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2000118: 20000118: unit errors in decoded sounding data (fwd)

Paul,

I was refering to you title:
>> >PRESS     WDIR    WSPD    UWND    VWND
>> > MB        DEG    KNTS    KNTS    KNTS

In particular, if you are plotting UWND and VWND in GEMPAK, then
the units are m/s not knts as you have labled.

If you want to use knts in GEMPAK, then use UKNT and VKNT.

I was assuming you were refering to data as listed by GEMPAK, though
you did not refer to using GEMPAK. Since the 4 characater
parameter names are simmilar to GEMPAK, but certainly not "PRESS"-
I believed you were refering to snlist with some cooked up
column lables from your own since that listing you
provided is definitely not GEMPAK.

Otherwise, I have no idea what you mean in your response below.

Steve Chiswell
Unidata User Support





>From: Paul Ruscher <address@hidden>
>Organization: .
>Keywords: 200001182100.OAA16583

>Thanks, doh!  My bad - I think he got this example from Albany - in any
>case, it is round off error, of course!  My site includes data to two
>digits and does not have this problem.  1 digit rounding for both u and v
>can lead to +/1 5% error or so, which is enough to explain his
>problem.  I'll write him again!
>
>Paul
>
>On Tue, 18 Jan 2000, Unidata Support wrote:
>
>> 
>> Paul,
>> 
>> UWND/VWND is meters per second. UKNT/VKNT are knots. If you want units
>> in knots, you need to use the appropriate parameter.
>> 
>> The units column label is not from GEMPAK, but apparently something you
>> have tacked on. You need to maintain that label to be consistent
>> with the parameter usage above.
>> 
>> Steve Chiswell
>> Unidata User Support
>> 
>> 
>> 
>> >From: Paul Ruscher <address@hidden>
>> >Organization: .
>> >Keywords: 200001181842.LAA08774
>> 
>> >Gempak decoding problem here, perhaps?  I've checked and I think Chris is
>> >correct - happens in other soundings, too.  Paul Ruscher
>> >
>> >---------- Forwarded message ----------
>> >Date: Tue, 18 Jan 2000 15:10:32 +0000 (GMT)
>> >From: Chris Walcek <address@hidden>
>> >To: address@hidden, address@hidden
>> >Subject: unit errors in decoded sounding data
>> >
>> >To whom it may concern,
>> >
>> >I regularly download and use decoded soundings
>> >from your web pages. There is an error in the
>> >units of the wind speeds presented in these tabulated
>> >data. For example, here is a excerp of Tuscon AZ
>> >0Z sounding, 18 January 2000
>> >
>> >PRESS     WDIR    WSPD    UWND    VWND
>> > MB        DEG    KNTS    KNTS    KNTS
>> >-----    -----    ----    -----   ----- 
>> >929.0    310.0     4.0    1.6    -1.3 
>> >925.0    310.0     4.0    1.6    -1.3
>> >
>> >
>> >First, wind directions and speeds are presented
>> >in degrees and "KNTS". Speed I assume is in
>> >nautical miles per hour.
>> >
>> >Later, U(west-east) and V(south-north) winds
>> >are tabulated, also in units of KNTS. However,
>> >when I take the square root of the sum of
>> >the squares of U and V (sqrt(U^2 + V^2) one
>> >does not get the original wind speed. In fact
>> >there is a discrepancy of a factor of 1.94 which
>> >is precisely the conversion of nautical miles per
>> >hour to meters per second.
>> >
>> >It looks like the units of U and V are WRONG and
>> >should be in meters per second (m/s)????
>> >
>> >Is this correct? If so please change the table
>> >headings appropriately. Other explanations
>> >of this discrepancy are possible.
>> >
>> >Thanks
>> >Chris Walcek
>> >
>> >(beware the Mars pathfinder fiasco where 
>> >sloppy unit conversions were responsbile for
>> >disaster!!)
>> >
>> >
>> 
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>