Posts Tagged ‘roll cloud’

So we’ve gone down-size and up-size looking at the sizes of things that produce weather effects on Earth. Now let’s get larger again:

[5] Weather forms in the 60-mile (or 100 km) range include such things as:

  • Simple roll clouds such as we often see crossing the sky. When the sky is too full of clouds to allow free convection up the center of each cloud and down the outside, the clouds combine in long sausage-type rolls which can cross the entire sky, visible for a distance of 60-80 miles. Convection takes air up one one side of the roll and down the other.
  • Lakes such as the Finger Lakes of New York State lie in this size range and definitely affect the weather nearby since tbey produce clouds differently from land, many times bringing rain and snow to lakeside areas.
  • New Zealand has a Maori name that means “land of the long white cloud.” Undoubtedly the first men to arrive in New Zealand from the Micronesian¬†islands to the west found this island because, long before they could see it over the horizon, they could see the clouds that formed above its hills and mountains.

[6] Are there single weather forms in the size range of 1,000 miles?

  • Of course! Hurricanes by whatever name — cyclones or typhoons. These are generally at least a few hundred miles wide, and they can grow to over 1000 miles across.
  • Besides that, the segments of jet stream wind that are over 60 miles an hour are often in the range of 1000 miles across. If you remember that the US is 3,000 miles across, you can readily recognize this size range in the jet stream images.
  • The Sahara desert, 1000 from north to south and three times that from east to west, is the birthplace of the winds that become hurricanes as they cross the Atlantic.
  • The Sahara and other large deserts mark the meeting place of Hadley and Ferrel cells, of which see more below.
  • The Moon, which pulls the tides and in turn gives an impetus to coastal weather, is in this size range.

[7] Our home planet, Earth, is about 8,000 miles in diameter on the large end of the seventh size range (the seventh order of magnitude) which is centered on 6,000 miles.

  • Six massive circulation cells encircle the globe — The northern and southern Hadley cells starting near the equator, the northern and southern Ferrell cells in the middle latitudes, north and south, and the two Polar cells.
  • Between the Polar and Ferrell cells, the world-encircling jet stream journeys on its sinuous path.
  • Of course the oceans fill the atmosphere with the water needed for rain and snow, so they are part of weather.

[8] The size range of our larger neighbor Jupiter is around ten times that of Earth.

  • I don’t suppose you imagine that Jupiter affects our weather, but it might; at least it might have. Because of its large size, it attracts various objects as they enter the solar system, and along with Saturn it protects Earth from most potential invasions by comets and things. When comets do get here, it’s pretty explosive; dust gets into the atmosphere, and clouds and rain follow.It would be fair to say that Jupiter affects the weather by protecting us from more explosive visitations from outer space.
  • But we don’t have to go to Jupiter to find things ten times the size of Earth, for our own magnetic field, particularly as expressed by the Van Allen Belts, is in this size range. The Aurora Borealis is one expression of this belt.
  • Solar flares are in this size range, and seem to be responsible for the massive “winds” of ionized particles that visit Earth when there are sunspots. These not only cause auroras, but the new supply of ionized particles help seed rain clouds. Times of more sunspots and therefore of more flares seem to be related (historically)¬†to warmer times on earth.

[9] The ninth order of magnitude is 100 times the diameter of our earthly home. Nothing that big affects us, right?

  • Except the sun. That’s a weather producer; that’s the weather producer. It builds the Hadley and other major wind cells, evaporates the oceans, heats the deserts, shifts air back and forth between water and land; the sun does everything to keep air and water in motion, and that’s what weather is.

It’s strange to think that such large and distant objects are concerned in the weather in your back yard; do you suppose that anything larger, or from the farther reaches of the universe, affects Earthly weather?

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Roll Cloud

Last week, as the cold and turbulent air was roiling around, I took this picture of a roll cloud. A mere photo doesn’t do the sky justice, because the amazing thing about this type of cloud bank is that it generally comes in from the west as a white bank of clouds across an entire quarter to half of the horizon, and it usually comes into a fairly clear sky.

Last week, however, the skies were never fully clear, and besides that, my camera couldn’t handle enough of the horizon to make it clear how far it stretched. Anyway, for what it’s worth, here it is:

Roll cloud from the south into South Dakota

Roll cloud from the south into South Dakota

Strangest of all, and invisible in a photo, it came in from the south. This type of white cloud bank, a roll cloud, is a classic cold front. How could we possibly get a cold front in from the south, never mind it was already quite cool?

The answer is to be found in the jet stream animation for September 25. There was a certain point when the little wind creature — we’ll call him the flying squirrel — had a paw reaching directly up into eastern South Dakota, bringing cold air from that curious gyre that formed in the middle plains between September 20 and September 25 or so. It has since flown away, replaced by a regular leviathan of wind that stood directly over our state for a few days, while the wind was quite strong, cool, and turbulent. It had to be 30 mph, judging by the size of the branches that were swaying in the wind.

Then, quite suddenly during the night, the leviathan arched its back into Canada and left our skies clear and our air gentle. I don’t know if we have so much as a whisper of wind.

To build an intersting animation of the jet stream, go to the blogroll at the side, and click on the jet stream. Find the flying squirrel and the leviathan for yourself.

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