Stupid Earth question from an infrequent flyer.

Factual Questions
1

Recently I flew from NYC to Las Vegas. Previously I’ve flown to Chicago and Florida. Each time it was at least an hour faster coming back home than going. I contribute this to the jet stream (except for Florida. How does that work?) because the pilots always mention the nice tailwind or strong head winds-- depending on whether we are flying east or west.

So. . . the jet stream is created by the Earth turning and yet the Earth is turning away from the way the plane is flying going eastward. How is the wind created by the Earth turning stronger than the actual movement of the Earth turning? I’m not sure I’m even making sense. Let’s start at the beginning.

When flying eastward the Earth is turning away from the plane you are on. Yes?
This creates winds but also moves your destination further away from you as you fly, yes?

How can the Earth turning create winds stronger than the actual movement of the Earth turning?

Please don’t make me feel stupider than I alreasy feel asking this question. Thanks.

2

I’ll let someone else tackle the specifics, but basically, the jet streams are the result of solar radiation heating up the atmosphere, and the coriolis force, which is the result of the rotation of the Earth. You can find out more here: Wiki on jet streams

3

Perfectly good question with no simple explanation. However, I think the large scale movement of the atmosphere and the winds is a bit more complicated that you might think. It’s not like the earth is moving underneath a blanket and therefore it should simply drag the air along with it, hence, the wind. There is some degree of truth in what you say and the rotation of the earth certainly does contribute to the root causes of movement of large masses of air. But there are complications, e.g. the air sinks at the poles and moves slowly toward the equator, where it is heated and rises and moves back toward the poles, so there’s a major circulation pattern there. And then the winds are twisted as they move north and south due to the rotation of the earth. And those patterns are made more complex as they whirl around and change directions, so that there are huge air mass movements that move west to east and others that move east to west - in different latitudes. So tail winds in certain areas and at certain latitudes will tend to blow from a certain direction, but they don’t always. In the U.S. the predominant air mass movement, and jet stream movement, is from west to east so that generally speaking, eastward travel takes less time than westward travel (to and from the same point). I doubt this answers your question, but I hope you realize it’s not a simple as we think at first.

4

Wikipedia’s article is pretty good.

5

@John Mace: The jet stream article is good as far as it goes. But there’s a lot more to prevailing winds at altitude besides the jet stream itself.

Your first part is 100% right. Irrelevant, but right.

Your second part is 100% wrong. Not stupid, just wrong. But since you’re starting from a bad idea, the rest of your good thinking after that is going off in a silly direction. Let’s see if we can fix that. :slight_smile:
The Earth is rotating towards the East. But it’s all the Earth, not just part of it. The rocks, the oceans, *and *the air are all turning at the same rate: 24 hours per day. There is no sense in which the air is lagging behind the ocean which is lagging behind the rocks; they all rotate together. So that’s not where wind is coming from.

There are two large-scale sources of wind.

One is that it’s hotter at the equator than the poles. This creates a net wind from poles to equator at the surface and a net wind the other way at altitude. As the wind moves poleward or equator-ward the Coriolis force curves what would otherwise be a wind to north or south into a wind to the east or west. See Hadley cell - Wikipedia for more.

The other is that as the Earth rotates different areas switch between day and night. All else equal air is heated and wants to rise in the day and cools and wants to descend in the night. The edge of twilight moves around the world at about 1000mph at the equator and about 500 mph at the latitude of Europe or southern Canada. Which means the edge of daylight is moving much faster than the wind can move to catch up. But it tries.

Then we can add in all the rest of the things that affect weather, such as fronts, terrain, clouds, precipitation, etc. Wind, and especially wind at the surface, is the result of all those factors.

Here is a live realtime map of wind in the Americas and adjacent oceans https://earth.nullschool.net/ . As you can see, it’s pretty complicated. Far more complicated than a simple straight flow from west to east.

The long term average effect is that at the latitude of the USA, the wind generally flows from generally west to generally east. But not in a simple linear fashion. At jetliner altitudes the wind is generally 10ish percent of the speed of the airplane. So as between going with or against the wind, the total difference is about 20%. Or about 1 hour in a nominally 5 hour flight.

6

Thanks for answering and not making me feel dumb, guys.

