I am trying to read GRIB files which have a number of messages including

  • 10 metre u component of wind
  • 10 metre v component of wind
  • u component of wind
  • v component of wind

I cannot seem to find any mention of a u component of wind on the internet, only 10 metre.

What is the difference?

  • Can you please post the output of gdalinfo or whatever you're using to view the GRIB metadata? It is possibly the wind at 10m above surface, and then a separate band with the wind with a vertical dimension. U and V as variables are used for notation in a vector field with strength and direction, see tutorial.math.lamar.edu/Classes/CalcIII/VectorFields.aspx and wx.gmu.edu/dev/clim301/lectures/wind/wind-uv.html for example. – alphabetasoup Feb 20 '16 at 22:10
  • I am using pygrib to read the GRIB files. I am just an engineering student trying to use this data for a project, not a professional so I am new to this. What would you suggest to view the meta data? @RichardLaw – Sood Feb 21 '16 at 12:03
  • I recommend gdalinfo – alphabetasoup Feb 21 '16 at 19:43

The u and v components for wind are dimensions parallel to the x axis and y axis respectively (just like uv values in other computing paradigms). Have a look here for a simple but more detailed explanation. This breaks the wind direction down into vectors.

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  • Thank you for your help. I was aware of the parallel between u and x axis and v and y axis. I was having trouble figuring out what the '10 metre' qualification meant. – Sood Feb 24 '16 at 6:04

I have found an answer after some searching.

Each GRIB file I was taking had several messages.

Among them was

  • 10 metre u/v component of wind
  • u/v component of wind

Each message would have 2 10 metre u/v component of wind and 10 u/v component of wind files.

The difference is that 10 metre u/v component of winds are at an altitude of 10 metres above the surface of the ground. The key 'level' returned '10' when I queried it using pygrib APIs.

U/V component of winds had various values when it's 'level' key was queried ranging from '100000' to '2000'. This would probably be in feet since 100000 metres is roughly 60 miles which is too far above the earths surface for weather balloons to go to.

So in this particular case, the difference is in altitude.

I am not sure if the GRIB files I am reading are "standardized" in any sense of the term so perhaps this question and answer is particular to only my set of files.

Thank you for all the interest.

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