Wikipedia:Reference desk/Archives/Science/2018 December 8

= December 8 =

Wind direction on a weather map
The little sticks here have a tip and on the other end like arrow feathers but only on one side. Which way is the wind going?

Also, the animated map shows wind from the west going east. I'm so confused.

Anna Frodesiak (talk) 05:36, 8 December 2018 (UTC)

And Index of meteorology articles and Glossary of meteorology need first caps per MOS:BULLETLIST I think. Am I wrong?

And where the heck is our article on those symbols on weather maps like in this map?

Anna Frodesiak (talk) 05:43, 8 December 2018 (UTC)


 * The wind points away from the arrows. Half stick is worth 5 knots, each stick is worth 10 knots, each flag is worth 50 knots, arrowless ring is 0 knots. 5.75, 11.5 and 57.5 in regular miles per hour instead of nautical. So an arrow of 2 flags, 1 stick and 1 half stick means 132 mph which means if you lean forward at any angle you will be blown away and bounce like a tumbleweed. Sagittarian Milky Way (talk) 06:01, 8 December 2018 (UTC)
 * Ah, away from the tip! So, wind goes from the tip to the flags! I've been getting it wrong all this time. It's like the clam chowder thing all over again. That clears everything up.


 * Now, about that symbols article?


 * Many thanks! Anna Frodesiak (talk) 06:16, 8 December 2018 (UTC)


 * The wind blows in the direction of the arrow, so a west wind is shown as an arrow from west to east (left to right if north is at the top). It's called a west wind because it comes from the west, so if you face west it will blow in your face.  Dbfirs  07:52, 8 December 2018 (UTC)


 * Hi User:Dbfirs. So, left to right according to that image, correct? Anna Frodesiak (talk) 11:18, 8 December 2018 (UTC)
 * Yes, I always imagine an arrow head on the opposite end to the speed flags.  Db<i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  11:54, 8 December 2018 (UTC)
 * Thank you!! Anna Frodesiak (talk) 12:32, 8 December 2018 (UTC)
 * The same way as a weather vane indicates wind direction, by pointing to where it's coming from. [Apparently NOT. Confused me too!] ←Baseball Bugs What's up, Doc? carrots→ 12:57, 8 December 2018 (UTC)
 * What????? Oh dear. Please someone explain in plain words for a dummy like me which is which. Anna Frodesiak (talk) 13:01, 8 December 2018 (UTC)

Sorry, all. You've been saying it plainly all along and I've been misunderstanding. I get it now. My humblest apologies. I just had to get my head around it. My brain has been trained my whole life to see an arrow meaning the direction of motion. With these wind things, it is opposite. Anna Frodesiak (talk) 13:21, 8 December 2018 (UTC)

This says wind is "NE". Shouldn't they say SW, as in coming from the SW? and press play show the wind is coming from the SW. Anna Frodesiak (talk) 13:28, 8 December 2018 (UTC)


 * MOS:BULLETLIST states Prefer sentence case, rather than making it mandatory. My preference for the long lists you referenced is to use lowercase except for terms which conventionally start with an uppercase letter (as you might see in a printed book's index); it seems to make scanning the lists easier. (Btw, is a nice concise list of weather symbols.) Bazza (talk) 10:47, 8 December 2018 (UTC)
 * And, unhelpfully, Station model describes those symbols. I tried Meteorological symbol but... Bazza (talk) 10:52, 8 December 2018 (UTC)
 * Hi Bazza. I'm going to make a whole bunch of redirects to that and maybe some sort of other action. I'm surprised that article gets 80 hits a day with that name. Cheers. Anna Frodesiak (talk) 11:18, 8 December 2018 (UTC)


 * And thank you for https://www.wpc.ncep.noaa.gov/dailywxmap/plottedwx.html, which is very helpful. Anna Frodesiak (talk) 11:20, 8 December 2018 (UTC)


