keta
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Usual High-altitude Wind Speed?

Wed Dec 14, 2005 8:20 pm

Hi all,

I have seen many times planes flying in 150 kt winds at high altitude, I have heard even 245 kts tailwinds. That's by far faster than the fastest wind at ground level (excluding tornadoes), which I see obvious. But are these speeds normal? What is the usual speed of wind at high altitude? I guess pilots should know this.  Wink

Thanks!
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Starlionblue
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RE: Usual High-altitude Wind Speed?

Wed Dec 14, 2005 10:41 pm

Quoting Keta (Thread starter):
I have seen many times planes flying in 150 kt winds at high altitude, I have heard even 245 kts tailwinds. That's by far faster than the fastest wind at ground level (excluding tornadoes), which I see obvious. But are these speeds normal? What is the usual speed of wind at high altitude? I guess pilots should know this.

These speeds are not unusual. Jetstreams can move at hundreds of knots. There's not ground stuff in the way to stop them  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
PhilSquares
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 12:05 am

Quoting Keta (Thread starter):
What is the usual speed of wind at high altitude?

Just operated a flight from HKG-ANC, 13 Dec, and off the coast of Japan, we had 270/255 knots of wind! It was great, nice smooth ride. Those winds lasted for about an hour. When we got in the NOPAC they had died down to about 120knots and as we went further east, they gradually went to 0. Abeam SYA the winds were light and variable. About 200NM out of ANC, they picked up slightly to about 280/40.

All in all, typical winds for this time of year.
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SlamClick
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 12:33 am

One of the reasons for these high speeds is the fact that so many of the world's major cities are found in latitudes near the boundary between the Ferrell Cell (temperate air circulation zone) and the Arctic or Polar Cell. The area where these meet is the location of the jetstream. So the most often flown air routes lie within a few hundred miles of the jet core.

Away from the jetstream, out in the middle of the cells, the flow in the middle of the air masses seems to be around 30-60 knots quite often. Compared with the surface winds that may still seem high, but remember there is no surface friction, hills, trees, buildings etc. to slow it down.
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ArcticTern
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 2:34 am

245 Knots, well is this speed of winds at high altitudes?

What will be the stress on an aircraft? If its 255 is the wind speeds what will be the IAS?

Thanks,
Sushant
I wanted to fly even before I knew how to pronounce the word 'Pilot'
 
PhilSquares
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 3:10 am

Quoting ArcticTern (Reply 4):
245 Knots, well is this speed of winds at high altitudes?

What will be the stress on an aircraft? If its 255 is the wind speeds what will be the IAS?

The speeds were at FL330. Our indicated speed was M.852. There really isn't any stress on the aircraft at all. Sometimes if you have to cross the jet you will experience some turbulence but that's about it.
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SlamClick
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 3:18 am

Quoting ArcticTern (Reply 4):
245 Knots, well is this speed of winds at high altitudes?

What will be the stress on an aircraft? If its 255 is the wind speeds what will be the IAS?

That is very high, even for the jetstream. A hundred knots or more is quite common though.

The IAS has nothing to do with wind speed. The IAS will be whatever the pilot commands. The groundspeed will be the algebraic summing of the true airspeed and the wind. This should be covered in your groundschool.

It will not place any stress on the airplane to fly in 245 knot winds because the airplane will not resist those winds but will just be carried along by them. The air, through which the plane is flying is simply moving in some direction at that speed. It is something like the effect of the earth's rotation on your house - there isn't any. Amazing, but your home is moving east at about 891 knots right at this moment. Can you feel that in any way?

Then there is the orbital speed of the earth around the sun, around sixty seven thousand miles per hour. We don't feel that either. Nor the orbit of the sun around the center of our galaxy which has to be tremendous. We don't feel any of it because we are carried along with it. It is only when we are in a fixed place that we can perceive the relative motion of the air passing us. That is why wind is more important during takeoff and landing than at any other time.
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Tornado82
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 3:46 am

Normally about the only thing I'm qualified to post in here on tech ops is a meteorlogy based question. However today, SlamClick did a great job, as did PhilSquares' real-world experience. If this was a union I'd get you guys for stepping on my toes, haha. Instead I'll just RU you guys, as I should have long ago.

