11 ms·
That's a beautiful graph but NOAA's insistence on non-metric units frustrates me endlessly. Knots for speed are bad enough but "inches" for pressure is multiple
by gilgoomesh 10y ago
That's a beautiful graph but NOAA's insistence on non-metric units frustrates me endlessly. Knots for speed are bad enough but "inches" for pressure is multiple levels of wrong.
- ared38 10y agoWhat's more wrong about inches than knots?
- Terribledactyl 10y agoIf taken literally the dimensionality is odd. Pressure is a force applied to an area (force/2-d), and that's just a length 1-d (as written)
- gizmo686 10y agoEven if not taken literally, the particular unit of "inches" is largly meaningless in this case. All we know (assuming the obvious mechanism of measurement) is that the air pressure in <choice of force units> is linear to the reported value. The conversion factor is dependent on the instrument itself (surface area, internal resistance, etc) although there may be a standard that is known specialists.
- tlb 10y agoInches of mercury -- the pressure exerted by a column of liquid mercury that high.
- labster 10y agoIt is a 1-D measurement. It's the pressure exerted by the atmosphere that would raise a column of mercury that 1-D length up a vacuum at 1g of gravity.
- caf 10y agoIt doesn't matter that you're measuring it in an odd way - pressure still has units of force per unit area. 1 "inch Hg" is 3386 Nm⁻². The fact that you can express length as "number of football fields" doesn't make length dimensionless.
- qbrass 10y agoTwo square inches of mercury an inch tall weights twice as much as one square inch of mercury an inch tall. But there's twice as much area, so it's applying the same amount of force to each square inch. The point is you care about the force, but don't care about the area, and a tube of mercury factors out the area.
- labster 10y agoKnots are one Nautical mile per hour, and 1 Nmi == 1 minute of latitude. Nautical miles are based on the shape of the earth and are thus independent from the rest of the US unit tragedy. And quite useful in navigation.
- jdavis703 10y agoWell to be honest America got these units from the British. Not every tragedy is America's fault.
- Aeolun 10y agoThe tragedy is that they're still used now. Not that they were once used.
- epimetheus 10y agoYet, the British still use "stone" to measure their weight, then complain about universal standards not being used by the Americans.
- bcatanzaro 10y agoOf course, the meter was originally based on the shape of the earth as well - the distance from the pole to the equator was defined as 10 Mm in 1793. As far as the US unit tragedy goes, I think it's important to remember that SI units are full of compromises in exactly the same way that US units are, because they need to accommodate practical, human scale concerns. For example, degrees Celsius is a ridiculous concept from a scientific point of view (ask any beginning chemistry student who just messed up their test because they forgot to convert to Celsius to Kelvin before applying PV=nRT). If you believe the point of a unit system is to be useful for science, it's hard to defend a unit where 0 doesn't actually mean 0, since it introduces all sorts of confusion in the same way as traditional units do. And why does the whole world still measure days with 24 hours in them, each with 60 minutes, each with 60 seconds? Because decimal time (although France tried to impose it during the transition to SI units) is just too darn inconvenient for humans to use. The failure of decimal time shows why humans prefer non-decimal units: because the resulting units are human-scale. Converting from seconds to hours or days is not as easy as multiplying by 1000, but kiloseconds is an inconvenient unit - too short for an hour, while 100 kiloseconds is significantly longer than a day. Somehow the metric world manages these conversions just fine (in the same way the US manages conversions between inches, feet and yards). The traditional units evolved over hundreds of years, and I'm glad the US keeps them around - like nautical miles, they are quite useful.
- EFruit 10y agoiirc its inches of mercury, which isn't much more helpful. I've frequently seen it labeled as "in. hg"
- psherman 10y agoYou can switch to the metric system on their website [1]. The graph can also be switched to metric by changing the "uom" query parameter from "E" to "M" [1] http://www.ndbc.noaa.gov/station_page.php?station=42058&unit=M&tz=STN http://www.ndbc.noaa.gov/station_page.php?station=42058&unit...
- thomasahle 10y agoHere is the plot on m/s and mbar: http://www.ndbc.noaa.gov/show_plot.php?station=42058&meas=wdpr&uom=M&time_diff=-5&time_label=EST http://www.ndbc.noaa.gov/show_plot.php?station=42058&meas=wd...
- StavrosK 10y ago"Oh wow, air pressure fell to almost zero, a person would suffocate in ther... Wait a minute, the ground unit is 940! This is a 6% difference!"
- zaroth 10y agoSometimes ground units reflect ground truths, even if the scale doesn't actually hit zero.
- thomasahle 10y agoYup, this is also why I like the metric version. With inches of quicksilver it's hard to know where zero is.
- nayuki 10y agoIt would be better if NOAA used kilopascal (an actual SI unit) instead of millibar, but I guess the conversion is not too bad since 1000 mbar = 100 kPa.