 * No I don't think that last diagram is right at all unless you are saying the arrow is pointing at where the wind is coming from which is the way normal English speech goes. I believe it is the complete reverse and the wind speed indicator is at the end where the wind is coming from. It is like your original idea of an arrow going with the wind and not like a weather vane. Dmcq (talk) 13:42, 8 December 2018 (UTC)
 * You can check this with a weather map, the wind should go anticlockwise round a low and clockwise round a high in the northern hemisphere. Dmcq (talk) 13:56, 8 December 2018 (UTC)
 * It is not right, indeed. The arrow goes in the opposite direction.--Jetstreamer $Talk$ 15:29, 8 December 2018 (UTC)
 * (EC) This is confusing! It's best to not consider these symbols to be arrows at all. When used on a weather map, they are often attached to a Station symbol (a circle) showing the location the reading was taken. The symbol has a line (a "wind barb") pointing in the direction the wind is coming from and has on it lines or triangles to show the wind's speed. explains it nicely. There's a real example for northern hemisphere high pressure at  (map image at ), with wind from the east near Honolulu and Midway, and from the north off shore from San Francisco. Bazza (talk) 15:45, 8 December 2018 (UTC)
 * Thank you for providing those links, they shed light into the subject.--Jetstreamer $Talk$ 15:58, 8 December 2018 (UTC)
 * If you've ever wondered what a 350 mph hurricane would look like on a weather map you'd want to see this image. That's not real, it's a computer bug that made the wind barbs reach 304.2 nautical miles per hour (292.5 to 297.5 is 10 feathers: 5 flags, 4 sticks and 1 half stick) Sagittarian Milky Way (talk) 16:09, 8 December 2018 (UTC)

Template plan
I plan to make a template that can go into weather articles. It will use the fuzzy symbols from Station model. Anna Frodesiak (talk) 12:32, 8 December 2018 (UTC)

Please see Wikipedia talk:WikiProject Meteorology.

Anna Frodesiak (talk) 12:33, 8 December 2018 (UTC)

Please say which is right


Now, before I burst into tears, please say which is right. Even though I made the cover of Daft Monthly twice, this still seems objectively confusing. I've read some of the above to others here, and they are confused too. It is about language and describing wind sources and direction of travel and what wind going away from tips of arrows means and such. It's making me nuts.

So, A or B? Thanks for your patience, all. Anna Frodesiak (talk) 21:19, 8 December 2018 (UTC)


 * According to the University of Illinois, B is correct. PaleCloudedWhite (talk) 21:32, 8 December 2018 (UTC)
 * B! Good. Sorted. Thanks, PaleCloudedWhite. Sooooo, not like a weather vane at all. And quite the opposite of an arrow too. Anna Frodesiak (talk) 22:46, 8 December 2018 (UTC)
 * Yes, the opposite of a weather vane. But it IS like an arrow, IF you take the little speed marks to be the "feather" and the little circle or dot at the other end to be the "arrowhead". ←Baseball Bugs What's up, Doc? carrots→ 23:19, 8 December 2018 (UTC)
 * An arrow? Quite the opposite. If it were like an arrow, then the fletchings would not be pointing into the wind. Ha! :) Anna Frodesiak (talk) 23:32, 8 December 2018 (UTC)
 * Since when do arrows fly tail-first? A weather vane points to where the wind is coming from. These arrow-like things the weather bureau uses point to where the wind is heading. Which is exactly what option B in your diagram shows. The descriptions had me confused too. ←Baseball Bugs What's up, Doc? carrots→ 23:39, 8 December 2018 (UTC)
 * What you are saying about arrows seems backwards to me. The tip of the arrow is where the wind is coming from as the arrow flies through the air. As the arrow moves, the air flows over the arrow toward the fletching. The wind barb is the opposite. The fletching, or little marks, is where the incoming wind hits first. That is the opposite of an arrow, right? Anna Frodesiak (talk) 23:55, 8 December 2018 (UTC)
 * By either your interpretation or mine, the net effect is an arrow which is pointing in the direction of the wind's flow (your option B). That's the opposite of a weather vane, where the arrow is pointing to where the wind is coming from (your option A). ←Baseball Bugs What's up, Doc? carrots→ 00:02, 9 December 2018 (UTC)
 * This is nuts, eh? :) To me, the arrow flies into the wind rather than following it. And this is not the first time I've noticed this ambiguity. A friend had problems with a tire once. Search "Now grab the new tire" here. I think it can all be seen two ways. I wonder if our brains are set up to see it only one way, or wind up confused, like me. Anna Frodesiak (talk) 00:06, 9 December 2018 (UTC)


