The Winds of Mars and Other Planets

Teacher's Notes

Things to emphasize

  1. The Earth's rotation is responsible for more than simply the cycles of day and night.

  2. The direction of winds and of ocean currents are strongly influenced by the rotation of the Earth.

  3. The apparent deflection of moving objects in a rotating system is called The Coriolis Effect.
  4. Science investigation involves a multi-step inquiry process: ask an initial question, plan the investigation, record observations and collect data, analyse data to draw a conclusion, and communicate the findings.

consider the following...

The Coriolis Effect

cyclonic circulation on the Earth
Transparency Master 		Air currents (and ocean currents) on the Earth are deflected from a straight North to South (or South to North flow) into large circular patterns called cyclonic patterns . This effect is caused by the Earth's rotation.

It is known as the Coriolis Effect. The large circular storm systems that this effect creates are called cyclones.

The image to the left shows a typical cyclonic storm.

Space Shuttle Image, courtesy National Space Science Data Center and NASA

cyclonic circulation on Mars

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Mars has an extremely thin atmosphere compared to the Earth. It has no oceans, and no significant water vapour in its atmosphere and aside from huge dust storms, Mars has very little observable weather.

Nevertheless, large cyclonic storms have been observed near the Martian Poles. The composition of the Martian clouds is uncertain, although the evidence seems to indicate that they are made from water-ice crystals, the same as clouds on Earth.

The Coriolis Effect on Mars is less than the Coriolis Effect on Earth because Mars has a smaller radius than the Earth and also because Mars rotates slightly more slowly than the Earth.

HST image, courtesy Space Telescope Institute and NASA

consider the following...

Build a Coriolis Simulator

Objective

To build a platform that can be set in rotation, simulating the rotation of the Earth, in order to observe the behaviour of objects as seen from a rotating frame of reference.

Materials

The mechanical parts scrounged from a discarded swivel chair work extremely well. Feel free to improvise.

The plank should be strong enough to support a student sitting on each end without fear of breakage.

The base should be stabilized with heavy weights (such as a wooden box filled with sand) or an extended base (such as a wooden Christmas tree style base) to prevent it from toppling over.

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The Experiment

  1. Have one student sit on each end of the plank so that it balances.
  2. Give one student a volley ball.
  3. While the system is stationary have the two students have a few practice tosses of the volleyball back and forth to each other.
  4. Gently set the plank in rotation (counter-clockwise if you wish to simulate the Earth's rotation as seen looking down on the North Pole).
  5. Now ask the students to toss the volleyball back and forth.

aha!

The Simulation
Motion of volleyball as seen from the rotating platform
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The Coriolis Effect

Students are always quite surprised when they first try this experiment. Even a modest rate of rotation causes the volleyball to "fly off course" in a very dramatic way.

With some practice the volleyball can be thrown to anticipate its relative change in direction.

The important lesson here is that the effect they observe is exactly the same effect that causes the winds around low pressure cyclonic storms to rotate counter-clockwise in the Northern Hemisphere and atmospheric circulation around high pressure systems to rotate clockwise in the Northern Hemisphere.
Motion of volleyball as seen from the classroom frame of reference
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As Seen from the Classroom

It should be emphasized that the Coriolis Effect creates the illusion that some mysterious force is causing the volleyball to change direction. In fact there is no force .

The volleyball moves in a straight line as seen from the point of view of the classroom floor. (Of course, gravity causes the path of the volleyball to curve as seen from the side).

The winds on the Earth's surface also attempt to move in a straight line with respect to the stars, but the Earth's rotation gives the illusion that there is some force causing them to change direction.

aha!

Winds on Other Planets
  1. How much time does it take for the Earth to rotate once on its axis?

  2. What would be the effect on the Earth's global wind systems if the Earth were to rotate much faster than it does at present?

  3. The planet Jupiter rotates on its axis approximately once in 10 hours. With the aid of a small telescope or even a good pair of binoculars, a patient observer can actually notice the rotation of Jupiter! The wind patterns on Jupiter can be seen by observing slight differences in the colour of the cloud tops in Jupiter's atmosphere. Obtain some photos of the planet Jupiter and comment on the influence of the Coriolis Effect on Jupiter.

  4. If astronauts are going to explore and work on the surface of Mars they will need to understand the behaviour of Martian weather systems in order to create reliable Martian weather forecasts.
    Visit the website

    http://www.msss.com/mars_images/moc/weather_reports/

    for weekly updates of weather on Mars.

aha!

Photographs of Other Planets

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Prepared by YES I Can! Science
Faculty of Pure and Applied Science, York University