Page 1 of 1
Hybrid-sigma pressure and a request
Posted: April 10th, 2020, 7:18 am
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.
Re: Hybrid-sigma pressure and a request
Posted: April 10th, 2020, 7:45 am
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.
Re: Hybrid-sigma pressure and a request
Posted: April 10th, 2020, 11:53 am
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.
Re: Hybrid-sigma pressure and a request
Posted: April 10th, 2020, 11:54 am
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.
Re: Hybrid-sigma pressure and a request
Posted: April 13th, 2020, 10:30 am
by barbara.stunder
Yes, it's on our list to fix it.
Re: Hybrid-sigma pressure and a request
Posted: April 13th, 2020, 11:41 am
by GeorgeMJ23
barbara.stunder wrote: ↑April 13th, 2020, 10:30 am
Yes, it's on our list to fix it.
Oh great, thanks!
Re: Hybrid-sigma pressure and a request
Posted: April 16th, 2020, 11:43 am
by sonny.zinn
One of our developers fixed the issue.