 * In your option B, the arrowhead is the little circle on the left, and the feather/tail is the "wind barbs" on the right. The arrow is pointing left, and that's also the direction of the breeze from the fan. If you want to think of the symbol as the wind "pushing" it in the direction it normally flies, that works too. ←Baseball Bugs What's up, Doc? carrots→ 00:09, 9 December 2018 (UTC)
 * That makes sense. By the way, I do get that it is B. My brain keeps wanting to see the arrows like a weather vane, but strangely, before this post, I think I knew it was B. You must think I'm bonkers. Also, the disagreeing maps made me wonder what was up. Anna Frodesiak (talk) 00:22, 9 December 2018 (UTC)

There! I added an image that is unambiguous. I will call the weather people and have that used from now on. (I'll probably be offline for a few months attending various award ceremonies.) Anna Frodesiak (talk) 00:27, 9 December 2018 (UTC)
 * <Throws hands up in horror>Oh no no, that last diagram is terrible That is showing an opposing force coming from the left to blow whatever comes from the right backwards so it must be showing a wind going from left to right ;-)
 * The difference about the arrows is whether the arrows coexist with the wind or represent the wind. In pictures of the wind they are normally shown representing the wind going the way the wind goes, whereas some here were thinking of them as fixed or going into the wind which is what weather vanes do. Dmcq (talk) 10:52, 9 December 2018 (UTC)
 * Hi Dmcq. The head of weather wrote back and said "The new image is lovely and the opposite of terrible and will now be used internationally from now on." That is a direct quote! Anna Frodesiak (talk) 20:50, 9 December 2018 (UTC)
 * Oh very good, it is quite nice :) Dmcq (talk) 21:12, 9 December 2018 (UTC)


 * Very, very lovely. They really should use your image. Looks like a fart drawing in comics where/and everybody knows where the wind is blowing from. You're a little genius, Anna! And a lovely one on top :) --TMCk (talk) 22:32, 9 December 2018 (UTC)
 * Thank you, Tracy. Anna Frodesiak (talk) 22:37, 9 December 2018 (UTC)


 * It's your kind and kindness that's enlightening the place.--TMCk (talk) 23:27, 9 December 2018 (UTC)
 * You are very sweet, Tracy. Thank you for the kind words. :) Anna Frodesiak (talk) 23:30, 9 December 2018 (UTC)

Conflicting info
and disagree, right?

The sat map shows a band of movement coming from the southwest heading northeast, i.e. a SW wind, right?

The graphic shows, where that same band is, barbs indicating movement coming from the northeast heading southwest, i.e. a NE wind, right?

What gives? Anna Frodesiak (talk) 22:46, 8 December 2018 (UTC)


 * It's B. Different layers of the atmosphere can move in different directions though. Sagittarian Milky Way (talk) 22:59, 8 December 2018 (UTC)


 * Ahhhhhhhhhh, I see. Anna Frodesiak (talk) 23:32, 8 December 2018 (UTC)


 * And the top layer of a typhoon is an anticyclone that blows the opposite compass direction because all that air it sucks has to go somewhere. Sagittarian Milky Way (talk) 00:00, 9 December 2018 (UTC)
 * My goodness. Weather is hard. I never realized just how hard. Anna Frodesiak (talk) 05:08, 9 December 2018 (UTC)

Case closed
'''A big thank you to all above who helped me understand. Your patience was very much appreciated.''' Anna Frodesiak (talk) 05:10, 9 December 2018 (UTC)


 * Yes, media weather forecasts in the UK use arrows and numbers to show which way the wind is blowing and how fast. A weather vane normally points INTO the wind, hence the confusion.   <i style="color: blue;">D</i><i style="color: #0cf;">b</i><i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  11:41, 9 December 2018 (UTC)
 * Hi,Dbfirs. Yes, it is that darn weather vane that forces my brain to switch the wind directions. I have it now, I'm sure. Many, many thanks! Anna Frodesiak (talk) 20:50, 9 December 2018 (UTC)

