The Wind Zones

It was a windy day and the lineup of the planets was in the news. So I thought of this.

This isn't anything breakthrough but I haven't seen it explained before. The earth has five zones of prevailing winds. In the following diagram, the black arrow shows the earth's eastward rotation. Winds are defined by the direction from which they come and the green arrow shows the easterly winds in the tropics, opposing the earth's rotation, that are known as the Trade Winds. 

The red arrows show the Westerlies, at higher latitudes, that are in the same direction as the earth's rotation. The blue arrows show the Polar Easterlies.

The wind is somewhat more complex than this. Air tends to rise at warmer, lower, latitudes and then sink at cooler, higher, latitudes. This forms what are known as Hadley Cells. The prevailing winds, as described above, usually form a vector with the movement of air due to the Hadley Cells.

These wind zones on the earth are not visible from outer space. But the larger planets of the Solar System rotate much faster than the earth does. A point on the earth's equator is actually moving at about 1,000 miles per hour, or about 1,500 kph, due to the earth's rotation. This causes an outward centrifugal force, known as the Coriolis Force.

Jupiter, the largest planet in the Solar System, has a circumference eleven times that of earth and it rotates in less than half the time the earth does. The result is that a point on Jupiter's equator is moving at 26 times the velocity of a corresponding point on earth's equator, due to the rotation. Since the value of the Coriolis Force is proportional to the angular velocity squared, that means the force is exponentially greater on Jupiter than on earth, although this is reduced somewhat by the fact that Jupiter's gravity is much greater than on earth.

The result is that the wind zones on Jupiter are visible from outside. In the following image, from the Wikipedia article "Jupiter", I see ten wind zones. The "Great Red Spot" is a storm that has been going on for centuries.

Jupiter is by far the most massive of the planets. It has about 2.5 times the mass of all of the other planets combined. The next most massive planet is Saturn. In the following image, from the Wikipedia article "Saturn", you can see that the wind zones, which always parallel the direction of rotation, are less pronounced. The halo is Saturn's rings.

On Neptune, as shown in the following image from the Wikipedia article "Neptune", the wind zones are faintly visible. The dark area in the center is the "Great Dark Spot", a storm just as is the "Great Red Spot" on Jupiter.

I believe that the great storms seen on Jupiter and Neptune were formed by comet impacts. Another factor is how powerful the winds are on these frigid outer planets. We saw in the posting "Summary Of Science On This Blog", July 2024, section 73) why the coldest planets have the strongest winds. 

But this banding that is seen on the outer planets is related to the wind zones on earth. 

It is in the news about how many of the planets are roughly lined up, as seen from earth, making it easier for observers to find them among the stars. For information about looking at the sky, here is a link to the posting "Stargazing".

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