Can gusts be less than 10m wind?

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norulz
Posts: 89
Joined: Thu Mar 12, 2015 1:43 pm

Can gusts be less than 10m wind?

Post by norulz » Sun Jun 28, 2015 11:00 am

Hello,

Using NMM I have noted that on occasion, the speed of SFC WIND GUST is actually less (by 1-2kt) than the wind speed calculated from U&V vectors at 10m.

The gusts are normally marginally higher to significantly higher than the 10m wind and the forecast is usually quite accurate.

Is lower gusts normal for NMM post processing? Has anyone else noticed this?

David

meteoadriatic
Posts: 1565
Joined: Wed Aug 19, 2009 10:05 am

Re: Can gusts be less than 10m wind?

Post by meteoadriatic » Sun Jun 28, 2015 12:49 pm

I believe that gust speed is calculated at ground level, while 10m speed is obviously 10m above ground...

norulz
Posts: 89
Joined: Thu Mar 12, 2015 1:43 pm

Re: Can gusts be less than 10m wind?

Post by norulz » Mon Jun 29, 2015 9:30 am

Hi,

According to the emsupp_cntrl.parm file, gust is a 10m value. The code that is given is 180, 105, 10 which implies the 'specified height' to be 10m.
I am beginning to suspect that the timing of the calculation is the issue as I see that the gust value is more behind the wind value when the wind is on the increase and the opposite when the wind is on the decrease. Perhaps one value is for start of period and one is middle or end of period.

Code: Select all

 #  Shelter (10m) Momentum Fields - Instantaneous, Period Maximum, Mean and Period Standard Deviation
 #
 (U WIND AT ANEMOM HT ) SCAL=( 4.0)
 L=(10000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (V WIND AT ANEMOM HT ) SCAL=( 4.0)
 L=(10000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (SFC WIND GUST       ) SCAL=( 4.0)
 L=(10000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)

 (MAX 10M WIND SPEED  ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (U-COMP MAX 10M WIND ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (V-COMP MAX 10M WIND ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (MAX SFC WIND GUST   ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)


 (MEAN 10M WIND SPEED ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (U-COMP MEAN 10M WIND) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)
 (V-COMP MEAN 10M WIND) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)

 (STD 10M WIND SPEED  ) SCAL=( 4.0)
 L=(00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000)

 #  Additional Sensible Weather Fields
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