To go a little further, 245kt is definitely not the norm, and honestly the fastest I've ever heard of actually being measured. T'is the season though.

These jet streams are common in areas of strong temperature gradient, such as the strong one running SW-NE in the area of our storm system last week in the Eastern US. Generally speaking, along and just ahead of a cold front you'll have a strong SW to NE running jet stream, along a warm front a NW-SE running one, typically weaker. This goes along with the ideas of troughs and ridges. Typically if you want to make the best time going east go just south of the coldest air to find the jet for your tailwind. Stronger storm centers are typically associated with a phasing (coming together of) the polar front jet, and the subtropical jet, as we saw last week. This is relatively common from the SE US and then up the east coast.
 
ArcticTern
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 3:48 am

Hi Slam,

Wonderful response, indeed! now about the IAS,

IAS is correct to get RAS, RAS corrected for height, temp will give TAS

TAS +- winds will give G/S

Correct me if i am wrong.

I should have used the TAS instead of IAS, I apologies!

Thank you.
Sushant
I wanted to fly even before I knew how to pronounce the word 'Pilot'
 
SlamClick
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 4:18 am

Quoting ArcticTern (Reply 8):
Correct me if i am wrong.

Not sure. I've never used the term RAS. What is common here is:

Directly off the airpspeed indicator you get:

IAS - Indicated airspeed


Which, when corrected for installation error gives:

CAS - calibrated airspeed


Which when corrected for compressibility gives:

EAS - equivalent airspeed


Which, when corrected for altitude and temperature gives:

TAS - True airspeed


True Airspeed is what is used in flight planning. As I might have said, the algebraic summing of TAS and wind factor (speed and direction relative to your speed and direction) gives us GS or groundspeed which is the only thing that is going to tell us how long it takes to get to point B.

Airplanes with air data computers and flight management computers can show us IAS, TAS, GS, OAT, TAT all at once. The old whizwheel got retired to my flight bag and eventually left at home. Of the above speeds we pilots never really deal with CAS or TAS. Those things are more for the performance engineers.
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Starlionblue
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 8:37 am

Quoting SlamClick (Reply 6):

It will not place any stress on the airplane to fly in 245 knot winds because the airplane will not resist those winds but will just be carried along by them. The air, through which the plane is flying is simply moving in some direction at that speed. It is something like the effect of the earth's rotation on your house - there isn't any. Amazing, but your home is moving east at about 891 knots right at this moment. Can you feel that in any way?

Then there is the orbital speed of the earth around the sun, around sixty seven thousand miles per hour. We don't feel that either. Nor the orbit of the sun around the center of our galaxy which has to be tremendous. We don't feel any of it because we are carried along with it. It is only when we are in a fixed place that we can perceive the relative motion of the air passing us. That is why wind is more important during takeoff and landing than at any other time.

If it weren't for replies like this Einstein would be turning in his grave right now  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
keta
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 6:37 pm

Thanks for you replies! So, I see that 60 kts or more are kind of normal.
Do you know what is the highest wind-speed ever measured?  Smile
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chksix
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 7:28 pm

Is there a way to get those wind data online like the METAR's are published now?

For use in flightsims that is...
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zeke
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RE: Usual High-altitude Wind Speed?

Thu Dec 15, 2005 7:47 pm

Quoting Keta (Thread starter):
But are these speeds normal? What is the usual speed of wind at high altitude? I guess pilots should know this.

Yes these are normal, they are seasonal, occour around the same time every year. The jetstream that passes over japan is know to have the strongest core speed of any jetstream, its known to go over 300 kts.
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Bellerophon
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RE: Usual High-altitude Wind Speed?

Fri Dec 16, 2005 12:48 am

SlamClick

...I've never used the term RAS...

Rectified Air Speed (RAS) is IAS which has been corrected for instrument and installation errors, which, as you point out, means it is the same as CAS.

