Hello,
I use NCL bilinear interpolation function "linint2_points" to carry out
interpolation from FNL 1x1 grid point surface pressure values to sites
locations over Tibetan Plateau.
The version of NCL I am running is 5.2.0. The type of system I am
on is Window XP.
The NCEP/NCAR-FNL data is available from the website:
http://dss.ucar.edu/datasets/ds083.2/%a3%ae%a1%a1I found that the ranges of diurnal
variation of surface pressure determined by NCEP/NCAR-Fnl are more than 300
hPa at Lhas, Naqu and Gaize sites over the Tibetan Plateau. I mail to the
FNL project supporter Mr. Gregg Walters to discuss this problem. He told me
that variable identifier being used consistently in the NCL software maybe
not proper. Please see the document attached for more details. Thanks a lot.
Best Regards.
Liang Hong
Chinese Academy of Meteorological Science, Beijing, China
email: liangh@cams.cma.gov.cn lhcams3000@sohu.com
The mails are as follows,
Dear Liang Hong,
I am having trouble reproducing the FNL problem. I used the GrADS
contouring software to plot the PRESsfc field and did not see the values
flipping back and forth like you report. However, it looks to me like the
values in your graph for the interpolated FNL values appear to be flipping
between sea level pressure and surface pressure, with the flips occurring at
the end of a month. Is the proper variable identifier being used
consistently in the NCL software?
What I am about to say is not direct proof of the integrity of the data, but
close to it. We have over 600 FNL users per month, for a few years, and no
one else has reported this kind of problem. Perhaps no one else has been
noticing the Tibet region, but this seems very unlikely.
Gregg
On 8/30/10 4:46 AM, 梁宏 wrote:
Hello Gregg Walters,
My surface pressure at the Lhas( station index number: 55591) and Naqu (add
a new one , station index number: 55299, 92.06oE, 31.47oN, 4477m) site both
came from station observations from CMA. These two sites both are
international exchange stations. Actually, the surface pressure at these two
sites is available from the website:
http://weather.uwyo.edu/upperair/sounding.html.
Horizontal interpolation from NCEP surface pressure can be carried out to
determine the pressure at the specific latitude and longitude of the sites
(Schueler et a. . 2001, http://forschung.unibw-muenchen.de/ainfo.php?
<http://forschung.unibw-muenchen.de/ainfo.php?&id=521> &id=521; Sridevi Jade
et al. 2008, Journal of Geophysical Research). So bilinear interpolation
from the 1x1 grid point values to the sites locations was performed using
NCL function "linint2_points" (
http://www.ncl.ucar.edu/Document/Functions/Built-in/linint2_points.shtml ).
Additionally, the FNL reanalysis product is four times (00, 06, 12, 18 UTC)
per day. The surface pressure for only two times per day is comparable with
the station observations at Lhas and Naqu site in the year of 2007. Please
see the document attached for more details.
Would the big range between low elevation stations and high elevation
stations likely "blow up " the FNL model tow times per day ?
Liang Hong
_____
发件人: Gregg Walters [mailto:baseball@ucar.edu]
发送时间: 2010年8月28日 3:21
收件人: 梁宏
主 题: Re: Help for ds083.2 - GRIB1 6 HOURLY FILES begin 1999.07.30!
Hello Liang Hong,
The difference is amazing. Is it safe for me to assume that your pressures
at the Lhas site came from station observations? How were the values in
your FNL chart prepared? I am guessing that I am looking at the results for
a region, where a big range could occur between low elevation stations and
high elevation stations, as represented in the FNL analyses. That kind of
rage would likely "blow up" the FNL model. Have you tried interpolating
from the 1x1 grid point values to the Lhas location?
Gregg Walters
On 8/27/10 5:37 AM, 梁宏 wrote:
Hi , Walters
The monthly mean surface pressure is about 640 hPa at Lhas site on the
Tibetan Plateau in January 2007. The ranges of the surface pressure
observations are less than 10 hPa (figure 1 (right panel), see the document
in the accessory ). However, the ranges of diurnal variation of surface
pressure determined by NCEP/NCAR-Fnl are more than 300 hPa (Figure 1 (left
panel)). Why?
Thanks a lot.
Best Regards.
Liang hong
Chinese Academy of Meteorological Science, Beijing, China
email: liangh@cams.cma.gov.cn lhcams3000@sohu.com
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