7

LSLguy, that link is amazing. thanks for the share

8

Here’s one that’s just the US itself at the surface. Wind Map

Here’s the official NWS info for pilots: http://aviationweather.gov/windtemp You can adjust the altitude up & down and see how things change from the surface up through altitudes just above the highest jetliners. It’s a forecast, not actual. But they offer predictions 6, 12, and 24 hours into the future. So you can fiddle with that setting to see how things commonly evolve over time.

If you have a tablet there are some truly cool apps out there that can show you the whole globe with the animated swirling surface wind patterns. You can rotate all around the globe, zoom in, etc. It’s the 21st Century Lava Lamp. :slight_smile:

9

I don’t have much to add to this …

Please don’t let LSLGuy’s elegant and succinct explanation belie the exceptional complications of your query … that was really smart question to ask, you’ve grown up to be an educated Biggirl now haven’t we !!!

Follow up question: Don’t commercial jet airliners fly above the troposphere … away from the jet streams … seems to me whenever I fly (and that’s not all that frequent) I can see the tropopause several thousand feet below me … where the cloud deck stops and there’s nothing but blue sky above me …

Follow up fight picking: Coriolis force? … please … it’s the pressure force that performs work here … not some damn pseudoforce that, you know, whose vector is pointed in the wrong direction … I know saying Coriolis force is a clever dodge because 99% of the people have no idea what the Coriolis force is … including The Fact that the Coriolis force cannot be observed from an inertial frame of reference … yet the wind is obvious from such an observation point …

Simply … an air parcel that is stationary with respect to Dallas, TX below has an instantaneous linear velocity of around 875 mph to the East … if we move the air parcel up to Chicago, Newton’s 2nd Law demands that the air parcel retain it’s velocity … but Chicago’s velocity is only 775 mph to the East … which results in a 100 mph velocity to the East with respect to Chicago … in this case, if we apply Coriolis force (which is pointed East) then our wind speed at Chicago will be higher than 100 mph … however we observe that the wind speed is actually considerably less … so that requires a force pointed to the West … we have to slow down the air parcel’s velocity …

The causative agent here is what aviators call drag … high pressure builds up to the East of our air parcel, low pressure to the West … Eureka, now we have an actual and real force pointed to the West called the pressure force … thanks to Navier/Stokes … easy peasy !!!

10

Good points overall and a nice addition to the discussion.

As to Coriolis I’ll stop with the thought that Coriolis is a first order effect. Which drives the second order and third effects that end up predominating in the details. It’s interesting to imagine weather on a non-rotating planet with even (or nearly even) insolation around the entire equator. It looks very, very different.

As to the snip above …

Trop height varies with latitude and season. In the tropical summer it’s higher than all jetliners and indeed almost all aircraft can fly. In the US & Canadian winter it’s well below the cruise altitude of most of the traffic.

As this diagram from the wiki on the jet stream shows Jet stream - Wikipedia the jet streams live in the “notches” in the trop height between the various north/south oriented Hadley cells.

It’s not true that all weather (= clouds) builds up to the trop height then stops. True, other than very active thunderstorms, stuff doesn’t much grow up past the trop. But the converse isn’t true; everything else doesn’t necessarily grow that high before stopping for other reasons. Specifically, it’s very common in the US to have a cirrostratus layer in the upper 20s to low 30s. Meanwhile in the same area the trop height is often in the high 30s pushing into the 40s.

With modern aircraft and weather data and flight planning systems we can do a pretty good job of minimizing fuel burn by trading off altitude and route of flight to avoid or seek out the maximum winds. Sometimes that’s above the trop, other times below. Because high altitude minor (and major) turbulence is so often associated with even benign-looking cirrostratus cloud tops, we usually avoid cruising right at the cloud top level.

11

The specific flight I was asking about was indeed up over an Arctic front that was pushing down to the Gulf Coast … God, even at cruising altitude you could tell it was bitter cold on the ground … but I see your point that the layer I thought was the tropopause could just have been an upper level inversion …

Your point about the tropics reminds me of a military hop I took down to Panama … flying around the big T-heads … I’ve heard commercial pilots try to keep their turns nice and gentle as to not scare the passengers … this damn Major was more than happy to scare the three of us in the jump seats on a C-141 … crazy bastard …

12

This has not been mentioned directly, but the jet stream is often referred to as a steering current, meaning that it drives to some degree the motion of large air masses on the surface. This, too, can cause wind to flow in one direction or another and impede or advance air travel to some extent. LSLGuy, a pilot, might tell us to what degree that is a factor in planning routes, but winds around the earth are pretty complex.