CAS seems to be the preferred modern term; I only came across RAS in some old British aerodynamics books, when I was learning to fly an old British aircraft.  Wink

Regards

Bellerophon
 
Tornado82
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RE: Usual High-altitude Wind Speed?

Fri Dec 16, 2005 6:19 am

Quoting Chksix (Reply 12):
Is there a way to get those wind data online like the METAR's are published now?

It's not the easiest thing to read in text format. But here's the second best thing, for the continental US anyways...

http://www.rap.ucar.edu/weather/upper/upaCNTR_250.gif
 
turnit56N
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RE: Usual High-altitude Wind Speed?

Mon Dec 19, 2005 7:51 am

Quoting SlamClick (Reply 3):
One of the reasons for these high speeds is the fact that so many of the world's major cities are found in latitudes near the boundary between the Ferrell Cell (temperate air circulation zone) and the Arctic or Polar Cell. The area where these meet is the location of the jetstream. So the most often flown air routes lie within a few hundred miles of the jet core.

You know, I never put two and two together before, but this does explain a lot. Well put. Learning occured today, at least for me.

Today, near the jetstream we had a 123 kt wind at FL350. On other days, farther away from it I've seen as low as 15 kts at FL330. The lowest I typically see is in the 30s, as was mentioned. I haven't yet been fortunate enough to get the 200+ tailwinds yet, though.

Quoting Chksix (Reply 12):
Is there a way to get those wind data online like the METAR's are published now?

I only know how to get the text of the winds aloft for the continental US. If you're interested in browsing that, the site I prefer is ADDS ( http://aviationweather.gov/products/nws/winds ). Clicking on a sector will bring up the text forecast of the winds aloft for that sector. If you can find the text for winds aloft in Europe, I'd assume that they'll be in a similar format. Since you can read a METAR, the winds/temp aloft should be pretty easy to decode.

For example, today in the southeast US an exerpt from the winds aloft reads:
FT__3000__6000___9000___12000___18000___24000__30000__34000_39000
RDU 0613 2909+01 2822-02 2732-06 2652-16 2687-26 760642 760852 750961

(They line up better on the actual chart)

The first line simply gives the altitude for each forecasted block of winds and temps below it. In each block, the first two digits are direction, the next two digits are velocity, and the last two digits are temperature. So, for this line RDU is Raleigh Durham, the station these winds are forecasted over. [0613] under the 3000 means that at 3,000 feet, the winds are 060 at 13kts. [2909+01] under the 6000 means that at 6,000 feet, they're 290 at 09kts. The +01 means that the temp is +01 Celsius at that altitude.

They're all pretty much similar until you get to 30,000', where it says [760642]. Since they only have two digits to tell velocity, they have to do something different when the wind gets over 100kts. 50 is added to the first two digits (the direction) to denote that the wind is over 100kts. Subtract 50 from the first two digits to get the actual wind direction. That leaves 26, so the wind direction is 260. The next two digits are 06, so that would make the wind 106 kts. The last two digits are still temperature, but above 24000 feet it's assumed that all temps are negative, so they don't bother with the sign. The temp is -42 C.

Someone correct me if I messed any of that up. I haven't had the privilege of reading winds aloft every day since I left instructing. When I was a CFI and hanging around the wx computers all day I would use the winds aloft maps to see where the strongest part of the jet stream was and then I'd check the text to see what some of the specific numbers were in the that area just for fun. Today over the US, it looks like Northern KY is getting the strongest winds, with a forecast of 754354 at FL340. In other words, 250 at 143kts. A few hundred miles away in SD, the same altitude is forecasted to have 331556, or winds that are 330 at 15kts.
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chksix
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RE: Usual High-altitude Wind Speed?

Mon Dec 19, 2005 6:56 pm

Thanks for that very useful information!
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sunrisevalley
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RE: Usual High-altitude Wind Speed?

Thu Dec 22, 2005 12:55 pm

 
sunrisevalley
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RE: Usual High-altitude Wind Speed?

Thu Dec 22, 2005 1:03 pm

The following site covers much of the Pacific and Indian Ocean..
http://www.bom.gov.au/cgi-bin/difacs.cgi?0196
You have to log on to bomw0007 the password is aviation

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