Cartography: bearing from one city to another
Every night I place my watch (in Los Angeles) so that it is pretty much pointing to WWVB in Fort Collins, Colorado. Is there an easy way to tell what compass heading points to Fort Collins from Los Angeles? I just looked at a map and eyeballed it. --Guy Macon (talk) 19:22, 8 December 2018 (UTC)
 * I've never had a radio clock, what happens if you leave the watch (strap?) pointing somewhere else? Sagittarian Milky Way (talk) 19:42, 8 December 2018 (UTC)
 * It appears to have a typical "figure 8" pattern, where you just have to be kind of close to the correct direction, to get a good signal, and you have to be at exactly 90 degrees sideways to get no signal at all. Mostly I ask asking because I am curious whether there is an easier way than using the Haversine formula. --Guy Macon (talk) 05:39, 9 December 2018 (UTC)
 * suggests that in Los Angeles a heading of 54 degrees will point you at Fort Collins. If you start walking, though, you'll need to gradually veer to 62 degrees. Bazza (talk) 19:59, 8 December 2018 (UTC)
 * An azimuth map may help. https://ns6t.net/azimuth/azimuth.html Greglocock (talk) 23:30, 8 December 2018 (UTC)
 * Incidentally the maths to do it right are not really beyond a high school student, although I suspect most high school students would disagree. Greglocock (talk) 23:32, 8 December 2018 (UTC)


 * www.gcmap.com is one of several sites that will compute a great circle route from one airport to another (or between any places, but it's designed to work most easily with airport codes, and allows you to look them up by place name). It also tells you what direction the initial compass heading is. From Los Angeles International to Ft. Collins / Loveland Airport, the answer is 55°.  In the other direction it would be 243°, so if you followed the great circle from Los Angeles, your bearing would gradually change to 243°−180° = 63°. --76.69.46.228 (talk) 05:52, 10 December 2018 (UTC)


