Science Questions

If the Earth's rotation is slowing down was it windier in the distant past?

Tue, 6th Sep 2016

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Question

Dr. Arv Edgeworth asked:

I have a question for you. I have contacted the scientists at NASA, and the National Weather Service, and so far have had no response. I was told that if you spin a planet faster you increase the wind speed. Jupiter and Saturn were given as evidences of that. Since we know the earth is slowing down in its rotation, and we know the rate at which it is slowing down, then if we went backwards in time at that rate, would it have an affect on the wind speed on earth? If we went back far enough in time would it possibly make earth uninhabitable?

 

Dorian Abbot of the University of Chicago is quoted as saying that new research has revealed that the rate at which a planet spins is instrumental in its ability to support life. He also said it affects the winds. Do you have any information on this? Thank you for your time.

Sincerely,

Dr. Arv Edgeworth

Answer

Adam Townsend put the wind up this one...The Windpump at Wicken Fen, Cambridgeshire. This windpump is the only working wooded windpump in the Fens.

Adam - Yeah. I thought this was an absolutely terrific question. The Earth slows down because of its gravitational interactions with the moon. So, every time the moon goes around, it affects the tides, robs the Earth a little bit of some rotation. I can tell you exactly how much itís slowing down. In fact, we lose about 2 milliseconds from the day every 100 years.

Kat - Yeah. I suppose over millions of years, thatís going to add up.

Adam - In fact, it does. So, if you are interested when weíre going to get 25-hour days? 200 million years, so not long. Anyway, to wind, wind is caused by warmÖ so the air on Earth gets heated up by the sun, rises and this causes a pressure difference because the hot air has gone up and so, cold air needs to be sucked and itís sucked in from the north pole or the south pole where itís colder. So, you end up with a circulation happening. But itís complicated because the Earth is spinning. So this is the famous coriolis force. If you sit on a spinning chair and you spin yourself around, and you throw like a tennis ball in front of you, the tennis ball seem to sort of veer off to the right from your perspective. And so, this confuses things because it means that the wind isn't directly going from the north pole or south pole to the equator. And, what I think is the absolute most interesting, despite the fact that we have these areas of high pressure and low pressure, and you would think therefore the wind goes from the high pressure to the low pressure, it doesnít. Actually, because of the rotation of the Earth, wind travels along lines of constant pressure. This is why we have isobars on newspaper weather reports.

Kat - The little lines when you see it, yeah.

Adam - Yeah, like from the Ď90s.

Kat - They are being replaced by little arrows now because weíre too stupid to understand isobars.

Adam - Right. but yeah, it turns out, wind goes along these and this sort of drops out of the maths of the coriolis force. Anyway, ďWas it windier in the past?Ē is the question. The answer is, itís complicated because lots of things affect it. So, continents slow down wind. If weíre standing right here and you want to go back millions of years, well obviously, you have the buildings that are going to make some effect. How much land there is around us? Wind could go slower over land because of friction. So it slows down becauseÖ

Kat - So basically, there's lots and lots of things that couldíve made a difference and we donít really know. We donít know if the dinosaurs were like blown around.

Adam - So in the question they asked, if you spin a planet faster, you increase the wind speed. I'm not convinced. I think there are lots of things that affect wind speed. The effect might in fact go the opposite direction. You can get planets that go around very, very slowly like Venus. Venus has a day of 116 days. Itís really slow.

Kat - I donít want to go to Venus and find out if itís windy out there.

Adam - 200 miles an hour, who knew?

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How would you go backwards in time? Tim the Plumber, Mon, 8th Aug 2016

Doubt it. Weather is complex but the main factors are likely to be energy input (solar powered for earth but not the gas giants which are internally powered) and the friction of surface features. The sun is slowly powering up so maybe there was lower wind speed back then.

The massive wind speeds of the gas giants have been attributed to low friction. Blame, Mon, 8th Aug 2016

Winds are driven to a large extent by temperature differences induced by the Sun. So if the Sun were hotter in the past, or greenhouse gases were more plentiful in the past, we might see stronger winds.

The direction of wind is driven by the Coriolis force - if the Earth were rotating more rapidly, the Coriolis force would be stronger, and the direction of winds would be bent more tightly into circles by the Earth's rotation. I guess this could produce faster winds without a change in temperature.

You have to look a long way back in time to see much of a change in length of Earth's day, currently about 2.3ms per century. This is due to tidal drag causing recession of the Moon.

When the Moon was much closer, tides would have been enormous and most life would have lived in the sea, where it is shielded to some extend from the winds. evan_au, Mon, 8th Aug 2016

Evan explanation is correct. If the rotation of the earth is faster (and all other factors are the same like the average temperature), there would stronger wind on average. Tornadoes would be more frequent and stronger. But like Evan said, the difference of Earth's rotation rate in the past is only slightly faster so probably other factors variations in the past were more significant than the faster rotation of the earth.
CPT ArkAngel, Tue, 9th Aug 2016

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