Part A: Planetary Circulation Patterns

Seeing the atmosphere through the clouds

Most days the atmosphere is transparent and difficult to see with the naked eye. Occasionally though, clouds, dust, fog, or smoke, allow us the see the movement of the air around us. Begin this lab by viewing the video animation entitled "GEOS 5 modeled clouds" linked below. While watching this short video clip, consider the following questions about clouds, and how they help us to better see and understand the atmosphere. (Note: you may need to watch the video several times to see all the details.)
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Video courtesy of NASA/Goddard Space Flight Center.

Discuss

From what you discovered in the water cycle lab (Lab 2A), describe what you think is causing the clouds to form. Recall a cloudy and breezy afternoon; how do clouds allow us to "see" the movement of the atmosphere? Discuss memorable cloud patterns with your neighbor.

Scales of weather and climate

The atmosphere is one interconnected system. For convenience of study, scientists subdivide the atmospheric circulation and weather patterns into categories based on their size and duration. In general, the smaller, local-scale weather events have the shortest life expectancy, while the global-scale patterns can persist for weeks or months. In this study, you will begin by exploring the largest scale patterns, the planetary or global scales, and work to the smallest scale patternsthose that take place in your own neighborhood, school yard, or park.

  1. Download and print out the map and organizing chart linked below. As you are reading, use the map and chart, a sample of which is pictured right, to record your notes about the time and space scales of weather and climate throughout Lab 3. Printable version of weather and climate scales (Acrobat (PDF) 51kB Apr4 12) in (PDF).
  2. Access, and print out a World: Climates map from Education Place collection of world maps.
  3. Use colored pencils to record the locations of the global and continental drivers of climate on the World: Climates map.


Introduction to Moving Heat Interactive

As you learned in Lab 2, much of the incoming solar radiation is not directly absorbed by the atmosphere itself but by Earth's surfaces, including both the land and the ocean. The atmosphere, therefore, is largely heated indirectly by long-wave radiation emitted from Earth's surface. The atmosphere is a gaseous fluid in which convection cells form. These cells transfer heat energy and moisture from one place to another. In this lab, you will examine global patterns of circulation in the ocean and atmosphere. The ocean and atmosphere combine forces to move both matter and energy around the globe.

Begin this section of the lab by exploring the features of the Moving Heat interactive, below. In this interactive, you will be examining animations, graphics, and short videos built from NASA satellite data. While investigating, you will be looking for ways that the ocean and atmosphere combine to move moisture and heat energy around the globe. Take a few minutes to explore the buttons and layers of this interactive learning tool. When you are done exploring, click the Air Flow button to return to the opening screen. (If you prefer, you can click this link to access the Moving Heat Interactive in a new window. )

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The directors of global weather and climate

In this section, you will be introduced to each of the major directors of global climate and weather. Take notes about each "director" in your notebook, or on the organizing chart provided at the beginning of the lab.

Global atmospheric circulation cells

Unequal heating of Earth's surface by the sun drives the movement of the atmosphere, which we experience as wind. Around Earth there are three major convection cells known as: Hadley, Ferrel, and Polar circulation cells. On a global level, they help to equalize the incoming solar radiation received on Earth by transporting the excess thermal (heat) energy from the Equatorial regions to the Poles.

Turn on and view the circulation cells (click the show button under Circulation Cells), note how these cells work in concert to move air and heat away from the Equator and towards the Polar Regions. The origin of the energy used to drive these air currents is incoming solar radiation. The process can be broken down into the following steps, beginning at the Equator.