 * I may be clueless on this, but my impression is that the angles on a Mercator projection are true - you can simply read the angle off the map and go that way. (Our article is written in Wikipedia-standard jargon about the angle being conserved, with a blue link looking down at you, that leaves it unclear to me if that is true without going on a wild goose chase)  If it is true, then an algorithm to find the angle should involve doing the cylindrical projection of the two cities and looking at the angle between them. Wnt (talk) 14:34, 10 December 2018 (UTC)
 * Indeed, Wnt is correct. A true Mercator projection map will provide the bearing from one city to the next.  You can get close - to within a few degrees - using a standard classroom-quality Mercator map of the USA.  But you won't find a really good navigationally-accurate Mercator projection for the entire Southwestern United States.
 * You can obtain navigational-grade maps at zero cost from FAA at: VFR Charts on the d-TPP website - but you'll need to reference multiple different charts, and it may take some effort to learn how to use them.
 * It will also matter how you measure your bearing: are you using a real magnetic compass or some other type of instrument to determine what direction you are pointing?
 * For what it's worth, I calculated a 42 degree magnetic heading (approximately 52 degrees true heading) from KLAX to WWVB (to the north antenna - but I rounded to the nearest single degree). I computed this bearing using Foreflight - which is not free to use - and then I spot-checked it by hand.  Interestingly, if you stand at the WWVB North Tower, the great-circle bearing to get back to Los Angeles is about 234 degrees magnetic (242 true), which is a turn-around of 192 degrees (not 180 degrees)!  This is because the Earth's magnetic field is imperfect, and the amount of imperfection is quite different between southern California and central Colorado.
 * Using a different software tool - the zero-cost web interface at SkyVector.com - I calculated a slightly different answer: 45 degrees magnetic (57 degrees true), which is what you could fly if you started in Los Angeles and held that magnetic heading the entire time. This is a different track out of Los Angeles, but over the entire route, it will more closely follow the great circle.  Just so there's clarity on this topic: if you were really navigating an airplane or a rocket-ship over such a great distance, it would be ... unwise to depart on a fixed bearing, and then trust that you could just follow a compass heading for the entire route.  That is called dead reckoning, and it has many practical limitations - not the least of which come from the complexities of the magnetic field.
 * It is not likely that you can point to 42, or 45, degrees of magnetic heading, with single-digit accuracy. For example, during testing, an aircraft pilot must demonstrate that they can correctly maintain a selected heading within ±5°, and that's using expensive, aviation-approved navigational equipment.  If we really want to compute a bearing, we use engineered tools and navigational knowledge to make sure that our bearings are calculated in a manner that accommodates all the practical realities and errors.
 * Real navigation on planet Earth is quite difficult! There's a great deal of coverage on this topic in the PHAK, Section 8-23 Compass Systems and other navigational information.  If you stand in Los Angeles, and you realistically expect as much as a five-degree error in your bearing, you might be pointing at a target that's almost 75 miles away from WWVB.
 * And if you were looking for the direct vector that went through the Earth - instead of the great circle that went along its surface - you'd have to do even more math!
 * Lastly, I would just point out that over very long distances in Earth's atmosphere, radio waves do not travel in straight lines: in fact, even though a lot of the transverse mode for an HF wave will propagate horizontally, the direction the radio energy is coming from can be any orientation depending on conditions. The shortest line to WWVB might be 42 or 45 degrees laterally, but the radio signal might be coming from up.  For best signal reception, that means you wouldn't actually want to point your watch at WWVB: rather, you want to orient your antenna so that it picks up the strongest signal, which would entail studying exactly what the orientation describes the arriving electromagnetic waves.  You'd have to measure and calculate a Poynting vector from measurements of the electric field; and it's a hard business.  It's called DFing, or direction-finding; at short ranges and very high frequencies, the wave goes in a straight line, but at long range and lower frequencies, you have skywave and a zillion other effects.  Here are a bunch of books on the topic.
 * Long story short: point your watch in any orientation; check the NIST WWVB monitor website for current conditions; and check the NOAA Space Weather website for the current and forecast K-index - a single number that rolls up how much radio interference there is. That's going to have a much bigger impact on your WWVB signal reception than the position and orientation of your watch.
 * Nimur (talk) 02:13, 11 December 2018 (UTC)
 * The Mercator says to go from 70N139W to Mecca go southeastish but when the Sun's exactly over Mecca it's almost exactly at the north horizon of 70N139W (midnight sun). Sagittarian Milky Way (talk) 04:44, 11 December 2018 (UTC)
 * I'm very surprised to hear that a "classroom-quality" Mercator map wouldn't be accurate. I mean, the GPS coordinates of every podunk town are known, and projecting them onto a sphere seems like simple math.  True, the Earth isn't really a sphere, but is that aberration actually enough to cause the level of error you're describing, or are the maps just made up totally carelessly? Wnt (talk) 02:12, 12 December 2018 (UTC)
