Hybrid-sigma pressure and a request

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sonny.zinn
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Joined: May 8th, 2019, 1:31 pm
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Hybrid-sigma pressure and a request

Post by sonny.zinn »

[Reproduced an email request]

Hello,

I would like to make a request.
In the https://ready.arl.noaa.gov/READYcmet.php you provide all kind of products.
I'm specifically interested in SOUNDING products where you provide 3 options, 2 of them are:
GFS model 1 degree, Global, Pressure and
GFS model 0.25 degree, Global, Pressure Global, Hybrid-sigma Pressure.

The problem with the GFS 0.25 data are it gives nonsensical heights for each pressure, e.g it puts 500 hPa level to 8000 meters while it's about on 5000 to 5500 meters.
I know these are hybrid-sigma levels of the model but i don't know how to convert to have sensible heights for each level.

So can you provide single pressure levels(like you do with GFS 1 degree) for 0.25 GFS data too?


Thanks in advance.
sonny.zinn
Posts: 65
Joined: May 8th, 2019, 1:31 pm
Registered HYSPLIT User: Yes

Re: Hybrid-sigma pressure and a request

Post by sonny.zinn »

[From one of our developers]

The sounding plot looks ok, but looking at the text output there seems to be a bug in the program that calculates height from the hybrid-level file.

Can you provide single pressure levels (like you do with GFS 1 degree) for 0.25 GFS data too? - the answer is No. Because it is hybrid-level, not pressure level. If we did interpolation, then yes, but that is another matter.
GeorgeMJ23
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Joined: April 10th, 2020, 11:48 am
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Re: Hybrid-sigma pressure and a request

Post by GeorgeMJ23 »

I was instructed to post it here, so: :)

Taking a sounding prediction from GFS 1° horizontal resolution(from your site: ready.arl.noaa.gov) with normal pressure levels looks like this:

Code: Select all

PRESS HGT(MSL) TEMP DEW PT  WND DIR  WND SPD
 HPA       M      C     C       DEG     M/S  
 E = Estimated Surface Height

  969.   438.    6.7    5.4   358.8     3.3
  950.   586.    5.1    4.4     1.8     5.0
  925.   803.    3.6    3.0    14.6     5.5
  900.  1025.    2.2    1.7    28.8     6.6
  850.  1485.   -0.2   -0.4    48.6     9.7
  800.  1970.   -2.2   -2.5    60.6    11.1
  750.  2480.   -4.6   -4.9    66.1    11.3
  700.  3020.   -7.0   -7.3    65.0    11.0
  650.  3597.   -8.9   -9.4    63.7    11.5
  600.  4215.  -10.9  -13.8    72.1    11.7
  550.  4878.  -15.3  -20.1    76.3     9.3
  500.  5591.  -20.6  -22.6    87.2     7.3
But doing the same with GFS 0.25° horizontal resolution
that is given only in Hybrid-sigma pressure levels seems
like this(for the same area and time and GFS run):

Code: Select all

PRESS HGT(MSL) TEMP DEW PT  WND DIR  WND SPD
     HPA       M      C     C       DEG     M/S  
     E = Estimated Surface Height

      998.   186.E
      995.   213.E   7.6    5.9    34.7     2.1
      990.   287.E   7.5    5.5    33.3     3.1
      983.   369.E   7.0    5.0    35.3     3.6
      975.   475.E   6.6    4.4    34.1     4.3
      967.   575.E   6.1    3.8    31.6     4.8
      958.   686.E   5.6    3.4    31.9     5.2
      948.   828.E   5.1    2.9    29.9     5.6
      936.   982.E   4.4    2.3    33.9     6.0
      923.  1147.E   3.8    1.9    36.5     6.7
      908.  1355.E   3.0    1.5    41.6     8.0
      893.  1572.E   2.2    1.2    46.3     9.4
      875.  1827.E   1.2    0.7    51.2    10.7
      856.  2111.E   0.3   -0.1    55.3    11.5
      835.  2426.E  -0.5   -0.9    59.1    11.9
      811.  2795.E  -1.5   -1.8    61.9    11.7
      786.  3189.E  -2.5   -2.8    64.3    11.2
      760.  3610.E  -3.9   -4.3    65.7    11.1
      731.  4093.E  -5.2   -5.6    65.7    11.1
      701.  4608.E  -7.7   -8.1    65.6    11.4
      670.  5168.E  -8.5   -8.9    67.9    12.2
      637.  5789.E  -9.2   -9.9    67.0    13.0
      603.  6443.E -11.1  -12.6    64.4    13.0
      568.  7135.E -14.0  -15.4    64.4    11.0
      533.  7863.E -17.6  -19.2    82.7     8.0
      498.  8582.E -20.8  -25.2    98.2     8.0

First normal sounding says that GFS's prediction about where 500 hPa would lie is 5591 meters geopotential height. Which is a normal value.
But the 2nd sounding with hybrid-sigma pressure levels says 498≈500 hPa level is on 8582 meters which is absurd.

The above soundings are for a low elevation area(200 m) and occurs for every place so it's a general phenomenon.
So i do wonder if this may be due to a bug in the interpolation code as the geopotential heights for GFS 0.2° soundings are way off.
GeorgeMJ23
Posts: 3
Joined: April 10th, 2020, 11:48 am
Registered HYSPLIT User: No

Re: Hybrid-sigma pressure and a request

Post by GeorgeMJ23 »

sonny.zinn wrote:
April 10th, 2020, 7:45 am
[From one of our developers]

The sounding plot looks ok, but looking at the text output there seems to be a bug in the program that calculates height from the hybrid-level file.
Oh, if that's the case can you please fix it? :)


Thanks.
barbara.stunder
Posts: 424
Joined: November 9th, 2012, 4:23 pm
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Re: Hybrid-sigma pressure and a request

Post by barbara.stunder »

Yes, it's on our list to fix it.
GeorgeMJ23
Posts: 3
Joined: April 10th, 2020, 11:48 am
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Re: Hybrid-sigma pressure and a request

Post by GeorgeMJ23 »

barbara.stunder wrote:
April 13th, 2020, 10:30 am
Yes, it's on our list to fix it.
Oh great, thanks!
sonny.zinn
Posts: 65
Joined: May 8th, 2019, 1:31 pm
Registered HYSPLIT User: Yes

Re: Hybrid-sigma pressure and a request

Post by sonny.zinn »

One of our developers fixed the issue.
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