  • First, the sun's radiation heats the Earth's surface, which, in turn, heats the atmosphere.
  • The heated air parcel, an imaginary section of air, becomes less dense and begins to rise.
  • The solar-heated airs moves upward, away from the surface of Earth, initiating a convection cell. You may have seen birds (or para-gliders) using local-scale versions of these types of "thermals" to move effortlessly upward in the sky with little or no apparent wing motion.
  • The air parcel cools as it rises, releasing latent (stored) heat and moisture, forming clouds.
  • When the air parcel reaches the edge of the troposphere, about 10 kilometers above Earth, it turns and begins to spread towards the Poles.
  • At about 30˚ latitude the air begins to sink, or subside. This sinking occurs because the air has become cooler and denser. The sinking air parcel is drier because it released its moisture as it was rising near the equator.
  • As the convection cycle of air returns earthward, it heats and dries due to compression, forming areas of high pressure. Each cycle is completed as the air moves back to the start and rises again.

Checking In

Describe the motion of the circulation cells in the interactive; are they all rotating in the same direction?
No, the middle cell, known as a Ferrel cell, rotates in the opposite direction. This air current, which is less organized, is driven primarily by the motion of the other two.

Winds and pressure

Use the Moving Heat interactive to explore the relationship between winds and pressure. Record your observations in your notebook or on the chart and map provided in the link above.
  1. Click the button to show the Winds & Pressure with the Circulation Cells on. Note where the High (H) and Low (L) pressure systems are located in relationship to the circulation cells. Where the air is rising, the air pressure is low; where it is descending, it is high. Note: the pressure over the Equator is also low.
  2. Hide the Circulation Cells and Pressure systems. Then, click the Winds Only button to observe the flow of the major global winds: the trade winds trade winds: these winds blow from east to west around the globe. They are surface winds, flowing in the lower section of the atmosphere. They are located in latitudes nearest to the equator. Trade winds steer the storm tracks of tropical storms and move large dust storms from Africa to the Caribbean. Their location, direction, and persistence allowed trade routes to be established across the Atlantic and Pacific Oceans. and the westerlieswesterlies: are named for their direction of flow, from west to east. They are surface winds, flowing in the lower section of the atmosphere. They are located from 30 to 60 degrees north and south latitude. They steer storms across North America. . The trade winds are the most persistent winds on the planet. They blow from the same direction more than 80 percent of the time! The westerlies are important to the weather and climate in the contiguous United States.
  3. Change the Earth View between Sea Surface Temperature (SST) and Blue Marble to study the relationship between cloud formation and SST. Note the alignment of the clouds and winds around the equator. The clouds formed from the moisture that evaporated from the ocean. Take a moment to replay the GEOS animation, shown at the beginning of the page, to confirm this relationship. Then, record your observations and answer the Checking In questions below.
  4. Checking In

    From which direction are the trade winds blowing?
    [INCORRECT]The winds are named for the direction that they blow from. The Westerlies blow from the west.
    [CORRECT] The trade winds are blowing from the east to the west; the opposite direction of the westerlies.
    [INCORRECT] Try again. Hint: They were named trade winds because ships sailed from the east on these winds.

Global water cycles of evaporation and precipitation

  1. Click the Play animations button to view four animations of NASA satellite imagery. Read the text above each animation for a description of the data that is being displayed. (Note: The video controller is below the image.) As the movie plays, the time period is displayed in days so that you can get a sense of the speed of movement of the air and ocean currents. Note the spatial (in space) and temporal (time) patterns of movement. Which way do the water and air currents move? As you learned in Lab 2A, the water cycle lab, on Earth, water generally evaporates from the ocean, moves with air currents, and precipitates over land.

  2. Use the Overlay and Compare buttons to look for relationships between data sets. Read the text above the animations describing what is playing in the animation. You may need to play these video several times to see all the details.
Global Precipitation Patterns. Click image for larger view. Image source: NASA

As you have seen in several examples, winds and ocean currents move more than just heat, they also transport substantial quantities of moisture around the globe. Study the image to the left. (Click image for larger view, in a new window.)

3. Look for the relationship between the air circulation patterns and the dry and wet regions. Notice the symmetrical banding of wet and dry regions around the Earth. While viewing the image, answer the Checking In questions, below.