 * Wnt, even if the classroom map is flawless, it almost surely doesn't mark the isogonic lines - so even if you can determine the true bearing, you need some other resource (like a real navigation chart) to calculate your magnetic bearing - assuming you want to use a magnetic compass. How else would you determine where in the real, outside world to actually point at in correspondance with some flawless line on the map?  Stellar alignment?  Perhaps you have technology - but your smart-phone compass still points at magnetic north - and if your device has got some kind of software correction, you'd better understand it before you head out 10 degrees off-course!  Nimur (talk) 16:37, 12 December 2018 (UTC)
 * I was mostly curious why the classroom map would be that bad. As for the compass bearing, honestly, I was assuming the OP was staying in a building or road that had been made to a precise east-west compass bearing by some sophisticated surveying method, or otherwise could look up the apparent angle on some kind of satellite map; but in any case it should be irrelevant because we're talking about a low-precision process of orienting a watch on a nightstand, presumably without help of a sextant. ;) Wnt (talk) 12:49, 13 December 2018 (UTC)
 * Per my usual demeanor, I'm simply trying to hold everything to the highest possible standard of accuracy and precision! Clearly, most classroom maps will serve well if you just want a rough estimate of the direction from LA to Denver.  Your classroom-grade protractor probably has more precision-problems than the chart itself.  But neither is as accurate or precise as a real navigational chart.  If you really like maps (and charts), you'll want to use something a little better than what they sell in the local bookstore.
 * In my opinion, you'll just find that the quality-standards for most cheap printed-paper maps really aren't navigational-grade. If you look at an approved navigation chart for a ship or an aircraft, you'll see a lot of ancillary details - like how exactly to line up the paper so it overlaps with precise navigational accuracy.  The front page of a folded government air navigation chart actually contains printed instructions for the procedure of plotting a straight line between two points, even if it crosses multiple sheets of paper.
 * The charts also contain the important legal-ese phrase, "... published from digital files compiled in accordance with ...(detailed) specifications." I bet you won't find that phrase on a classroom wall-chart!
 * Here are some authentic chart resources for the United States of America:
 * the Office of the Coast Survey, a division of NOAA, for nautical charts
 * Digital Products from the FAA, for free Mercator maps and other digital products for all parts of the USA, plus many of our overseas territories and holdings, and a few boundary areas
 * Data products and tools from the U.S. Geological Survey - note that these are not necessarily Mercator-style projections nor are they necessarily suitable for navigation. And let me say - navigating the absolutely immense USGS map catalog is really difficult for the novice user!  They have so many types and styles and formats and scales and map-purposes....
 * Outside the United States - even our neighbors in Canada - such resources are not always made available at zero cost. For example, in Canada, even digital copies of Government-approved navigation charts are sold by subscription via Nav Canada, and in my experience, they are more expensive than the cost of commercial subscription providers for paper or digital copies - like ForeFlight or Jeppesen.  If you travel to the far-flung reaches of the planet, and you want a good navigational-quality Mercator map, you can buy those too.  The U.S. Government used to provide, for a brief time, world-wide navigation maps (in paper and digital format) at zero-cost; but these are no longer kept current, nor are they free to users.
 * Nimur (talk) 19:27, 13 December 2018 (UTC)
 * A straight line on a Mercator map represents a rhumb line: a path whose angle to the local meridian is constant. It is not a great circle, which OP presumably prefers. —Tamfang (talk) 02:40, 13 December 2018 (UTC)
 * That's what I was getting at with my post a few posts up. Though it takes many miles or high/Antarctic latitude for the difference to become noticeable. Sagittarian Milky Way (talk) 04:01, 13 December 2018 (UTC)
 * Ah, that's the heart of the matter, and a reason not to trust Mercator after all. (that and making Russia look way more intimidating than it should be ... our article deflates it nicely) Wnt (talk) 12:53, 13 December 2018 (UTC)
 * Tamfang is absolutely correct. A rhumb line is not a great circle; and neither is a representative characterization of the actual path that an HF radio wave will travel over great distances.  HF radio waves will bend and bounce, (refract and reflect), all subject to the imperfections of Earth's atmosphere, magnetic field, and lots of weird details of physics.  Nimur (talk) 19:31, 13 December 2018 (UTC)
 * In 2004 I wrote a program to calculate the distance and bearing between two points on Earth. Well, the old EXE won't run because of a missing DLL and I can't recompile the Windows version because some tools I used for the interface, I no longer have.  But I put in 34.03N, 118.15W for L.A. and 40.56N, 105.08W for Fort Collins and had it runthe calculations.  It returned the bearing of 305.98 degrees NW, which I think means 54.02 degrees East of North.  The distance is 1362.10 km, 846.37 statute miles, 735.47 nautical miles.  Bubba73 You talkin' to me? 03:35, 11 December 2018 (UTC)


 * What I needed instead of Mercator was a gnomonic projection ... invented by Thales of Miletus in the 6th century BC, according to our article, perhaps not coincidentally also the first person known to have written about lodestones. I feel behind the times.  But these aren't true to area or angle, so apparently the great circle route is worked out on a gnomonic map, then transcribed to a Mercator map to read off the angles? Wnt (talk) 21:57, 13 December 2018 (UTC)