Ipswichweather.co.uk
-
Posts
5 -
Joined
-
Last visited
Content Type
Forums
Blogs
Gallery
Events
Learn About Weather and Meteorology
Community guides
Posts posted by Ipswichweather.co.uk
-
-
I did something very similar in my MRes project at Leeds.
My understanding is that U (+ve) = west-east, and V (+ve) = south-north, corresponding to the x and y axis respectively.
Thus, I'd have thought that if U and V were positive the wind would be coming from the SW quadrant, i.e. from west-east and from south-north.
My thoughts exactly.
John - The replys I get from NOAA are very hard to understand, they do not make things clear to me. I think that because they are all hold Phd's they are unable to explain in simple terms to the likes of which i can understand.
While the Met Office forecast did make to clear, but i believe they got it wrong. I reply i got from the UKMO was infact relayed though their customer enquires, so perhaps thats where the mistake was made.
Mind you they did get the 1987 storm wrong - perhaps if they new which way the wind was blowing, they would of got it right LOL.
Ian
-
Hello John,
Why do you need u and v components?
I am procducing my own forecasts based on the GFS 0.05deg NWP model. Unlike others who use this data I use a program that converts GRIB data into its raw state.
and does not do the caculations for me.
The reason for this is: I can then add my own caculations based on the topography of the area i am forecasting. Plus I can change the data, if some of the values are missing - quite comman with data set as large as the GFS.
This should allow me to produce a more realistic forecast - Well thats the plan away
Now wind is packed in a GRIB message as U m/s and V m/s at the required height
Example: A wind @10 meters would return as 10 HGTL V=2.3 m/s U=2.6 m/s
Now to caculate the direction you need for find the angle
V = North to South if V<0
V= South to North if V>0
U= West to East if U>0
U= East to West if U<0
Next you need to find the Quadrent, and this is where my trouble lies.
Now
N 360
|
|
W 270-----------90 E
|
|
S 180
Now based on the example above U=2.6 and V=2.3, this to me would put it in the quadrent SW (between S and W)
As U>0 and V>0.
I caculated the angle and ask if a met office forecaster would check the anwser and my formula, before i placed it in to my math model.
The relpy was that it should be in the SE quadrant, but i can't see how.
I contacted NOAA who gave me the formula in my earlier message, with should caculate the Quadrent for me, as well as the angle.
I just need some further advice weather this formula is correct, so it can be placed in my model, and carry on with my work.
Ian
-
Hello,
I am not to sure weather i have posted this in the right section of this forum.
I need help caculating wind direction from the U and V components of wind.
I can caculate the angle and degree, but having trouble detrerming the quadrent.
After spending many weeks on this i think i have come up with a function that returns the inverse tangent of (y/x) in the range -π ≤ return_val ≤ π, using the signs of both arguments to determine the quadrant of the return value
The formula:
r2d = 45.0/atan(1.0) (radians to degrees) or 57.2957795
dir = atan2(u, v) * r2d + 180
If some one here is able to check this formula, or knows another way please post.
I would be most greatful.
Ian Gooch
-
Current Conditions For Ipswich UK
Temp : 6.8 °C
Wind :NW at 2.0 mph
Rainfall : 0.6 mm
Barometer : 1006.9 mb
Today's Extremes
Temp Hi : 10.8 °C Lo : 4.7 °C
Wind Gust : 20.0 mph
Rain Rate : 0.2 mm/hr
Barometer Hi : 1012.9 mb Lo : 1006.8 mb
Forecast: Mostly cloudy and cooler. Precipitation possible within 12 hours, possibly heavy at times. Windy.
Sunrise: 7:18
Sunset: 16:12
Moon phase: Full Moon
Hi all , not to sure if this is the right place to post this, you will have to tell me.
wind direction
in Spring Weather Discussion
Posted
That is the same as my first formula 57.2957*ATAN2(u,v)+180
That, as well as yours, should determing the quadrant in the sum.
Ian