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RE: 20000703: ALTI to PMSL?

Darrell,

As you said, PMSL is station dependent - and usually involves a 12 hour
temperature change/average. Since the GEMPAK ALTM calculation
uses the single temperature at the observation time, there will already
be 1 difference. In NewMexico (and Mexico) you are looking at significant
station elevations, so the air column to sea level will magnify the
differences in the methods. You will probably find ALTM
and PMSL are pretty close for lower elevations, but trying to mix the
analysis using both PMSL and ALTM more problematic.

Steve Chiswell

On Mon, 3 Jul 2000, Darrell Ensley wrote:

> 
> Thanks!
> 
> I had already concluded that the ALTM data had somehow 
> been reduced to sea level (i "assumed" it had something 
> to do with standard atmosphere). anyways, in surface 
> data i have for say, New Mexico, for example, i find 
> that the PMSL and ALTM data usually differ by 1 to 3 mb.
> 
> The mexican data I am working with only have ALTM. I 
> didn't realize that PMSL is usually calculated with a 
> station-dependent local formula. A few millibar difference 
> will have a definite impact on my surface analyses, but 
> since i don't have PMSL, i'll *assume* ALTM data is better 
> than nothing.
> 
> Thanks again!
> 
> Darrell
> 
> On 03-Jul-00 Steve Chiswell wrote:
> >
> >
> >Darrell,
> >
> >You should be able to use ALTM.
> >
> >See the GEMPAK support archives response:
> >http://www.unidata.ucar.edu/glimpse/gempak/3655
> >
> >as well as the SFPARM section of chapter 3 of the user guide and
> >appendix A. The mean column reduction is used for sea level.
> >
> >
> >Steve Chiswell
> >Unidata User Support
> >
> >
> >On Mon, 3 Jul 2000, Darrell Ensley wrote:
> >
> >> 
> >> Does anyone know of a 'pre-defined' way in GEMPAK 
> >> to convert ALTI to PMSL? 
> >> 
> >> I've got some Mexican surface data GEMPAK files with 
> >> ALTI but no PMSL. Am I going to need to take the SELV 
> >> and convert to PMSL using Standard Atmosphere myself?
> >> Or is there a way to do this in GEMPAK already...or 
> >> any other 'non-manual' ways to do this? 
> >> 
> >> Thanks!
> >> 
> >> Darrell
> >> 
> >> 
> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> Darrell Bryan Ensley         <address@hidden>      
> >> Mesoscale Dynamics Lab          5703 Windlestraw Dr.
> >> Rm 135, Research III            Apartment 37
> >> North Carolina State Univ.      Durham, NC 27713
> >> W: (919) 515-1437               H: (919) 361-1346  
> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> 
> >
> 
> 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Darrell Bryan Ensley         <address@hidden>      
> Mesoscale Dynamics Lab          5703 Windlestraw Dr.
> Rm 135, Research III            Apartment 37
> North Carolina State Univ.      Durham, NC 27713
> W: (919) 515-1437               H: (919) 361-1346  
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> When the sunshine burns the darkness,
> Remove the veil that lingers on Your face,
> The stains of time still mark us,
> Standing in the aftermath of Grace... 
>                    -- "Stains of Time"
>                        Common Children
>