Checking In

While viewing the image to the right, answer the following questions.
  • Which latitude ranges are consistently wet?
  • Areas around the Equator have abundant year-round precipitation. The air here is rising and warm.
  • Which latitude ranges are consistently dry?
  • The polar regions have sparse precipitation in all seasons. The air here is descending, dry and cold. The air is also dry (and hot) in the regions of descending air located in the sub-tropical high pressure zones.

Jet Streams

Jet Streams are areas of fast-moving rivers of air that circle Earth. They can reach speeds of more than 160 km per hour (100 mph). They are located at the boundaries of the Hadley, Ferrel, and Polar cells, described above. They influence the movement of larger air masses that reside over the continents and oceans. The Jet Streams are 6 to 15 kilometers above the surface of the Earth, in the boundary between the troposphere and stratosphere. They follow the meandering boundaries between the polar and mid-latitude air masses. The Polar Jet Stream, which flows over North America, is generally stronger in the United States during the winter months. It directs such notorious winter weather events as the "Alberta Clipper" and "Polar Vortex" across the Great Lakes and New England. As a general rule, when the Polar Jet Stream is located south of your location, the weather is relatively cold.

Click this link to view a map of today's Jet Streams on Globe location. On the globe, look for the region of the fastest air flow, colored red. Information about the data can be found by clicking the word "earth" below the graphic. View the globe to see how the Jet Streams meander over time. Record your observations of the general location of the Jet Streams on your printed world map.

Thermohaline Ocean Circulation Patterns

Wind patterns and storms combine to move the majority of the heat around the Earth. According to scientists at the National Center for Atmospheric Research (NCAR), 78% of the poleward heat transport in the Northern Hemisphere, and 92% in the Southern Hemisphere, is due to atmospheric processes. To get a feel for this, consider, for example, how much solar energy was needed to drive the water cycle in Lab 2A. As the water changed state from liquid to gas, energy was absorbed, forming a "cloud" of water vapor. In the atmosphere, clouds are transporters of both moisture and heat energy.

Ocean currents transport the remainder of the heat. These currents include both surface, or wind-driven currents, and thermohaline (thermo=heat; haline=salt) or density currents. A simple schematic of these currents is pictured, left. It is estimated that the water in these currents may take a thousand or more years to circulate the globe! View the short narrated video, below, from the National Science Foundation (NSF), to learn more about this important global conveyor of heat. While viewing, observe how the heat is distributed around the world by ocean currents.

After watching the video, answer the Checking In questions, below. (Note: click the arrow, below the image screen, to start the video.)
Earth's Heat Balance is one a series of videos on Science 360.

Checking In

According to the video:
  • What part of Earth receives the most solar energy (insolation) year-round?
    The tropics.
  • What mechanisms move heat away from the tropics?
    Oceanic and atmospheric circulation move heat from the tropics to the poles.
  • When the cold, dense ocean water sinks at the poles, where does it travel to?
    It travels down to the bottom of the ocean and then travels north or south toward the equator. view the schematic right to see the pattern of movement.

Stop and Think

Use the information given in the text, graphics, Moving Heat interactive, and videos in this section to answer the following questions. Use the notes that you took on your world climate map and weather and climate timescale chart. Whenever possible, give specific examples.
  1. Describe the global patterns of motion of the atmosphere and ocean. List specific examples of global climate drivers.
  2. What do the atmosphere and ocean currents transport?
  3. Explain how the ocean and atmosphere are interconnected.
  4. How would Earth's weather and climate be different if these currents of air and water did not exist?

Global precipitation and temperature patterns combine with other regional and local influences, such as geography, to determine an area's climate and, ultimately, vegetation patterns. In Lab 4: Climate Patterns and Life, you will more closely examine the influence of climate on the spatial distribution of plant and animal life.

Optional Extensions
The MeteoEarth App for ipad and android tablets, is a fun way to explore the relationships between weather drivers, such as pressure systems and wind patterns.