Re: Problem about the bilinear interpolation from FNL 1x1 grid point values to sites locations over Tibtean Plateau

Umm. This seems unusual. NCL just reads the grib records.
I see the plot but could you please provide the specific
files where you see the problem.

On 9/2/10 7:47 PM, 梁宏 wrote:
> 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 <mailto:liangh@cams.cma.gov.cn>
> lhcams3000@sohu.com <mailto: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, 92.06^o E, 31.47^o N,
> 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?&id=521
> <http://forschung.unibw-muenchen.de/ainfo.php?&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 <mailto:liangh@cams.cma.gov.cn>
> lhcams3000@sohu.com <mailto:lhcams3000@sohu.com>
>
>
>
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Received on Tue Sep 7 16:49:06 2010