- Declanomous 10y agoThe NOAA data isn't consumed solely by scientists though. I'm sure millibars were chosen as the metric measurement of pressure because people actually use them, such as mariners.
- leohutson 10y agoTry: http://www.ndbc.noaa.gov/show_plot.php?station=42058&meas=wdpr&uom=M&time_diff=-5&time_label=EST http://www.ndbc.noaa.gov/show_plot.php?station=42058&meas=wd...
- Justin_K 10y agoFYI a Knot is standard for navigation world wide because the unit is standardized on earth's size. 1kt = 1 nautical mile per hour. 1 nautical mile = one minute of Earth's longitude. Learned this in sailing class :) Wikipedia: "Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour."
- LeifCarrotson 10y agoLatitude, not longitude - the length of one minute of longitude changes with your distance from the equator. Also, I am not sure how that's relevant to NOAA?
- Spooky23 10y agoNOAA is part of the Commerce Department and Oceanic is part of their name. An important consumer of the data are entities who navigate the sea and air. Both constituencies use knots and nautical miles.
- kqr 10y ago> An important consumer of the data are entities who navigate the sea and air. You make it sound like birds and fish check in with the NOAA before planning migrations. Edit: and that they're really picky about units of measurement.
- gilgoomesh 10y agoUsing "Knot" because it's tied to longitude and latitude is the exact point the metric system is designed to avoid: needless and inaccurate attachments between system of units and specific phenomena that actually complicate rather than simplify and hinder interoperation with every other system. As you state: 1. a knot is only approximately equal to 1 min of latitude per hour (there are numerous cases where it's unusably wrong) 2. doesn't really help for longitudinal travel 3. maps are continuously projected to favor this mediocre form of navigation instead of something more accurate (see Mercator projection) 4. you could easily put kilometre lines on your charts instead of minutes of latitude and fix all the previous problems
- hudibras 10y agoOne of the few things I remember from my 20-year-old meteorology degree is that 1 meter/second is very close to 2 knots. This conversion was also useful when I was in the Navy, especially for coming alongside piers or other ships.
- eCa 10y agoUnderstanding the conversion is helped by using the same time unit: 1 knot (per hour): 1852 meters/hour 1 meter per second: 3600 meters/hour So 2 knots is 3704 meters/h, or less than 3% more than 1 meter/s. Good rule of thumb.
- niccaluim 10y agoI like metric as much as the next guy but you can pry knots from my cold, dead hands. Sincerely, An aviator and sailor
- bisRepetita 10y agoYour cold hands, Fahrenheit or Celsius? ;)
- MaulingMonkey 10y agoKelvin
- omegant 10y agoYou may add feet for altitude (you fly in levels that are in hundreds of feet, like FL300 is 30000'. In meters you get to fly separations of 300m which can be much more error prone). I've flown to Moscow dozens of times and the altitude in meters is much more confusing(even if you only use it now below the transition level, from 0 to 3000'), the wind speed in m/s you may get used to, but Knots is much better for all speed units (also the mach num aproximately corresponds with NM/min, example 0.80 Mach is 8 NM/min.) Another pilot and weekend sailor.
- jonathansizz 10y agoThis could just be down to politics. As a government agency that studies climate and environmental issues, their very existence already has plenty of ideological opposition. So why risk alienating the public further by using a non-traditional measurement system?
- redwood 10y agoI think it's a nice quirk to be honest, keeps us on our toes doing more math (good for our brains). I think it's interesting that we champion diverse languages and cultures but balk when distinct measurement systems with their own quirks are used. Even though the metric system has plenty of brilliance to it, each has its own forms of human intuition backed in. And further, they're both completely arbitrary really.
- jjp 10y agoRaw data is reported in different units and presentation in formats that the consumer might find useful - See http://www.ndbc.noaa.gov/measdes.shtml http://www.ndbc.noaa.gov/measdes.shtml for explanation of the raw data.
- jordanb 10y agoKnots are much more useful for the primary consumers of this data: mariners. Knots are a global standard for measuring speed at sea. And virtually every weather bureau reports windspeeds in knots or Beaufort scale in their maritime reports with the notable exception being the French who insist using meters/second. inHg measures are used in aviation btw, but yeah it's less ideal for a maritime report: mariners use millibars for pressure.
- lultimouomo 10y agoThe good thing is that 1m/s is close enough to 2kts that once you have a mental map of "how much wind" is something in knots you can trivially apply it to m/s and vice versa. inHg on the other hand always has me completely lost.
- JshWright 10y agoinHg is easy... 1 inHg is roughly 1 ftH2O. Hope that helps ;)
- imglorp 10y agoActually knots are derived from SI, being based on nautical miles (which are SI), which are 1/60th of a degree of latitude. So they're not completely useless or arbitrary like other imperial units.